Pre-Flashing prints?

Discussion in 'Enlarging' started by htmlguru4242, May 8, 2006.

  1. htmlguru4242

    htmlguru4242 Member

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    I occasionally run into a situation where my prints have good midtones and shadows, but the highlights lack detail (though the detail is in the negative). I know that in many cases, I could burn those areas in (which is what I normally do), but in some cases, the shapes of the highlights are rather too complex to burn, and the exposure needed is ever - so slight that burning would have to be very quick.

    Is this a case where pre-flashing the paper may be us use? If so, does anyone have suggestions for methods / times? (I'm using Ilford MGIV and Kodak Polycontrast for my paper).
     
  2. gr82bart

    gr82bart Member

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    Coming back from the APUG Conference and watching Les do his magic, all I can say is DON'T DO IT. Use post flashing instead. Brings out the details much more.

    Regards, Art.
     
  3. grahamp

    grahamp Subscriber

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    Pre-flashing will raise the paper inertia point, though getting the right amount without risking safelight fog and veiling the highlights takes some doing. About the only time I use pre-flash is when I am doing safelight tests and want to err on the side of caution!

    It is really tedious to do if you only have one enlarger, and you cannot stock pre-flashed paper for very long.

    Other options are split-grading - put the highlights in with a soft grade and the shadows with the hard grade - or local application of warm developer on fibre prints. There is also the print heavy and light bleach approach, but it does not sound like you have enough detail to do this.

    All these methods can get that little bit of tone in fine highlights, but they do have slightly different effects on the mid-tones and shadows.
     
  4. TheFlyingCamera

    TheFlyingCamera Membership Council

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    You might try split-grade printing. There is a lot of info out here on APUG on how-to, so I won't repeat it here. The short version is that you make two separate exposures, one at minimum contrast, one at maximum contrast. You vary the length of each exposure based on what you need to accomplish with your highlights and your shadows.
     
  5. glbeas

    glbeas Member

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    I use a little desk lamp with a dimmer wired in plugged into an enlarger timer and hundg on the wall for some distance. It's a very simple procedure to lay a sheet on the table under the lamp and give it a preflash bump before loading it into the easel.

    For what its worth this is the very same technique used in graphic arts predigital while making halftones. They required a preflash to bring up the shadow detail and correct for ink bleed in the printing process. The time was standardised for all shots as it was just to bump the dot formation over the threshold exposure.
     
  6. Nige

    Nige Subscriber

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    I'm a pre-flasher...

    Everything I've read (until today) has said that pre and post flashing have the same effect, although I've always thought it must have some however slight differences. never seen them myself as on occasion I have completed my enlarger exposure and think, oops, forgot the pre-flash so I post-flash and stil get the print I was aiming for. But if Les can demonstrate a difference, I'll believe 'ya.

    If you are going to flash the paper, you must test to work out your enlarger/paper combination, so if you use two papers, you need to do two tests to determine the appropiate time for each.
     
  7. unregistered

    unregistered Inactive

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    It does make a difference if you do before or after the main exposure. Either one will work but each produces a different result. Sometimes it is necessary, or you want a certain look/effect, to do both, but it is tricky to get the balance right. A slight pre-flash to "sensitize" the paper, then an exposure/burn in your highlight area on a low filter (doesn't have to be a 00 or 0...sometimes those are too much), then your main exposure on whatever grade you want the rest to be on, then an additional burn, on that filter you used for your main exposure). Balancing all these takes paying attention to what you are doing, and the results you get from them. Trying different combinations and watching those results, will make you a better printer in the long run. Since the combinations are endless, it is important to notice the changes that happen with each combintation.
    BTW, post flashing can flatten out the internal contrast of your mid and lower value tones, since it will be putting a flatter exposure on thise subtle highlights, so be careful.

    Hope that helps.
     
  8. jeroldharter

    jeroldharter Member

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    I just tried flashing for the first time last weekend. I used the RH Designs flasher mounted next to my enlarging lens. It has a nice test strip feature and digital timer. I pre-flashed the top half of the 16 x 20 paper for 32 seconds and dodged the rest while split printing thenegative. Made a big difference in the highlights.

    However, post flashing would make it easier to gauge the desired effect so I will likely do that next time. The flashing device works very well.
     
  9. Neal

    Neal Subscriber

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    Dear htmlguru4242,

    I keep a piece of frosted glass at the side of the enlarger. If I run into a print that needs pre-flashing, I burn a sheet with an exposure test. I suppose I should invest some time with a known light source. Maybe an old flash with some tape over it.

    Neal Wydra
     
  10. ChuckP

    ChuckP Subscriber

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    Can anyone explain why post flash is different then pre? Looking for a technical explaination in plain language. The way I understand it the flash exposure adds to the negative exposure to help bring highlight details above the threshold of the paper. Looked at in this simple way it won't matter if it was pre or post.
     
