Though at the danger of hijacking this thread, what base exposure times for RA-4 would be least likely to cause reciprocity failure woes?
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Though at the danger of hijacking this thread, what base exposure times for RA-4 would be least likely to cause reciprocity failure woes?
Ned,
Making a percentage test strip is easy. I like a 20% difference for my initial strip. I start with 10 seconds then cover a bit of the strip and count 20%, i.e., 2 seconds. The next strip should be 20% of 12 seconds, but that's close enough to 2 seconds, so I just give 2 seconds to the next bit of the strip. Now I have 14 seconds; 20% of that is really close to 3 seconds, so that's what I give the next bit. Now I have 17 seconds; 20% of that is rounded to 3 seconds as well so that's what the next bit gets. Now I have 20 seconds; 20% = 4 seconds here, so the next bit gets 4 seconds for a total of 24 seconds. The next strip will get 5 seconds to make 29 seconds, then the next gets 6 seconds to make 35 seconds total and finally, 7 seconds to make 42 seconds total.
Seems complicated, but once you figure it out you just count (with the metronome keeping seconds for you): 10 - 2 - 2 - 3 - 3 - 4 - 5 - 6 - 7 - off; easy and close enough to 20% so that the longer exposures have adequate separation - and you have a range of 10 - 42 seconds to choose from.
I think of all my dodging an burning in percentages also, and notate them as such in my exposure records. This is very helpful when scaling a print up or down. One simply finds the correct base exposure and then calculates the dodging and burning using the percentage of the base exposure. Of course, this is only a starting point, since different size prints almost always need some adjustments in this regard, but it is a very close starting point.
Best,
Doremus
Doremus,
Thanks, yes very simple! I too use the metronome, and my typical strips start at 8 or 10 and then go:
10-2-2-2-2-2-3-3-3-3... for low contrast, the change from 2 to 3 seconds at about 20.
then 2-1-1-1-1-1... for high contrast.
So they are fussier to make. Also I always mark the edge of the test strip with pencil lines, which takes extra time. ( But you can vary how far apart to make the important part of the test strip in the important part of the picture! ) For dodging and burning I probably think just like you "10% here, 40% in sky... ".
I will try your test strip approach the next time I make prints, probably toni`ght!
-Ned
Hi Doremus,
I like simple and functional too, so we definitely have that in common.
f/stop printing was pioneered by Gene Nocon, and is not difficult at all to do; no more difficult than counting any other sequence of seconds.
When I use f/stop printing I use full stops, but stopped down to f/5.6 or f/8 on the enlarger lens. If you wanted to do half stops, for example, just close the enlarging lens down one stop and boom you'll get the same results as half stops with the lens aperture one stop wider.
When I make my test strip I start at 90 seconds, and go backwards to 45s, 32s, 22s, 16s, 11s, 8s. Just like the f/stops on the lens. What's nice about that is that I see what extreme under/over-exposure of the paper does to shadows and highlights, and that always teaches me something about how I want to print the negative.
If I went about it by adding smaller increments, the spread from lightest to darkest would be smaller, and while it's not a method I recommend against, to me I wouldn't be exploring the negative enough.
Once I've nailed down a good base exposure, I start fine tuning it, and now I just add/subtract seconds with no concern for f/stops. After the base exposure is perfect I start working on details in the print, whether I want to add high contrast blasts or not, dodging, burning, diffusing, etc.
I test in 1/3-stops as well. The benefit of this method is that every strip has the same apparent visual increase in exposure effect because it is geometric in nature. Conversely, a constant increase in time by some fixed interval (e.g., 4 seconds) produces less and less exposure effect in each subsequent strip as the cumulative exposure increases. For example, going from 4 seconds to 8 seconds is 100% increase in exposure while going from 36 to 40 seconds is only about 10%.
While you can buy an f-stop timer to do a geometric sequence automatically, it isn't too hard to figure out a working sequence and set a timer manually. The sequence I use is:
start @ 8-seconds at some intermediate f-stop (e.g., f/11)
add 2 seconds to get 10 cumulative which is ~1/3-stop more
add 2.5 seconds to get 12.5 cumulative which is ~1/3-stop more
add 3.5 seconds to get 16 cumulative which is ~1/3-stop more
add 4 seconds to get 20 cumulative which is ~1/3-stop more
add 5 seconds to get 25 cumulative which is ~1/3-stop more
add 7 seconds to get 32 cumulative which is ~1/3-stop more
add 8 seconds to get 40 cumulative which is ~1/3-stop more
add 10 seconds to get 50 cumulative which is ~1/3-stop more
add 14 seconds to get 64 cumulative which is ~1/3-stop more
The full sequence above will give a series of strips that cover a 3-stop range in 1/3-stop intervals that appear equally distinct from one another. You will almost certainly hit the proper exposure somewhere in there if you are printing a decent negative. You could actually start at any initial time in the cumulative sequence (and end anywhere) as long as the next exposure follows the other sequence. IOW, start at 10 seconds then add 2.5 seconds, then 3.5, 4, 5, 7, 8, 10, 14. Every third number in the sequence doubles so the next few exposures to add would be 8 x 2 = 16, 10 x 2 = 20, 14 x 2 = 28, etc. So, it is easy to generate the entire sequence from any starting point if you can just remember the next three sequential additions (e.g., start at 16 and then add 4, then 5, then 7).
FWIW, shifting the decimal point in the ISO sequence for films (i.e., 80, 100, 125, 160, 200, 250, 320, 400, 500, 640...,) produces the cumulative exposure sequence above. Remembering that ISO sequence, I can quickly determine the cumulative time needed to expose the print. For example, if the 5th stripe looks good I think 80, 100, 125, 160, 200, so I know that stripe equates to 20 seconds for the print.
I keep a two-column table of these numbers on the wall next to the enlarger for quick reference. The first column is the exposure addition needed and the second column is the resultant cumulative exposure. That makes it extremely easy to generate or interpret a sequence of test exposures.
Hope that all makes sense. It is much, much easier to do than to explain.