The Geometric Test Strip
The Geometric Test Strip is so named because, instead of adding the same incremental exposure (see test strip 1), the exposure is doubled each time.
Needed:
- Photo paper
- Negatives
- Tape
- Board
A geometric test print.
1. Start by putting the negative in the enlarger, get it focused, get it sized, and stop the enlarger down to ƒ8 or ƒ11. You want an aperture that's somewhere in the middle. The size of your enlargements, and the general density of your negatives will determine exactly what aperture you start at. Smaller enlargemennts will usually take a smaller aperture, and denser negatives will usually require a larger aperture. Regardless, the first test will show you.
2. Cut a piece of paper into strips. I usually use 4 x 5" pieces, just quartering an 8 x 10 sheet. If you want to use actual strips, cut the paper into quarters lengthwise. The idea here is to use a piece of paper big enough to tell you something. Little strips torn off a corner don't even make good bookmarks.
3. The differences from the mathematical method start here. Instead of covering 4/5ths of the test strip, pop the timer for a 2-second exposure (or whatever increment you are using) OVER THE ENTIRE STRIP.
4. This is where you need to really start paying attention. We want to cover about 1/5 the strip, and give it enough exposure to double it: 2 seconds, or 1 increment.
5. Continue making exposures, but double the time each time. So,to double the previous exposure, you need to pop the timer twice, adding 4 seconds (or 2 increments). The next exposure would add 8 seconds (or 4 increments). As I said, you need to pay attention.
Notes
— This method is best to use with dense negatives or large enlargements— any time the exposure may be much more than normal.
— The exposure will get very dark, quickly. That is, the difference between exposures on the test will be much more than on a standard test. Because of this, you can use this method to get in range, then use the standard method to further refine.