Contrast Filters
The photo paper we use in the dark room is called polycontrast paper because it contains 2 layers of emulsion, a low contrast layer that that responds to yellow light and a high contrast layer that responds to magenta light. You can thereby increase or decrease the contrast in your prints by placing a yellow or magenta polycontrast filter in the path of the light coming from the enlarger.
- More often you will need to increase contrast in a print to get an effective range of tones dark blacks, through the middle grays, to the bright whites (you will rarely need to decrease contrast).
- Using a filter reduces the amount of light emitted by the enlarger, so it is necessary to compensate for this by opening the aperture 1-2 stops, and you must make a new test strip to determine the proper exposure time.
- A number 2 filter will not affect your print, a 3 or above will increase contrast while a 1 or below will decrease contrast (although I have rarely had a reason to reduce contrast).
- If you are trying to increase the contrast in a photo that looks flat, or has too much middle gray (this is the most common reason you will use a filter) I recommend starting with a number 3.5 magenta filter and increasing from there if necessary. It is possible to have too much contrast where you start to lose the middle grays, which you may observe if you use a filter which is too high.
- Don't forget to put these back in the kit where you got them so the next person can use them. It's easy to forget them in the enlarger tray!
The two photos below were developed by one of my student's Carolin Spaar (2016). The one on the left was printed without the use of a filter, the one on the right with a number 4 magenta (higher contrast) filter. Notice (in the photo on the right) how the background is actually black, as well as the words in the book, and the pages appear to be brighter white. That's what we want!
Below: Flowers at left, exposed with 3.5 contrast filter, at right no filter, the result is subtle but there is a better range of values in the photo at left, Jesse Helser, 2018.
Download the file below for a more thorough explanation of contrast filters:
contrast_filters.pdf | |
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