Have a close look at the Kodak specs for Tmax 400. The marketing men have written the opening stuff about shooting at 800 and developing as normal then the PE's take over and introduce some sanity by giving a time for 800 which is 1.5 mins more.
I think that Kodak are really saying that if you want to develop both 400 and 800 in the same tank then use the 400 time and it works OK. I have tried this. However if you want to develop the 800 by itself then use the 800 time. The times are for 400 and 800 respectively 9.25 mins and 10.75 mins
I have done both at the times for 400 speed at 9.25( the stated Kodak time) and the box speed 400 looks better than 800 at the 400 time.
I should add this is with Xtol at 1+1. I cannot speak for other developers
pentaxuser
I'll repeat a post that I made earlier today in regards to Tmax 100 - the same analysis applies for Tmax 400 2:
Originally Posted by
Helinophoto (there was a url link here which no longer exists)
Well, according to Kodak, TMax 100 can be shot at 100 or 200 without needing to change the development time (weird)."
Actually, not weird at all.
"Pushing" doesn't significantly change the film's sensitivity, it just increases contrast.
So while a a push development may improve the contrast in the near shadows (where underexposure will cause low contrast), it will also increase contrast in the highlights, which may very well be detrimental to the image.
So Kodak is saying that the improvement you will gain in the shadows from a one stop push isn't worth the loss of quality in the highlights you will experience.
I have a feeling as well that pentaxuser may have been looking at Kodak's publication F-4016 when he made his post. That no longer applies to the current version of the film, although it still applies to the current TMax 100.
The current publication, which applies to the current 400 TMY-2, is F-4043, which came out in 2007. It does not list times for EI 800.
If you look at the Kodak datasheet for XTol (J-109) you will note that it does provide a time for EI800, but that it is the same time as EI400 (for certain temperatures). What I find fascinating is it also lists the Contrast Indexes (CI) for various EI and that, despite the fact that the development times are the same, the CI is higher for EI 800 - no doubt due to the loss of shadow detail.