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Photo Forum / Film Photography / Darkroom / January 2005What to do with Base + (plus) Fog
I'm shooting PX-125. Using the density function of my scanner I measure the base on clear piece of developed film to be about .42 density units. So at 0.15 d.u.'s per half stop that's nearly a stop-and-a-half loss for base + fog. Is that too much? What's base + fog costing me in terms of image quality or is it treated as neutral density when I print? What you really need to know, is how much is base density, and how much is fog. Do the same experiment again, cut the film in half, and normally develop half, and just fix the other half. Then compare the density's. My money says most of the density you see is film base assuming you have 35mm. The thin base of 120 film has a lower density. The film base is treated as neutral density, the fog encroaches on the toe of the film, and if extensive will alter the shape of the d-log e (density vs exposure) curve, from what is designed, and muddy up the image. A low amount of fog can be treated as neutral density. When in doubt, print it. Adams defines zone 1 as .1 above film base+fog. Dan >I'm shooting PX-125. Using the density function of my scanner I measure the >base on clear piece of developed film to be about .42 density units. So at >0.15 d.u.'s per half stop that's nearly a stop-and-a-half loss for base + >fog. Is that too much? What's base + fog costing me in terms of image >quality or is it treated as neutral density when I print? Thx Dan. Thanks I will try running a strip developed and fixed and then one just fixed and see what the difference is. My development was ~5:36 seconds (7 minutes - 20 per cent = 5:36) in Ilfosol-S at 1:9. I minus the 20 per cent because I'm printing on a condensor head. > What you really need to know, is how much is base density, and how > much is fog. [quoted text clipped - 16 lines] > >fog. Is that too much? What's base + fog costing me in terms of image > >quality or is it treated as neutral density when I print? > I'm shooting PX-125. Using the density function of my scanner I measure the > base on clear piece of developed film to be about .42 density units. So at > 0.15 d.u.'s per half stop that's nearly a stop-and-a-half loss for base + > fog. Is that too much? What's base + fog costing me in terms of image > quality or is it treated as neutral density when I print? Its rather difficult to comment. Why, you ask? Well,.... Is it sheet film or roll? The density function of your scanner and its "accuracy" is an unknown. Its not standard photo sensitometeric nomenclature, nor can it be without very precise specific guidelines to determine its calibration values.  SignatureLF Website @ http://members.verizon.net/~gregoryblank "To announce that there must be no criticism of the President, or that we are to stand by the President, right or wrong, is not only unpatriotic and servile, but is morally treasonable to the American public."--Theodore Roosevelt, May 7, 1918 > > [quoted text clipped - 4 lines] >>quality or is it treated as neutral density when I print? >> Just dunk a piece of leader in full strength Clorox to remove the emulsion. What remains will be the base density which is a dye in the plastic, not a coating on 35 mm. Ilford HP5+ has a base density of about 0.2. I think most Kodak films are clearer. The purpose of the base density in 35 mm film is mostly to prevent light piping through the film from frame to frame. If the base were perfectly transparent, exposure of one end would send light all the way to the othe end, even though it is in a light tight cartridge. The film could have an opaque undercoating. but why bother when a base density of 0.1 will do the job? > Just dunk a piece of leader in full strength Clorox to remove the > emulsion. What remains will be the base density which is a dye in the [quoted text clipped - 5 lines] > in a light tight cartridge. The film could have an opaque undercoating. > but why bother when a base density of 0.1 will do the job? Patrick; Is there a relatively simple way to extract the silver from emulsion and reuse it as emulsion again for something like albumen printing. Any thoughts? Greg >greg....<@gregblankphoto.com SignatureLF Website @ http://members.verizon.net/~gregoryblank "To announce that there must be no criticism of the President, or that we are to stand by the President, right or wrong, is not only unpatriotic and servile, but is morally treasonable to the American public."--Theodore Roosevelt, May 7, 1918 An easy way used by those who do darkroom work is to soak the silver containing emulsion in a thiosulfate solution. The thiosulfate will dissolve the silver. May be you know of that. After treatment of that solution will depend upon your end usage. The form of silver needed for albumen prints, whatever that may be, is likely an easy conversion process. Dan > An easy way used by those who do darkroom work is to > soak the silver containing emulsion in a thiosulfate solution. > The thiosulfate will dissolve the silver. May be you know > of that. Yes sir I does. > After treatment of that solution will depend upon your > end usage. The form of silver needed for albumen prints, > whatever that may be, is likely an easy > conversion process. Dan Specifically silver nitrate. SignatureLF Website @ http://members.verizon.net/~gregoryblank "To announce that there must be no criticism of the President, or that we are to stand by the President, right or wrong, is not only unpatriotic and servile, but is morally treasonable to the American public."