I have been developing my own B&W film for about six months now and have been puzzled by a recent result using Ilfosol S @ 1:9. I had exposed a roll of HP5+ at 1600 ISO but had developed it at 400 ISO @20C, (9 min, i think , from memory). The negatives were fine, with nice tonal range and good contrast. XP2 has the ability to have different frames rated at different speeds, because of HP5's latitude can i conclude the same thing? I am currently reading Gene Nocon'c Photographic Printing where he advocates developing at the manufacturers speed regardless of how film was exposed. Does anyone have any comments? Many thanks in advance Andrew

-- Andrew Buckley (da_buckley@yahoo.com), February 15, 2001

Answers

Push processing doesn't actually alter the film speed. The shift in the toe of the film curve is minimal to zero. All that push processing does is increase the mid-tone and highlight density, making an underexposed negative easier to print.

Take a good look at the published sensitometry curves for 400, 1600, and 3200 ISO rated films. NONE of them show any density much below -3log Lux-seconds. In fact, the curves for Fuji Neopan 400 and 1600 are *identical*.
The simple reason is that film naturally tops out at around 400 ISO, because it requires a minimum of 3 photons to expose one Agx grain.
Some recent research has shown it possible to 'dope' grains to acheive a single photon sensitivity, but there's no film on dealers shelves using that technology yet. Even so, this would only mean a true top speed of 1200 ISO.

-- Pete Andrews (p.l.andrews@bham.ac.uk), February 15, 2001.

Pushing is an iffy thing....

The fact is that upon extended development there's no useful increase in shadow density, just increased contrast; the reason for extending development is so the neg will print on a "normal" paper of grade 2-3 rather than needing, say, grade 5.

Also of course how you meter the scene and the brightness range of the scene are major factors; could be you used EI 1600 and I might meter the same scene and come up with the same camera settings using EI 400...or vice-versa.

The developer you use of course has an effect; if you use the traditional .10 DU above fb&f as the speedpoint, you'll find that HP5+ in Microdol-X is EI 200 at best, it's EI 400 in D-76H 1:1 and it's EI 640 in Microphen.

I don't know the context in which Nocon's writing, but the _fact_ that various films give different speeds in different developers pretty much nukes his assertion. Within limits what he recommends would work in that most likly all negs would be _usable_ but there's a big difference between usable and _good_.

There's really no such thing as latitude, whether it's a traditional film, chromogenic or whatever; there's only the correct exposure and development for the scene brightness range and the materials it'll be printed on. While you can certainly give more or less exposure and development you'll be losing a little quality if you do.

-- John Hicks (jbh@magicnet.net), February 15, 2001.

HP5+ in HC-110 is quite forgiving. I had a roll which I'd shot at EI 400 for the first half and EI 1600 for the second half (don't ask why!). Instead of cutting it in 1/2 and processing each part for the EI it was shot at, I just processed the whole thing as if it had been shot at EI 800. Both halves of the film had perfectly good negatives. Now they might have been a *bit* better if they'd had the "right" processing, but they were certainly acceptable (to me).

-- Bob Atkins (bobatkins@hotmail.com), February 15, 2001.

Many thanks for your responses to my query regarding push processing HP5. I think i will read more widely and then 'experiment' some more. Again many thanks for all the contributions Best Wishes Andrew

-- Andrew Buckley (da_buckley@yahoo.com), February 28, 2001.