Different official times for 35mm and medium format

[Juan Valdenebro]

In the past I've heard different opinions ranging from not necessary to only with HP5+ to it's because of the different physical characteristics of each format.
I've been using the small 600ml Perceptol boxes (from the 60's?), those in the wallet sized cardboard boxes... They list HP4 and FP4/HP5 not +. And G0.55/G0.70 separately.
For each contrast level, the same film & EI requires different times for sheets and rolls, and some films have different times for 35mm and 120, and some films have small time differences in Microphen depending on format, but no difference at all in Perceptol, and bigger differences in ID-11.
This is interesting.

 

[cmacd123]

I recall a note on a data sheet from the mid 70s that metioned that they expected that 35mm would be printed with a condensor enlarger, and sheet and 120 would be printed with a difusion enlarger. thus different aim Gamma required.

 

[brian steinberger]

I develop my HP5 35mm quite a bit less than 120. About 25%. I’m using ID-11 1:1.

 

[Bill Burk]

I recall a note on a data sheet from the mid 70s that metioned that they expected that 35mm would be printed with a condensor enlarger, and sheet and 120 would be printed with a difusion enlarger. thus different aim Gamma required.

This makes sense, since I find that contrast per time is consistent across formats in most film.

 

[pentaxuser]

I develop my HP5 35mm quite a bit less than 120. About 25%. I’m using ID-11 1:1.

I take it that the 25% makes them look the same and under a densitometer they measure the same?

Ilford gives the same time for ID 11 1+1 in 120 . What does Kodak give for D76?

Have you ever used the same time for both to see what difference this made v 25% less?

Thanks

pentaxuser

 

[Sirius Glass]

The film bases for 35mm, 120 and 4"x5" differ in thickness as well as the emulsion thicknesses which drive the different development times.

 

[Bill Burk]

The film bases for 35mm, 120 and 4"x5" differ in thickness as well as the emulsion thicknesses which drive the different development times.

But I find the same contrast index for same film different formats

 

[Sirius Glass]

But I find the same contrast index for same film different formats

Yes, that is so. In the end, the films are developed to the same contrast, as a standard. Once a starting place is established, one can wander anywhere.

 

[brian steinberger]

I take it that the 25% makes them look the same and under a densitometer they measure the same?

Ilford gives the same time for ID 11 1+1 in 120 . What does Kodak give for D76?

Have you ever used the same time for both to see what difference this made v 25% less?

Thanks

pentaxuser

I don’t have a densitometer. I look at contact sheets and prints made at grade 2 or 2 1/2. If I develop my 35mm HP5 for the same time as my 120 HP5 they are overdeveloped.

 

[Bill Burk]

Yes, that is so. In the end, the films are developed to the same contrast, as a standard. Once a starting place is established, one can wander anywhere.

What I mean is that I find, for TMY2, at 13:30 reaches 0.62 CI in D-76 1:1 at 20-degrees C whether it’s 35mm, 120 or 4x5 so different development times for different formats are not justified on the basis of the same aim contrast.

Unless someone else has different development contrast for the same times, and my experience is atypical

 

[freecitizen]

Film base plus fog can vary depending on the format size, even between films of the same name by the same manufacturer.

Fred Picker used to teach that a personal film speed should be determined by testing for each size of a type of film. I have found different film base plus fog for 35mm vs 120 Hp5 and it was true for TriX when 35mm was compared to 4x5. I no longer use TriX ...... beyond my budget now.

 

[pentaxuser]

Film base plus fog can vary depending on the format size, even between films of the same name by the same manufacturer.

Fred Picker used to teach that a personal film speed should be determined by testing for each size of a type of film. I have found different film base plus fog for 35mm vs 120 Hp5 and it was true for TriX when 35mm was compared to 4x5. I no longer use TriX ...... beyond my budget now.

How much does it differ in your experience? Can you gives us any measurements and film types and makes?

Thanks

pentaxuser

Unless someone else has different development contrast for the same times, and my experience is atypical

Well Bill, it would seem that if your experience is atypical then it is atypical for the film makers as well

pentaxuser

 

[Bill Burk]

I don’t have a densitometer. I look at contact sheets and prints made at grade 2 or 2 1/2. If I develop my 35mm HP5 for the same time as my 120 HP5 they are overdeveloped.

Remember that many 35mm films have a tinted base to help with anti-halation so you need longer printing time. But not different film developing time. At least not for this reason.

Well Bill, it would seem that if your experience is atypical then it is atypical for the film makers as well

pentaxuser

It sound like you got me wrong, my comment wasn’t clear.

My experience suggests that developing times for the same contrast are the same. The explanation I offer for the different times is that they aim for different contrast… because they think you need less contrast for 35mm the suggested development time is less for 35mm.

The comment you quoted - I meant it to mean…

I could be wrong. Someone else might have different results than me.

Maybe the formats are formulated differently and the times are specified to aim for the same contrast with different times.

I would be able to tell better if the specifications sheets included Time-Contrast charts.

 

[pentaxuser]

Thanks Bill, I said what I said because of this sentence you used in which I thought you were agreeing with the film makers such as Ilford who generally quote the same time be it 35mm or 120 and do not quote different contrast index or Gbar or whatever measurement they use for the different types of film. Here's your sentence:

"What I mean is that I find, for TMY2, at 13:30 reaches 0.62 CI in D-76 1:1 at 20-degrees C whether it’s 35mm, 120 or 4x5 so different development times for different formats are not justified on the basis of the same aim contrast."

Yes I note you are accepting that your experience may be wrong and Brian's experience is that he needs 25% longer. As I said it would be interesting to find out what difference the 25% makes in terms of measurement but Brian has said he does not have the "tools" to measure the difference or in his case the same as 25% is needed to get his 35mm v 120 negs to look the same

pentaxuser

 

[Bill Burk]

I knew that was confusing.

Anyway my results could suffer from confirmation bias too… I could go over the statistics and see if perhaps I have misinterpreted my own results.

 

[logan2z]

film makers such as Ilford who generally quote the same time be it 35mm or 120

I was looking at Ilford's data sheet for HP5+ yesterday and you are correct that they list the same development times for '35mm and roll film'.

I haven't shot any HP5+ in 120 yet, but I do shoot FP4+ in both formats and develop them both for the same length of time in the same developer (Rodinal 1:50). I haven't checked with a densitometer, bur don't see any significant difference in negative densities between them.

I'd personally stick to Ilford's directions and develop HP5+ the same regardless if it's 35mm or 120.