Film speed testing: Help! am doing something wrong

[aruns]

Hello LF'ers,
I need some help with figuring out what I am doing wrong:
I apologize for the long post, but I wanted to add relevant details.

Objective/background:
Am trying to determine my personal film speed using Bruce Barlow's instructions in his book (Great book, thanks Bruce!).
Film: Arista Edu Ultra 100 4x5 film. Lens: Rodenstock f/6.8 90mm. I don't have a densitometer, so I wanted to try it with 0.1 ND filter.

Setup:
* flat, dark brown towel in almost-even shade, Sunny day
* filled the ground glass with subject, set lens to 90mm from film plane ("infinity?").
* metered the center of towel, with spot meter, stopped down 4 stops.
* stayed with 1/4 and 1/8 sec for shutter speed, to avoid reciprocity variables.
* ended up with four exposures.
A. around f18, 1/4 sec. (ISO 100). Exposed full slide (by mistake).
B. around f18, 1/8 sec. (EI 200). Exposed half slide. Remaining half should be FB+F.
C. f/16, 1/4 sec. (EI 75). Exposed half slide. Remaining half should be FB+F.
D. around f/14, 1/4 sec. (EI 50). Exposed half slide. Remaining half should be FB+F.

Development:
Rodinal "normal" 1+50 development: 7 minutes at 68F (I started with 68, but it crept up with time. the room / tap water temp was about 75F). Gentle Agitation: 30 sec in the first minute, then 10 sec / min.
Stop: I used plain water for 2 minutes.
Fix: Ilford Rapid fix - 1+4, for 5 minutes.
Wash: 5 minutes in water.
(I made a mistake during development - I lost track of slides between A and B, as well as between C and D. But I do know which sheets are A&B and C&D).

Problem:
The negatives do not show the density differences as they should. Please see attached images.
1st pic shows the negatives in a sleeve (with a white paper underneath).
2nd pic shows negs with 0.1 ND filter placed on the FBF area of one negative. The exposed areas of the negatives are nowhere close to how it should look.
3rd pic - it is a scan of RC print I made using the film and lens, exp. @ 100. I know this combo works.. But what am I doing wrong? why this under exposure?.. (I checked the lens/shutter, but it seems to open properly).

Please help, Thanks much in advance!

Regards,
Arun

102621102622102623

[ic-racer]

The density you got 'is what it is.' That is to say the EI in your system is going to be lower than your lowest test. That could easily be the case for that EDU-100 film. Which is to say try doing your test at EI of 50, 25, 12, 6 etc and see what you get.

[ic-racer]

Also, consider using a light table when checking the negatives. If you set any ND filter on a white piece of paper, its apparent density will double. The light is filtered once when it goes through to the paper and a second time after it bounces off the paper on its way to your eye.

[C_Remington]

Just use box speed and an incident meter and be done with it. As long as your shutter is in working order, and most of your subjects are of average contrast, you'll be fine 99% of the time. Any other adjustments you can make in the print process where all the magic happens anyway.

[Bill Burk]

Like ic-racer hinted, I believe your lowest rating (EI 50) is probably where you should work.

That only one sheet of all four show anything apparent, is the clue. I wouldn't expect to hold 1/3 stop accuracy if your temperature is between 68-75-degrees F.

You could re-do the test, but 50 seems a perfectly reasonable EI result of a Zone System camera test for an ISO 100 film.

[Robert Langham]

A properly exposed silver negative will have all of the information from the exposure- (the actual picture), rendered as silver sitting on, (or in) a base of plastic film. The exposed silver is the image. The base is the base. When you contact print the negative on a #2 grade paper just long enough for the film base to print down to maximum black the tones you see are the actual exposed silver negative. Any meter should have the ISO adjusted until you make negatives that will contact print just long enough to print the base down to maximum black....and have the image of silver visible in its appropriate values.

Some developers give more ISO speed, some less. Some meters have to have the ISO cheated up, some down. It shouldn't be anything too far off the mark or something is amiss. TriX and HP5 run between 200 to 600. FP4 tends to run from 64 to 200. If you get TX at 64 and FP4 at 400....something is not working.

