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Photo Forum / Film Photography / Darkroom / December 2004preflashing tools?
I've heard that you can use a piece of diffused plastic for pre-flash under the enlarging lens... problem is i have no idea what kind of household item to try, ive thought about using plastic coke bottles or something of that sort, any recommendations? k Why are you doing this? You're fogging your paper? to boost the base / foot of the tonal curve curve. k > Why are you doing this? You're fogging your paper? What paper are you using? : to boost the base / foot of the tonal curve curve. Ignore the troll.  SignatureKeep working millions on welfare depend on you ------------------- fwp@deepthought.com > I've heard that you can use a piece of diffused plastic for pre-flash > under the enlarging lens... [quoted text clipped - 4 lines] > > k You want to use a piece of plastic that is milky white and translucent. Some plastic milk cartons have this characteristic. If you have a piece of Plexiglas (or similar) you can make it into a diffuser by sanding it in a circular pattern until it's fully and evenly scratched and you cannot see through it any longer. You can also use tracing paper. It might be better in some ways as you'll use a lot of light going through it. Ignore radioactive isotopes. He has a propensity of providing really one sided recommendations - his side only! > I've heard that you can use a piece of diffused plastic for pre-flash under > the enlarging lens... > > problem is i have no idea what kind of household item to try, ive thought > about > using plastic coke bottles or something of that sort, any recommendations? Styrofoam coffee cups over the lens. You can vary the amount of diffuseness and dimness by stacking the cups. What you want is white plastic from a milk jug, I think. > I've heard that you can use a piece of diffused plastic for pre-flash > under the enlarging lens... [quoted text clipped - 5 lines] > > k I use a sheet of semi-translucent paper that I have glued to a sheet of cardboard with a large cut-out in the center. BTW, I don't know if this is necessary, but it seem to me that it is a good idea to keep the diffuser moving in order to avoid projecting the image of whatever grain there is in the diffuser onto the print. Why pre-expose with the enlarger as the light source? Dan > Why pre-expose with the enlarger as the light source? Dan It's convenient: You don't need a separate flashing station. And with a reasonable diffuser (I use two nested styrofoam cups over the lens), you don't even have to remove the negative from the enlarger. -t > tony wingo wingo@spamcop.ne >n article <1102639725.981509.112100@c13g2000cwb.googlegroups.com>, > [quoted text clipped - 3 lines] >reasonable diffuser (I use two nested styrofoam cups over the lens), you >don't even have to remove the negative from the enlarger. Doesn't your flash exposure change depending on the negative density? I've never used this method. Always used a separate light in a calibrated setup as I assumed this would be more accurate. > > tony wingo wingo@spamcop.ne > [quoted text clipped - 9 lines] > never used this method. Always used a separate light in a calibrated setup as > I assumed this would be more accurate. The whole point of flashing is to increase the base paper density (essentially fog), usually to fine tune highlight tonalities. You could calibrate flashing for a particular paper and light source, but creatively it will vary depending on the image and especially negative densities. So if I flash I test it for each negative and the degree of flashing would vary with each negative. Personally, I am not a fan of flashing. > Tom Phillips nospam777@aol.com >The whole point of flashing is to increase the base >paper density (essentially fog), usually to fine [quoted text clipped - 5 lines] >if I flash I test it for each negative and the degree >of flashing would vary with each negative. Most people I know flash to just below the paper threshold. They don't actually fog the paper. So a calibrated setup makes more sense. > > Tom Phillips nospam777@aol.com > [quoted text clipped - 10 lines] > Most people I know flash to just below the paper threshold. They don't > actually fog the paper. So a calibrated setup makes more sense. Flashing is fogging; it's just a matter of degree. Both flashing and what we consider "fogged" paper or film are the result of non-image forming light. Aesthetically there's a difference in effect; technically there's not. You are in fact adding overall (light) density to paper that wasn't there before that in fact reduces the contrast (grade) of the paper. The reason it works is because just the right amount of preflashing affects only the print highlights (paper base), not the denser areas (blacks) of the print. Henry (p 67) states his test show that preflashing at greater than 1/32 the print exposure time is unlikely to be beneficial and that preflash exposures between 1/64 and 1/32 the print exposure time