Question On Subject Brightness Range

[IanBarber]

If a subject has a low reading of 10 EV and a high reading of 16 EV, is the SBR for this subject 7 stops (10, 11, 12, 13, 14, 15, 16) or 6 stops (11,12,13,14,15,16)

[Ken Lee]

A "normal" subject has a 7-stop SBR and the difference between low and high readings is 2 stops. It requires neither contraction nor expansion to look normal.

A "flat" scene has an SBR of 5 and because there are no shadows, there is no difference in readings: the difference is 0. It will require a Plus 2 expansion to look pleasing, according to the basic principles. (Of course, how we artistically render a scene is our choice.)

Because your reading indicates a difference of 4 stops, we would say that it has an SBR of 9, namely 2 more than normal. All things being equal, it requires a Minus 2 contraction to tame the high contrast.

[IanBarber]

Because your reading indicates a difference of 4 stops, we would say that it has an SBR of 9, namely 2 more than normal. All things being equal, it requires a Minus 2 contraction to tame the high contrast.

Ken, could you clarify where you are calculating 9 stops sbr please

[Peter De Smidt]

Spot meter or incident?

[IanBarber]

Spot meter or incident?

Spot meter

[Peter De Smidt]

I call it 6 stops. If you need detail at both extremes, I'd place 10 EV on Zone III, which would have EV 16 fall on Zone IX. With today's films, I'd use normal development, unless the scene call for non-normal tone separation.

[David Schaller]

I'm with Ken, and would do N-2 on that, putting the shadow in Zone III.

[Leigh]

A "normal" subject has a 7-stop SBR and the difference between low and high readings is 2 stops.
Forgive me, Ken, but that makes no sense.

You've described SBR, but you have not defined it.

Could you please define it?

- Leigh

[IanBarber]

I'm with Ken, and would do N-2 on that, putting the shadow in Zone III.

6 stops (11,12,13,14,15,16)

Am I correct in thinking that you are removing the bottom and top reading which ends up as 4 stops.

You are then adding this to 5 to get the 9 stop SBR and applying N-2 to bring it down to the 7 stop Normal range.

Do you always use this approach whether you are using a spot meter or incident meter.

[Ken Lee]

Ken, could you clarify where you are calculating 9 stops sbr please

Sorry if I was unclear. Because you used the term SBR (which is often used by practitioners of BTZS) and you mentioned taking 2 readings (another approach from BTZS), I presumed your two readings were the standard BTZS readings, made with an incident meter in the open shadows (low reading) and direct light (high reading). My analysis was therefore based on standard BTZS nomenclature and practice.

If in fact you were simply measuring the darkest and lightest areas of the scene with a spot meter and you found a difference of 4 stops, then my BTZS analysis is not appropriate and you can ignore my reply.

[David Schaller]

6 stops (11,12,13,14,15,16)

Am I correct in thinking that you are removing the bottom and top reading which ends up as 4 stops.

You are then adding this to 5 to get the 9 stop SBR and applying N-2 to bring it down to the 7 stop Normal range.

Do you always use this approach whether you are using a spot meter or incident meter.

I'm used to basic Zone system thinking,whitch would be that if the shadow is Zone III, there would be two darker zones below it (above B+F), which is why I said assuming the shadow is Zone III.

From a practical point of view, using his EV measurements, if EV 10 is placed in Zone III, the exposure would be made on EV 12, and I would develop the EV 16 highlight N-2, to bring it down to Zone VII. Other people would think this is overly conservative, but I prefer to reduce contrast in the negative rather than in the print, where I can always add it back easily if I want to.

[Ted R]

If a subject has a low reading of 10 EV and a high reading of 16 EV, is the SBR for this subject 7 stops (10, 11, 12, 13, 14, 15, 16) or 6 stops (11,12,13,14,15,16)

When the two readings are 10 and 11 the range is one stop. 10 and 12 two stops. 10 and 13 three stops. 10 and 14 four stops. 10 and 15 five stops. 10 and 16 six stops. Answer six stops.

[Doremus Scudder]

If a subject has a low reading of 10 EV and a high reading of 16 EV, is the SBR for this subject 7 stops (10, 11, 12, 13, 14, 15, 16) or 6 stops (11,12,13,14,15,16)

Subject Brightness Range has to do with the total range of light reflected from the subject from its lowest to its highest. Where those things get placed depends on what the photographer wants from the final print.

Placing, say, EV 10 on Zone III implies that there are at least Zones I and II below it, since Zone III is a "light black" value with detail. No Zones I & II = no detail in Zone III.

However, the OP is just giving us values read by a spotmeter, from lowest to highest. If we assume that the low value of EV 10 is Zone I, then EV11 would be Zone II, EV 13 would be Zone III, etc. up to EV 16 falling on Zone VII. As far as I'm concerned, that is 7 Zones and a 6-stop spread.

The confusion in this thread comes from two sources. One is that a "low reading" with a spotmeter in Zone System usage usually means that it is placed in Zone III, therefore implying that there are two "phantom Zones" below it, thereby expanding the total SBR to 9. If this, indeed is what the OP meant, then this is, indeed, valid.

Another source of confusion is the BTZS method of using incident readings taken in shade and direct sunlight. An incident reading assumes all Zones in flat lighting, i.e., around 5-6. The difference in the two incident readings shows the difference in illumination and the amount of "Zones" that need to be added to a single incident reading. For example, if there are three stops difference between the low and high incident readings, then we expand the number of Zones expected in the scene to 8-9. This would indicate a reduced development from "Normal."

@OP: If you're using the Zone System, quit worrying about SBR and worry more about careful placement of shadow values and then where the other values fall after you've arrived at that. This latter will determine your choice of development time. We Zonies talk more about "spread" and less about SBR, which is more at home in BTZS parlance. E.g., from Zone III to Zone VIII is 6 Zones and a 5-stop spread. Think of spread as the difference and the number of Zones as the total number of "stripes" or "positions" from top to bottom.

Best,

Doremus

[Peter De Smidt]

This is just a personal preference, and it likely depends on the type of light where I photograph, but I don't generally like minus development, as it leads to diminished separation of tones, and many modern films don't shoulder until extremes of exposure are reached. If the subject has a huge luminous range, I'd rather do divided development with Pyrocat than a traditional minus development.

[Vaughn]

I wrap my mind around it about the same way as Doremus -- I think.

