True speed of Tri-X in Diafine

I developed a test roll of Tri-X (400TX) in Diafine this weekend.

The speed I found for it is around EI400 to 500 (using density 0.1

above fb+f). There has been a lot of talk on this site about

the "big speed gain" of Tri-X in Diafine. So is there really a speed

gain ?

I think a 3rd of a stop may actually BE a significant speed gain, as most processes just boost contrast of what's already there.

How was your agitation ? What is your tank capacity and how much developper did you use

?

 

If, say, you use 600ml of diafine in a 1000ml tank and agitate by twisting, you will create a

massive over-agitation. The B bath will wash the A bath from the film before having made

it all react, creating under-development. I had that and I got less than EI100 with an FP4+

that way.

 

Maybe it is not your case, but just in case...

Some skeptics believe that exposing Tri-X at the recommended EI of 1600 for development in Diafine merely results in underexposure. I find it's not quite that simple. There are unique tonal range and separation of tones that can defy definitive statements about Diafine's behavior.

 

I've exposed Tri-X 400 in 35mm and 120 at EIs varying from 400 to 1600 for development in Diafine. Photos were taken under all conceivable typical conditions: daylight, sunny to cloudy; handheld in dim light indoors, theatre, etc.; long exposure nighttime photos under full moon.

 

I've decided that for my purposes EI 1200-1250 (depending on your meter's increments) works best for me. Shadow is a bit thin but usable. Midtones are well separated for easy printing and highlights resist blocking up.

 

At 1600, the manufacturer's suggested EI, I find that shadow details thin out beyond an acceptable level.

 

However at 400 I didn't see any significant improvement, just a different set of problems other than underexposure. Shadow detail and midtones had poor separation. Even under bright or contrasty lighting the photos were grayish and flat. This does not occur under the same lighting at EI 1200.

 

Or, to cut through the B.S., only the user - after giving it a sincere try - can evaluate whether Diafine in combination with a compatible film (Tri-X is very compatible; TMY is not) delivers an *effective* speed boost, which is not quite the same thing as using density 0.1 above fb+f.

Lex,

 

So reading between the lines of your reply, my measured speed using density 0.1 above fb+f could be valid. So there was no issue with development failing to give a speed increase (which is more or less what I expected).

 

I have not had time to plot the response curve for the Tri-X in Diafine combination, but eyeballing it, there seems to be a big shoulder starting in the mid tones (which is expected for a compensating developer). So your comparison of the different EIs suggests that the issue is really how your meter responds to the light conditions, rather than any "speed increase" of Diafine.

 

Anyway as you say it comes down to trying it for oneself.

Richard, keep doing your testing and analyzing,I can tell you on your way to understanding what's really going on. Any real speed increasing effect developer would be raising zone I density well above .10(above Fbf). Any developer that really raised an iso 400 film to 800, then a zone 0 exposed negative would give a density of .10 above Fbf. Furthermore, in the 400 to 800 case, a zone V exposure would have a zone VI density, any more than that is just a raise in contrast(or as some use the term"effective speed"). For all practical reasons zone I density is what determines a B&W negatives speed...Keep thinking, you're going to get it...Jim

I think I understand what is going on. Tri-X in Diafine has a high contrast in the shadows, and a significant shoulder which starts at a low level. The result of this is that a Zone V exposure (a middle tone) prints as a light grey, rather than a mid-grey. This is basically because the shoulder makes it closer to the pure white end of the scale, than a "normal" film / developer combination. To get a mid-grey it is necessary to place the object around the Zone 3 region. The easy way of doing this is to simply set the light meter for a faster speed (the 1200 to 1600 ASA that people claim). Now what the people doing this fail to understand is that this is not a film speed increase, because you lose around 2 full stops of shadow detail.

 

This loss of shadow detail is unacceptable for me, so I shall be looking at different developers, in the hope of getting good shadows, but with control of the highlights, with a shoulder much further up the scale.