Do you test your film for true ISO?

Bill Burk · Oct 10, 2015

I wanted to show from page 725 of Mees, an illustration used to explain why the minimum useful gradient does not always correlate to fixed density criteria...

Long sweeping toes useful film speeds don't correlate well to the usual fixed density criteria.

https://archive.org/details/TheTheoryOfThePhotographicProcess

Stephen Benskin · Oct 10, 2015

Bill Burk said:
But you know, ultimately the "first excellent print" criterion is the ruler of the land. In the case of special developers we may need to toss all the characteristic curve criteria and go all the way to the print series and pick the best print.

Bill, I know you're mostly being whimsical. In a way we all do print tests to help determine our EIs, but as you know the level of precision to do anything close to the psychophysical testing of the first excellent print test is prohibitive. My real purpose for this post is to show one of the images and test data from the first excellent print test. It's of the famous "Willow Pond" image. You can see from the accompanying table that they didn't use just one negative of the image, but produced multiple negatives all developed at different gradients.

georg16nik · Oct 10, 2015

Stephen Benskin said:
...Don't know if you noticed, but I'm not suggesting people should exposure at the ISO rating...

That's a relief, for a moment you got me there.
So, do you agree that the ISO number serves mostly typographical purpose and it's a suggestion for “thin negatives” under general purpose use?

Alan Klein · Oct 10, 2015

I have a question along this line that maybe you all can help me. I shoot MF 120 film and have developed in a pro lab (Tmax 100 in Xtol); normal although pushing and pulling are available. I have the lab provide a contact print as well. So, I bracket my shots +1 and -1 stops after metering exposure based on box speed of 100. So how do I use the contact to determine which is the best negative? How do I know the contact print process provides the correct info. In other words, if the lab's contact process shifted the results so the prints may show the wrong exposure as the best. Do I just assume my eyes are telling the truth as to best?

By comparison, I scan the three samples measures exposure and the +1 and -1 alternates and assume that the one that falls in the middle of the histogram is providing the shot that has the best exposure. Does this make sense to you? Any suggestions?

Stephen Benskin · Oct 10, 2015

georg16nik said:
That's a relief, for a moment you got me there.
So, do you agree that the ISO number serves mostly typographical purpose and it's a suggestion for thin negatives under general purpose use?

You haven't been following my posts then.

Fractional gradient speed is the limiting gradient, so it would produce the thinnest negative that would yield high quality results. The pre and post 1960 ASA speeds and current ISO speed all utilize and are determined in relation to the fractional gradient speed. Technically speaking, they should be considered EIs. The current ISO speed is around a stop over fractional gradient speed and the pre 1960 ASA is around an additional 2/3 to 1 stops more. The standard's speeds use the limiting gradient as a base reference and create a working speed from there. A personal EI can be done in a similar manor, but instead of using the fractional gradient speed which is unknown unless tested for, the personal EI can use readily available ISO speed as it has a direct correlation with the fractional gradient speed.

Film speed is only part of exposure. Metering practices, flare, and preference are as much a part or more in deciding on a personal EI. Ultimately photographic results are subjective. All of us being human, we tend to have a common response to stimuli, which will get us into the ball park; but the art aspect will continue to be too elusive to predict. However, there is a clear distinction between stating a personal preference and claiming error and misconduct in the standard.

georg16nik · Oct 10, 2015

Stephen Benskin said:
You haven't been following my posts then.

Fractional gradient speed is the limiting gradient, so it would produce the thinnest negative that would yield high quality results. The pre and post 1960 ASA speeds and current ISO speed all utilize and are determined in relation to the fractional gradient speed. Technically speaking, they should be considered EIs. The current ISO speed is around a stop over fractional gradient speed and the pre 1960 ASA is around an additional 2/3 to 1 stops more. The standard's speeds use the limiting gradient as a base reference and create a working speed from there. A personal EI can be done in a similar manor, but instead of using the fractional gradient speed which is unknown unless tested for, the personal EI can use readily available ISO speed as it has a direct correlation with the fractional gradient speed.

Film speed is only part of exposure. Metering practices, flare, and preference are as much a part or more in deciding on a personal EI. Ultimately photographic results are subjective. All of us being human, we tend to have a common response to stimuli, which will get us into the ball park; but the art aspect will continue to be too elusive to predict. However, there is a clear distinction between stating a personal preference and claiming error and misconduct in the standard.