I keep a close eye on meters and exposure. I keep a couple of spot meters and check them against each other regularly. If you WRITE DOWN your exposures you will quickly get to where you know what they are going to be for more situations than you might imagine. The writing down part seems to train your mind quicker.

102649 Map of the South Dike at Shiprock of printed googlemaps taped together.

[aruns]

Hello all,
Thank you for your inputs, really appreciate it.

IC-Racer, Bill, thanks for the leads. I will try to do another set of tests starting from Iso 50 and below.

Remington, as I was explaining to Tim, I started off with incident metering, box iso speed, diafine (no time / temperature constraints)..
After several sheets of film, a few printing sessions, couple other developers, etc. am questioning myself if there's a better way to get negatives that would make printing easier.
Per my understanding, one of the important factors in standardization and exposure predictability is film speed testing (am also working on the others such as contrast control, development time/ temperature control, etc.). that's what led me here.

Robert, Yes, i am working on the "contact printing of the negative on a #2 grade paper just long enough for the film base to print down to maximum black". I some times compare the sekonic meter with my nikon digital meter, and they seem to agree. Thanks for your other inputs too, I will work on the note taking.

Best regards,
Arun

[Sevo]

A properly exposed silver negative will have all of the information from the exposure- (the actual picture), rendered as silver sitting on, (or in) a base of plastic film. The exposed silver is the image. The base is the base.

As far as I understand the ISO (German translated version as per DIN publication) specifications, "base fog" (in the German translation "Grunddichte") is NOT the tint of the plastic base substrate! It would be the cumulated density of the base substrate tint plus any gelatin layers tint and most notably the exposure independent constant fog ("Schleier") across the entire film area. In practical terms, you must zero the densitometer on an unexposed area of the same film. You can't zero it on a area of bare plastics, nor on reference film fixed without development or treated in a different process.

Besides, there is no printing going on in a proper test - the sensitivity is calculated from step wedge exposures measured with a densitometer right on the negative. And "base fog" is not the deepest shadows, but 0.1D beyond it.

[Leigh]

Just use box speed and an incident meter and be done with it. As long as your shutter is in working order, and most of your subjects are of average contrast, you'll be fine 99% of the time. Any other adjustments you can make in the print process where all the magic happens anyway.
Definitely true.

The manufacturers have run more tests than you could in three lifetimes, using accurate laboratory equipment and tightly-controlled processes.

If you find that your results are not "proper", by whatever definition you choose, then you can adjust your processes accordingly.
The trick is to look at real images of real subjects.

As an aside, I can make absolutely no sense of the negatives presented in the original post.
They certainly do not represent a three-stop exposure range, and none of them show an unexposed half-sheet.

- Leigh

[Leigh]

As far as I understand the ISO (German translated version as per DIN publication) specifications, "base fog" (in the German translation "Grunddichte") is NOT the tint of the plastic base substrate! It would be the cumulated density of the base substrate tint plus any gelatin layers tint and most notably the exposure independent constant fog ("Schleier") across the entire film area. In practical terms, you must zero the densitometer on an unexposed area of the same film. You can't zero it on a area of bare plastics, nor on reference film fixed without development or treated in a different process.
That's correct. The "fog" is the result of the developer acting on unexposed emulsion.

It has a measurable density greater than the bare film support (plastic or whatever), but not by much.

- Leigh

[aruns]

Thanks, Sevo.

Hi Leigh,
Thanks for the response.


Definitely true.
As an aside, I can make absolutely no sense of the negatives presented in the original post.
They certainly do not represent a three-stop exposure range, and none of them show an unexposed half-sheet.
- Leigh

Exactly!!! - that's my problem: Aren't the sheets supposed to show the three stop exposure range, and the left and right sides supposed to show the difference between exposed and unexposed halves?!
Conventional wisdom says that for the (box and slower) ISO’s / apertures / shutter speeds exposed, there should be SOMETHING between the left and right half of the sheets. Why isn’t there any difference?
This is why I was confused, and started this thread. The only logical explanation that I can think of, is what IC-Racer and Bill Burk said.