--Theodore Roosevelt, May 7, 1918 > I'm shooting PX-125. Using the density function of my > scanner I measure the [quoted text clipped - 5 lines] > terms of image > quality or is it treated as neutral density when I print? Have you any means of calibrating the scanner? Photographic density is usually stated as Log density where density is the reciprocal of transmission. Typical roll and sheet film bases are very clear. 35mm B&W negative film is usually coated on a base containing a gray pigment with density of around 0.2. This has no effect on tonal rendition but extends printing exposure a little. Fog is usually uniform and has the effect of lowering the toe contrast which is equivalent to lowering speed. The use of an anti-foggant in the developer will result in eliminating the fog but also lowers speed so there is not much net gain. Increasing exposure will generally overcome the fog. If you want to use an anti-foggant Benzotriazole is more effective than Bromide and has less effect on the latent image (i.e., does not lower speed so much). All film has some fog even when fresh, but slow films, like Plus-X Pan, have very little. The ideal method of calibrating the scanner is by using a step wedge like the Stauffer wedge. However even a neutral density filter of known density can be used. This will tell you if the "density units" of the scanner have any relation to the normally used Log density. Signature--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com > > I'm shooting PX-125. Using the density function of my > > scanner I measure the [quoted text clipped - 28 lines] > you if the "density units" of the scanner have any relation > to the normally used Log density. Thx Richard. I'm currently waiting for two T2115s and two R1215s from Stouffer which I order last week. Currently, the only thing I'm comparing to is the grey-scale on a Q-60 card from Wolf Faust. The scanner (Epson 3200) is surprising accurate to that, but it's not transmissive. The densitometer function is from VueScan which uses data from the RAW file instead of "corrected" data -- so while not exact it is ball park I'm guessing. The film is 35mm, but was a hand me down from a retired photog' who'd had it in the freezer. I rate at 100 and generally try to give the shadows a chance. The neg looks dark or darker in comparison than what I usually shoot on, TMY. I've used both D-76 and Ilfosol-S and am less than happy with my results. I get strange posterization in places where I don't think there should be any (in the mids) and the shadows look a bit muddy. Maybe it's just old film. Maybe it just that I'm not use to Plus X. I'll keep tinkering, and dig out my ND filters...good tip. > > > I'm shooting PX-125. Using the density function of my > > > scanner I measure the [quoted text clipped - 43 lines] > just old film. Maybe it just that I'm not use to Plus X. I'll keep > tinkering, and dig out my ND filters...good tip. Do you see the strange effects on the negatives directly or on the scanned image? D-76 should give you good tonal rendition. I've not used Ilfosol-S but it should also be good. Its a Phenidone/Hydroquinone/Ascorbic acid developer. If the negatives appear to have blotchy fog it may be due to some damage it suffered while refrigerated. Plus-X roll and 35mm film is a good general purpose film. It should be giving you good results without any special fuss. What is your developing routine? If you get good results with T-Max you should not be having trouble with Plus-X Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com > > > > I'm shooting PX-125. Using the density function of my > > > > scanner I measure the [quoted text clipped - 67 lines] > Los Angeles, CA, USA > dickburk@ix.netcom.com You were bang on about the film base being 0.20. I did the bleach test you suggested. My VueScan Densitometer measures bleached plus-x film "base" at 0.20 ~ 0.22, probably not perfect but amateur "accurate". An unexposed strip that was "fixed only" measured 0.34 and the "developed and fixed" piece measured 0.44. So, I guess this is telling me that the fog on the film itself is almost a stop (0.34 - 0.2 = 0.14) In addition, the developer (Ilfosol-S) causes another two-thirds of a stop loss (0.44 - 0.34 = 0.10) I'll also correct my initial posting -- it's a two-and-half stop base+fog loss not one-and-a-half as I misstated. I'll repeat my initial question. Do these number look too high? Thx again. 0.10 is one third stop. 0.30 is one stop. 0.15 is one half stop. There are one third and one half stop step tablets. Dan Thx. I figured that out (again) after my post. My bad. ;^0 > 0.10 is one third stop. 0.30 is one stop. 0.15 is one half stop. > There are one third and one half stop step tablets. Dan >> > > > I'm shooting PX-125. Using the density function of >> > > > my [quoted text clipped - 129 lines] > question. Do these > number look too high? Thx again. If the numbers are actual log density they are quite high. I measured some negatives to see what sort of numbers I got. I don't have any Plus-X 35mm but it should not be too different. 