Have I Misunderstood ISO?

focus_on_infinity · Jan 3, 2020

For some reason, I've been struggling with Tri-X, and only Tri-X. I've been getting really good results shooting and developing HP5+, Kodak 5222, Foma 100, and a couple of others. I'm using both 35mm, 120, and in the case of Foma 100, 4x5.

I'm working on a controlled test to try to validate whether my impressions are true. However, it seems like Tri-X isn't really a 400 speed film, at least as far as I've understood ISO. I've had a couple of challenges in conducting a perfectly controlled test of both exposure and development, but I wanted to check whether I've misunderstood something before I go too much further.

My belief up to this point was that for a given ISO and exposure, all negatives will yield a standardized density when processed according to manufacturer's instructions. However, my experience with Tri-X has challenged that understanding. I'm now wondering whether I've misunderstood the definition of box speed.

My understanding is further complicated by Kodak's advice that Tri-X can be pushed one stop without changes in development process. I understand that this is advice about latitude as much as anything. I can see that Tri-X has tremendous latitude. But that's not what's in question here. My question is basically, why is it when I shoot an 18% grey card under controlled lighting, Tri-X seems so much underexposed compared to other films at the same exposure settings?

Lachlan Young · Jan 3, 2020

Probably because you aren't taking into account the differences in specified contrast index that each manufacturer recommends. For example, are you developing to a (tested) contrast index of 0.6 across everything?

pwitkop · Jan 3, 2020

All else being equal, you are correct. ISO and development time, etc are not absolutely standardized in that you're taking the manufacturers assessment of their product, and what they consider is acceptable and within tolerance. There's a lot of variables too, including the shape of the each film's curve, your shutter and meter, developing technique and equipment (i.e. your thermometer), the chemistry of your water (ph, mineral content). Most of the time these aren't big factors, but these are all things you're calibrating for when you test films. And sometimes all these things stacked together go in the same direction and make a bigger difference than you'd expect. So when you come up with your ISO, it's really not just talking about your film, it's the whole system. I'd say if you're getting too little density for your gray card, the film probably isn't getting enough exposure, and/or possibly not enough development. Your lower values are going to tell you about how you're doing exposure wise, and your higher values will give give a good indication of development.

pentaxuser · Jan 3, 2020

Lachlan Young said:
Probably because you aren't taking into account the differences in specified contrast index that each manufacturer recommends. For example, are you developing to a (tested) contrast index of 0.6 across everything?

This may be the case but it seems that he uses other film makes and it is only Tri-X that he has a problem with.

OP is it the same camera and lens used on Tri-X as on the other films? Could it also be that there are contrast differences with the rest but none of them sufficient to detect the difference you see with Tri-X?

Can you show us the differences by pics of the respective grey cards. Digital pics of the prints or the negs would be best

Thanks

pentaxuser

removed account4 · Jan 3, 2020

hey focus_on_infinity:

are you sure it is iso400 ? tri x has had a 320 and 400 version for ages
you might be a stop off because ... its truly a iso200 film..

jnantz

Saganich · Jan 3, 2020

I see evidence in film speed testing that triX 400 be more like a 200 regarding where usable density in shadow details starts BUT the difference seems to be highly dependent on testing technique, so for example if I do a film speed test i'll develop only half the time like 4 minutes, which gives you ASA 200 in D23 but at full development time like 8 minutes it's closer to ASA 400. This becomes part of the calculus, but since I don't like doing calculus unless I'm being paid I shoot all TriX at ASA 320.

jeffreyg · Jan 3, 2020

There is a way to test for your personal ISO for each film/developer combination that takes in consideration your camera/shutter equipment.

http://www.jeffreyglasser.com/

http://www.sculptureandphotography.com/

MattKing · Jan 3, 2020

focus_on_infinity said:
My belief up to this point was that for a given ISO and exposure, all negatives will yield a standardized density when processed according to manufacturer's instructions.