The manufacturers have run more tests than you could in three lifetimes, using accurate laboratory equipment and tightly-controlled processes.

If you find that your results are not "proper", by whatever definition you choose, then you can adjust your processes accordingly.
The trick is to look at real images of real subjects.


I agree. Here are scans of two negatives, exposed with the same lens, film and same box ISO 100 and same developer (Rodinal).
The lakebed image was anticipated to have a wide Subject Brightness Range, and was given 1+100 compensating development.
The Bodie image was given 1+50 “normal” development.
http://www.flickr.com/photos/suspended-animation/10002835876/
http://www.flickr.com/photos/suspended-animation/10002834866/

While the Bodie negative has a well defined tonal range, I had to “print through” the lakebed to get the image details that I was looking for. When I print for shadows, am losing highlights, and vice versa.
Research on this led me to "printing the negative just long enough for the film base to print down to maximum black" -- which finally led me to give film speed testing a shot.

Of course, I readily admit that I am a noob, been doing LF / Film for 1 year, have only done 3 or 4 print sessions in my life. I only have a condenser enlarger and use RC MG paper. I consider myself a student, and all this a part of the learning process. As I learn, I'd like to keep things simple, reduce the variables, etc., and was certainly influenced by your earlier posts on the topic (ex., keep it simple, use incident metering, box iso, etc.).

But the questions I am asking myself are:
- Is “personal film speed determination” is part of “... you can adjust your processes accordingly... ”
- Will it help me get negatives with better tonal range, and make the whole exercise (of exposing, developing, printing) more predictable?
I am not (yet) wedded to the personalized film speed approach. If it doesn't work for me, I may go back to box ISO. But am curious to see how others are handling this, and if it is something that I can learn/adapt.

Thanks much once again,
Arun.
(By the way, the responses to this thread has been a tremendous learning opportunity! I have taken these responses, gone back to the books, my other negatives, and been trying to crystallize the problem as well as logical options for solutions. Thanks for all the LF'ers who make this forum so great!!)

[Leigh]

Exactly!!! - that's my problem: Aren't the sheets supposed to show the three stop exposure range, and the left and right sides supposed to show the difference between exposed and unexposed halves?!
Conventional wisdom says that for the (box and slower) ISO’s / apertures / shutter speeds exposed, there should be SOMETHING between the left and right half of the sheets. Why isn’t there any difference?
You're correct. We certainly should see a difference from one neg to another, and between the two halves of each.

I've been using Rodinal as my standard developer for almost 50 years, so I'm reasonably familiar with its behavior.
This is either a processing problem or a gross under-exposure (no effective exposure at all).

On edit: I just noticed this line from your original post: "* metered the center of towel, with spot meter, stopped down 4 stops."
That's your problem. The metered exposure will put the reflectance of the towel at 18%, which is medium gray.
The four-stop reduction will reduce that by a factor of 16, to about 1%, which is dead black. The negative received no exposure.

It sounds like that procedure is designed to determine the threshold sensitivity of the film, which requires a densitometer.
That is one accurate way of measuring film speed, particularly for those who consider shadow detail to be important.


I had to “print through” the lake bed to get the image details that I was looking for. When I print for shadows, am losing highlights, and vice versa. Research on this led me to "printing the negative just long enough for the film base to print down to maximum black" -- which finally led me to give film speed testing a shot.
That sounds like you're using the wrong paper grade. If your density range exceeds what you can realize in a print, use a lower paper grade.

Also, this is a creative decision based on how you want the final image to look. Absolute adherence to a luminance/density correlation from
subject to final print may not produce the photograph you want. Ansel Adams was a wizard at modifying tonal ranges to change emphasis.