If I took those reading on my Pentax Digital Meter (10 to 16), I would think I got 7 zones represented here...measuring the darkest value I can find, then up to the highest value I can read in the scene. But I would also call it a 6 stop range. If I wanted detail in the areas I metered as 10, then I would expose at 12. My exposures are usually long -- so I may or may not fully correct for reciprocity failure depending on the scene and my contrast needs. If I am not hording film, I will usually take a 2nd exposure at the same or at one stop more exposure -- developing the second based on the first.

In my field notes, I'll denote of the range of my readings of the scene and where my exposure(s) falls in that range. Back at the ranch, I can find like-minded sheets of 8x10 and develop them together in an Expert 3005 Drum. In this particular situation (6-stops and/or 7 zones) I would give the film extra development to boost the contrast for alt printing -- with how much 'extra' depending on the process.

I'll be developing some 4x5 Ilford Ortho Plus, rated at 50 ASA, tomorrow. Some 6-stop range (metered 7 to 13) scenes and some 8-stop range (metered 5 to 13) scenes to work with (an old hallowed hall at Cornell University, and some gorge in central NY, respectively).

The Ilford Ortho is tricky stuff...trying to control it it in my usual haphazard fashion has not been easy. On earlier attempts I aimed for platinum/palladium quality negatives, but I over-did it and the negatives' contrast was too high for Pt/pd; but a great fit for the carbon process! The Ortho Plus is proving as interesting to work with as the Tech Pan I am running out of. I am field testing it for an on-going project in the redwoods. The project will be carbon prints, but I am testing its limits (or they are testing me!) and looking for some finer control.

Peter -- that is what originally drew me to carbon printing...not having to compress the light to match the material.

[IanBarber]

@OP: If you're using the Zone System, quit worrying about SBR and worry more about careful placement of shadow values and then where the other values fall after you've arrived at that. This latter will determine your choice of development time. We Zonies talk more about "spread" and less about SBR, which is more at home in BTZS parlance. E.g., from Zone III to Zone VIII is 6 Zones and a 5-stop spread. Think of spread as the difference and the number of Zones as the total number of "stripes" or "positions" from top to bottom.

I think this summed it up nicely, thank you

[Bill Burk]

If a subject has a low reading of 10 EV and a high reading of 16 EV, is the SBR for this subject 7 stops (10, 11, 12, 13, 14, 15, 16) or 6 stops (11,12,13,14,15,16)

You've gotten many thoughtful answers about how to interpret your readings... I don't want to detract from that.

But let's say you decided the two points on which you want to determine the subject luminance range are 10EV and 16EV.

The simple answer to your question is to count it as 6 stops of range. The stop from 10 to 11, then to 12, 13, 14, 15 and 16

[interneg]

I'll be developing some 4x5 Ilford Ortho Plus, rated at 50 ASA, tomorrow. Some 6-stop range (metered 7 to 13) scenes and some 8-stop range (metered 5 to 13) scenes to work with (an old hallowed hall at Cornell University, and some gorge in central NY, respectively).

The Ilford Ortho is tricky stuff...trying to control it it in my usual haphazard fashion has not been easy. On earlier attempts I aimed for platinum/palladium quality negatives, but I over-did it and the negatives' contrast was too high for Pt/pd; but a great fit for the carbon process! The Ortho Plus is proving as interesting to work with as the Tech Pan I am running out of. I am field testing it for an on-going project in the redwoods. The project will be carbon prints, but I am testing its limits (or they are testing me!) and looking for some finer control.

I've found Ortho+ pretty easy to control - that said, the ability to fairly easily DBI the stuff is handy...

What are you developing it in?

[Pere Casals]

If a subject has a low reading of 10 EV and a high reading of 16 EV, is the SBR for this subject 7 stops (10, 11, 12, 13, 14, 15, 16) or 6 stops (11,12,13,14,15,16)

It depends on how you meter. An EV value has a brightness range of 1 EV, with a low point, a center point and a high point.

From the center of 10 EV to the center of 16 EV we have 6 stops.

From the lowest point of 10 EV to the highest point of 16 EV you have 7 stops.

From the highest point of 10 EV to the lowest point of 16 EV you have 5 stops.


So true Dynamic range will depend on if you have spots in the limits of the zones or not.

If textures in 10 EV and 16 EV are important then better to consider you have 7 stops range, if no important textures (washed sky...) in the extremes you can consider 6.


You got different answers from different posters because that. A metering system is a practical simplification that works very well, the exact way is using a sensitometric curve, calibrating your personal process: Lux*second vs density!!!


Regards.

[Stephen Benskin]

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Thanks Bill for using the term Subject Luminace Range.

[Peter De Smidt]

In the Zone System, Zone I is not a detailed shadow.

[Jac@stafford.net]

In my modest experience those who obsess with the Zone System make no better pictures than those who use a reasonable compromise. The Zone System is for desktop photographers with too much time to post during their desk bound day-job.

Keep in mind that Adams with huge input from Fred Archer (a pictoralist) developed the system when emulsions were not well standardized and often crap compared to today's products. Y'all would be lucky to find in Adams' notes the day he discovered color contrast filters.
.

[Pere Casals]

In my modest experience those who obsess with the Zone System make no better pictures than those who use a reasonable compromise. The Zone System is for desktop photographers with too much time to post during their desk bound day-job.

Keep in mind that Adams with huge input from Fred Archer (a pictoralist) developed the system when emulsions were not well standardized and often crap compared to today's products. Y'all would be lucky to find in Adams' notes the day he discovered color contrast filters.
.

Well... IMHO the Zone System is not good or bad, it's the photographer who is good or bad. A photographer should know what shadow detail will record the Z-II of his film+processing, this ends in knowing what kind of shadow detail will get recorded in those scene areas underexposed by 3 stops from ISO rating.

What's about highlights, an skilled photographer should guess what density will reach in the negative, to adjust processing. With or without Zone System...

Even films are well different than Super-XX, a film Ansel used, the present ISO rating also allows for 4 stops max underexposure before detail is lost, as the "n point" is at log H = 1.3 from toe.

https://upload.wikimedia.org/wikipedia/commons/thumb/c/ca/ISO6speedMethod.png/540px-ISO6speedMethod.png

If we see the AA images... it would take a very good photographer to get similar good results with a modern film.

To me present films are not better for the job, just less grain for same speed, but grain is not much a problem for 8x10, now and then.

The great thing about LF is that we have similar tools than AA and Krash, and still it takes a sound photographer to imitate those masters, with not that great true advantage from tools.

