film calibration: what is the difference between using a DSLR and Spot Meter?

[dikaiosune01]

I’m currently profiling some Ilford HP5 with my DSLR (500D +24mm f/2.8). Sure, having a custom profile that fits for Ilford HP5 would be awesome, and I can profile some similar films as well. However, I wonder if there is any significant differences between using the Sekonic 758D (with profile targets) against a normal DSLR.

[dperez]

I’m currently profiling some Ilford HP5 with my DSLR (500D +24mm f/2.8). Sure, having a custom profile that fits for Ilford HP5 would be awesome, and I can profile some similar films as well. However, I wonder if there is any significant differences between using the Sekonic 758D (with profile targets) against a normal DSLR.

There are several threads on this already. You might search the forum.

[Bob Salomon]

Angle of view. Are you reading the same thing? The meter reads one degree, do you know how long a lens you would need to read one degree?
The spectral response of the camera and the meter can be quite different. It is very easy to hand hold a one degree spot meter for a reading.

[Leigh]

DSLRs attempt to "analyze" the scene and suggest an exposure based on that analysis, which may not agree with your analysis.

Better to avoid them entirely if you want to use your view of reality rather than some engineer's.

- Leigh

[Brian Ellis]

DSLRs attempt to "analyze" the scene and suggest an exposure based on that analysis, which may not agree with your analysis.

Better to avoid them entirely if you want to use your view of reality rather than some engineer's.

- Leigh

I'm not sure I understand. I use the spot meter on my DLSR pretty often. I'm not aware that it is suggesting an exposure on any analysis other than evaluating the spot I'm metering. Isn't that what a hand-held spot meter would also be doing?

[Leigh]

I'm not sure I understand. I use the spot meter on my DLSR pretty often. I'm not aware that it is suggesting an exposure on any analysis other than evaluating the spot I'm metering. Isn't that what a hand-held spot meter would also be doing?
The OP did not mention a spot meter, nor did I in my response to his post.

He did mention a 24mm lens, which would render a spot meter rather useless due to the wide angle of view.

My comments were based on the operation of the matrix meter system used by all modern DSLRs. They say right in the manual that these systems attempt to "analyze" the scene and determine the most appropriate exposure based on that analysis.

If you choose to use an internal spot meter function, your results will vary depending on the focal length and speed of the lens in use. A real spot meter would not suffer from these limitations.

- Leigh

[Nathan Potter]

What can I say? I think I know what you want to do. I believe you want to calibrate your HP5 film using your DSLR. First if you do that the film response will be calibrated only to that DSLR. Unless you use that DSLR as your exposure meter in the field your film will not be calibrated.

Second if you use a wide angle lens with the DSLR, make sure the whole field of view is evenly illuminated OR if the exposure determining area is different than the complete field of view make sure that it is evenly illuminated. You want to accurately sense a field of known brightness then relate that to a resulting film density for a particular set of processing conditions.

There would be no significant difference in using a DSLR than the Sekonic since you are calibrating your film based on one or the other. But you need to use the unit you calibrated with for all the subsequent exposure determinations.

Remember that full film calibration takes place with a particular meter, film and process. Change any of the three elements and you will no longer be calibrated.

Nate Potter, Austin TX.

[Frank Petronio]

Even Ansel didn't profile his film to his meter. But surely it must be urgent to do it now.

[Brian Ellis]

The OP did not mention a spot meter, nor did I in my response to his post.

He did mention a 24mm lens, which would render a spot meter rather useless due to the wide angle of view.

My comments were based on the operation of the matrix meter system used by all modern DSLRs. They say right in the manual that these systems attempt to "analyze" the scene and determine the most appropriate exposure based on that analysis.

If you choose to use an internal spot meter function, your results will vary depending on the focal length and speed of the lens in use. A real spot meter would not suffer from these limitations.

- Leigh

True, you didn't mention spot metering. You didn't mention matrix metering either or any other particular method, you just talked about "dslrs," many of which have three, four, or five different methods of metering. I wasn't arguing with you, I was just trying to understand what you were saying. And now that I understand you were talking about matrix metering I understand. Thanks.

[dikaiosune01]

I would like to thank everyone for their responses. Through the clarity of not writing late at night, and rethinking what I want to say; I acknowledge that this question does seem a lot of a similar threads on the forums. So allow me to rephase, if you will bear with me please.

