This was discussed on another example a few weeks ago, where I was reminded that additional exposure initially increases negative contrast, since the shadow densities come off the shoulder and then decreases again as the highlight densities get onto the shoulder. So, negative contrast starts out low, increases a bit with exposure and then decreases again. Regards Ralph W. Lambrecht On 2/2/05 11:51 AM, "Richard Knoppow" <dickburk@xxxxxxxxxxxxx> wrote: > > > -----Original Message----- > From: Peter Badcock <forums@xxxxxxxxxxxxxxxx> > Sent: Feb 2, 2005 12:34 AM > To: pure-silver@xxxxxxxxxxxxx > Cc: Richard Knoppow <dickburk@xxxxxxxxxxxxx> > Subject: [pure-silver] Re: Pure Black and Golden. > > Richard, > thanks for taking the time to explain this. > >> -----Original Message----- >> Because the current >> ISO speed method yields about the minimum exposure that >> will result in good shadow detail there is practically no >> underexposure latitude for B&W negative films. OTOH, there >> is lots of overexposure latitude, many stops for most >> films.=20 > > I was hoping to rely on this fact with the Delta 400. In > fact by exposing it at the rated ASA and developing for the > recommended time I was also assuming that this would > increase the contrast on the neg. (in comparison to exposing > for longer but developing for less). BUT read on below, > where I think I have realised the error of my ways. > >> One can render long scale subjects by lowering >> either negative or print contrast but the visual >> appearance may be unsatisfactory; the eye wants to see >> about normal contrast in the mid-tones. > > OK, I think I've got it now, I stupidly assumed that because > I was taking the shots on an overcast day that the > brightness range between the black and golden lab would be > less somehow - when in fact they will ALWAYS be 4 stops as > metered whether in full sunlight or indoors!! So maybe what > I need to do is to develop the film for less time to cater > for the 'long scale' between the 2 dogs. > > I will also check out the response curves for the film and > compare them to other films with different exposure > lattitudes to see if I can accomplish a brightness range of > 4 stops between my zone III and zone VII while retaining > sufficient local contrast. > > regards > Peter Badcock > > Contrast is almost completely a function of the degree of development. I= > ncreasing exposure beyond the minimum will not increase overall contrast bu= > t will push the shadows up the toe increasing the contrast there. Eventuall= > y, if one exposes enough, you will reach the "shoulder" of the curve where = > the contrast again becomes less. Most modern films have a tremendous range = > before this shoulder is reached. Its usually safe to increase exposure a bi= > t. It often results in better shadow detail.=20 > In the case of the two dogs I think the problem is that the brightness = > range is greater than can be accomodated by the print. Reflection prints ha= > ve quite limited range, perhaps 30:1. Note that this is not the contrast gr= > ade of the paper, all papers with similar surfaces have about the same brig= > htness range. It is limited by the maximum visual density on the one end an= > d the maximum reflectivity of the paper on the other, the absolute limit of= > highlight brightness being the ambient light illuminating the print. Maxi= > mum visual density is around 1.8 which is available only on glossy surfaced= > paper. Any texture or matting scatters light and raises the brightness of = > the minimum black. Matte and textured surfaces also lower overall contrast = > because they limit the brightness range of the paper even further. Film is,= > in general, capable of recording a much greater range of brightness than c= > an be reproduced on a reflection print. About the best one can do is to cho= > ose the part of this range that is to be reproduced as mid- grays and choos= > e print contrast and exposure so that it prints as such. The eye wants to s= > ee "normal" contrast in the mid grays. Increased or decreased contrast is u= > seful as a special effect, but, for instance, printing a picture of a very = > long range subject so that its compressed to fit onto a reflection print wi= > ll look dull and grayed down. Sometimes prints like this are useful, for in= > stance for scientific work or as evidence photos, but generally they will b= > e seen as defective.=20 > Burning and dodging allows placing parts of the image with varying aver= > age brightness so that they are mid-gray, or near it. Variable contrast pap= > er gives one the further option of changing the printing contrast as desire= > d for different areas of the picture.=20 > A great many very different prints can be made from the same negative; = > its an interesting excercize to try it. You may find that you can get a var= > iety of equally desirable images this way.=20 > > > > -- > Richard Knoppow > dickburk@xxxxxxxxxxxxx > Los Angeles, CA, USA > ============================================================================== > =============================== > To unsubscribe from this list, go to www.freelists.org and logon to your > account (the same e-mail address and password you set-up when you subscribed,) > and unsubscribe from there. ============================================================================================================= To unsubscribe from this list, go to www.freelists.org and logon to your account (the same e-mail address and password you set-up when you subscribed,) and unsubscribe from there.