But the questions I am asking myself are:
- Is “personal film speed determination” is part of “... you can adjust your processes accordingly... ”
- Will it help me get negatives with better tonal range, and make the whole exercise (of exposing, developing, printing) more predictable?
I am not (yet) wedded to the personalized film speed approach.
Regarding "personal" film speed, there are actually two components...
1) Adjustments required because you use a development regimen that differs from that used by the manufacturer for testing.
2) Adjustments that change the results to better correspond with your personal opinion of how the finished print should look.

Changing development times (N-1, N+2, etc, in Zone System terms) changes the density of the highlights.
It does not change the density of the shadows at all. Shadow density is controlled solely by the exposure the film receives, nothing else.
Of course you'll find this cast in stone in "Expose for the shadows, develop for the highlights."
As a practical matter, film speed relates directly to shadow detail, not to highlights. If there's zero density in the shadows, they print black.

Unless you shoot unusual subjects (coal in a snowscape at high noon), you should find the standard film speeds to be accurate.
Some processing adjustment can be made if necessary to restrain the highlights, or boost them if the scene is abnormally flat.

If possible, try to standardize on this phase of the process, and reserve your adjustments for the printing phase.
That's why graded (and variable-grade) papers exist. It's much easier to use the tools that have already been invented.

I must confess that in almost 60 years of darkroom work, I've never adjusted development times in the sense of N+1 et al.
I have adjusted times due to different temperature, but not with the intent of changing the luminance/density correlation.
I suppose some of my negatives might have benefited from such an adjustment, but they've all printed to my satisfaction.

- Leigh

[aruns]

Hi Leigh,
I just got a chance to check the forum, so I apologize for the delay. Also, thanks very much for the detailed post.
I will need to read it a few more times before I understand the content fully!
If I have more questions on this topic, I will post a follow up here (or start a new topic).

Best regards,
Arun

[Bill Burk]

Hi Arun,

I think Leigh wrote some good wisdom.

While I regard box speed with respect, I wonder if maybe box speed is something you achieve when you are good at developing film. I figure even when I do a good job, I probably get 1/3 stop less than box speed. I plan to do some more research on this, but I am thinking that a student might make a mistake or two in processing and that the usual result is a "loss" of speed.

So the simple solution, and I think it is a good solution, is to "overexpose" by rating the film at 2/3 stop less than box speed. For example to shoot 400 speed film at 250. So far that "strategy" has been serving me well...

[Doremus Scudder]

Arun,

Apologies in advance if this is long, but there seems a lot to address here.

I do film-speed tests similarly to how you did yours. Your approach is basically sound. I would advocate a couple of changes and retesting.

First, by filling the frame with your towel, and getting very close to it, you may be eliminating a lot of flare from your exposure, something that does not happen in real life. Repeat your test with a white and dark towel, filling half your frame with the white towel (meter it too, and note which Zone it falls on for control reference). Do set your lens at infinity, like you did, so you have no bellows factor messing up the results. Keep your shutter speeds low, like you did. Meter the dark towel, place it on Zone I by underexposing 4 stops like you did. And, pull the darkslide halfway, like you did, so you have a large area of film base + fog (fb+f).

The reason for the white towel is to introduce some flare into your system. Even the best optical systems have flare. Unless you take photos of only dark things, there will be light areas in your scene, which will cause flare and affect the shadow values. Manufacturers take this into account when designing meters, film, etc. You should too, especially with your older, single-coated lens.

So far, so good... You should have the following exposures: Zone 0, the fb+f area, Zone I, the dark towel and some higher Zone for the lighter towel (which you have determined with your meter).

Given your previous results, base your exposures around half box speed. Make big differences; one exposure at box speed, one at one stop under and another at one stop over. Develop for the same time you develop negatives of average scenes that print well for you.

Your resulting negs should have a clear fb+f area, a noticeable fairly dense area (the white towel) and your Zone I exposure (your dark towel).

If you are not getting Zone I densities with the test performed this way on at least two of the negs, something is very wrong with your meter/shutter/etc.

I am not familiar with Bruce Barlow's method of comparing the Zone I density to the fb+f area and a 0.1ND filter. However, the ND filter you show in your pictures is definitely NOT 0.1. A 0.1 ND filter should be 1/3-stop density, i.e., Zone I, which is really, really light. Either get yourself a reliable 0.1 ND, send your negs to be tested with a densitometer, or do as I do, and as suggested above, and determine your effective Zone I by "proper proofing" your neg.

