Why flash your paper???

[stradibarrius]

I would like to know under what circumstances do you choose to flash your paper? How do you you know how much to flash?

[henk@lf]

I flash paper when I want to get detail in highlights that are difficult to burn in the "normal" way.
I do teststrips for the amount of flash needed.

Usualy I spend a lot of time (teststrips) on an image that needs flash.
I use multigrade paper and I mostly flash at grade 0.

First I do teststrips on the image to define exposure and contrast.
Then I do teststrips for the amount of flash.
After this I do teststrips again to check if contrast grade is still ok.

[N Dhananjay]

Flashing distorts the toe of the characterisitic curve of the paper - the toe portion becomes longer. So the overall negative density range accomodated becomes larger and the highlights will print with less contrast. It's one of the tools in the 'robbing Peter to pay Paul' game that we have to play to get contrast looking right in all the parts of the image while accomodating the overall negative density range that is required. The basic game goes something like this - the paper has a certain density range (let's say it runs from density of 0.05 to 2.05). The tonalities of all the areas of the print have to be distributed within this gamut. Sometimes, a nominal paper contrast grade that accomodates the overall negative density range may leave the shadows or highlights at the wrong local contrast. Then, if we want greater contrast in one area, it has to be stolen from some other areas. This is easiest done by distorting the toe and shoulder of the paper's characterisitic curve through various controls (preflashing, predevelopment bleaching, water baths etc). The idea is that you steal contrast from one area (by distorting the scale there) and use that to pump up the contrast in the area that is required.

So, you can pick a contrast grade and exposure that gets the shadow areas looking correct and then preflash to accomodate the highlights. Or you might find your highlights look fine but your shadows need more contrast. Going to the next higher grade of paper contrast would get the shadow looking right but now the entire negative density range is not being accomodated and the highlights have vanished - you can preflash to retain the highlights. I find preflashing usually works where the highlight areas in the negative have a lot of local contrast and can make up for the reduced contrast in the toe of the flashed paper. In the reverse situation, where highlight contrast is more important and you cannot put up with any distortion in the toe portion, you can use a water bath or predevelopment bleaching to introduce a more pronounced shoulder so that the shadows print with less contrast and that is used to get the highlights (or other area) looking right.

Hope that helps.
Cheers, DJ

[Vaughn]

Another way to look at it is that the paper takes a certain amount of exposure before the paper white changes to off-white. It takes an amount of light to reach the threshold of showing any tone. Flashing was used a lot before variable contrast paper, but can still be used with VC paper (tho it might be easier just burning with a 0 filter).

Let's say it takes 10 units of light, just as an example, to reach the threshold to show any tone. A deep black requires much more light -- let's say 300 units of light. Don't worry about what these 'units' are -- you can find the exact amount of light it takes by making a test strip without a negative and seeing where the first off-white strip occurs.

So let's say you have a print that mid-tones and shadows look fine, but the highlights you want some detail in are only getting 4 units of light due to the negative highlight density, and thus remain paper white. You could just burn these highlights until they get enough light to start showing detail, but the mid-tones and shadows areas around the highlights might receive too much light and get too dark.

So you do the above test and find that it takes 8 seconds at f22 (w/o neg) to get your first off-white strip -- the 10 units of light mentioned earlier. Back off a little, say to 6 seconds and flash the paper (or portion of it) at f22...or in this example about 7 or 8 units of light. If you were to develop the sheet right now, it is still would be white because even though you have given it exposure, it is not enough to bring it up to the 10 unit threshold needed for getting any tone on the paper.

Now when you make your same original exposure thru the negative onto the flashed paper, the highlights still get the 4 units of light, but it is put on top of the 7 or 8 units of the flashed exposure. Your highlights now have a total of 11 or 12 units -- bringing the values above that 10 unit threshold and they will have tonality and not be paper white.

The mid-tones and shadows receive hundreds of units of light, and you only flashed with 7 or 8 units-- so this small amount of light does not significantly change the mid-tones and shadows -- unlike normal burning does. The only danger is over-flashing the paper and killing all one's highlights.

[patrickjames]

Ditto what Vaughn wrote.

I find flashing to be consistent and subtle whereas burning in can be problematic.

[bigdog]

Recommended reading: http://www.lesmcleanphotography.com/articles.php?page=full&article=27

[Michael W]

Vaughn - excellent explanation, very clear.

[Doug Howk]

I use an RH Flasher with my enlarger. The light emitting square is velcro'd to the lensboard. As others have stated above, once you know the level of flash per graded paper, then flashing is a very convenient tool for working with high contrast negatives.
For contact printing on Lodima or Fomalux, I use a Bessler audible timer that gives me very precise flash control down to as low as 1/10 second. As taught to me by Michael Smith, can even use dodging/burning tools while flashing, though its most convenient with a foot switch to control the timer start.

[Chuck Pere]

Also a penlight type flasher can be used to tone down small hot spots to make them less noticeable in the final print.