[Stephen Benskin]

the present ISO rating also allows for 4 stops max underexposure before detail is lost, as the "n point" is at log H = 1.3 from toe.

Forgive me if I've misinterpreted the above sentence, but the ISO B&W Speed Diagram isn't about exposure range or underexposure. It is an illustration on how to determine b&w negative film speed. If you are interested in theory, standards are not the place to look unless the particular standard has an appendix. Safety Factors in Camera Exposure, C.N. Nelson, Photographic Science and Engineering, 1960 is the place to look. FYI, the contrast parameters are part of the Delta-X Criterion equation that ties a fixed density method into the fractional gradient method. Under the ISO contrast parameters, the fractional gradient speed point always falls Δ0.29 log-H to the left of Hm. Technically, this makes Hm an EI. It also proves Hm is not the minimum useful gradient point. Delta-X is explained in Simple Methods of Approximating the Fractional Gradient Speeds of Photographic Materials, C.N. Nelson and J.L. Simonds, JOSA, 1956.

[Pere Casals]

Forgive me if I've misinterpreted the above sentence, but the ISO B&W Speed Diagram isn't about exposure range or underexposure. It is an illustration on how to determine b&w negative film speed. If you are interested in theory, standards are not the place to look unless the particular standard has an appendix. Safety Factors in Camera Exposure, C.N. Nelson, Photographic Science and Engineering, 1960 is the place to look. FYI, the contrast parameters are part of the Delta-X Criterion equation that ties a fixed density method into the fractional gradient method. Under the ISO contrast parameters, the fractional gradient speed point always falls Δ0.29 log-H to the left of Hm. Technically, this makes Hm an EI. It also proves Hm is not the minimum useful gradient point. Delta-X is explained in Simple Methods of Approximating the Fractional Gradient Speeds of Photographic Materials, C.N. Nelson and J.L. Simonds, JOSA, 1956.

Hello Stephen,

Thanks for that information, http://www.apug.org/forum/index.php?attachments/safety-factors-in-camera-exposure-pdf.23850/

Still I'm not sure how ASA/ISO major upgrade of 1961 relates to these (1959, 60) older documents, in 1961 box speeds were doubled, because the safety factor changed. So I'm not sure if the meter point is the same related to film speed.

166009



I think this is (to me) interesting to be discussed:


I've a question, given this chart:

https://upload.wikimedia.org/wikipedia/commons/thumb/c/ca/ISO6speedMethod.png/540px-ISO6speedMethod.png


the "n" point determines a precise amount of lux*second...

Is this the same amount of light (irradiance) that a calibrated meter would recommend for a gray card ?

(this will be aprox because meters vary at least 1/6 of EV because ISO 2720:1974 recommended K and C values)


Regards,
Pere

[David Hedley]

I think Doremus' answer in post 13 above is closest to my understanding. The only thing I would add to that is that exposure is primarily your choice, based on what you want to achieve (in other words, your visualisation of the final print).

A literal interpretation of a scene, based on a standard progression of tones, might require an N, N-1, or N+1 exposure, but you don't have to follow the standard if you want to achieve a different effect. Photoshop makes it easier to achieve different interpretations of a given scene now, of course, but the choice you make at the time of exposure, in anticipation of how you will develop and print, remains of real importance, imho, and does to some extent differentiate LF film photography from other formats and digital.

[Stephen Benskin]

Hello Stephen,

Thanks for that information, http://www.apug.org/forum/index.php?attachments/safety-factors-in-camera-exposure-pdf.23850/

Still I'm not sure how ASA/ISO major upgrade of 1961 relates to these (1959, 60) older documents, in 1961 box speeds were doubled, because the safety factor changed. So I'm not sure if the meter point is the same related to film speed.

166009






I've a question, given this chart:

https://upload.wikimedia.org/wikipedia/commons/thumb/c/ca/ISO6speedMethod.png/540px-ISO6speedMethod.png


the "n" point determines a precise amount of lux*second...

Is this the same amount of light (irradiance) that a calibrated meter would recommend for a gray card ?

(this will be aprox because meters vary at least 1/6 of EV because ISO 2720:1974 recommended K and C values)

Regards,
Pere


Hi Pere, I'm getting ready for work, so let me throw this out for now and I'll go into more detail later. n does not equal the meter calibration point. The contrast parameters are part of an equation. The standard doesn't discuss the equation because that is not the purpose of the standard. By adhere to the contrast parameter, the result will always be the same. Only when the processing is different, does the Delta-X equation need to be used. This means that the fixed density method produces an "accurate" film speed only under the ISO parameters. Here is the ISO speed diagram with Delta-X.

166010

[Pere Casals]

Hi Pere, I'm getting ready for work, so let me throw this out for now and I'll go into more detail later. n does not equal the meter calibration point. The contrast parameters are part of an equation. The standard doesn't discuss the equation because that is not the purpose of the standard. By adhere to the contrast parameter, the result will always be the same. Only when the processing is different, does the Delta-X equation need to be used. This means that the fixed density method produces an "accurate" film speed only under the ISO parameters. Here is the ISO speed diagram with Delta-X.

166010

Ok, I'll wait for your comments later...

But let me point something... (talking for Normal development, for ISO calibration)


The "n point" in the ISO rating is at 1.3 Log H from the toe.

In this document http://www.apug.org/forum/index.php?...ure-pdf.23850/ the meter point is at 1.25 Log H from the toe, just 0.05 difference, this is 1.8-0.55 = 1.25

So the meter point ("a" in the 1960 document) and the (ISO procedure) n point are the same irradiance (1/6 stop difference, perhaps)


166012


But I don't know if the meter point changed after 1961 new rules...


My guess (not sure) it that yes, it changed, so under present specifications we should have 3 linearly underexposed stops plus toe, if toe takes one stop then we should have 4 underexposed stops, with some toe detail at -4. And -5 should be pure black. This is the same than with zone system gray levels...

If I'm right (not sure) since 1961 the "n point" of ISO rating is at 0.3 Log H at the right of the C point of the 1960 graph. Simply the C point moved an stop (0.3H) to the left because 1961 rules doubled on box speed...

[Bill Burk]

Hello Stephen,

Thanks for that information, http://www.apug.org/forum/index.php?attachments/safety-factors-in-camera-exposure-pdf.23850/

Still I'm not sure how ASA/ISO major upgrade of 1961 relates to these (1959, 60) older documents, in 1961 box speeds were doubled, because the safety factor changed. So I'm not sure if the meter point is the same related to film speed.