The ISO definition has as much to do with contrast as it does with density, so I would suggest looking at the contrast index you are achieving. The Kodak datasheet development recommendations are based on a contrast index of 0.56 which is lower than the contrast index that some prefer.
And by the way, a "push" is something that by definition involves an increase in development time. Push development is often used to help compensate for decreased exposure, but decreased exposure itself isn't a "push".
ISO box speeds are determined based on a number of factors, but the "best print" analysis behind them is strongly rooted in our subjective sensitivity to mid-tone and highlight rendition. Films shot at box speed often result in better looking prints if you are using volume labs and automatic printers.
By way of comparison, those who analyze exposure using Zone System criteria usually put much more emphasis on shadow rendition, most likely because most Zone System followers have available to them more controls at the printing stage to adjust highlights and mid-tones.
The methods used to determine Exposure Indexes using Zone System criteria actually build in a 2/3 stop difference in speed - a film rated 400 under ISO criteria is a 250 EI film if you base speed measurements on Zone System criteria.

138S · Jan 3, 2020

focus_on_infinity said:
For some reason, I've been struggling with Tri-X, and only Tri-X.

TX and TXP are a bit different, but...

For TX do may also do the easy thing, bracket for testing !

Take reference scenes, spot meter sky, water, vegetation, people... and then make bracketings, do a side by side with HP5.

If you are used to HP5 then from the side by side you will know how to expose, and from the bracketings and spot metering you will know how each kind of subject is rendered at any level of under/over exposure.

Anon Ymous · Jan 3, 2020

focus_on_infinity said:
... I'm working on a controlled test to try to validate whether my impressions are true...

It would be nice to tell us what this test is. If not, we won't be able to give any meaningful advice.

focus_on_infinity said:
...However, it seems like Tri-X isn't really a 400 speed film, at least as far as I've understood ISO...

Highly unlikely.

focus_on_infinity said:
...My belief up to this point was that for a given ISO and exposure, all negatives will yield a standardized density when processed according to manufacturer's instructions. However, my experience with Tri-X has challenged that understanding. I'm now wondering whether I've misunderstood the definition of box speed...

All films have a very specific ISO speed when developed in developer XYZ. The same film may have different ISO speeds when developed in different developers. There are densities involved, but for very specific points, with very specific exposure difference. The wikipedia article about film speed covers the current ISO film speed specification quite nicely. Have a look at the characteristic curve figure, the points m and n are of interest. Keep in mind that the characteristic curve must pass from these points, but how it goes from point m to point n doesn't matter. So, a shot of a gray card can have different densities in different films because of this. And it's not only this, because film base + fog can vary between films as well, or even for the same film when developed in a different developer.

focus_on_infinity said:
... My understanding is further complicated by Kodak's advice that Tri-X can be pushed one stop without changes in development process. I understand that this is advice about latitude as much as anything...

That's correct. A one stop underexposure isn't severe and you can get away with it for the most part if you need to underexpose by only one stop. Using a harder paper/filter grade will take care of this.

Once more, tell us what your methodology is, we need to know more. We don't even know what developer you're using.

Oh, while we are at it, there's no such thing as a "personal ISO". There's a "personal exposure index" that you like to expose film XYZ at, but that's all. ISO film speed is very specific and there's nothing personal about it.

PS Kodak uses the term contrast index, but there's also the term gamma. The aforementioned points m, n in the ISO film speed characteristic curve can be used to calculate a gamma value, which happens to be ~=0,62. This doesn't mean that the contrast index is also 0,62. For more information about these terms, have a look at Kodak's Basic Photographic Sensitometry Workbook.

Hope this helps a bit.

focus_on_infinity · Jan 3, 2020

Anon Ymous said:
It would be nice to tell us what this test is. If not, we won't be able to give any meaningful advice.

Well, first I'm asking if my impression makes sense, which I had come by from shooting under a variety of conditions, using a couple of films, cameras, and developers. I found that whether I was using TTL or incident metering, I was pretty consistently adding 3 stops of exposure to my scans* of Tri-X to get them to look right, and I didn't have to do that with other films in the same cameras.

