Sounds like you on the way to sorting this out. If you're having trouble working out how many segments to expose, you could try marking the paper before exposing with a fat felt tip marker to indicate where you are to move your blocker to to make sure you only do how many you've got space for. Another issue you can have that will confuse is if you manage to bump the paper while covering up a section, although you should notice that the image formed is blurry for that one. If you do manage this, chuck that test strip out and do another as nothing good can be determined from one of those.
Thanks for the advice Nige.
If this is what happened, don't worry it can easily happen to the best printer. The important thing is to find the problem and fix it.
Originally Posted by SloboM
I suggest double-checking by re-running the experiment again just so you're sure. Also make sure the 32s looked exactly right compared with the test print, not just close enough. We want to make sure this was the problem and nothing else is going on.
Thanks Michael. I'll run the process again as you suggested.
Exactly. I feel the same way about short exposures and the ideal range to be printing at. I always try to print longer, hopefully around 24 to 36 seconds or so. And after thinking about all three testing methods yesterday, I grabbed a difficult negative and ran a test using each method. I earnestly tried to judge the best strip, and then made a quick print from the chosen time. All three strips chosen were at different times. I then scanned the results which are shown below.
Originally Posted by edcculus
When I tried Thomas' method yesterday, I screwed up a couple of attempts when the time got down to 8/5.6/4. But since I knew I didn't want to print at such short times anyways, I ended up using the sequence 45/32/22/16/11/8 instead. Since I usually start with my method at 8 seconds, to make the first strips identical, I thought that sequence would be better for that reason as well. One test used the OP's additive arithmetic method with a constant interval and times of 5/10/15/20/25/30/35/40/45. For my usual method I used 8+2+2.5+3.5+4+5+7+8 (producing 8,10,12.5,16,20,25,32,40-second exposures). Note that the latter two methods have coincident times (20/25) in the middle of the respective sequences. And that's usually as short as I'd ever want to be printing. It also coincides with your lower limit.
I found progressively covering the paper to be a much easier way whether the exposure change was arithmetic (i.e., 5-seconds) or geometric. No surprise there since I normally use the covering (rather than uncovering) method and found out a long time ago that I prefer it. It also seems less confusing to novice students.
That's correct. Indeed, another thing I like about my method is that I can start anywhere on one of the ISO film speed numbers and proceed from there. I could begin at 8 or 16 or 25 or 64, etc., and just keep building that sequence. Every third strip will be 1/3-stop different whereas the uncovering sequence is progressing by 1/2 stops. In that method, every other number represents a full-stop difference in exposure, the interval is coarser, and I found the shortest times difficult to do accurately and screwed up twice.
Originally Posted by edcculus
Surprisingly, I think the constant arithmetic interval method led to the better initial work print in this instance. IMO, it was off slightly but mine was very close and the print from the least familiar method came in third. So, I guess I will back up and keep printing with my regular geometric method since it seems much easier for me in practice. Although it was not as accurate in this particular case, I believe it will generally produce better results and I like the fact that each strip shows an equal visual change.
Here they are (not in any particular order, but marked so I can ID the method):
OK. Time for me to stop beating this horse.
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I came late to this thread. Glad the OP's problem is solved, but the discussion of test strips has been fascinating. You would think they'd be simple.
At present I have only a clockwork timer, and have always done test strips on an arithmetic scale centred around a guess at the right exposure. I have been considering making myself a digital timer using an Arduino so that I could develop the functionality further at a later stage; but while thinking out the code for 1/3 stop increments I began to wonder how accurate it needed to be. The contrast between Smiegltiz's covering method and Thomas' uncovering method set me thinking about the errors involved in each method. It occured to me that in the covering method any timing errors accumulate to affect all subsequent strips. However, if you start at 8 sec as described and your timer can be set to, say, the nearest second, the accumulated error in the covering method is never more than 2% of the exposure. In the uncovering method the errors do not accumulate, and the accuracy of each strip is as good as your timing with the card against the second counter - except with the exposure that should be 5.6 sec: if you make this 6 sec you have incurred a 7% error. I have seen 5% quoted as the difference between a wet and a dried print, so that error would be quite significant.
Would be glad to hear your thoughts.
I guess it depends on your printing method, but personally, unless somehow forced to, I would not use an f stop that would give me a 5.6 second exposure. Like I said before, I prefer an exposure greater than 20 seconds. If you do it that way, you can reduce some error, since you could start your first strip at 16 seconds and work up from there. If they all come out too dark, reduce the aperture to get the exposure in the window you want.
They ARE simple! Use whatever time intervals work for you. Fixed intervals, f-stops, whatever. All you're trying to do is make a test print that gives you useful information. The keys to a good, intelligent test strip/print are simply:
Originally Posted by Jonathan R
1. The exposures go from obviously too dark to obviously too light
2. There is enough image in each of the exposure strips to give you some good preliminary information on both exposure and contrast. ie: don't skimp out on paper and try to use some little piece that only covers a sliver of the image, and don't make 25 exposures 1/4" wide either. You can't tell anything this way. It is best to start with some wider intervals, and then refine from there. For example you might do a first test strip that goes from 5s to 25s seconds in 5s increments, decide the right exposure is somewhere in the 10-20s range, and then make a second test strip that goes from 10-20s in 2s increments. That sort of thing.
