Differentiating between underdevelopment and underexposing of a step wedge tablet

Hi all,

So my brain has stopped and I cannot think this through. First let me explain my setup

I can shoot a pure white A4 sheet, by measuring with a light meter. If I increase the measurement by 5 stops and shoot the paper that should give me max density on the negative. (I have densitometer to measure this)

However let's assume I put a Stoufer 31 steps wedge tablet on my 4x5 holder and put a film behind it. If I do exactly what I have described above, I should get a various readings through out the film.

But what would happen if I underexpose the negative and what would happen if I under develop the negative (assuming 2 separate negatives).

My assumption is, underexpose but correct development will give me a lower max density.

Here I am getting confused, an underdevelopment will give me a lower max density.

So how can I distinguish the issue then?

Best wishes,
Fatih

Fatih Ayoglu said:

If I increase the measurement by 5 stops and shoot the paper that should give me max density on the negative.

Click to expand...

Is that a goal or an assumption? Either way - I don't think so. The latitude of most film is more than that. But +5 stops will be pretty darn dense by any standard, I'll grant you that.

Fatih Ayoglu said:

My assumption is, underexpose but correct development will give me a lower max density.

Click to expand...

Yep. And underdevelop and expose 'correctly' will also give lower max density. The difference is in the first visible step you'll capture, and thus, the contrast range and range of densities. The HD curve, if you plot one, will show the difference.

The key is to not stare yourself blind on dmax. It's a pretty irrelevant parameter for a negative most of the time, anyway.

What are you trying to figure out?

koraks said:

The key is to not stare yourself blind on dmax. It's a pretty irrelevant parameter for a negative most of the time, anyway.

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Right!

Determine your Dmax using your paper(s). You don't need a negative -- other than Base + fog. Determine how you want to process your paper first, then determine how long you have to exposure your paper to achieve Dmax.

Doesn't Mat Marrash go through this exact process in one of his LFF (large Format Friday) videos? There's another "author" behind this process and I cannot remember his name. I'm somewhat certain it was a photographer from or in Australia.

koraks said:

Is that a goal or an assumption? Either way - I don't think so. The latitude of most film is more than that. But +5 stops will be pretty darn dense by any standard, I'll grant you that.



Yep. And underdevelop and expose 'correctly' will also give lower max density. The difference is in the first visible step you'll capture, and thus, the contrast range and range of densities. The HD curve, if you plot one, will show the difference.

The key is to not stare yourself blind on dmax. It's a pretty irrelevant parameter for a negative most of the time, anyway.

What are you trying to figure out?

Click to expand...

@koraks thanks a lot for your answer.

I am actually trying to figure out multiple things.
1) I have 3 light meters which shows different readings, I want to find out which is correct
2) I also want to find out if my development time is correct, as I expose for shadows and develop for highlights. Granted I don’t think I have had an issue yet but I also want to know if I’m doing optimally.

MTGseattle said:

Doesn't Mat Marrash go through this exact process in one of his LFF (large Format Friday) videos? There's another "author" behind this process and I cannot remember his name. I'm somewhat certain it was a photographer from or in Australia.

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Yes, the one from Australia (Alex Bond) actually do something similar but he doesn’t go into the detail so I don’t know how I can distinguish.

You may have to "waste" a couple more sheets with one being purposely overexposed, and possibly one overdeveloped so you know for sure which error you are seeing.

I'm very inconsistent in my actual film use, I wish I could say for certain that overexposure = blown shadows and over development = blown highlights but I cannot remember if there is a hard and fast direct correlation like that.

If you already consider yourself to have consistent exposures and decent negatives when you are not testing, I would not suspect your processing to be the error if you haven't altered any of the steps.

Fatih Ayoglu said:

1) I have 3 light meters which shows different readings, I want to find out which is correct

Click to expand...

I don't think testing with film is a very good approach for this, honestly. If you want to (quasi) calibrate them, I'd stick to comparing them to a meter that you can assume with reasonable certainty is good enough for what you do. If you need proper calibration, you're better off looking for a shop/company that might do this for you.