In the test, I blew off a couple of rolls of 35mm shooting the setup that you see in my avatar, varying the exposure in 1/2 stop increments from light to dark. I then developed in Xtol according to the instructions, and I was surprised that it seemed to bear out my impressions. The HP5+ was exactly where I expected it, but the Tri-X was a couple of stops darker. There was at least one flaw in the test, though, so I'm going to re-run it to be 100% sure I've done it right, before I risk wasting anyone's time asking for specific advice. I may expand it to a couple of other films, and I have to decide how to handle the development so that I can make an accurate and valid comparison.

But at the moment, I'm just experiencing some degree of self-doubt, because I was so surprised that my impression may have some validity, and I'm wondering if perhaps my expectations were wrong to begin with.

*note: it's not the scanner. it's pretty clear just by eyeballing the negatives.

Sirius Glass · Jan 3, 2020

The OP is not developing to the density that he desires. Look at the developer information sheet and increase the development. The Tri-X film is working properly, but it has not been developed to the desired density.

removed account4 · Jan 3, 2020

focus_on_infinity said:
My question is basically, why is it when I shoot an 18% grey card under controlled lighting, Tri-X seems so much underexposed compared to other films at the same exposure settings?

there are different ways to use a grey/gray card
have you seen this thread >>> https://www.photrio.com/forum/threads/kodak-grey-card-usage.135637/

maybe you are underexposing you film because your meter isn't calibrated, you aren't getting a good grey card reading, your in-camera meter isn't calibrated right, iso400 isnt' your "sweet spot" or you are using txp320 pro instead of txp400 ...

ic-racer · Jan 3, 2020

...at least as far as I've understood ISO...

These clips from ISO6 1993 may help. There is no specified 'gray card' value in either ISO or ASA. Film speeds can be traced to experimental work on toe density and slope.

focus_on_infinity · Jan 3, 2020

Yeah, I think the information presented here seems to show that my understanding of ISO was incorrect. Now I think it's up to some real world testing to determine how far off it was. If I have further questions about Tri-X specifically, they will come with controlled test shots so I can ask them clearly.

Thanks, everyone.

Grim Tuesday · Jan 3, 2020

OP are you by any chance using HC-110? The times on the datasheet for Tri-X and HC-110 are known to be wrong and for some reason Kodak has never fixed them.

focus_on_infinity · Jan 3, 2020

Grim Tuesday said:
OP are you by any chance using HC-110? The times on the datasheet for Tri-X and HC-110 are known to be wrong and for some reason Kodak has never fixed them.

No, for my test and some of my regular shots, I used Xtol stock. Prior to that I was developing with Cinestill Df96, and the results were the same. I shot one roll at 1600 and developed in Xtol 1+1 according to the info on DigitalTruth, and that turned out to be one of my best rolls.

I'm just a beginner at developing, though, so I don't make any representations as to the consistency of my procedures. But I am getting more efficient with every roll.

Bill Burk · Jan 4, 2020

Hi focus_on_infinity,

You should really be looking at 1/10th the exposure metered on your gray card and looking for 0.1 density over base+fog.

This is 3 1/3 stop less than the metered point. (Or you could set the EI to 4,000 and shoot the gray card as metered).

Even though I expect you will find the true speed is 400, there are benefits from shooting it at 250.

The question I think will need to be answered is ... are you going to use a yellow filter (Now effectively 125)... or would you rather use TMAX 400 (at 250 and you don’t need a yellow filter)?

Rudeofus · Jan 4, 2020

focus_on_infinity said:
No, for my test and some of my regular shots, I used Xtol stock. Prior to that I was developing with Cinestill Df96, and the results were the same. I shot one roll at 1600 and developed in Xtol 1+1 according to the info on DigitalTruth, and that turned out to be one of my best rolls.

Different developers will sometimes give you different effective speeds with some films, but a required 3 stop overexposure over box speed seems really excessive, especially with a speed enhancing developer like XTol stock. Something must be way off here, and your reported results certainly do not match other people's experiences here with Tri-X.