166009



I think this is (to me) interesting to be discussed:


I've a question, given this chart:

https://upload.wikimedia.org/wikipedia/commons/thumb/c/ca/ISO6speedMethod.png/540px-ISO6speedMethod.png


the "n" point determines a precise amount of lux*second...

Is this the same amount of light (irradiance) that a calibrated meter would recommend for a gray card ?

(this will be aprox because meters vary at least 1/6 of EV because ISO 2720:1974 recommended K and C values)


Regards,
Pere

Look for a reflected light exposure meter to aim at 10 times the amount of light at m

[Pere Casals]

Look for a reflected light exposure meter to aim at 10 times the amount of light at m

Thanks, Bill

So this is 3.3 stops of linear response for underexposure (Log210 = 3.3), before we are in the toe, as toe is defined by ISO speed method. The fourth underexposure stop it would be well in the toe, and -5 should be plain black. (With normal development...)

So it looks that the charts made before 1961 had 1 stop more (safety factor) as rated speed was just the half. Before 1961 it was 20 times the amount of light at m, I guess... as the exposure meter had an ASA speed setting that was just the half...


...And the n point it was the irradiance targeted by exposure meters before 1961change, so today the n point is considered 1 stop overexposed.

[Peter De Smidt]

When the Zone System was formulated, nothing about sensitometry changed. What worked before still worked after, and there are a ton of different ways of getting where you need to be to get what you want out of your photos. For instance, if you use Mortensen's techniques, i.e. lighting, development, and appropriate film...., then "exposing for the highlights and developing for the shadows" (Mortensen On the Negative), the opposite of Ansel's maxim, will work fine. If you photograph scenes with important shadows, it will not work fine The important thing is to try what seems best to you, evaluate the results, make changes......

There seems to be a lot of animus against "The Zone System". It's hard for me to understand. In the first place, there are lot's of alternatives. So, which system is the problem? Adams? Minor Whites?.... And then there are people who treat general pronouncements as if they were categorical imperatives. Usually, they're not. You don't have always put a detailed shadow on Zone III and a detailed highlight on Zone VIII. That's just a starting point. If you read Adams, he stresses the importance of visualization (knowing what you want to get), and then applying systematic steps to achieve that end. If a visualization is better achieved by different placement, well, then so be it.

What's really nice about the Zone System is the terminology, as how we photograph revolves around f-stops, and so it's very natural to think in those terms. For instance, many years ago now I switched from a regular timer to an f-stop timer. It lead to a big improvement in my printing, as I could ignore times and concentrate on stops (or zones.) This doesn't put a straight jacket on technique. It just provides a useful way to think about print exposure.

Getting back to photographing, if I'm using a tripod, I'll use a spot meter, read the values, and decide on a placement. Given my visualization, I'll decide on a method of development, mainly a normal one, but occasionally a +1.5 or divided development. So I use some of the testing and terminology of the zone system. What's wrong with that? It's what works for me. If something else works for you, then by all means carry on.

[Bill Burk]

Response to Pere Casals... It's almost that simple. The shadows are hard to predict or nail down when you take a picture.

Every kind of scene has a different amount of flare. For simplicity I just use the average flare 0.4

[Pere Casals]

When the Zone System was formulated, nothing about sensitometry changed.

I completely agree. The Zone system is abaut spot metering, because one relates the metering of every area to resulting densities in the negative. Ansel never told if a photographer should place an scene area in a zone or another, he simply described how consistent areas end in particular negative densities after a particular +/- processing, and that what's in toe/shoulder get crunched.

IMHO the mess comes when a simplified metering system recommends an exposure from averaging things. An incident light system don't tell if we are to have detail in the scene shadows...


Response to Pere Casals... It's almost that simple. The shadows are hard to predict or nail down when you take a picture.

Every kind of scene has a different amount of flare. For simplicity I just use the average flare 0.4

Yes, this is true, IMHO shadows have 2 problems, one is the unknown flare amount, the other (for long exposures, not that uncommon) is LIRF, as shadows have more LIRF...


I found very useful to meter by using the SLR (Nikon F5 in my case) spot meter. I found a multicoated prime SLR lens working very similar than an LF lens, same transmission and same scene depending flare. Sun in the framming will cast aprox same flare on the shadows in the SLR metering system than the LF lens, so metering is pretty accurate.

Another way I found is using a fixture to place the SLR in place of the ground glass, without the SLR lens, so in fact I have a TTL metering for the view camera, with the rise/shift I can explore all the scene with a TTL spot meter...

The other important thing I found important is testing LF shutters, IMHO it is the greatest factor for uncertainty in a LF shot, at least with my beaten shutters...


... It weights a lot, but if one has to kill an agressive bear, the F5 also is always an effective weapon :)

[Stephen Benskin]

Ok, I'll wait for your comments later...

But let me point something... (talking for Normal development, for ISO calibration)


The "n point" in the ISO rating is at 1.3 Log H from the toe.

In this document http://www.apug.org/forum/index.php?...ure-pdf.23850/ the meter point is at 1.25 Log H from the toe, just 0.05 difference, this is 1.8-0.55 = 1.25

So the meter point ("a" in the 1960 document) and the (ISO procedure) n point are the same irradiance (1/6 stop difference, perhaps)


166012


But I don't know if the meter point changed after 1961 new rules...


My guess (not sure) it that yes, it changed, so under present specifications we should have 3 linearly underexposed stops plus toe, if toe takes one stop then we should have 4 underexposed stops, with some toe detail at -4. And -5 should be pure black. This is the same than with zone system gray levels...

If I'm right (not sure) since 1961 the "n point" of ISO rating is at 0.3 Log H at the right of the C point of the 1960 graph. Simply the C point moved an stop (0.3H) to the left because 1961 rules doubled on box speed...

Pere, where to start. First, think of the parameters of the ISO speed graph as no more than how to determine a gradient, not unlike other methods like Contrast Index or average gradient. All three are a way of determining or defining contrast, not exposure. Once the film conforms to the ISO contrast parameter, the ISO speed can be determined; however, it still doesn't say anything about exposure. On the other hand, your other example comes from the paper Safety Factors does. It illustrates the average scene and it's placement based on the old ASA speed derived from the fractional gradient method. The "speed point" in that example is the fractional gradient speed. Jack Dunn has a similar diagram based on the post 1960 ASA standard.

