I am trying to save a little money on paper. Can I make test prints on 3x5 or 4x6 paper to get contrast filters and exposure times, and then use those settings (plus a factor for increased lamp distance) to make 8x10 final prints? For example, if maximum black plus 1/2 stop at contrast filter #1 gave a full toned print on 4x6 would the same be true for 8x10? I'm using ilford MG IV RC. Thanks Ryan

-- Ryan Olson (ryno@bitstream.net), June 24, 1999

Answers

The correction for increased lamp distance is quite easy to compute:

Time Factor = (D2/D1)^2

where - D2 is the distance between the negative plane and the paper for the print in question, and - D1 is the distance at which you made the test exposure.

This is quite straightforward: The squared ratio of the distances is, in fact, the ratio of the illuminated areas. So the factor takes into account that the same "quantity" of light is now distributed to a different area. (This works both ways: from small to large and vice versa.)

The approximation works fine as long as you don't change the distance considerably. If the distance changes considerably, I would just use the approximated time as an indication of the time for new test exposures.

Whilst the idea of "same light on different area" is still true, there are two effects that limit the usefulness of the formula:

1) reciprocity failure, particularly when the extrappolated time is much longer than the test time, and

2) loss of contrast as the print size increases (in relation to the negative size).

I have my rules of thumb, which work quite well for my hard- and software, but you must test yours. To give you a starting point: When a contact print on grade X paper at standard exposure looks as though the grade were OK, I would start testing for large formats (4 times the negative format and larger) at grade X + 1/2 or X + 1.

To come back to your question: Going from 4x5 to 8x10 amounts to two f-stops. (The ratio of the areas is four.) I would try to print a test strip of the 8x10 image with the grade 1 1/2 or grade 2 filter at 4 times the original exposure time plus a few steps of 1/4 f-stop (1,2 times in terms of exposure time) each from the extrapolated exposure time. That way, you may not save as much paper, but you are sure to find the correct exposure quite quickly.

-- Thomas Wollstein (wollstein@compuserve.com), June 25, 1999.

Actually, there usually isn't any need to make your test print of the full image. Most negatives will have a sufficient range of contrast inside a small 4x5 (or smaller) area, even if enlarged to 16x20. Using 4x5 test prints gives four tests per sheet of 8x10, plus lots of room to get the full range of contrast/brightness. It is a rare negative that needs larger percentages of the image used for the test. Select the key part of your image, and get the filtration and exposure directly. Mental math as suggested above invites errors which waste papter. Its worked well for me for many years.

-- Richard Newman (rnewman@snip.net), June 25, 1999.

Since my method has been criticised, I would like to comment:

1) I don't think the case of the highlights being in one corner of the negative with the shadows being in the opposite corner is so rare.

2) I don't quite understand why the "mental math" should be so error-prone. Use a pocket calculator for the number-crunching. Applying the factor does not demand great skill.

3) I did stress the limitations of the method. However, I think it saves me paper, because in spite of the cautions, the extrapolation works surprisingly well. The very least is that it gives me a pretty good guess at the exposure time when I want to make a large print after having made a small one. (It happens all the time that I make a fairly good 8 x 10 print, and later on, I need a bigger print.) With that good guess, I can start a series of test exposures at finer intervals, thus saving at least one test strip and some time.

-- Thomas Wollstein (wollstein@compuserve.com), June 30, 1999.

I use what I call "test squares". These are 1" squares of paper. I place one on a midtone area - like part of a face. I place one on a highlight, sometimes with a paper clip on it, to cast a shadow making a total white for reference. Less often I place a square in a dark area to see if there's still detail. I really don't give a damn about maximum black. I look at the squares and judge by experience how much to change exposure/contrast.

-- Tim Brown (brownt@ase.com), July 08, 1999.

I print by cutting paper, either 11x14 or 16x20 into four equal pieces(Ilford MG FB). I make the prints on the 51/2 x7 or 8x10 pieces of paper and get everything right. Then I rack up the enlarger to the full size, increase the contrast 1/2 filter grade, open the lens either 2 stops and use the same exposure range to make a final test for the final exposure, or open the lens one stop and double the exposure to make the test exposure. Then for the final print, I cut the exposure 8% to compensate for dry down and selenium toning. Then edge burn for 10% of the exposure time. This usually nails it for me!

-- Gene Crumpler (nikonguy@worldnet.att.net), July 12, 1999.

-->(plus a factor for increased lamp distance). I HAVEN'T read the other responses yet, but, even though I am fairly new to printing, I have discovered one thing: tests are more uselsee the more variables there are which are different from the final conditions of the print. Using a different enlargement from the anticipated final enlargement is the biggest way to make a tests useless: contrast and grain are variables which I believe must be eliminated from the get-go. It is more expensive, but I have started using the same paper for my tests as I plan on using for the fine print, I enlarge in the test to the anticipated final enlargement, and I go through the whole process from exposure to tone to final wash, all on the test print. The only thing I do differently is to blow-dry the test print, to save time (Adams say nuke 'em, if you have access to a microwave...), and air dry the (hopefully) final print, though occasionally I try to warm up the final print with LITTLE blow-drying and slightly warmer water.

-- shawn gibson (shawn.gibson@utoronto.ca), July 13, 1999.