Can't say I am following particular poster posts on APUG, so no offense.
The “thinnest negative that would yield high quality results” is the part where my personal standard for quality drifts apart from the ISO play.
Since I don't have a horse in this race and I am not affiliated with film manufacturers and ISO folks - beside the fact that I've purchased a dozen ISO standards over the decades... - I'd say it's a zero sum game.
Hey, the ƒ stops on our lenses are not as accurate as T stops, so all subjective stuff added.. still photography is spare-time-filler and nothing more.

MattKing · Oct 10, 2015

I expect that the subjective tests of un-manipulated prints that yielded the current ISO standard of approximately one stop more exposure than that which would yield the “thinnest negative that would yield high quality results" reflect more appreciation for highlight detail than shadow detail. In particular, appreciation for the rendering of things in everyday life that are lighter in tone.

Out of curiosity, I looked at Georg's uploads to the APUG gallery. I don't know whether they are representative of his preferences, but I would hazard a guess that his apparent liking for contrasty, large luminance range subjects where detailed shadows play a large role would lead him value more exposure than someone who prefers shots of their kids and Disneyland.

RobC · Oct 10, 2015

who gives a stuff what the "true" ISO is. Any sane photographer will test to find their own EI from their own working pratices and materials and ignore the ISO on the box. They may get the same or they may not. Does it matter if its different? No it doesn't. What's the problem requiring 113 posts (so far).

Oh, and since it was the manufacturer who did the test in their own labs, how can anyone replicate those tests 100% accurately? They can't so the only person who has ever produced a "True" ISO is the manufacturer. Everyone else produces "lies".

Old-N-Feeble · Oct 10, 2015

When I get started again (soon, I hope) I'll test to get 'close enough'. After that IDGAS.

Bill Burk · Oct 10, 2015

Alan Klein said:
I have the lab provide a contact print as well. So, I bracket my shots +1 and -1 stops after metering exposure based on box speed of 100. So how do I use the contact to determine which is the best negative?

If you want to try working with negatives with slight overexposure, a frame that looks a little light on the contact print may be the best negative for printing.

If you subscribe to "the least, if it is enough, is often the best," then you can pick the best from the contact print.

Bill Burk · Oct 10, 2015

Stephen Benskin said:
The current ISO speed is around a stop over fractional gradient speed.

This is something I'm curious about... Is the current ISO really a stop over fractional gradient? Or is the speed point there knowing Delta-X is about a stop "to the left"?

NedL · Oct 10, 2015

I have carefully and systematically homed in on development times for each film I use, and how to expose it, to make it easiest to print with my enlarger.... but I don't think of it in terms of ISO or ASA or EI.... it's not a formal or mathematical system. It's about how I meter or think about exposing the film.

Reading threads like these actually got me off to a bad start... I started a by exposing FP4+ setting my F3 to ISO 100, but in the end it was better to set it to 125, be careful not to overexpose it ( when in doubt, err on the side of less exposure ) and I develop it for less time than the various "development tables" say to. Now I get negatives that are consistently easy to print. Tri-X is set to 400 and I develop it a bit longer than the manufacturer's recommendation, and for Acros I err on the side of more exposure, consistently about 1/2 stop, and develop a little longer. So each of those 3 films is treated differently with regard to exposure and development time to make nice negatives..... what helped me home in on good negatives was keeping notes about development times and notes about what I was thinking when I exposed. The other thing that was important for me was not to make notes about what to change until I'd made some prints... I have a tendency to always think the negatives look great when they are hanging to dry

I entered "No" in the poll, even though I've done quite a lot of refining over several years...

Stephen Benskin · Oct 10, 2015

Bill Burk said:
This is something I'm curious about... Is the current ISO really a stop over fractional gradient? Or is the speed point there knowing Delta-X is about a stop "to the left"?

Both. ΔX is the difference between the 0.10 fixed density point and the fractional gradient point. For the ISO contrast parameters, ΔX = 0.29.

Bill Burk · Oct 10, 2015

georg16nik said:
The thinnest negative that would yield high quality results is the part where my personal standard for quality drifts apart from the ISO play.