166063

And one I put together.

166064

A number of years ago, I put together a document titled "Defining K." It explained the process from light source illuminance to tone reproduction, focusing mostly on exposure theory. The .pdf is too big to upload here. I can email it if anyone wants. The original thread is over at APUG somewhere.

And here is an example of the camera image and it's relationship to the negative for zero flare and one stop flare scenarios.

166062

I don't want these posts to be too long. Next one will be on exposure.

[Vaughn]

I've found Ortho+ pretty easy to control - that said, the ability to fairly easily DBI the stuff is handy...

What are you developing it in?
Ilford PQ Universal Developer in a 3006 Jobo Expert Drum. This last batch was developed at 1:19, 68F, 5 minutes. I found that 1:19 is working out nicely for me. I started off trying 1:9, but had to back way off. I just jumped in with both feet, and am not too surprised to end up with dense highlights! Some of the negatives will print well in Platinum/palladium (I generally do not use contrast agents).

It feels like I'll be able to get repeatable usable results with this combination. It might be fun to give it a try in a Pryo developer, but I think I'll try to keep it simple!

[Pere Casals]

I don't want these posts to be too long. Next one will be on exposure.

OK, thanks in advance, I'll wait for that...



Anyway this graph:




Jack Dunn has a similar diagram based on the post 1960 ASA standard.

166063




...Says we have 10x from photometer point to the left, where toe starts crunching. That 10x is 3.3 stops, so areas beyond 3.3 underexposure are in the toe, not in the linear part of the curve. So from film ISO calibration and a spot photometer reading, with "normal" development, we know if an scene spot is in the toe or not.

If we use an SLR as a TTL spot photometer it will include similar flare than the LF lens, is both lenses are consistent (SLR is a multicoated prime, and LF lens is also MC...).

The flare impact graph sample is very interesting... it tells about the importance of flare... and comparing both one can guess how shadow microcontrast is lowered by flare.

I guess the way to recover shadow microcontrast in the darkroom should be SCIM masking...




I think this is useful for knowing what's in the linear part and what's in the toe, anyway determining the exposure/process for our visualization should be more complex, I'm sure your next post would enlighten that, thanks in advance.

[interneg]

Ilford PQ Universal Developer in a 3006 Jobo Expert Drum. This last batch was developed at 1:19, 68F, 5 minutes. I found that 1:19 is working out nicely for me. I started off trying 1:9, but had to back way off. I just jumped in with both feet, and am not too surprised to end up with dense highlights! Some of the negatives will print well in Platinum/palladium (I generally do not use contrast agents).

It feels like I'll be able to get repeatable usable results with this combination. It might be fun to give it a try in a Pryo developer, but I think I'll try to keep it simple!

PQ Universal & O+ user here too - mainly for masks, & ID-11 for more 'normal' contrast work on silver gelatin. PQU at 1+9 can be pretty intense on film, unless you're going for printing-out materials. Your times sound about right for platinum/ palladium relative to Ilford's suggestions for 1+19 times in PQU (4m at 20c for a G-Bar of 0.62) - glad it's all getting under control!

[Stephen Benskin]

Sorry, I spent around two hour writing a post and when I went to upload it, the site had logged me off and I lost 95% of it. All that survives is the bit of intro below. Not really in the mood to redo tonight.

For any speed or contrast methodology to be relevant, the psychophysical nature of the photography must be considered. This is what Jones did in with The First Excellent Print test. He established a criterion of excellence for the photographic image, and established the definition of exposure.

Jones concluded negative density is not a practical criteria for determining quality. Contrast is, or more accurately, film gradient. More specifically quality is determinant by the gradient of the toe in relation to the overall gradient of the film. This conclusion came after comparing various speeds methods with the test print judgement speeds under the greatest number of conditions with the greatest number of emulsions and degree of processing to determine the method that most accurately corresponded to the results from the prints judged to be excellent.

[Bill Burk]

I found a spot meter that has 0.4 flare similar to the camera image, so I agree your meter might already help you integrate flare into your readings. In practice, you might compensate for "already-included" flare by simply placing the shadow reading a stop higher than you otherwise thought, for instance on Zone IV instead of Zone III*. I wouldn't bother over that last third-stop at this point.

The 3 1/3 stops down to the speed point is sensitometric exposure as opposed to what you get in the camera-image.

*Maybe the switch in practice from close-up reading with Weston Master meters to camera-position spotmeter readings had something to do with the change from Zone II shadows to Zone III that I noticed between older references and more up-to-date ones. (So if you use a Weston, place in Zone II or III... if you use a spotmeter place shadows in Zone III or IV).

[Peter De Smidt]

Just something I learned the hard way, if you're going to write a long post, it's best to write it in something like Google docs, cutting and pasting onto the forum.

[Pere Casals]

Sorry, I spent around two hour writing a post and when I went to upload it, the site had logged me off and I lost 95% of it. All that survives is the bit of intro below. Not really in the mood to redo tonight.

For any speed or contrast methodology to be relevant, the psychophysical nature of the photography must be considered. This is what Jones did in with The First Excellent Print test. He established a criterion of excellence for the photographic image, and established the definition of exposure.

Jones concluded negative density is not a practical criteria for determining quality. Contrast is, or more accurately, film gradient. More specifically quality is determinant by the gradient of the toe in relation to the overall gradient of the film. This conclusion came after comparing various speeds methods with the test print judgement speeds under the greatest number of conditions with the greatest number of emulsions and degree of processing to determine the method that most accurately corresponded to the results from the prints judged to be excellent.

Thanks Stephen, I know how you felt... condensing all that knowledge is a great effort.

I agree... paper can show 1:100 contray. st, but scenes can have have much more, so the way those gradients are used to take the paper (or monitor) range is critical to get a natural image and depth...


Perhaps one key issue about shadow detail quality may be flare, I'm thinking that a 3 stops underexposed area may receive flare enough to decrease microcontrast. Perhaps film can record it, but the scene nature and lens flare can damage that shadow gradient quality.

I'll read about Jones, thanks !

[Pere Casals]

I found a spot meter that has 0.4 flare similar to the camera image, so I agree your meter might already help you integrate flare into your readings. In practice, you might compensate for "already-included" flare by simply placing the shadow reading a stop higher than you otherwise thought, for instance on Zone IV instead of Zone III*. I wouldn't bother over that last third-stop at this point.

