adrian_freire said:
Can anyone tell me how can I ( if it is possible) develope common black and white film (in this case agfa apx 400) as a diapositive?
And how can this change the quality of the image?
Thanks.
In principle it's pretty simple -- you develop more or less normally (perhaps to higher contrast than you normally would) but without fixing, bleach away the developed image with a non-halogenating bleach (so the bleached silver is completely removed but undeveloped halide remains -- potassium dichromate is one common reversal bleach), then fog the remaining halide with light or chemicals and redevelop, followed by normal fixing (and a few extra wash steps various places in that sequence to prevent carry over). Once you get the right conditions for EI and first developer, you get nice B&W positive transparencies, frequently at higher EI than would be the case with negatives for printing.
In practice, it's a bit more complicated -- you have to be concerned about undevelopable silver in the highlights showing up as dark fog after reversal, you have to shoot a lot of tests to get the right combination of EI and first dev, and everything works backward from negatives so you're likely to make a relatively high number of mistakes in getting the process right -- and then you have to start all over if you switch films or first developers (though the rest of the process is carried to completion on all steps and is relatively tolerant).
Quality of the image is affected by the developers used (both of them), and by the fact that projected images are typically magnified much more than prints would be (though that's offset by the fact that they aren't viewed at arm's length when projected), and as with any other process, different films and first developers will give different characters to the image. Panatomic-X used to be the standard film for B&W reversal, but now Kodak's reversal kit is aimed mainly at T-Max 100 -- not a coincidence that those are and were the finest grained films of their era. DR5 does reversals of Tech Pan (if you still have any) that, from what I've seen, are very nice indeed, with the twist that redevelopment can be selected as either neutral or sepia. In practice, however, any B&W material can be reversed -- the question is what the final image will look like, and what look you want.