Fatih Ayoglu said:

2) I also want to find out if my development time is correct, as I expose for shadows and develop for highlights. Granted I don’t think I have had an issue yet but I also want to know if I’m doing optimally.

Click to expand...

I'd be pragmatic about it and conclude that if you don't run into problems during printing, your negatives are evidently fine. The whole concept of a 'correct' development time should always be seen in the context of what you want to do with the negatives and what kind of images you're after. If you print on variable contrast silver gelatin paper, there's also the massive leeway that this gives you in working around any incidental or systematic failures to get it 'right'.

It sounds to me like you've got a good and dependable process; don't try to fix it if it ain't broken!

Actually the more I think about it, the more I’m less willing to do any test. As you’ve said, I print my negatives perfectly fine, there are only very few instances that I have had issues and the over/under exposure is always too evident. Plus all these meters are within 0.8EV difference and as I overexpose 1 stop and under develop %15 to make sure my shadows have enough density and highlights are not blown out, I don’t think I’ll get even into an issue.

Ok so even if I don’t do the test, so I can sleep better, how would I understand from 2 negatives which one is under exposed and which one is under developed?

Plot the values from your densitometer reading of the developed step wedge exposure. The slope of the H-D curve will be changed by development and the position, right to left, of the H-D curve will be changed by exposure.

Fatih Ayoglu said:

Hi all,

So my brain has stopped and I cannot think this through. First let me explain my setup

I can shoot a pure white A4 sheet, by measuring with a light meter. If I increase the measurement by 5 stops and shoot the paper that should give me max density on the negative. (I have densitometer to measure this)

However let's assume I put a Stoufer 31 steps wedge tablet on my 4x5 holder and put a film behind it. If I do exactly what I have described above, I should get a various readings through out the film.

But what would happen if I underexpose the negative and what would happen if I under develop the negative (assuming 2 separate negatives).

My assumption is, underexpose but correct development will give me a lower max density.

Here I am getting confused, an underdevelopment will give me a lower max density.

So how can I distinguish the issue then?

Best wishes,
Fatih

Click to expand...

Fatih Ayoglu said:

Ok so even if I don’t do the test, so I can sleep better, how would I understand from 2 negatives which one is under exposed and which one is under developed?

Click to expand...

It would depend on how you define 'underexposed' and 'underdeveloped'. Part of my earlier response revolves around the issue that there's no absolute standard for this. You can of course establish your own, personal film speed/EI...but before you know it, you'll be going down some zone system or BTZS rabbit hole. Again, I'd advocate a more practical approach and shoot some (for you) typical scenes at different film speeds, and then pick the negatives that give you the best prints/easiest job in the darkroom. Not exactly a scientific approach, but in practice, it'll get you where you need to do virtually every time.

Fatih Ayoglu said:

1) I have 3 light meters which shows different readings, I want to find out which is correct

Click to expand...

Why are you assuming that one of them is correct? They might all be incorrect -- or they might all be correct. Since we don't know what meters these are or how you are testing them, we are working in the dark.

It's completely normal for three meters to provide different readings if they are used in different ways or metering different things.

ic-racer said:

Plot the values from your densitometer reading of the developed step wedge exposure. The slope of the H-D curve will be changed by development and the position, right to left, of the H-D curve will be changed by exposure.

Click to expand...

That is how you’ll know.

By eye, an underexposed strip will have fewer steps of detail (many clear steps), if you expose it properly there will be a couple clear steps. If you overexpose the first steps will be darker than you want (won’t be any steps less than 0.1 density above base+fog).

It is not necessary to hit the exposure “just right”, you just want density in most of the steps.

Fatih Ayoglu said:

1) I have 3 light meters which shows different readings, I want to find out which is correct.

Click to expand...

