Why would film size matter in BTZS film testing?

I remember being told that if you were doing film testing for 4x5, 120, and 35mm versions of the same film you needed to do separate testing. Assuming you process exactly the same way (for example in a Paterson tank) without changing the agitation, this does not make a ton of sense to me, it is after all the same emulsion?

One thing also that jumped out at me is that Barnbaum lists different target zone densities for normal development for different size film in "Beyond basic photography"" (page 47). This also is counter intuitive. For example, zone X density for sheetfilm he lists as 1.6 where as for 35mm it is 1.4. Why would film size matter?

What am I missing?

I think you could test one size and take what you learn as fairly applicable for other sizes. As long as you confirm the emulsions are the same or similar.

I develop 4x5 in trays and 35mm and 120 in small tanks. Although I would think there should be differences between tray and tank, I find my "time-ci" correlates well between different film sizes despite this difference. At least for TMAX 400 and 100.

Bill Burk said:

I think you could test one size and take what you learn as fairly applicable for other sizes. As long as you confirm the emulsions are the same or similar.

I develop 4x5 in trays and 35mm and 120 in small tanks. Although I would think there should be differences between tray and tank, I find my "time-ci" correlates well between different film sizes despite this difference. At least for TMAX 400 and 100.

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Well, I assume that HP5+ in 35mm has exactly the same emulsion as HP5+ in 4x5. I don't know why it would be different.

The emulsion and the substrate do work together to provide the film.
The different anti-halation properties alone are capable of yielding different results. As do the different levels of flare in the various systems.
That being said, the differences may very well end up being small. I would suggest determine one, and tweak the others if your prints tell you you need to do so.

MattKing said:

The emulsion and the substrate do work together to provide the film.
The different anti-halation properties alone are capable of yielding different results. As do the different levels of flare in the various systems.
That being said, the differences may very well end up being small. I would suggest determine one, and tweak the others if your prints tell you you need to do so.

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The flare factor is added manually in the btzs film analysis so that is controlled for. As for antihalation later, I would have thought it would be the same. However, you may be onto something about substrate differences. Thanks for the brainstorm!

Per Bjesse said:

The flare factor is added manually in the btzs film analysis so that is controlled for. As for antihalation later, I would have thought it would be the same. However, you may be onto something about substrate differences. Thanks for the brainstorm!

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35mm and 4"x5" have built in anti-halation, but it definitely differs, not least because of the difference between the substrate materials.
120 depends at least partly on the backing paper for anti-halation.
And with respect to flare, that includes flare within the substrate.
Remember that flare and halation combine to increase the apparent speed.

MattKing said:

35mm and 4"x5" have built in anti-halation, but it definitely differs, not least because of the difference between the substrate materials.
120 depends at least partly on the backing paper for anti-halation.
And with respect to flare, that includes flare within the substrate.
Remember that flare and halation combine to increase the apparent speed.

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Alright. Thanks for the well-thought out answer. This all makes sense. I am guessing that in practice the differences are minor though but when I have extra time I may just run a check.

Analysis of control strips In my darkroom demonstrates, a 30cm strip of 35mm HP5 film receives much more development activity alone in a 1510 size drum with 140ml, compared to 8 35mm films in a 1520 Tank + (2x)1530 with 900ml and still different from 5 8x10 sheets of HP5 in a 3005 drum with 450ml.

In terms of exposure, however, fractions of a stop are inconsequential in my work, so they all get the same EI in camera.

Per Bjesse said:

Assuming you process exactly the same way (for example in a Paterson tank) without changing the agitation, this does not make a ton of sense to me, it is after all the same emulsion?

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Perhaps that is an unsafe assumption? For example agitation is inherently different for Paterson tank and open tray development which introduces a variable into the process. The developer and film makers probably give recommended sequences and times for tray and tank and who knows how much this affects things. I raise this to illustrate that sometimes "assuming" may be misleading.

The film base is often different between sheet film and 35mm (with 120 going either way). In 35mm color neg and b&w, the film base is often mildly tinted. This is done to reduce light piping on the edge of the film. It will change the d min of the film. Roll films also have more of an emphasis on preventing the film from curling (a coating on the back side of the film). That and the anti-halation layer is often different as mentioned. Also sometimes (not often) the emulsion or coating is actually different. For instance Tri-X in large format (gone now) was labeled as TMX 320, and actually was a different emulsion that Tri-X 400 35mm. Large format films are often cut from the same roll, so you should get the same results between 4x5 and 8x10 of the same emulsion. When an emulsion is updated, it also doesn't happen for different formats at the same time. The take home is large format is similar but not exact.

Given that film testing is to establish the correct speed for the user which might be different from the box speed then there is usually only say 3 likely applicable EIs that can be dialled in on the camera. If it is a 400 box speed film then the usual available film speeds are 320,250 and 200. Given that each represents an appreciable jump, is it likely that sticking with the same development time and agitation for all three formats will alter the results to an extent that will be noticeable in a visual sense from what would be the case if each were developed separately?

