preflashing paper

[Jim Olson]

I read up on preflashing paper and it says one should put a difusion material in place of the negative and do a test at one second intervals to see where the threshold of the paper is. What type of material should one use as the difusion material ? I have an Omega 4x5 D2 enlarger.

[RichardRitter]

One to three sheets of clear film will work With my enlarger I us one sheet of film.

[Gem Singer]

Hi Jim,

You can accomplish the same result by merely using a blank negative holder and throwing the enlarger out of focus. Diffusion material, such as a piece of ground glass in place of the negative, will serve to cut down the intensity of the light. However, that can be accomplished by closing down the lens.

[Ralph Barker]

Like Eugene, I just defocus the enlarger with the empty negative carrier in place. That, combined with the air pollution, seems to be enough for my old D2V. On bad days, some of the pollutants come into sharp focus, however, and mess up the print. ;-)

Alternatively, a piece of 1/8" white translucent plastic from the craft store might work as a means of gaining additional exposure control. But, you'd still want to defocus the enlarger.

[Kevin M Bourque]

Conventional wisdom says to find the exposure time that gives the first signs of fog, and then flash the paper for slightly less than that. In practice, I’ve found this to be too much. The overall effect on contrast is worse than whatever problem you’re trying to fix.

Your mileage may vary, of course.

[Louie Powell]

Jim -
the problem with most of these suggestions is that they require you to disturb your setup to flash the print by removing the negative from the enlarger, etc.

A method that I learned and that works very well for me involves the use of acetate drafting film (admittedly, a archaic product in the days of AutoCad!). It involves giving the print an additional exposure without removing the negative, changing the aperture, or making any other change - simply give the print an additional short exposure with a sheet of matte acetate held between the lens and the easel. The acetate drafting film breaks up the projected image so that the paper "sees" textureless light. Like any pre- or post-flashing process, it is experimental, and you need to apply trial-and-error to achieve ideal results. But typically, an exposure of 5-10% of the base printing exposure is the ballpark to work in.

The objective of flashing is to add a minute amount of overall exposure to the printed image - a small increment in exposure will have essentially no impact on the shadows, but can subdue extreme highlights, thereby reducing the overall print contrast by 1/4 to 1/2 grade.

I made a frame for my matte acetatee using a sheet of heavy cardboard - the opening is about 7x9 inches giving lots of area to work with. To make sure that the matte acetate does not contributed to any texture in the print, I tend to keep in moving during the flashing exposure.

[Ben Calwell]

A styrofoam coffee cup taped over the lens has worked great for me. I also have the D2

[CP Goerz]

If the photograph you are working on requires a bit of pre-flash but only in one section then only pre-flash in that area, no need to affect the whole sheet. Make a few sheets so you have some extras to play with as its most likely that you'll use a few up and to reset the enlarger each time is a pain.

When doing a localised pre-flash cast a wide penumbra by using a card half way between the lens and the paper, this way there won't be a telltale 'edge' to the flashed section.

For overall flashing just leave the negative carrier empty, stop the lens down to F16 and with an 8x10 sheet of fiber paper use about 1/4- 1/2 second bursts as a guide. Move the card covering the paper back a couple of inches each time. Now pop the pre-flashed paper in a dark drawer and pop the negative back in the carrier. Compose on the easel and then lights out and bring the pre-flashed sheet out and expose about 5-10% less than you need to for an unflashed sheet (each paper is a little different). Much like a normal test strip sheet you'll have an idea of where the final image will go. In most cases the test flashes aren't too seperate/distinct so you may want to mark the paper with a sharpie in a manner such as +1, +2 etc.

Flashed paper will increase in fog quite rapidly so its best to use it within three days approx, any more and the flash will grow till the paper has an overall very light grey look. Remember you are only building up a bit of exposure on the paper and not really breaking the 'threshold' so if you were to develop a sheet of flashed paper you wouldn't see anything if done properly.

Hope that helps! Flashing is an excellent tool much overlooked in the darkroom. There are other variations but this one has worked for me.

CP Goerz

[Reinhold Schable]

I agree with Louie; don't fuss with the negative. I've been using a piece of 3 inch square frosted plastic that I scrounged years ago as a diffuser.. I'd guess that it transmits about 90% of the light, but totally diffuses the image, so I don't need to "keep it moving". I find that it works just fine if I hold the diffuser an inch or so below the lens. If I had to make one today, I'd find a piece of clear plastic and ruff up the surfaces with a piece of sandpaper. Like Louie, I add about 10% to the base exposure. Try It; it can make a significant difference to detail in dense highlight areas. (Interior shots with windows to the outside, for example)

[Henry Ambrose]

Here's some high science for you. I open the darkroom door about six inches or a foot and flip the light switch in the outer hallway. A real quick flip gets me a preflash! Counting "one thousand one" is too long. A quick flip is just right most of the time.

I'd also try a low wattage light plugged into a timer for more control. An old safelight with the filter removed might be worth trying.

When I've tried a diffuser with the negative in place I've not gotten good results. But as others have written here, it works for some.

[Neal Wydra]

Dear Jim,

I keep a 3"x3" pice of frosted glass on hand and I hold it directly under the lens without moving the negative or changing focus.

Neal Wydra

[Chris Ellinger]

I also use the diffuser-under-the-lens method, without removing the negative.