  11. Mick Fagan

    Mick Fagan Subscriber

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    ChuckP, I'm in the same boat as GlBeas, having worked in the graphic arts field for 15 years and watched the pre-exposure on our Klimsch gallery cameras using 8 arc lights running at 10% of power with a minimum f stop for a pre-determined time, then main exposure on full power at a correct f stop, it works beautifully.

    However a few times we forgot to pre-expose and decided to add the pre-expose as a post expose, halftone dot was all over the place by comparison and we really didn't ever look into changing our technique. In short I'm not saying it couldn't be done but it appeared from empirical experience that pre rather than post does make a difference and pre seemed to be better in that situation.

    I have pre-exposed (flashed) B&W and colour neg paper in the past for difficult negs, sort of reckon I'll be doing more of it in the future, maybe I'll try post exposure flashing to what it does.

    I would though, be very interested in this post exposure technique as mentioned in a previous post in this thread.

    Perhaps I had really better start looking into this RH designs thing, to see if it could be useful. Going on my family history I have about 20 years of darkroom work left in the body, I would hate to discover the joys of a different tool just as I'm winding down!

    Mick.
     
  12. climbabout

    climbabout Member

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    I use preflashing quite often to reduce contrast - I happen to have a 2-1/4 enlarger next to my 5x7 so I use the 2-1/4 enlarger as the light source when I print large format - but any controllable, repeatable, light source will do - (I have a friend (Steve Sherman) who uses an old hanging bullet safelight with on old enlarging lens attached to control the light.)

    My procedure is as follows - To determine the flashing time I place the enlarger at a fixed height and aperature and make a test strip at say 2 second intervals and develop it and dry it - what you want to find is the time that creates the first hint of tonality above paper base - then back off your exposure slightly so that the flashing creates no percitable tone - this brings the paper to just below it's threshold so that any additional exposure during printing will produce tonality immediately. You would naturally have to run this test for each paper you use as the flashing time may vary. But once you determine you papers threshold time - you've got it! During printing I will will set my flashing source to it's predetermined height and aperature (which for my paper is 27" and f16 @10 seconds), expose the paper and then put the paper under the other enlarger and make my negative exposure. As I prefer graded paper, this has become an invaluable tool in my printing procedure when contrasts reduction is needed. I sometimes flash to less than threshold when minor adjustments are needed. I hope this helps you.
    Climbabout
     
  13. unregistered

    unregistered Inactive

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    Chuck, I'll explain my understanding of it, although I have no scientific basis for the explaination. I just know it works this way so take it for what it's worth.

    When you give the paper a pre-flash, you are changing the contrast of the paper, (and the possibilities are wide, since you can use any filter to expose your pre-flash exposure thru, or you can just use unfiltered light...which will be like a grade 2) and are giving it some density to work with during the main exposure. Of course, how much it changes depends on how much pre-flash you give it. Lets say if you exposed a print on a grade 1 1/2, and the contrast looks great, but you want some pre-flash (because you've determined that the pre and not the post flash will be better). And lets say you chose to do the pre flash on a grade 00 (because they are really blocked up. You could use a 1, or any filter for that matter, it just depends on the density of your highlights), because your highlights are the problem. So, you've changed the basic "grade" of the paper because you've "fogged" it with a flat exposure. When you go to make your main exposure, since you are starting with a flatter paper, you will need to change your contrast, made a #2, to make up for the paper being "flatter" to begin with. You will also need to change the time, since you are starting your main exposure with a paper that already has density on it.

    Now when you post flash, and lets go with everything above...main exposure on a 1 1/2, you are basically "filling in" highlight areas with density...kind of like fill flash when shooting and you have a main light source and are using fill flash to fill in dark areas. This post flash can effect the shadow area, but usually it doesn't, unless you are giving it a substantial amount. You could dodge the shadows some if need be, but most of the time it isn't necessary.

    Sometimes you'll need/want to do both, and then that throws a whole bunch more variables into the mix. Try to remember whats been done is the hardest part...especially at my age.

    This is a simple explaination...I could write a book on the whole proceedure, and maybe I'll make a few samples one day and make a web page with them. However, its a lot of work and the possibilities are endless. As always, you are going to need to try it out and pay attention to the results. After a few years, you'll get the hang of it :smile: For me it comes pretty easy and I can see after 1 test strip and 1 full test print, what I need and how much.

    BTY, I use a seperate enlarger so I can adjust the height (for different print sizes), bellow amount (I always throw the flash light out of focus even though I am going to stop down quite a bit and bring some of it back in focus), f-stop and exposure.

    Hope this helps.
     
    Last edited by a moderator: May 9, 2006
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  15. Donald Miller

    Donald Miller Member

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    Flashing paper whether that is by pre or post will work wonders in some difficult printing situations. However some people use it as the method of choice in each and every situation and that, I think, is unfortunate.