If there not a real chance that in a practical sense there a danger that we may end up seeking a spurious accuracy which cannot be attained in the same way that presumably there is a difference between a film requiring a "best" development of 12 minutes but which gets only 11 minutes and 45 seconds or even 11 minutes and 30 seconds?

pentaxuser

I think a lot of the testing is for spurious accuracy as, generally speaking, shutter speed can only be set in full stop increments and aperture in half stop increments. And what happens if that meter needle isn't exactly centered? One argument for testing different film formats separately is that you are using different shutters for each format which can be off 20%-30% and still be within spec. So if your 35mm is 20%-30% fast and your 120 shutter is 20%-30% slow, there's a half stop difference. Given the variance even within a shutter, you could even have different EIs for different shutter speeds. And then there is zone placement accuracy. Can you reliably place something in Zone III? How do you know it's not Zone II 2/3 or Zone III 1/3? After all, the zones are not 10 discrete steps like you see in the charts, but a continuum. Are you really that good? While acknowledging the importance of sensitometry, there is certainly the opportunity for a lot of wheel spinning. Given all the variables in exposure and development, I'm just not sure mathematical precision is possible, or even necessary. Of course, you do want to do the best you can. Just be realistic about what you can accomplish. At some point, you have to stop testing, take photographs, and make adjustments in the printing process. You might even decide to print an image differently than you originally visualized it, in which case all that exposure and development accuracy is out the window.

Different target densities for different formats is suggested because film grain is more evident in denser negatives; for 35mm the usual suggestion is to develop to a lower density to minimize grain. Large formats rarely suffer from excessive grain because they tend to be enlarged less. Develop to the density that gives you results that you like.

It used to be that different formats used different emulsions, even though they had the same name. I don't know if that is still the case.

Per Bjesse said:

I remember being told that if you were doing film testing for 4x5, 120, and 35mm versions of the same film you needed to do separate testing. Assuming you process exactly the same way (for example in a Paterson tank) without changing the agitation, this does not make a ton of sense to me, it is after all the same emulsion?

One thing also that jumped out at me is that Barnbaum lists different target zone densities for normal development for different size film in "Beyond basic photography"" (page 47). This also is counter intuitive. For example, zone X density for sheetfilm he lists as 1.6 where as for 35mm it is 1.4. Why would film size matter?

What am I missing?

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Each of these films has a different film base which affects the light passing through it. Most of the Gurus say to run separate tests on each film size and some say to test for each brand of film also...........Regards!

Per Bjesse said:

I remember being told that if you were doing film testing for 4x5, 120, and 35mm versions of the same film you needed to do separate testing. Assuming you process exactly the same way (for example in a Paterson tank) without changing the agitation, this does not make a ton of sense to me, it is after all the same emulsion?

One thing also that jumped out at me is that Barnbaum lists different target zone densities for normal development for different size film in "Beyond basic photography"" (page 47). This also is counter intuitive. For example, zone X density for sheetfilm he lists as 1.6 where as for 35mm it is 1.4. Why would film size matter?

What am I missing?

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different film sizes have different substrate thicknesses and different emulsion sicknesses but, I admit, I have always ignored this fact and only tested one film size (typically 120) and went with the result for all sizes.

Thanks everyone for the exhaustive discussion. For now I will just test one version, but it might be interesting to compare down the road.

Per Bjesse said:

Well, I assume that HP5+ in 35mm has exactly the same emulsion as HP5+ in 4x5. I don't know why it would be different.

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Per Bjesse said:

Thanks everyone for the exhaustive discussion. For now I will just test one version, but it might be interesting to compare down the road.

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If you are going to test only one size film, make it medium format. Filmbase plus fog is less in MF and in LF than in 35mm and would put you in a similar ballpark with LF. Also according to Fred Picker, there was a difference in Kodak Tri-X and an Ilford film of the same emulsion speed with one of the two being a whole f stop faster than the other. I would test every film that I intended to use. What's the rush?.......Regards!

Arklatexian said:

If you are going to test only one size film, make it medium format. Filmbase plus fog is less in MF and in LF than in 35mm and would put you in a similar ballpark with LF. Also according to Fred Picker, there was a difference in Kodak Tri-X and an Ilford film of the same emulsion speed with one of the two being a whole f stop faster than the other. I would test every film that I intended to use. What's the rush?.......Regards!

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Well, that two different films needed to be tested individually is a nobrainer. Andd commenters above have given some arguments why the same film in different dimensions might test differently. However: as for "What is the rush?": it takes five different development runs to test a film completely which is significant when it has to be mixed in with all the other development I have to do plus the "life factor". I am about halfway done testing Hp5+ in 4x5 and it has been more than three weeks of wall clock time. As a consequence, unless there was real arguments, I was not going to spend six weeks to get 120 results for the exact same flm unless the results really would be significantly different..

Per Bjesse said:

I was not going to spend six weeks to get 120 results for the exact same flm unless the results really would be significantly different..

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Run one example test on 120, and see if it diverges markedly from the same test on your testing format.
That will go a long way to telling you if you need to test 120 as if it was a separate film.

MattKing said:

Run one example test on 120, and see if it diverges markedly from the same test on your testing format.
That will go a long way to telling you if you need to test 120 as if it was a separate film.

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Yes, that makes a lot of sense as a check and balance!