It is also helpful to keep the test strips because in addition to helping you find a base exposure time and contrast, they can also help you figure out how much burning and dodging might be necessary.
Originally Posted by Michael R 1974
I agree with almost everything you've said. [The exception is the shorter exposure range (< 20 seconds) you've suggested.]
Test strips are (or should be) simple. If you have some darkroom experience and have been shooting, developing, and printing for awhile, chances are you can walk into your darkroom and already have the timer set to an exposure that will give you a decent 1st work print at a certain degree of enlargement without even bothering to run a test. That lightbulb probably clicked on long ago.
But, to someone starting out, running tests strips is often confusing and seen as a waste of time and resources. If they don't understand why something has gone wrong, chances are they will abandon any sort of systematic method and just try random guessing that ends up having no consistency. Then, confusion really sets in and they may abandon the whole darkroom experience.
I have worked with beginning students in a community college darkroom for over 23 years and I know where they stumble. You would be surprised at how many never realize that "the exposures go from obviously too dark to obviously too light" until they have that specifically pointed out to them (perhaps more than once). The more common experience is that they get a range of exposures that are all too light and then they choose the darkest of those to use. Many are satisfied just to get any image. Many never end up getting proper dark values or contrast in their prints because they don't get the obviously too light/dark thing, and yet they may be satisfied with that print without understanding the further potential. I always tell them to shoot for that middle area on the strip because if one end is obviously too light and the other obviously too dark, the proper exposure has to be somewhere in between on their test. I never tell them to print the first or last strip on a test sheet unless I qualify it with "how do we know the next time out might not be better? Adjust the f/stop or extend the time to shift that presumed correct strip to the middle and run another test to be sure."
I usually use a full sheet of paper (and never less than 1/3rd) to run tests because I want to gauge what the light is doing over the entire image. That also comes in very handy when determining dodge/burn times as you have suggested. Running 1/4"-wide strips is false economy and I think leads to an ultimate waste of paper. If an incorrect area is chosen to make a small test strip, a print is subsequently run, discovered to be incorrect, and perhaps at that point confusion sets in. At least a full sheet + 1/4" will have been wasted along with the time taken to print and process both. The whole sheet approach helps prevent this kind of waste and provides a lot more exposure information all in one cycle.
If I am printing for myself, I don't want to be printing at less than 24 seconds unless I absolutely have too (e.g, when making very small enlargements from medium format negatives). I want some time to accurately be able to burn & dodge. I don't want to feel rushed. I'd rather double a 15-second exposure to 30 seconds than to attempt to manipulate things at shorter times that would double any error and not be as controlled and accurate. Have I really wasted 15 seconds initially when making the longer 30-second print? Or, have I saved myself a reprint and all the time associated with exposing and developing two (or more) prints when the longer first time would have required only one cycle?
Whether someone uses a geometric vs arithmetic strip to me is not a big issue. I personally think the geometric test provides better information, but admit it is harder to grasp at first. What I don't like is when a method is suggested to a novice printer in such a way that they never realize what is going on or make any connections about reciprocity between time and apertures. Why would anyone even try to make a good print at 5 or 10 seconds? Set the timer way out to some multiple of the interval at least twice as long in duration as the starting point (e.g., 40, 45, 50 seconds or higher), then after or 20 seconds have elapsed, start progressively covering the paper and move the card every 5 seconds until the time runs out. That will almost ensure a good, readable test if anywhere close to the correct f/stop. The method usually works because it covers over a full stop in exposure time. And that's the benefit of a geometric test as well. But with the geometric test a constant visual change is occurring as exposures get longer. With an arithmetic test, the visual effect is becoming less and less noticeable as exposure time increases. So, there is a danger for beginning printers to have an exposure at the very short end being not enough to see and then having big changes shortly afterward (- is that first visible strip 5 or 10 seconds, or was the last part of the paper even given an exposure...), while at the opposite end the strips are getting less and less and less distinct. As long as they realize what is happening and why, that's fine.
So the big message is don't waste paper on very short exposures or small strips of paper and if doing an arithmetic strip, understand that the exposure rate of change is decreasing the further out one proceeds with a constant time interval.
Another benefit of learning the geometric f-stop sequence is that information transfers to other photographic concepts once learned. Walk into a lighting studio and move a light from 11' to 8' and know it is suddenly twice as bright on the subject and then figure out lighting ratios with little difficulty. Or, figure out a bellows extension factor in your head without having to be that Manhattan Project dude.
The range of 20 seconds was only an illustrative example to make the point about wider intervals. The total range is whatever the printer thinks it needs to be. The point is the intervals should bear some relation to the total range, so that you get a decent portion of the image (preferably lights and darks) in each exposure strip. If the range is 60 seconds for example, I wouldn't suggest using 3 second intervals.
Originally Posted by smieglitz
Just keep it simple, people.