The 3 1/3 stops down to the speed point is sensitometric exposure as opposed to what you get in the camera-image.

*Maybe the switch in practice from close-up reading with Weston Master meters to camera-position spotmeter readings had something to do with the change from Zone II shadows to Zone III that I noticed between older references and more up-to-date ones. (So if you use a Weston, place in Zone II or III... if you use a spotmeter place shadows in Zone III or IV).

Now I understand the importance it could had using a probe for metering in the GG, as this metering is TTL and includes flare.

IMHO placing the SLR in the back of the view camera it will be near the same, this is not perhaps necessary for all shots, but IMHO it is a good way to understand the importance of flare, and learning when it is going to have an impact.

Perhaps the change from Z-II to Z-III is due to the 1961 ASA speed change, box speed where changed to the double without any change in the product... this would be a factor if comparing pre to post 1961 literature...

I've a Weston that not works well, but I'll get another one. My plan is uisng the Nikon F5 in the back to make accurate readings and understanding the weston readings, but I feel very pleasing using a weston...

[Stephen Benskin]

Now I understand the importance it could had using a probe for metering in the GG, as this metering is TTL and includes flare.

IMHO placing the SLR in the back of the view camera it will be near the same, this is not perhaps necessary for all shots, but IMHO it is a good way to understand the importance of flare, and learning when it is going to have an impact.

Perhaps the change from Z-II to Z-III is due to the 1961 ASA speed change, box speed where changed to the double without any change in the product... this would be a factor if comparing pre to post 1961 literature...

I've a Weston that not works well, but I'll get another one. My plan is uisng the Nikon F5 in the back to make accurate readings and understanding the weston readings, but I feel very pleasing using a weston...

I would like to emphasize Bill's spot meter flare came from a scene with a full luminance range and not from a test target.

The Zone System didn't change with the change in the speed standard. Even though the older ASA method that used the fractional gradient method and the new ASA method were different, they produced similar speed results. When the standard changed, the results no longer correlated. The change in results naturally lead to conspiracy theories. Many that persist to this very day. When was the last time you read ISO speeds are different than in practice because they are laboratory tested and not testing in a real world situation?

[Bill Burk]

Yes my example scenario was a full range scene. Really, any meter is useful when you adapt to using it. I get a little tripped up when my Zone sticker falls off though.

A Weston meter is calibrated to a different color temperature than modern meters so that can complicate comparisons a little. Your SLR is probably fine.

The flare I see in the meter... I also see by eye. It's really obvious.

[Stephen Benskin]

Yes my example scenario was a full range scene. Really, any meter is useful when you adapt to using it. I get a little tripped up when my Zone sticker falls off though.

A Weston meter is calibrated to a different color temperature than modern meters so that can complicate comparisons a little. Your SLR is probably fine.

The flare I see in the meter... I also see by eye. It's really obvious.

Something else to keep in mind, the full range needs to be within the meter's field of view (spot meter because it has an optical system to create flare). If you are measuring a small dark area and the highlight is outside the optics of the spot meter, then there's no highlight to flare into the shadows. Also keep in mind, the optics of a spot meter aren't the same as the camera lens, so whatever flare is produced in the meter's optics, isn't representative.

[Bill Burk]

Something else to keep in mind, the full range needs to be within the meter's field of view (spot meter because it has an optical system to create flare). If you are measuring a small dark area and the highlight is outside the optics of the spot meter, then there's no highlight to flare into the shadows. Also keep in mind, the optics of a spot meter aren't the same as the camera lens, so whatever flare is produced in the meter's optics, isn't representative.


Haa all these representatives... True the flare I see in my spotmeter is a good "representative" of flare only when my highlights shadows and other tones that I can see in the viewfinder of the spotmeter are distributed in about the same proportions as you might find in the entire camera scene. I thought I had a pretty good test where the result would have been about the same even if I had taken in a wider view. I think the distribution of luminances changed from being isolated to a single dark tone when I was close-up to about average when I stepped back.

If you fill your spotmeter viewfinder with a single tone, easiest way is to move in close, then you remove the flare from the measurement.

Likewise, although the spotmeter optics are not the same as the camera, I think the "calibration" of the meter included assumptions about what the camera optics would be (so it was likely designed to be reasonably representative even though not literally a true representative).

[Stephen Benskin]

Jones was the first to approach the determination of film speed using psychophysics. Previous film speed methods were generally based on an assumption of a characteristic of the film curve. As photography is about the image, the best way is to work backward starting with images considered to be of high quality. The first excellent print test was an exhaustive test where multiple film stocks were exposed differently and processed in different developers to a range of gradients. Then they were printed with a range of print exposure and grades. The prints were then judged for the best quality. Jones found shadow detail was the most critical component in quality determination.

The first excellent print was at a point where print quality drops off quickly as shadow exposure moves to the left of that point. On the other hand, quality increases slightly as the shadow exposure moves to the right and then levels off. The limiting factor with increased exposure is mostly dependent on film size and degree of enlargement. As exposure increases, grain tends to increase and sharpness tend to decrease. The smaller the format, the more pronounced the effect.

166299 166300

The first excellent print represents the extent of the lower limits of exposure that will still produce a quality print. The next step is to find a way to obtain the same results through sensitometrical means. After comparing the predicted results from various speed methods with the print judgement speeds, Jones found the method that came closest to the print judgement speeds under the greatest range of condition is where the shadow gradient is 0.3x the film's average gradient. To be clear, this is not a point of density as the shadow gradient increases and decreases with changes in the degree of development. In fact, Jones states that density is not a measurement of quality.

The determination of exposure and film speed is accomplished using this point as a base, not the aim. Any shadow exposure that falls within reason above 0.3x average gradient will produce a quality image. By using the fractional gradient point as the speed point, it's easy to include a constant into the speed equation to have the exposure fall further up the curve.

The ISO speed fixed density point falls 0.10 above fb+f. The fractional gradient speed point falls approximately one stop to the left, so why wasn't the pre 1960 speed about twice as fast as the post 1960 speed? The ISO speed equation is 0.8/Hm. For a 125 speed film, Hm would equal 0.0064 lxs. The exposure at the fractional gradient speed point would be 0.0032 lxs. Film speed at this point would be 1/0.0032 = 312. Fractional gradient speed is not the pre 1960 ASA speed. Technically speaking, the fractional gradient speed point is the only true speed point. Everything else is an EI. The pre 1960 ASA speed and today's ISO speed is an EI based on the fractional speed point. With the pre 1960 ASA speed, a constant is included in the equation: 1/ (4 * exposure at fractional gradient point). For our .0032 lxs exposure, the resulting speed is 78.