- What advantages does the Sekonic 758D have over the a DSLR for calibrating film?
- When assessing the film/scan/print process... ... Am I correct to say that more detail is lost in a scan than a wet print process? Or is the evaulation of the Negative more ideal.
- What are your experiences with the Sekon 758D? Did you regret your purchase?

[Ken Lee]

Most people shoot most films at the manufacturer's recommended speed, or at 1 stop slower. For HP5+, that means either 400 or 200.

What really matters is developing time in your developer of choice, if you develop your own film. (If you don't, then the whole exercise is questionable.)

When it comes to developing, most people end up rather close to one another too. That makes sense: same film, same developer, etc. In this era, it's not too hard to get an accurate thermometer. What really vary are agitation and water. If you use distilled water, then you've eliminated that variable too.

When doing your own developing, it's helpful to establish your N-1 and N+1 times. If you perform development by inspection, even this is rarely necessary.

[Neal Chaves]

I am using HP5+ now, having formally used TXP. I ran some HP5+ exposure and development tests and also used a digital camera in B&W manual mode at film speed of 400. The results agreed with my Spectra incident meter with flat diffuser. Rating the HP5+ at 400, I make prints on grade 2 paper with cold light head that match the digital proof from negatives developed in Kodak HC110 1:31 for 5 minutes at 75F. You might try this as a starting point.

If you don't need the speed and want the best quality and easy printing, try rating at 100 and develop in HC110 1:63 for 6:30 at 75F or 1:31 for 5:00 at 68F.

Expansions and contractions can be done by varying dilutions and keeping development time constant. For example, developing for 5:00

N-2, rate film at 25 and dilute .5:31.5
N-1, rate film at 50 and dilute .75:31.25
N, rate film at 100 and dilute 1:31
N+1, rate film at 200 and dilute 1.5:30.5
N+2, rate film at 400 and dilute 2:30

Make sure to use at least .5 oz, preferably 1.0 oz of the concentrate for each 8X10 sheet or four sheets of 4X5 film. HP5+ seems to me to be a near clone of TPX as far as exposure and development.

[Henry Ambrose]

I think you can do this with our DSLR by simply being consistent with your metering technique. But you're carrying two cameras and probably more stuff to go on them. I'd buy a meter. I have a couple of Sekonics and they work very well but not as new or as the one you mention.

The meter is not all that important as long as it gives repeatable readings and you use it consistently. For much outdoor photography you should be able to get by without looking at a meter. "Sunny 16" works just as it always has.

I'd rate HP5 at 250 for convenience sake. You could use 200 or 320 and get fine results but 250 is good since it coincides with a standard shutter speed and the math is easier. HP5 may be one of the most adaptable and easy to use films ever, just work out a consistent scheme of exposure and development that works for you.

[Kevin Crisp]

It depends on what you mean by "calibrating film." And it REALLY depends on what you are going to use for a meter in the field. If your plan is to carry around a DSLR then you should be adjusting film speed and development times so you like your negatives when you use your DSLR for a meter.

There are a fair number of people who do use a DSLR for exposing tricky, less forgiving materials like transparencies. The theory is that the programmers' judgment on the DSLR is probably as good as their own with a hand meter. For B&W, I certainly wouldn't suggest doing that. Get a spot meter, learn the proper way to do a film speed test and a development test and away you go. Fred Picker's Zone VI Workshop describes a good, simple approach.

You certainly can, as Frank suggests, simply use a meter at whatever film speed you want to try (rated speed, maybe half rated speed) and make minor adjustments in developing time and get decent negatives. I think doing a proper test and then using a spot meter is worth the one time effort, but not everybody feels that way.

[Ken Lee]

I think a digital camera serves much better as a "B&W Viewing Filter" than as a light meter. For that, a simple point-and-shoot camera is sufficient. I never used Polaroid for this purpose, but I can see why a digital camera could prevent the waste of Large Format film - especially when shooting 8x10.

[Brian Ellis]

Angle of view. Are you reading the same thing? The meter reads one degree, do you know how long a lens you would need to read one degree?
The spectral response of the camera and the meter can be quite different. It is very easy to hand hold a one degree spot meter for a reading.

