>>What determines how long you expose a negative for when making a >>print? Does fiber-based paper need a longer exposure than RC?? How >>do you know when you should maybe open the lens up a stop and >>reduce the time of the exposure?
There is a somewhat repeatable approach that may be of use to you.
You will need two negatives. One is the one you wish to enlarge. The other is just a blank frame from the same roll. There are usually a couple of blank frames after the last exposure on the roll.
First, adjust your enlarger up and down to get the size print that you want. Then put the image neg in the carrier and focus the image. (A grain focuser is worth its weight in gold. They cost little and will make your prints sharper.)
Second, remove the image neg from the carrier and replace it with the blank frame. Obviously, take care not to disturb focus, etc.
Now, with the blank frame in the carrier, make a test strip as described earlier. Start with the lens two stops closed down from max aperture. Just lay the strip of paper in the easel and expose it in half-inch segments. Each exposure should be the same amount of time - say, three seconds. (A good timer is as valuable as the grain focuser.) Twelve or thirteen segments should be more than enough. You will then have a test strip with one segment that has seen three seconds of exposure, next to a segment that has six seconds, then nine and so on up the line. Develop the test strip.
Here is the best part: look carefully at the dried test strip. You will see that it gets progressively darker for several steps. Then it stops getting darker no matter how much more light hits it!! For instance, you might find that there are eight segments that darken progressively, but the ninth is no darker than the eighth and the tenth no darker than the ninth or the eighth. Thus after 24 seconds (eight pops at three seconds each) the darkest tones in the print will get no darker regardless of how much additional exposure they receive. This hugely useful piece of info is "the minimum time to maximum black" for the combination of negative, paper, print size, etc that you are using.
Now comes the fun. Remove the blank frame from the neg carrier and replace it with the image you wish to enlarge. Give this neg the exact same exposure that you needed to reach max black (in our example, 8 pops at 3 seconds = 24 seconds). Use grade 2 contrast. The resulting print will show what you neg is really like. If everything is muddy and you find yourself reflexively reaching for grade 4, then the neg is not exposed and/or developed correctly. If everything is crying to be burned-in, then the neg is too hot.
If your prints never look anywhere near decent using this "min time to max black" test then you should consider modifying your film exposures and/or your film development times. Ideally grade 2 will handle most negs and the soft or hard stuff will be for special effects.
If all this sounds like a pain, consider this: I ran one test strip last night before printing a new neg that had never been enlarged. I printed at my "min time to max black" setting and the very first print was frame ready - no muss, no fuss, no guessing about anything at all. In the end, it will save paper and time so you can shoot more!!
Hope this helps. It is just my solution - not a prescription for world peace. Any and all corrections, comments and criticisms are welcome.
Enjoy,
Jon
Patience! Patience!