This latter, i.e., "proper proofing" is not as accurate as using a densitometer, but has the advantage that it uses your enlarger and printing paper, thus tying your entire work-flow together. The idea is to print your test negs at the minimum exposure it takes to reach maximum paper black for the fb+f areas of your negative. Don't contact print! Enlarge your negative using the lens you plan to use printing (or a representative lens if you have many). Again, this is to introduce the flare present in your enlarger's optical system into the test.

Make a test strip with large intervals to find about where your "proper-proofing" exposure should be, then refine this using smaller intervals. Include the white towel in your test strip if you can.

Now, examine your negatives in light that approximates the kind of display lighting you would like for your prints. Too strong or dim and you'll end up rating your film wrong. The problem is with "first maximum black." In bright light, you will see a lot more gradations of black as your test print exposures get longer than in dimmer light. In too dim light, your "first maximum black" will be rather gray in brighter light. Our eyes are much more sensitive in bright light than in dim. Err on the side of too bright light if you have to.

Anyway, realizing that this is a subjective part of the test, evaluate your negs at your chosen light level and find the minimum exposure that prints the fb+f areas of your negative to a black that is indiscernible from the next more-exposed strip. Use this as your "proper proof" exposure and make prints of your negatives.

Find the Zone I density that is just slightly above the black of the fb+f area. Remember, Zone 0 and Zone I are NOT one stop apart. Ideally, Zone I should be exactly as black as Zone 0 without having got too much exposure. The only way to really know, however, that we are at the threshold of exposure is if there is a tiny, minuscule difference between Zone 0 (fb+f area) and Zone I. If you choose a Zone I density too much lighter than Zone 0, you will end up rating your film too slow. Remember, we really want Zone I to be as close to maximum black as possible.

The Zone I exposure that appears almost as black, but not quite as black... maybe it's the same... maybe it's a skosh lighter.... Anyway, that one, that is almost indistinguishable from Zone 0 is the exposure you should base your film speed on.

If the ideal place for Zone I falls in between the exposures on your test negs, then extrapolate. At this point, you will only be off by 1/3 stop and that's well within an acceptable margin of error. If you shoot on a tripod and don't have too much problem with subject movement usually, err on the side of overexposure when determining this.

Now, check the value of the lighter towel on your proper proof. If it is close to where you metered it, then you are good to go. If it is way off, say two Zones lighter or darker than you metered it, then there is something wrong with your development time or, more likely, the way you evaluated your test results. Keep in mind, this is a subjective way of learning how your materials and equipment work together. Sometimes, all it takes to get a usable result is re-evaluating what we think of/perceive as "maximum black" in our test results.

Admittedly, the above is not as straightforward as just reading your negative with a densitometer, but I believe it is more useful to the practical photographer to explore and get to know his/her materials than to just follow instructions. After doing these tests in this way you will have a much richer idea of how the paper responds at its shoulder, how the film responds at the toe, what "maximum black" is, and how all these relate to making a satisfying final print.

Apologies again for the length of this. It should take you less time to test than to read this :) And remember, the only reason to do this is to ensure you get the shadow detail and separation you want. The danger with this whole film-testing process is ending up rating your film slower than necessary. Keep that in mind when evaluating your tests.

Best,

Doremus

[Steve Barber]

Doremus,

Thank you for taking the time to post that.

Steve Barber

[aruns]

Bill and Doremus,
Thank you both for the detailed posts. There's a lot of information in Leigh's and your posts than I can digest in one go.
I will go through them in detail this weekend and come back if I have more questions.. (I know I do!)

Best regards,
Arun

[aruns]

Hi Bill,
I have a quick question about your post:
You mention that you overexpose by 2/3rd stop from box speed. What development specification do you use then.. (i.e., the one recommended by the manufacturer or do you modify it to suit your purpose)..

Thanks!
Arun