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!
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.)
Originally Posted by htmlguru4242
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.
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 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 Alexis Neel; 05-09-2006 at 02:40 PM. Click to view previous post history.
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.
By stretching might that be considered a method of dodging? Dan
Originally Posted by Donald Miller
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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.
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.
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...
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.
Originally Posted by glbeas
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.