No, I don't know how long a lens I'd need because that varies. I often can just walk up to the subject and read the darkest important shadow with whatever lens is on the DSLR, same as I often do with a hand-held meter. Do you know how big a spot you're reading with a one degree meter when the object you're metering is hundreds of yards away?

[Bob Salomon]

No, I don't know how long a lens I'd need because that varies. I often can just walk up to the subject and read the darkest important shadow with whatever lens is on the DSLR, same as I often do with a hand-held meter. Do you know how big a spot you're reading with a one degree meter when the object you're metering is hundreds of yards away?

Yes, whatever shows in the finder of a 1° spot meter. But you would not know how big that spot is when using a camera to do the reading.

[Brian Ellis]

Yes, whatever shows in the finder of a 1° spot meter. But you would not know how big that spot is when using a camera to do the reading.

I'm pretty sure the spot meter in my camera works the same way as a hand-held spot meter.

[Drew Wiley]

Just too much extraneous nonsense going on inside most techie cameras to make them
a good substitute for a dedicated spotmeter. If you're used to them I guess it's OK,
but they have certain kinds of bias based on what the camera is programmed to do.
I do sometimes use the internal meter on my otherwise totally mechanical Nikons.
But I just don't like any kind of camera where your viewfinder resembles the control
panel clutter in an airplane cockpit. Pentax digital spot meters for me. Predictable day
in/day out, and only need minor recalibration about every ten years.

[John Koehrer]

I'm pretty sure the spot meter in my camera works the same way as a hand-held spot meter.

But you said you didn't actually know the angle of view of the DSLR. But you know it changes with different lenses.
It works the same way as a spot meter in that it reads reflected light, But not at a consistant angle.
Even at closer distance your camera reads a larger section of the subject(dependent on lens), The spot always reads a smaller section!

Face it, you're just arguing because the facts presented don't agree with your opinion.

[Nathan Potter]

Some interesting points here. In fact the reading of the Pentax 1 degree meter is influenced by the intensity of the light surrounding the 1 degree spot. If that difference is great (several stops) the influence can be a stop or more. This can be checked by doing a test by back lighting an area equal to the 1 degree spot. Of course normally, in general use, the brightness surrounding the 1 degree spot is quite similar to the area of the 1 degree spot so the influence is small to negligible. Under most circumstances it is advisable to have the area being 1 degree metered a fair bit larger than the 1 degree spot in order to minimize off axis brightness influence.

In the case of a DSLR you really need to know what subject area you are metering, and that is often ill defined. The only safe method with the DSLR is too make sure the subject area to be measured is contained wholly within the field of view and is of uniform brightness. I suppose there are some DSLR cameras that have the sensing area delineated by markings in the viewfinder but I've not run into that kind yet.

The issue of angle of view at the sensor when using a DSLR is irrelevant, as long as you use the same lens for metering as used for the initial calibration. Changing lenses would be an unacceptable variable making calibration useless unless one generates a chart of brightness vs lens correction values.

Nate Potter, Austin TX.

[Ivan J. Eberle]

Apart from smaller package, from my point of view there's not much to recommend a dedicated spot meter over a really good SLRs spot meter. Something that I'd definitely check before spending as much on a dedicated spot meter as a camera with one is what type photo cell it uses for metering.
One major benefit to the 1% spot metering in my late model Nikons is that the metering is using an RGB sensor which is largely immune from errors due to color temperature. Traditional meters using Selenium or CDS or Silicon cells are calibrated at one specific color temperature and you have to extrapolate from there. (There's a long thread from last year relating many user's experiences with their spot meter calibration.)
Another major benefit to a camera used as a 1% spot meter is that it also takes photographs-- e.g for times when the light is changing too fast to set up a view camera.

[Drew Wiley]

Use a lens shade on a spotmeter just like on a camera lens and flare will be a minor
issue unless you're aiming right toward the sun or some other intolerable source of
glare. And multicoated meters like the Pentax digital are obviously going to be better in this respect. A major advantage of a dedicted meter over a DLSR is that
those things aren't calibrated to any universal standard, just to the needs of the
particular model. You might get accustomed to how a particular DLSR metering mode works, but when the camera itself becomes unservicable or you just get tired
of it, you have to start the learning curve over. Besides, a good spotmeter doesn't
cost anymore than a typical lens for one of those things.

