F-stop Printing & Contrast

[Henry Yorke]

Hi, everyone.

I got lucky last week and was given a Stopclock Pro for free by a photographer who was dismantling his darkroom. I'd had my eye on one of these for ages but could never quite justify the expense - so I'm really grateful I was in the right place at the right time.

I've been reading what I can about f-stop printing and have have experimented a little in the darkroom - but one thing I haven't seen addressed in any detail anywhere is the question of paper stops. That is, if I establish an exposure based on a test strip done at a Grade 2 and then determine that I should print it at Grade 4, how do I calculate the additional f-stops required to go up two grades (for instance). And - once I know what this stop difference is, I suspect that it then becomes standard for the paper I'm using (I use Ilford Multigrade IV) regardless of the other variables, yes? Thanks for helping me think this through.

[ic-racer]

Contact print a step wedge on both papers at the same exposure. Choose a value on which to base your relative speed (I use the gray step half way between the first off-white and first off-black steps).
The number of steps between that same gray on the two contact prints times the number of stops-per-step (0.5 for a 21step wedge ) is the relative speed difference in stops.

[Jerry Bodine]

You will need to determine experimentally, with your choice of paper and developer, a chart as shown on page 7 here (http://www.waybeyondmonochrome.com/WBM2/Library_files/WBM-Edition1Errata.pdf). The procedure for doing so is explained in detail. This info comes from “Way Beyond Monochrome, 2nd Ed.” This hardbound reference book is well worth your investment at a very reasonable price (google the title and find Amazon price to be ~$44).

[Bill Burk]

I consider this one of the "limitations" of the f/stop printing method.

If you get accustomed to the difference in appearance you get on a print from a certain change of f/stop time (say one-third f/stop) at a certain grade of paper (say Grade 2)... You cannot carry that impression with you as you consider changes in time for a print that you make at a different grade (say Grade 4). The same one-third f/stop change in exposure time at Grade 4 makes as significant a change in the print as a full stop exposure difference at Grade 2 (not precisely but you get the idea - time affects the print faster for higher grades). I believe the Analyser Pro works that all out for you - if you wanted some reason to jump at another piece of fine gear from the same company... (think of it as a 50% discount).

It would be nicer to have a working method of printing, where each increment of change was the amount of time necessary to cause a least noticeable difference in the print at whatever grade you are working with. You could probably work that out by trial and error and then come to a decision to use a specific sequence (for example 1/3 stops at Grade 2, 1/4 stops at Grade 3, 1/9 stops at Grade 4)... I don't know the appropriate series but it may turn out to be something simple like that in practice.

[Jim Jones]

When using Multigrade filters to vary contrast with Multigrade paper, I found the density of mid-tone grays consistent from grades 00 to 3 filters with no change in aperture or time. Grades 4 and 5 required twice the exposure, and using no filter required 2/5 the exposure of the grade 00 to 3 filter. For me, variable contrast enlarging heads and automatic timers complicate printing.