----- Original Message ----- From: Anthony Farr Subject: Re: Push Processing Film
> William, > > Are these results scanned from the negatives or from RA-4 prints of those > negatives. I couldn't really see far into the dark end of the grey-scale on > any result, but there are many places between your scanning and my viewing > where the losses can occur, if there are losses at all. On my monitor I > could ~just~ discern the separation between steps 13 & 14 of the ISO800 > sample, 12 & 13 for both the others, is that a fair appraisal? Brightening > the display didn't improve the separation, it did enhance it slightly but it > still ran out at the same steps. Could it be that the scanning is imposing > its own limits on the results. > > Colourwise, my experience is that the Kodak colour control patches are > difficult to see colour shifts on, because they are pure colours. Better > than that are the patches with many pastel shades (I think Macbeth makes > one) where a small colour shift will make an original colour look like a > completely different one. > > Otherwise it's a good guide to C-41 pushability considering that you used a > reputably pushable film, a test like your's with consumer film would be > illustrative. But I fear it's an unwinnable argument because "not good > enough" for one persons needs will always be "good enough for government > work" to someone else. I think I scanned the prints on this one. I (stupidly, it seems) disposed of the negatives just a couple of weeks ago, but I dug around and found the prints that I made. I will describe the results, since you aready know what the test target looks like. on the N print, I can see separation between patch B and patch 17 on the 1 stop push, I can see separation between patch 14 and 15. on the 2 stop push, I can see separation between patch 12 and 13. The deal with classic pushing, is that you are deliberately underexposing the film. As soon as you underexpose, you are risking loss of shadow detai l, as once the detail is not recorded, it is gone forever. No amount of over development will bring it back. What over development will do is to straighten out the toe of the exposure slope somewhat, thereby giving more separation to the low exposure values. So, lets presume that we have correct metering for a moment. An average scene type is around 5 or 6 stops of exposure range. A conventional negative film will record somewhere around 8 stops (colour), or 10 stops or more (black and white). We can see that we have some margin of error, both for over exposure and under exposure, without seriously degrading the image, with no processor intervention. Most negative films can be underexposed by a stop, with no real visible effect, in most scene types. One of the things that I missed in the good Doctors test was reading if he actually speed tested the film he was using. The Ferrania films traditionally are quite a bit more sensitive than the box speed would indicate. I recall speed testing a whole bunch of films a few years back, and the Ferrania films tested out close to a full stop faster than the box speed. This was no fly by night test, either. This was tested using a constant and repeatable light source (daylight), with densitometer readings to determine the speed points. My contention is that you cannot increase effective film speed by increasing development time on any film type, be it colour negative, black and white or reversal. What you can do is use the films latitude to your advantage. If your scene type is 4 stops, and you have an 8 stop film, then you can underexpose by 2 stops, increase development to straighten out the curve, and get a picture that will look fairly normal. If your scene type is closer to the range of the film, and you underexpose, then you will lose shadow detail, and no amount of excess development will get it back for you. With C-41 process film, you have the added complication of the mask density building up, pretty much in lock step with the increase in shadow detail contrast, which can cause loss of some shadow detail as well. William Robb - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