[Brian Ellis]

Use a lens shade on a spotmeter just like on a camera lens and flare will be a minor
issue unless you're aiming right toward the sun or some other intolerable source of
glare. And multicoated meters like the Pentax digital are obviously going to be better in this respect. A major advantage of a dedicted meter over a DLSR is that
those things aren't calibrated to any universal standard, just to the needs of the
particular model. You might get accustomed to how a particular DLSR metering mode works, but when the camera itself becomes unservicable or you just get tired
of it, you have to start the learning curve over. Besides, a good spotmeter doesn't
cost anymore than a typical lens for one of those things.

I'm not sure exactly what you mean when you say "those things aren't calibrated to any universal standard, just to the needs of the particular model." I've read that Nikon says it uses the ANSI standard. Where do you see that Nikon and others don't or that manufacturers of hand-held meters do? And of course even the ANSI standard itself doesn't mandate the exact same calibration standard for all meter manufacturers.

A few months ago I sold a Pentax digital spot meter to a member here. He wanted some indication of the accuracy of the meter. I ran some comparison tests between it and the spot meter in my digital camera. The readings were virtually identical. So I'm as comfortable with the accuracy of the meter in my digital camera as I would be with a hand-held spot meter.

[Nathan Potter]

There are three kinds of meter calibration that are relevant. Intensity, linearity and spectral response. Of the three linearity is the most important since you want a subject brightness reading to be consistent over a range of brightnesses. The spectral response is a characteristic of the sensor and is fixed for a particular kind of sensor material (there is nothing you can do about it). The absolute intensity calibration is really irrelevant as long as it remains consistent over time.

The task of the photographer is not to calibrate the meter but to calibrate the film using the meter in its current condition, then periodically check that the meter remains calibrated by exposing the film and processing it in a consistent fashion. Essentially the film itself is used to ensure the meter calibration remains constant.

It doesn't really matter what the meter is, DSLR, spot meter, home made, etc. as long as it's linear over a SBR and produces a consistent film density.

Nate Potter, Austin TX.

[Tony Evans]

As is well known, digital cameras underexpose by about 1/3 to 2/3 a stop, in order to protect against overblown highlights. My K20D in spot mode does this, checked against my Soligar Digital Spot which is callibrated annually. For 4x5 I always use the Soligor.

[Leigh]

The spectral response is a characteristic of the sensor and is fixed for a particular kind of sensor material (there is nothing you can do about it).
That's true if you look at the sensor as an individual component, but not when you look at it as a component of a metering system.

Zone VI installed a filter to change the spectral response to match that of the film.

- Leigh

[engl]

Yes, whatever shows in the finder of a 1° spot meter. But you would not know how big that spot is when using a camera to do the reading.

The viewfinder of my DSLR has markings for the area used for spot metering, as do many other SLR/DSLRs.

Many compact cameras have this as well. As an example, a Samsung WB650 at the tele end has a 7 degree diagonal field of view. The spot used for spot metering is incidentally about 1/7th of the full image diagonal, in other words a 1 degree spot. The lens can of course be zoomed out if you'd rather have a 3 degree or 10 degree spot.

A spot meter is a tool built specifically for one purpose and is of course better, no setup time, easier read-out, no risk of menu choices spoiling your metering, or reliance on special batteries and chargers. A digital camera can be a very good meter though, and it is also quite handy as a viewfinder, B&W viewer, and sometimes even as a camera :)

[Drew Wiley]

Well, movie sets have used spotmeters for a long time because they're so functional. If you're traveling with both a view camera and DLSR anyway, why not
use the little camera for metering? But I'd personally just find all the interpolation software built into those things to be highly distracting, especially if you have to
routinely switch from various snapshot programs to something better suited to view
camera film. Just one more thing to go haywire when you're under pressure. We all
get used to our meters, however. When I was a teenager, all I shot was Kodachrome
and Agfachrome in an early Pentax with a coupled external CDS meter which read
at a 45% angle of view, just like a 'normal' lens. Primitive or not, I can't ever recall
an incorrect exposure after thousands of shots. But what goes on inside a camera
does affect things, and now I have two manual Nikons, an fm2n and fm3a which
meter differently, even though if you read a gray card they come out identical.
The only way to know for sure is either to routinely practice with each meter separately, or make the readings with the spotmeter, which is predictable in the
same manner with every potential application.