Why did the speed method change in 1960 if the fractional gradient method is superior? Because of the complexity of determining 0.3X, experimental error was easily introduced into the process. The US and Britain wanted an international standard, but Germany didn't like the fractional gradient methodology. C.N. Nelson and J.L. Simonds found an equation that could identify where 0.3X would fall in relation to the easily us use 0.10 over fb+f. When the now ISO contrast parameters of Δ1.30 log-H and Δ0.80 density are maintained, the fractional gradient always falls Δ0.29 to the left of the fixed density point. Any processing above or below the ISO parameters needs to use the Delta-X equation. The ISO standard uses it too as it is part of the parameters. Without incorporating the fixed density method into the Delta-X equation, "the fixed density criterion tends to underrate films that are developed to a lower average gradient and to overrate films that are developed to a higher average gradient," according to Nelson. The safety factor was reduced because accurate exposure meters were more available and small formats were more prevalent. If the fractional gradient criterion was kept, the reduction of the safety factor could have been done by simply changing the constant in the speed equation to 0.4/fractional gradient exposure: .4/0.0032 = 125.

So how does the exposure meter work with the film speed to determine exposure placement on the film, especially when the meter needs to work with b&w negative, color negative, and color reversal films?

[Pere Casals]

Jones was the first to approach the determination of film speed using psychophysics...

Very interesting reading... I've been reading it with a lot of interest.

I found that now we have a new tool in darkrooms: variable contrast paper !

The great thing about variable contrast paper is split grade printing, so we can burn/dodge when the low or high contrast share is exposed. Also SCIM...

IMHO the classic technique you describe it's very interesting... because I guess it is linked with the way Karsh used toe...

Today I see a trend, taking all linearly and then cooking the image in the postprocess, but the way you tell it's very interesting, I'll investigate more about that, thanks for making the effort to write (twice) all that, it has been very interesting to me !

[Pere Casals]

So how does the exposure meter work with the film speed to determine exposure placement on the film, especially when the meter needs to work with b&w negative, color negative, and color reversal films?


Color negative film ISO 5800:2001

Black-and-white negative film ISO 6:1993

Color reversal film ISO 2240:2003

[cowanw]

Very interesting reading... I've been reading it with a lot of interest.

I found that now we have a new tool in darkrooms: variable contrast paper !

The great thing about variable contrast paper is split grade printing, so we can burn/dodge when the low or high contrast share is exposed. Also SCIM...

IMHO the classic technique you describe it's very interesting... because I guess it is linked with the way Karsh used toe...

Today I see a trend, taking all linearly and then cooking the image in the postprocess, but the way you tell it's very interesting, I'll investigate more about that, thanks for making the effort to write (twice) all that, it has been very interesting to me !

How did Karsh use the toe?

[Pere Casals]

How did Karsh use the toe?


Placing his shadows in the right point of the toe, IMHO with concepts described by Stephen in post #47. Shadows can also be placed more in the linear part and worked in the print.

Some of his portraits show it very well, IMHO:


http://farm7.static.flickr.com/6147/5996995473_02e808023a_b.jpg

http://farm7.static.flickr.com/6014/5996996329_282a6bafcb_b.jpg


Here you have a negative

http://img-fotki.yandex.ru/get/6803/165187900.238/0_cf712_979f661a_orig

[Stephen Benskin]

Color negative film ISO 5800:2001

Black-and-white negative film ISO 6:1993

Color reversal film ISO 2240:2003

There are two ways of thinking about film speed, speed as a property of a photographic emulsion, and speed as a practical approach to have as an index to enter into a meter.

From Jack Holm, "Mononumeric speed values provide information about the predicted output at only one point on the characteristic curve. If a speed value is based on shadow density, it will predict only the exposure required to produce that density, and similarly for highlight and other speed point exposure criteria. Also, typical light meters can only read one luminance value for a scene and thereby predict only one film plane exposure. The actual tone reproduction is therefore dependent on: the speed point exposure, the metered exposure, the desired reproduction of the metered exposure, and the difference between the speed point and metered exposures."

This can be seen in the relationship between the exposure constants: P = K * q

P = Exposure constant
K = Exposure meter constant
q = Exposure equation constant

[Pere Casals]

There are two ways of thinking about film speed, speed as a property of a photographic emulsion, and speed as a practical approach to have as an index to enter into a meter.

From Jack Holm, "Mononumeric speed values provide information about the predicted output at only one point on the characteristic curve. If a speed value is based on shadow density, it will predict only the exposure required to produce that density, and similarly for highlight and other speed point exposure criteria. Also, typical light meters can only read one luminance value for a scene and thereby predict only one film plane exposure. The actual tone reproduction is therefore dependent on: the speed point exposure, the metered exposure, the desired reproduction of the metered exposure, and the difference between the speed point and metered exposures."

This can be seen in the relationship between the exposure constants: P = K * q

P = Exposure constant
K = Exposure meter constant
q = Exposure equation constant


What I've seen in ISO norms is a regular way to calculate speed. Speaking about BW, there is a rule that says where (irradiance amount) the linear line starts, with normal contrast, and then we have 3 1/3 stops at right to the grey card irradiance. There is something not strict or ruled: the developer used for the calibration. The exposure meters have a variability of 1/6 stop (IIRC) from ISO min/max recommended K factors.

That "speed as a practical approach to have as an index to enter into a meter", of course, depends on our metering and our process...

So at the end the thing works well, we have an ISO reference, and a practical usage from that reference, what you quote from Holm explains it very well...

[Stephen Benskin]

Real quick on K. K is a constant used in the calibration of exposure meters. It can be considered a light loss constant.

166365

Within the K equation are the elements of the equation to determine the constant q which is part of the camera exposure equation.

166366 166367

And if you look carefully at the equation for K, you can see the exposure constant P designated as K1.

K in part takes into consideration with hand held meters the light loss of the camera's optical system, the target camera illuminance, and any discrepancies created by the meter. The biggest factor being the spectral sensitivity of the meter's photo cell. A selenium cell can have values of r from 1.0 to 1.2 which can create a value of K from 12.5 to 15.0. 12.5 for K is considered the average value where the variables associated with the exposure meter all equal 1.