provided an optimum decrease in print highlight contrast. Given preflashing is contingent on the results desired for a given print/negative, it makes more sense to test for each negative/print. I assume by what you mean by "below the paper threshold" is a preflash that doesn't add enough significant density to apparently fog the paper (which would actually be at the paper's base reflection density threshold since it seems impossible to me that one could get/flash below the paper's density threshold.) I.e., just enough to reduce the contrast of highlight areas where softer tonal detail is desired. With variable contrast papers I would tend to think pre- flashing is unnecessary, since you can expose different areas of the print to lower or higher contrast filters. > Tom Phillips nospam777@aol.com >I assume by what you mean by "below the paper threshold" >is a preflash that doesn't add enough significant density [quoted text clipped - 4 lines] >contrast of highlight areas where softer tonal detail is >desired. The flash exposure just adds to the exposure from the negative. It basically raises the exposure over the paper threshold so the highlight details normally under the threshold are now visible. But with reduced contrast that has a much greater impact on highlights than shadows. The flash exposure by itself doesn't have to result in a visible paper density to work. lots.of.people@everywhere wrote: >>>>> Paper flashing ... I find ferricyanide bleaching works very well with paper flashing. It increases local contrast in the highlights and allows quite a bit of flash - an almost visible flash that is removed by the bleach. This can work wonders in recovering the blocked highlights that sit on the shoulder of the film curve and the toe of the paper curve and thus have miserable contrast. Try this if flashing just leads to grey highlights. SignatureNicholas O. Lindan, Cleveland, Ohio Consulting Engineer: Electronics; Informatics; Photonics. Remove spaces etc. to reply: n o lindan at net com dot com psst.. want to buy an f-stop timer? nolindan.com/da/fstop/ > lots.of.people@everywhere wrote: > >>>>> Paper flashing ... [quoted text clipped - 9 lines] > > Try this if flashing just leads to grey highlights. Slight overprinting and then careful bleaching of highlights would probably be my preferred method. > > Tom Phillips nospam777@aol.com > [quoted text clipped - 12 lines] > greater impact on highlights than shadows. The flash exposure by itself > doesn't have to result in a visible paper density to work. The flash exposure doesn't need to result in a readable increase in reflection density. But the result is visible. I think we're talking about the same thing :) I'd think that much more convenient. I played a bit with pre-exposure using one of my safelights just where it was. Safelights that are not overly safe, how about that? Dan > > tony wingo wingo@spamcop.ne > [quoted text clipped - 9 lines] > never used this method. Always used a separate light in a calibrated setup as > I assumed this would be more accurate. Well, yes. But I use flashing rarely enough that i just recalibrate the flash time on a per print basis, then include that information in my notes for the print, so I can reproduce it in the future. -t Yeah, I used to do this a lot when printing black and white wedding shots of the "happy couple" for the paper. This was I could get detail in the dress and not blast the tux into a black hole, without burning and dodging. I calibrated my flashing exposure to be just threshold or sub-threshold for the paper I was using and used the second enlarger in the darkroom for the light source. It was calibrated, had a timer and an aperture (long slow exposure easier to accurately time with a 40+ year old mechanical timer) and pretty repeatable. I used two different papers, Panalure II RC and Polycontrast III RC, so had only two espouses to remember and wrote them on the enlarger baseboard in grease pencil. Signaturedarkroommike ---------- > Why pre-expose with the enlarger as the light source? Dan I use it if I am having problems with the high end of a print. I have a night-light on the far end of my darkroom plugged into an extension cord that connects to an old Omega digital timer I picked up for a few dollars at a swap meet and have dedicated to this use. My total cost for the timer, the cord and the night-light is under $20. I did threshold tests for the papers I use. With my setup and papers, my times run between 2 and 3.5 seconds. This isn't something I use a lot but, when I need it, it is nice to have. I dodge and burn a lot more than I use flashing but, like having some difusion material at hand, when it is the right tool, it is the right tool. Just make sure the enlarger is NOT focussed and the lens is well stoppe down. You might not need a diffuser. If you need less light output so you can control the exposure - try N filters as used on your camera lens. Cheers Ra -- Rollei Ray From UK |
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