Film Testing - are emulsions the same in different formats?

[Doc W]

I want to do some film tests, starting with FP4. I shoot this film in 4x5, 5x7, and 8x10. In the past, I have assumed that 5x7 and 8x10 are the same emulsion, i.e., my development times will be the same for both but I have assumed that 4x5 is slightly different and requires additional testing. Is this correct or are they all the same, or all different?

 

[Photo Engineer]

They are the same emulsion, but have slightly different coating formulas and so they may differ slightly in processing.

PE

 

[Ian Grant]

I found most of the films I've tested were close enough 35mm to LF to do my Zone system tests with 35mm which made like easier and cheaper. I use the same EI and dev times regardless of format and get excellent results.

Ian

 

[wildbill]

PE, why would one sheet film size differ from another? This makes no sense.
Ilford sheet films are all the same thickness and cut from the same master rolls. If I'm wrong Simon, please correct me.

 

[Photo Engineer]

Why differ, well 8x10 and 4x5 are the same, but the 120 is slightly different and so is the 35 mm. This is due to the difference in support and the need to adjust micro and macro contrast for the film size.

PE

 

[Gerald C Koch]

While the emulsions may be the same for major film manufactures this may not be true for rebranded films. Some years ago there was a company that put their name on anything that they could get in sufficient quantity. What the buyer got could vary from month to month.

 

[RobC]

yes each production batch can be slightly different if the manufacturer hasn't got very fine quality control.
And like paper, film ages and contrast goes down over time so if the batch dates are different for the difderent formats, that could be a cause of different curves being produced.

 

[Simon R Galley]

Dear All,

As usual PE is spot on, the emulsions are 'the same' but have different coating formula dependent on the base, Miniature ( 35mm ) roll film and sheet film.

Simon ILFORD photo / HARMAN technology Limited :

 

[wildbill]

Dear All,

As usual PE is spot on, the emulsions are 'the same' but have different coating formula dependent on the base, Miniature ( 35mm ) roll film and sheet film.

Simon ILFORD photo / HARMAN technology Limited :

Yes, That I'm aware of. The OP only mentioned sheet film sizes so that's why I questioned it.

 

[Doc W]

PE and Simon, how much impact would these slight differences in coating have on processing times? Also, it sounds like both of you are saying that all sheet film has the same coating whilst all roll film has another coating. Thus, there would be no difference between, say, 4x5 and 8x10. Is that correct?

 

[Photo Engineer]

Doc, there might be depending on other factors such as the required gelatin laydown, silver laydown or backing layer. This might be due to the buckling tendency of 8x10 vs 4x5. OTOMH, IDK if there is but these are things I have run into.

PE