    I think that the reason that some use the method indiscriminantly is that they do not know of another method to reduce contrast.

    Let's be honest here. The affect of flashing is proportional to highlight values in a print. The compression of tonal scale is far greater in the highlight values then in any other portion of the tonal scale. That sometimes is appropriate and sometimes is highly inappropriate.

    The reason for reduction in tonal scale is to allow higher local contrast to exist within the limitations of overall contrast characteristics of the printing material. Most people are capable of visually responding to greater local contrast in the mid tones and the high values. So in effect flashing produces a reduction in local contrast in one of the regions of desired greatest local contrast.

    So is there another method that will work? Yes, there is. Contrast reduction masking of the camera negative whether that is through the use of low density and low contrast unsharp masking or through some other type of contrast reduction masking does work on the other end of the tonal scale. The compression in tonal scale, using masking, occurs in the low tonal values. The effects are predictable and repeatable. The effects are also widely variable depending on the type of mask one produces.

    No specialized registration equipment is required for the process. A bit more work, undoubtedly. But for those of us who want to produce the best that we can, then the results are worthwhile and the efforts required not unwarranted.

    I post this as information only. I encourage those who aspire to be fine printers to learn and to use the appropriate method for the requirement.
     
  16. dancqu

    dancqu Member

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    By stretching might that be considered a method of dodging? Dan
     
  17. Woolliscroft

    Woolliscroft Member

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    I would prefer burning/dodging. If the times are too short to do it accurately, just stop the enlarger lens down a bit.

    David
     
  18. Rob Archer

    Rob Archer Member

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    I don't have room for 2 enlargers, so I'developed my own system using an old diffuser filter from an old slide copier. For pre-flashing I just do a simple test strip. I usually use the exposure just before the one that shows a visible tone. If I want to give an overall slight fog I use the 1st visible value - I find this works quite well with snow scenes - particularly if I want to tone the print.

    For post-flashing I do the usual test strips (and probably a work print for comparison). I then print a 6x4in section of the print containing the 'problem' highlights. I then run use that as a test strip for post flashing.

    The beauty of using a diffuser is that you don't have to keep moving the paper or changing the lens aperture.

    For pre-flashing I find it useful to keep a record of exposures for different papers to avoid having to do test strips.

    Having said all that, I only use pre or post flashing on graded papers, I find split-grading more effective with VC papers.

    Rob
     
  19. 127

    127 Member

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    I'd also like to hear a rational explantation of the pre-vs-post argument.

    I've used preflashing to GREAT effect (in terms of the change in the image, rather than the images being particularly great...). It's something that should be taught as standard practice. If you haven't tried it then do so at once. It does allow you to move the highlights without touching the mids or blacks signifigantly. As such it's an extra tool that does something you can't do with exposure and contrast alone.

    I've heard several times the pre-vs-post argument, but if the halides just counts photons that hit it, then why do they care if they're hit by flash then print or print then flash light? photons is photons. 3 flash + 2 print = 5 photons which ever way you add them up.

    The only explanation which MIGHT ring true is that the flash pushes them to a critical level (which is the point). Some highlights might receive no further light from the main exposure, and the halides recombine by the time the print hits the dev (after a longer time than post flash). Pre-exposure would therefore affect the mids more (where they receive more additional exposure), but produce less fogging in the real highlights, as these don't develop at all. However - this is a MIGHT, MAYBE, if I HAD TO explain it kind of explanation - I don't actually believe it myself. If it were true you could "save" accidently exposed paper by putting it back in the dark for a year or so.

    I do know someone to ask though... I'll ask him next time i see him...

    Ian
     
  20. donbga

    donbga Member

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    FWIW, I use a method very similar to what Gary describes. I use a 7 watt bulb that screws into the base of a lamp socket mounted in the ceiling of my darkroom positioned directly above the counter next to my enlarger. The bulb is almost completely masked by black photo tape and the exposure is controlled by a timer. I usually need a few attempts to get the pre-flash exposure correct. In short it's an easy technique to use if you need it.
     
  21. htmlguru4242

    htmlguru4242 Member

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    Ok, I gave this a try. I stopped the enlarger down (f / 16), with no filter, and did a test strip at 1 second intervals. 1 & 2 seconds had no easily visible density (no densiometer to check), three did. So I pre-flashed under the enlarger for a bit more than two seconds.

    I then exposed the print (27 sec. @ f/11). The difference between it and the non - flashed version was subtle but noticeable. It's still going to need some burning - as it was shot up into the fairly bright sky. There were some highlights that did show more detail ... I'll continue to play around with this and see what happens.

    You never do realize how quickly 25 sheets of paper can go away until you have three sheets left and B&H is not accepting orders on Saturday ...