When I read this, it reminded me of one of Alan Ross's blog posts where he indicates that he checks his spot meter's in the following manner:

"The only requirement I have of a meter is that it be linear – that is – if I expose a gray or white card in dim light, bright light , medium and dim again and expose exactly as the meter indicates, each exposure should yield the same density on film. If the densities match closely, my meter is good, but if one exposure doesn’t match the others, the meter needs to go to the shop. This test is well worth the time and cost of a roll or few sheets of film!"

Perhaps home in on your issue by evaluating your meters in this way..........it's something to consider.

Chuck_P said:

"The only requirement I have of a meter is that it be linear – that is – if I expose a gray or white card in dim light, bright light , medium and dim again and expose exactly as the meter indicates, each exposure should yield the same density on film. If the densities match closely, my meter is good, but if one exposure doesn’t match the others, the meter needs to go to the shop. This test is well worth the time and cost of a roll or few sheets of film!"

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That's one way to test for consistency (reliability). That's not a way to test for accuracy (validity). A meter should be both.

When it’s not, it’s usually not both.

A good test is to see if meter agrees with the light standard nominal value.

Bill Burk said:

When it’s not, it’s usually not both.

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To clarify, you mean if it's not linear then it usually has an accuracy problem as well.

This case involves three meters with different readings. We know nothing about the meters or how they were used. So we really can't say anything about their accuracy. Whether they are consistent or not is another issue.

If one has two absolutely identical meters and uses them side-by-side to meter the same area at the same time, I'd expect the readings to agree within the allowed tolerances of the meters. If one starts mixing up meter models, I can think of a bunch of reasons offhand why two meters would give different readings that could both still be "correct"

1. For a reflective meter, especially if two different brands, the manufacturers may have a different idea about what constitutes "middle gray."

2. Even if a meter gives a nominal coverage area(say 5º or 30º) how close to the state coverage angle is the actual reading angle? Is it perfectly round or is it more oval or rectangular? Does the meter average perfectly over the coverage area or does it weight some areas more? Especially with wider angle meters, I'd expect some amount of center weighting, but how much it is and how it falls off from the center could certainly vary even in models from the same company

3. What's the spectral sensitivity of the meter cell? CdS and silicon are definitely different, and different types of silicon cells can have different responses. Just as an an example, outdoors my Gossen LunaSix(CdS) and Luna Pro SBC(silicon) agree pretty well, but they are often a stop or more apart under artificial light.

4. If an incident meter, the size and shape of the dome will play a role, as will the color and condition of it. Some of my really old selenium meters(like my Brockway Director) have almost pearlescent domes and not the white ones of newer meters, and old domes can certainly yellow...

The real test of a meter is if delivers properly exposed images. You can of course do formal tests or get out, shoot the film you're planning to use in the camera/lens you want to use, and develop the way you're planning to develop. If your negatives are less than perfect and you decide it's an exposure issue, investigate that, or if you're happy with your negatives it's probably all fine. Literally every step from metering to printing introduces its own variables, and as much as the scientist in me would always love to characterize all of them, there's almost no end to it if you really get down to it, chances are the lgiht is going to change before you finish adjusting for all of them!

Chuck_P said:

To clarify, you mean if it's not linear then it usually has an accuracy problem as well.

Click to expand...

Right, just a remark that if it doesn’t give a correct reading, it’s likely to be non-linear as well. Most often I think a meter is OK because it passes the sunny sixteen vibe check but does a bad job in low light. So bad that it thinks there’s more light than there is and you underexpose two stops before catching it. Mostly a Weston Master II in my case. But I think it’s a fair rule of thumb.

If a meter is off on one reading you should check it over a wide range. It’s likely to be inaccurate and non-linear.

Fatih Ayoglu said:

I also want to find out if my development time is correct, as I expose for shadows and develop for highlights. Granted I don’t think I have had an issue yet but I also want to know if I’m doing optimally.

Click to expand...

If it ain't broken, don't fix it. If you are happy with the level of details in the shadows, you are exposing the film correctly. If all negatives come out with high contrast, you are overdeveloping and vice versa.