166368

[Pere Casals]

Real quick on K. K is a constant used in the calibration of exposure meters. It can be considered a light loss constant.

166365

Within the K equation are the elements of the equation to determine the constant q which is part of the camera exposure equation.

166366 166367

And if you look carefully at the equation for K, you can see the exposure constant P designated as K1.

K in part takes into consideration with hand held meters the light loss of the camera's optical system, the target camera illuminance, and any discrepancies created by the meter. The biggest factor being the spectral sensitivity of the meter's photo cell. A selenium cell can have values of r from 1.0 to 1.2 which can create a value of K from 12.5 to 15.0. 12.5 for K is considered the average value where the variables associated with the exposure meter all equal 1.

166368

It is interesting to see how complex are K and q for technicians. I think I finally undertood these formulas. Fortunately photographers don't need to make the calualtion in that way :)

Also it happens that TTL metering bypasses a lot of of the calculation process...

[Stephen Benskin]

It is interesting to see how complex are K and q for technicians. I think I finally undertood these formulas. Fortunately photographers don't need to make the calualtion in that way :)




True, it is theory, and I find understanding theory helps to avoid misconceptions. Adam's K factor conspiracy rant in The Negative is a good example. The exposure meter seeing 18% gray is another. The fixed density of 0.10 over fb+f is 4 stops down from the metered exposure, and on and on...

[Pere Casals]

True, it is theory, and I find understanding theory helps to eliminate misconceptions. Adam's K factor conspiracy rant in The Negative is a good example. The exposure meter seeing 18% gray is another.

Stephen, I'd like to discuss that, because I saw some discrepances.

If I take an spot meter, say a TTL for simplification (Nikon F5 in spot mode for example) and I point to grey card, then the irradiance the meter will recommend should be the point "5" in this chart you posted, does not ?


http://www.largeformatphotography.info/forum/attachment.php?attachmentid=166063&d=1497314127

[Stephen Benskin]

Stephen, I'd like to discuss that, because I saw some discrepances.

If I take an spot meter, say a TTL for simplification (Nikon F5 in spot mode for example) and I point to grey card, then the irradiance the meter will recommend should be the point "5" in this chart you posted, does not ?


http://www.largeformatphotography.info/forum/attachment.php?attachmentid=166063&d=1497314127

It actually does. That is what Holmes meant when he referred to the importance of knowing the values and their relationships. The relationship between Hm and Hg (Hm/Hg), points 4 and 5 on Dunn's graph, is 10x (or 1.0 log-H, or 3 1/3 stops). I started working on a post about this. The importance is expressed in the constant's equation P = K * q. P is K1 in the K equation. 12.5 * 0.65 = ~ 8 (8.11). Factor that into the Sunny 16 equation then compare it to the value of Hm and you'll get 10.

[Pere Casals]

It actually does. That is what Holmes meant when he referred to the importance of knowing the values and their relationships. The relationship between Hm and Hg (Hm/Hg)is 10x (or 1.0 log-H, or 3 1/3 stops). I started working on a post about this. The importance is expressed in the constant's equation P = K * q. P is K1 in the K equation. 12.5 * 0.65 = ~ 8 (8.11). Factor that into the Sunny 16 equation then compare it to the value of Hm and you'll get 10.


OK, I've learned a lot with all that. It was interesting to me to know the intrinsics of K and q. Now I've see all that more clearly. Thanks for teaching all that !!

[Stephen Benskin]

Just to be clear, the note along side of point 5 stating "Statistical average scene with equivocal gray calibration surface" doesn't refer to 18% gray. Under the statistically average conditions, the metered exposure would be an equivalent of 12% reflectance. Now meters read Luminance not reflectance, so 12% is only what the equivalent reflectance would be under certain conditions. What a meter wants to really do is to create an exposure at the film plane of 8 / ISO.

[bob carnie]

My second year instructor was a good friend of Mr Karsh , I was lucky enough to meet him at our school when he visited George Lazi . As well a student Dean Macdonell worked at Karsh Studios for a period of time.

Not sure if mentioned here, but Red Coccine was used to open up shadow detail and pencil retouching was applied in all the printing for Mr Karsh. There is a reason why he gets the sparkle so to speak.

My first boss Slobodan Filipovich was a master of Red Coccine like many, many of the European Photographers that came to North America
after World War 11.

[Pere Casals]

Red Coccine was used to open up shadow detail and pencil retouching was applied in all the printing for Mr Karsh.


Red Coccine and a pencil... these tools is what defines what a master is. Today we have tons of supercomputing power, and no portrait like those.

[bob carnie]

We still have people making great portraits, don't kid yourself thinking otherwise.

[Pere Casals]

We still have people making great portraits, don't kid yourself thinking otherwise.

Yes, great portraits, but not like those, IMHO. Technically perfect, aesthetically perfect, perfect illumination, perfect (14") perspective, perfect toe, perfect highlights, perfect volumes, perfect defocus, perfect depth, perfect chiaroscuro, perfect psycho, ...and perfect subjects !

Pulling Churchill's cigar to make him look like that... britons got the message, and nazis understood they were not going to surrender.

One thing is taking a photograph of a face, another one is to photograph the soul.

I'm still a green learner, but as I know the more about portrait I feel the more that YK was the single one of a kind.

[bob carnie]

I am not a big fan of his work, yes there are some great historic images, but get past Churchill and he has a weird way of posing with the hands which I find quite silly. I would take August Sanders portraits any day of the week.

[Pere Casals]

I am not a big fan of his work, yes there are some great historic images, but get past Churchill and he has a weird way of posing with the hands which I find quite silly. I would take August Sanders portraits any day of the week.

There a lot of brilliant portrait photographers, of course, I like a lot Newton in the fashion side. But with YK I see the 3D in a very special way, I feel the volumes like if it was about stereo images.

I think he only respected 3 subjects, with true solemnity: Mother Theresa, Mandela and Queen Elisabeth II. In this order.

With others I see a big deal of irony and humor.

Kennedy was karshed as if it was his First Communion, when he was a happy womanizer...

Andy, with big brush, Bardot vs Audrey (different way to have sex?) , Picasso with his big nose always near to a naked woman :) A lot showed insane proud from their achievements, or their narcissism, like Castro...

All that irony makes smile...


Mother Theresa portrait is the one I like the more. Soul can be seen. She was a humble person, and my guess is that he used humble light to make that soul shine the most.

No other portrait of Theresa shows that plain goodness.