    The prints (5x7) also look (rather) grainy, but that's a function of the Tmax, which is an entirely different rant.
     
  22. Monophoto

    Monophoto Member

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    Re the question from 127 - it doesn't matter whether you pre or post flash. The results are the same.

    Flashing adds a small, uniform amount of exposure to the entire print. In the shadows, this amount of additional exposure is trivial compared with the blast of light through the clear areas of the negative, and so the amount of increased density in the print due to flashing is negligible. But in the highlights, which are the areas of the negative with the greatest density, the incremental flashing exposure is more significant and results in a perceptable amount of increased tonality.

    Flashing is an experimental process - the amount to do depends on the amount of contrast reduction you are seeking and the way you go about doing it. It's relatively easy to get a decrease in contrast of a quarter grade or thereabouts.

    I do it using a flashing card. This is a sheet of heavy cardboard with a large (about 8x10") opening cut into it. I glued a sheet of drafting film onto the cardboard. After I have made the base exposure and done whatever burning I feel appropriate, I slip the cardboard under the enlarge and give the print an additional bit of exposure through the drafting film while jiggling the flashing card. Note that this approach does not require a second enlarger, an auxiliary light source, or that the negative be removed from the enlarger. The image-bearing light from the enlarge passes through the drafting film which acts as the mother of all diffusers, completly obliterating the image and producing instead pure light on the easel. It also absorbs quite a bit of light. I find that a flashing exposure of about 5 - 7% of the base exposure is the ballpark necessary to reduce contrast a bit and give a little texture to marginally blown out highlights.
     
  23. Lee L

    Lee L Member

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    About 20 years ago I worked in a lab making about 2,000 B&W custom prints a month with two D5's and a roller processor. For blown highlights I'd take the pre-flash diffuser I had made from the Ansel Adams design (two spaced pieces of translucent white plex/perspex, sized to slip a 75mm gel into the slot between them) and hold it against the enlarger lens. About 20% of the main exposure worked to increase highlight detail without fogging the paper. I left the negative in because I had to work quickly and it was more convenient if I needed to make a second print. One layer would have worked and given me shorter flash times, but I didn't need that extra speed and didn't want to take the pieces apart. I got the plex for free from the cut-off bin at the sales counter at Cadillac Plastics in Minneapolis.

    I didn't test for before/after differences. Hopefully Les will chime in on that.

    Lately I've been thinking about testing for the differences in flashing VC paper with blue and/or green light. I have some LEDs that should be coming on Monday so I can make myself a dimmable, switchable blue/green flashing box similar to the RH Designs flasher, running off it's own timer. There goes that patent out the window. :smile:

    Lee

    P.S. Any lawyers know if an APUG post qualifies as prior art? :smile:
     
  24. 127

    127 Member

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    Thats what I think - though I haven't tested it. I can't see how it could matter at all.

    HOWEVER, plenty of people swear it makes a difference (including plenty in this thread). Some of them have claimed experimental evidence, and most have far more experience than I do. I've heard it enough to wonder if there actually is anything in it, or is it simply folklore that has got passed around.

    Ian
     
  25. unregistered

    unregistered Inactive

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    Its not folklore and I could explain it in a way I think it works. However, I'm not sure if the explaination, and what terms I use, would be acceptable or at least the right description of whats happening, so I'm reluctant to do so. I can only say that after 30+ years of printing professionally, it makes a difference...not only which goes first but if you are using, pure light, or filtered light...and then which filter you are using.
     
  26. Loren Sattler

    Loren Sattler Subscriber

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    Flashing notes

    I took an advanced printing workshop last fall from Howard Bond, a noted teacher and master photographer/printer. He uses Ilford paper and teaches a simple flashing technique for burned highlights. Here is information from my notes.

    Dim down small 7-1/2 watt night light bulb. This can be done with a rheostat or electrical tape over a portion of the bulb. Dim the bulb brightness down so the threshold exposure is say 10 seconds.

    Make a mask for the area you want to reduce the contrast for by cutting out the shape on a thin piece of cardboard such as the material normally furnished with enlarging paper in the wrapper. Simply put the cardboard in your easel, project the image on the cardboard, and draw a pencil line, then cut the shape with a razor blade.

    Now, mask out the area of the print that needs normal contrast treatment, and flash the problem area to 2/3 of the threshold time. Move the mask around while flashing as you do when dodging and burning to soften the edges.

    Your final exposure will yield less contrast in the highlighted area that was flashed.

    I saw this demonstrated, but haven't tried it yet. I forget whether the highlighted area should be exposed with a lower numbered filter (say 00) as was described in a post above. This is called split printing and it can be very effective in lowering contrast when burning in highlights.

    I hope this provides a starting point to give the technique a try. I believe it can be a problem solver.