In this post I look at standardising contact proofs.


In my last post I explained how I worked out my personal film speed. Having a new enlarger and changes to my development process require further steps to be taken in standardising my darkroom set-up. In this post I look at how an 18% density negative helps to standardise the making of proper proofs.

18% density negatives.

An 18% density negative is simply a negative of an 18% grey card. One of the steps in corroborating my personal film speed was to take a pcture of an 18% card as set out in my last post.

Standard Proof

The objective here is to have a standard way of making contact proofs so that we have consistency and maximum efficiency in our darkroom work.

Firstly we set up the enlarger so that the light source covers an 8×10 area with, say, 3 inches to spare on all sides. We make a note of the enlarger height that achieves this. On the baseboard I mark the edges of this area with sticky tape so that it can be found under the redlight and in future sessions.

I set the lens to 2 stops down from maximum aperture, which for my 50mm lens is f8.

The combination of 1 and 2 above is the standard proofing setup. It never varies for 35mm strip film.

Next we take our 18% density negative and place below it a strip of our photographic paper under glass for contact printing. I then test-expose it to produce a final dry print of the test strip that that matches 18% grey from an 18% grey card in ordinary daylight conditions.

To find the exposure that gives this middle grey, I use f-stop test exposures. For example, my first attempt at encompassing the required exposure involved the following 1-stop sequence: 3 seconds, 3 seconds, 6 seconds and finally 12 seconds. This gives total exposures of each strip as 3 seconds, 6 seconds, 12 seconds and 24 seconds. My result gave approximately something in the range 12 to 24 seconds.

I next used 1/3 stops 1 to get a more precise exposure starting with 12 seconds: 12 seconds, 3.1 seconds, 4 seconds and 4.8 seconds. So total strip exposures were 12 seconds, 15.1 seconds, 19 seconds and finally 23.8 seconds. The exposure that best matched 18% grey was 19 seconds. So, I was able to work out a precise exposure on the strength of two small paper strips. My standard proof exposure time for my standard proofing setup is the sequence 12 seconds: 3.1 seconds: 4 seconds. A bit of trial and error is then used to work out what single exposure is required to match this sequence. This was 17 seconds.

Contact Sheet

We have now all the information required to produce contact sheets for a particular film/paper/enlarger setup combination.

Below is a scan of the contact sheet of the images taken and explained in my last post.

I set up my enlarger for standard proofing (see above). I then exposed the negatives over 8×10 sheet of paper for 17 seconds.

Let me make a few observations about this:

  • You can see that the images are slightly underexposed. This was to be expected as, for test purposes, I had rated the film at ISO 400. If I had used my personal film speed of 200 ISO, then these pictures would have been better exposed, although in some cases the highlights would have been blown out. (But that’s a different story which I will cover in my next post).
  • I use the unfiltered light from my enlarger when I make contact sheets. The unfiltered light is c. grade 2. So when I examine the contacts, I can see roughly what starting grade to print an enlarged image.
  • I can also assess the degree of burning and dodging that will be required.


I have described how finding a standard setup for assessing standard proofs helps consistency and efficiency. I used to be one of those photographers that didn’t bother with contact sheets, but I have learned how useful they are, not only in terms of assessing a printing plan but also for filing purposes. I have never been very good at assessing negatives in the raw!

  1. The formula for 1/3 stop increments is starting time multiplied by 2 to the power of 1/3.

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