Here is a method for finding a single printing exposure for all of your contact sheets. It takes a few minutes to go through this, but it will save you time in the long run by eliminating the need to guess at your contact sheet exposures or to make a test strip each time that you want to do a contact sheet. A fringe benefit of this method is that it will produce a contact sheet that will let you know if you are exposing your film properly.

This procedure requires a certain amount of standardization. You must use the same type of paper (brand, grade or filter) for all of the contact sheets. We recommend using RC paper for contact sheets in order to save time. This method will work best if you use the same enlarger each time you print, but if this is not possible, it will still work reasonably well so long as you select the same type of enlarger with the same time of lens each time you print.

1. Rack your enlarger all the way to the top of the post and close down the enlarging lens one or two stops from maximum aperture. (For example, if the maximum aperture is f4, close it down to f5.6). Make a note of this aperture because you’ll use it for all future contact sheets. Insert an empty negative carrier in the enlarger and focus the light on the edges of the carrier. This is now your light source for contact printing.
   
2. Do a contact sheet test strip with a strip of negatives from the type of film that you normally use. Uncover successive portions of the strip, giving a 5 second exposure each time. The result will be a test strip with exposure steps of 5-10-15-20-25-30 seconds.
   
3. Develop (use your normal development time, 1 ½ - 2 minutes for RC, 3 minutes for fiber), stop and fix. Take the strip out of the darkroom to inspect it under a good light.
   
4. Inspect the strip, looking only at the edges of the 35mm film: the film base and the dark holes that are the perforations in the film. Scanning from the lightest section to the darkest, find the first interval at which the film base just about matches the blackness of the perforations, the interval at which you can no longer see clearly the holes in the film. This interval is your standard contact printing time.

Note: If all of the intervals show a film edge that looks completely black (no perforations visible) go back and repeat the procedure, but first close down the lens one more stop. Conversely, if none of the sections approach the point at which the film edge is as dark as the perforations, repeat the procedure, first opening up one stop. (Once you get a usable test strip, remember the aperture that you used.)

You now have the aperture and exposure time for this and all future contact sheets. When you return to the darkroom to do your next set of contacts, rack the enlarger to the top of the post, stop down to the aperture that you used above, set the timer to your standard contact printing time, and expose away.

This method of will produce good contact sheets if your negatives are exposed reasonably well. An extremely thin, underexposed roll will yield a dark contact sheet and a very dense, overexposed roll will yield a light contact sheet. Therefore, the above method becomes a valuable check on the quality of your film exposure. With a well-exposed roll of film, your standard contact printing time should produce a very readable contact sheet.