Me too. I don't want the thinnest negative either unless I need a fast shutter speed under the circumstances.

My horse in the race - of course - is Kodak. But the opinions and positions I take may drift from EKC in these matters (because I work in a different department).

O-N-F, I figured out a couple letters of that abbreviation. "I don't". And I know what GAS means. So you're not buying any more gear?

Old-N-Feeble · Oct 10, 2015

Bill Burk said:
Me too. I don't want the thinnest negative either unless I need a fast shutter speed under the circumstances.

My horse in the race - of course - is Kodak. But the opinions and positions I take may drift from EKC in these matters (because I work in a different department).

O-N-F, I figured out a couple letters of that abbreviation. "I don't". And I know what GAS means. So you're not buying any more gear?

I'm not buying gear at the moment because I haven't had much money for a long time but my financial situation will soon improve a little bit. The acronym I used is I Don't Give A S***. What I mean is I don't intend to be ultraprecise... on the edge of underexposure.

Bill Burk · Oct 10, 2015

Stephen Benskin said:
Both. ΔX is the difference between the 0.10 fixed density point and the fractional gradient point. For the ISO contrast parameters, ΔX = 0.29.

Wow. Thanks. That is pretty clear on these diagrams.

Xmas · Oct 11, 2015

Old-N-Feeble said:
I'm not buying gear at the moment because I haven't had much money for a long time but my financial situation will soon improve a little bit. The acronym I used is I Don't Give A S***. What I mean is I don't intend to be ultraprecise... on the edge of underexposure.

Ditto

In 1961 I did not see the (any) reduction of a safety factor as a wonderful idea and trying to print shadows that were not silver on a negative has not there confirmed this appreciation every time I need to do that.
You need to read the article rationalising the change, it is too risible for me to read all the way through.

But the article did teach me how to use a light meter, ie that my Weston was not an exposure meter.

I'm also poor too.

Bill Burk · Oct 11, 2015

This is the break I was looking for. Here's where my new realization is taking me...

I've been fighting all along the idea of "first excellent print," thinking that I want more shadow detail than the standard provides.

I thought the ISO aimed to place shadows at 0.3 gradient point, despite what Stephen Benskin has been saying all along. I didn't see where that safety factor was hiding.

So instead of the ISO speed being the mark of the least exposure that produces a straight print that looks good.

It is one stop more than that (considering Delta-X 0.29) according to Stephen Benskin, look at his Goldilocks graph.

So what if you double the box speed for starters? What will your carefully metered exposures look like?

They will nail it, if you develop to 0.62 the approximate ISO average gradient.

Now you had better be careful with your metering, because you will not have any safety factor.

The desire for additional shadow detail remains to be figured out. What will you lose in terms of extra shadow detail? Maybe you won't be able to dodge your deepest shadow to reveal additional detail. It won't be there to bring up. You will always be able to dodge dark gray to bring it up to middle gray (Maybe that's what I want to do anyway). Suppose I want 1/3 stop additional shadow detail?

If I want additional shadow detail, I should add 2/3 stop additional exposure to get additional shadow detail to my preferred dodging time (I always look at my test strips and will freely dodge and burn 1/3 stop because I know it gives a noticeable change on the print, without being obvious)

Then if I want to use Zone System spot and place, I will use 2/3 stop less exposure. (Notice these two reasons cancel each other out)

Start with double ISO so for TMY-2:

400 ISO = TMY-2 rated speed

800 EI = 1 stop higher to eliminate safety factor

500 EI = 2/3 stop lower to accommodate Zone System metering desire (Meter Zone V and stop down to Zone I differs from ISO test method 2/3 stop).

400 EI = 1/3 stop lower because I always seem to get a little less than ISO speed when I test my film speed

250 EI = 2/3 stop lower to allow additional shadow detail per the discussion above.

Hey look! I always shot TMY-2 at 250 anyway. So now I have the whole story why.

frank · Oct 11, 2015

Some people really get off on the precise control of everything.
I admire them, but that's not me.
The beauty of photography is in its blend of science and art.
Each of us can find our own comfort zone in this blend.

About true film speed: I know that negative film tolerates over exposure much better than under exposure.
When unsure of the best exposure to give, I tend towards over exposure.