There are two things which could have happened:

Have you by any chance underdeveloped Tri-X? Can you give us time and temperature of your standard development for Tri-X? How does it compare to standard parameters provided in the data sheet and in Massive Dev Chart?
Is your batch of Tri-X fresh? If it is 20+ years old, then one would expect the results you reported. This would be immediately obvious by looking at developed density of unexposed areas. If these areas are very dense, then chances are your film is very old.

focus_on_infinity · Jan 4, 2020

Rudeofus said:
Different developers will sometimes give you different effective speeds with some films, but a required 3 stop overexposure over box speed seems really excessive, especially with a speed enhancing developer like XTol stock. Something must be way off here, and your reported results certainly do not match other people's experiences here with Tri-X.

There are two things which could have happened:

Have you by any chance underdeveloped Tri-X? Can you give us time and temperature of your standard development for Tri-X? How does it compare to standard parameters provided in the data sheet and in Massive Dev Chart?

Is your batch of Tri-X fresh? If it is 20+ years old, then one would expect the results you reported. This would be immediately obvious by looking at developed density of unexposed areas. If these areas are very dense, then chances are your film is very old.

Brand new Tri-X. I used the Kodak sheet for development timing, which matches the Massive Dev Chart values (the ones without the notes).

I have a few rolls planned for today. I'm going to shoot off one or two rolls of 6x7 outdoors trying to do the zone system with my Fuji as a spot meter. When it gets dark and I have no ambient light, I'll probably re-run the controlled light test on 35mm with Tri-X and HP5+, and maybe TMY if I have a roll in the fridge. I have to correct a light leak on my old Minolta before I do that.

I haven't yet decided on the developer. Everything I shoot today will be the same. It'll probably be Xtol again, most likely in a 1+1 1-shot so I can be 100% consistent. But I could do D76 or Rodinal if someone persuades me there's a super good reason to use one of those for the test instead.

Anon Ymous · Jan 4, 2020

@focus_on_infinity There is a small chance that your Xtol developer is almost dead. It doesn't happen all that frequently, but there is such a chance. If the last films you processed in Xtol are these Tri-X ones you mentioned, then this could explain your experience. If you have processed other films after the Tri-X ones, and they came out nice, then your Xtol is obviously fine.

So, if you have doubts about the condition of your Xtol, you can try ID11, which should give you fairly similar results. Rodinal is basically bullet proof, but also a bit of special case - acquired taste. It is very sharp, but also considerably grainier. IMHO, not exactly ideal for Tri-X.

removed account4 · Jan 4, 2020

Anon Ymous said:
if you have doubts about the condition of your Xtol, you can try ID11

i'd use ID11 anyday over xtol any day of the week, you will get better results off the bat. while xtol i am sure is good for certain situations ID11 or D76 or Sprint Film Developer
is good in most all situations...

Sirius Glass · Jan 4, 2020

focus_on_infinity said:
Brand new Tri-X. I used the Kodak sheet for development timing, which matches the Massive Dev Chart values (the ones without the notes).

The Massive Development Chart has errors. Always trust the manufacturers' datasheets over the Massive Development Chart.

focus_on_infinity · Jan 4, 2020

No, the Xtol is working great for other films. I just mixed it about two weeks ago.

I happen to have some 40yo ID-11 that was never mixed. But, I don't think I'm gonna try it.

Bill Burk · Jan 4, 2020

Ok. If you use D-76 1:1 at 68 F for 13:30 minutes it will be the time temperature and developer that I use to reach ASA/ISO contrast parameters. So we can compare notes.

Any shorter time that you find recommend is likely to be aiming for a lesser contrast, which is common practice for normal picture taking.

But you are trying to test speed... so you should aim for the speed testing parameters. Afterwards you shoot at the speed you discovered but develop a little less. We can talk about how Delta-X can explain why the speed is still valid when you develop less.

Have I Misunderstood ISO?

Moderator

Privacy & Transparency

Privacy & Transparency