Contact printing, as one might imagine, places the image in direct contact with the paper, as opposed to projecting an image on to the paper. With large format, it may produce the final image, but most often contact printing is done to produce a contact sheet or photograms. Contact printing is also used to produce reversals, either negative prints or when enlarging smaller negatives onto film for alternative processes.
The Contact Sheet
Sometimes called a proof sheet, a contact sheet simply produces a sheet of negatives of the same size as the negatives, in positive. The contact sheet can be very useful, especially for beginners, in determining what negatives are worth printing. They may not give fully conclusive evidence of image quality, but are a valuable step in editing.
Using an enlarger for the light source, the set up for contact sheets is relatively straightforward, and is repeatable in general. The three variables in printing are enlarger height, lens opening, and exposure time. Contacts are no different.
Place a negative carrier (empty) in the enlarger. Turn the enlarger on (focus on the timer). Raise the enlager to the height where the light spreads form the left edge of the baseboard to the right. That is the height. This will yield an area of light large enough to easily cover an 8 × 10 inch piece of paper. You can use masking tape to mark the front and back edges of the pool of light if you wish.
Begin by setting the enlarger lens for ƒ/8 or ƒ/11. In the case of contact printing, the idea is to have enough light that the exposure time is reasonable, but not so much that it that is is very short. The middle apertures will usually work fine. This will be confirmed when the exposure time is tested.
With contact sheets, the goal is to get to the standard printing time, which means we want to just barely be able to see the sprocket holes. We are not looking at the images. Place a test strip under the sheet of negatives (emulsion side up), and cover both with a piece of glass, or use a contact printing frame, the goal being to press the negative sheet firmly against paper.
Using a piece of mat board or cardboard (something opaque), cover about four-fifths of the test, with the exposed strip perpendicular to the rows of negatives. We want to keep the gap between strips of film, along with the sprocket holes in each strip of the test. Expose for the first increment (usually two seconds), then continue the test.
Process the test completely. Examine that space between the strips of negatives. The correct time to use is where you can just make out the difference between the gap and the clear film where the sprocket holes are.
With the time determined, it reamins to make the full sheet. Place a full (8 × 10″) piece of paper under the negatives (emulsion side up). Place the paper and negatives in a contact frame or weight with glass, and make the exposure. Process fully, and dry.
Once dry, the contact sheet becomes another chance to edit. Since the contact sheet was printed at the standard print time, it will show if images are overexposed (distinctly light) or underexposed (distinctly dark). While they may well be printable, over- and under-exposed images are much more difficult to print. The images that look normal (or near normal) will be far more likely to make successful prints. Using a standard (8x) loupe will allow you to examine the images more closely, for composition and focus.