35mm film. T-Max 100 in D-76 1:1, several samples, around logd = 0.25 to 0.27 A sample of some of this film outdated by 10 years and processed a few days ago showed the same B+F level! T-Max 100, T-Max RS full strength B+F = logd 0.22 I was using T-Max RS in a replenished system so there was probably some bromide build up, hense the very low fog. T-max 400, D-76 1:1 logd =0.3 Arista (probably Ilford FP-4) D-76 1:1 logd = 0.22 Some 120 films: Fresh 100T-Max, Xtol 1:1 but somewhat underdeveloped, logd =0.16 Verichrome Pan (somewhat outdated at the time of exposure) D-76 1:1, 0.18 These films were all exposed for their rated ISO speeds and developed to a CI suitable for diffusion enlarging. Lower contrast processing for a condenser enlarger would probably show somewhat lower fog. Base density of the 35mm film is about 0.2 (measured by removing the emulsion and back coating). Two samples of very outdated film processed recently are given below. Both are 120 Verichrome Pan, the last of some left over film which is outdated by probably 15 years. One sample was processed in T-Max RS, (stock diluted 1:1), the other in Rodinal 1:50 Both have B+F or log 0.3 These densities were measured in an old, but quite accurate, densitometer made by the Weston Instrument Co. It is possible the high fog level of your negatives is due to incomplete fixing. The remaining halide will make the emulsion turbid resulting in the high density. It is possible that refixing might lower this although the effectiveness of refixing decreases with time. If you want to experiment with this I would also treat the film in Kodak Hypo Clearing Agent after refixing. KHCA will make soluble some otherwise insoluble fixer reaction products. It is also possible the film got fogged in some way. There are all sorts of possibilities although usually when film is light struck the fogging is not uniform. I hope this is helpful. Signature--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com > >> > > > I'm shooting PX-125. Using the density function of > >> > > > my [quoted text clipped - 167 lines] > It is possible the high fog level of your negatives is > due to incomplete fixing. I suggest the high fog level is due to scanner noise. I've yet to see a scanner (especially from Epson) that delivers it's stated Dmax via s/n ratio. > The remaining halide will make the > emulsion turbid resulting in the high density. It is [quoted text clipped - 14 lines] > Los Angeles, CA, USA > dickburk@ix.netcom.com [Snip] > I suggest the high fog level is due to scanner noise. > I've yet to see a scanner (especially from Epson) > that delivers it's stated Dmax via s/n ratio. [Snip] I have a Stouffer target now (a T2115). When I scan it you can see the noise slowly creeping in to the histogram around step number 10. But in the clearer regions the noise is very low. So I'm thinking noise might not be an influence at the film base level. Another thing, when I fixed the undeveloped piece of film I just snipped a piece out of my bulk loader in total darkness and put it in a half full tank of fix, then came back in 20-30 minutes, no agitation, rinsed it. When I looked at it the film looked bubbly, almost like an irregular honeycomb effect or like little interconnecting rivers, clear bubbles surrounded by darker lines. What could that be? It went away after it dried - I think. > [Snip] >> I suggest the high fog level is due to scanner noise. [quoted text clipped - 21 lines] > lines. What could > that be? It went away after it dried - I think. That sounds like reticulation, a sort of wrinkling of the emulsion. Reticulation is rare in modern films but used to be common when processing at high temperatures. It could also be a coating defect if you see it in all the film from the bulk roll. Try another sample but fix normally, i.e., for sodium thiosulfate fixer about 10 minutes _with_ agitation, for rapid fixer at film strength about five minutes with agitation. See if the turbid appearance recurs. Because scanner noise my be exagerated by the grain structure of the film its possible that it might not show up when scanning the very fine grain step tablets. However, since there is a visible defect in the film I would pursue that before blaming the scanner. Signature--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com >> I'm shooting PX-125. Using the density function of my >> scanner I measure the [quoted text clipped - 5 lines] >> terms of image >> quality or is it treated as neutral density when I print? > Have you any means of calibrating the scanner? >Photographic density is usually stated as Log density where [quoted text clipped - 18 lines] >you if the "density units" of the scanner have any relation >to the normally used Log density. I'd like to know more about how to do this. Thanks a million. |
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