Bill Burk · Oct 11, 2015

frank,

You can see this is all armchair explanations. In the field, I will set my meter at 250 and run with it, since I know all the above factors make that speed the right speed for me. I'm not that much into tight control, just explanations to make me comfortable with my choice.

frank · Oct 11, 2015

Hi Bill. Even though I posted after your post, I wasn't referring specifically to you. Just speaking generally.

Peace

Xmas · Oct 11, 2015

Bill Burk said:
This is the break I was looking for. Here's where my new realization is taking me...

I've been fighting all along the idea of "first excellent print," thinking that I want more shadow detail than the standard provides.

I thought the ISO aimed to place shadows at 0.3 gradient point, despite what Stephen Benskin has been saying all along. I didn't see where that safety factor was hiding.

So instead of the ISO speed being the mark of the least exposure that produces a straight print that looks good.

It is one stop more than that (considering Delta-X 0.29) according to Stephen Benskin, look at his Goldilocks graph.

So what if you double the box speed for starters? What will your carefully metered exposures look like?

They will nail it, if you develop to 0.62 the approximate ISO average gradient.

Now you had better be careful with your metering, because you will not have any safety factor.

The desire for additional shadow detail remains to be figured out. What will you lose in terms of extra shadow detail? Maybe you won't be able to dodge your deepest shadow to reveal additional detail. It won't be there to bring up. You will always be able to dodge dark gray to bring it up to middle gray (Maybe that's what I want to do anyway). Suppose I want 1/3 stop additional shadow detail?

If I want additional shadow detail, I should add 2/3 stop additional exposure to get additional shadow detail to my preferred dodging time (I always look at my test strips and will freely dodge and burn 1/3 stop because I know it gives a noticeable change on the print, without being obvious)

Then if I want to use Zone System spot and place, I will use 2/3 stop less exposure. (Notice these two reasons cancel each other out)

Start with double ISO so for TMY-2:

400 ISO = TMY-2 rated speed

800 EI = 1 stop higher to eliminate safety factor

500 EI = 2/3 stop lower to accommodate Zone System metering desire (Meter Zone V and stop down to Zone I differs from ISO test method 2/3 stop).

400 EI = 1/3 stop lower because I always seem to get a little less than ISO speed when I test my film speed

250 EI = 2/3 stop lower to allow additional shadow detail per the discussion above.

Hey look! I always shot TMY-2 at 250 anyway. So now I have the whole story why.

There is also a dependency on how you meter.

Average reflectance
Incident
Spot

And

Brightness range of sceane

Simpler for me though HP3 changed by magic from 200 ASA to 400 ASA... about 1961
Seemed like a fairy tale, goblins, etc.,...

I have too much difficulty printing already to change.

Bill Burk · Oct 12, 2015

frank said:
Hi Bill. Even though I posted after your post, I wasn't referring specifically to you. Just speaking generally.

Peace

It's OK, sometimes I resemble remarks...

So this weekend for example, at EI 250, I shot a roll at Corgi-Con with a point and shoot (Canon AF35ML). You know I had little control over that.

And a roll at the Renaissance Festival (OM-4... Rick A's camera).

Although I thought about eliminating the safety factor and using spot-shadow for every single shot... I decided just to set it on Auto and fire away.

The negatives look OK. Interesting thing happened though. You know how some cameras have a reverse wind on the takeup reel. The design is intended to counteract the curl. Well it's worth noting... When you take a roll of film and immediately unload and try to reel it... The film goes wild trying to straighten itself out. Was a pain to reel that roll from the OM-4.

Bill Burk · Oct 12, 2015

Xmas said:
There is also a dependency on how you meter.

Average reflectance
Incident
Spot.

Soon as you decide NOT to use Zone System... You can add 2/3 stop to the EI.

frank · Oct 12, 2015

The OM4 has an amazing meter with multiple spot averaging and highlight/shadow spot reading. For those who are in control of everything, this must be the ultimate experience. I found it simply too distracting for the way I work, and sold it on. I'm happy with a centre-weighted camera meter which I usually just point down towards the ground so the sky brightness does not influence the meter recommendation.

I'm certainly not saying that everyone needs to work this way, I've just learned that this approach works best for me. One of my favourite sayings is: Relax. Nothing is under control.

Do you test your film for true ISO?