Lachlan717 wrote:Maris wrote:The exposure sequence with respect to "box speed" goes 1/16, 1/8, 1/4, 1/2 1x, 2x, 4x, 8x, 16x, and 32x….
I've got 10 exposures at 1 stop increments...
It seems to me that, if you don't start with a repeated time, you will not have an accurate 10-stop range; it will be just over 11 stops (1025/16th to be exact).
With the spread that you gave, you would need to run the shots as 1/16, 1/16, 1/8, 1/4
etc. As you have detailed it, the first exposure will be 1/16, the second will be 3/16 (rather than the required 2/16), the third on 7/16 (not the 4/16 needed), the forth 15/16 (not the 8/16) and so on down to a 32 second exposure being a cumulative total of 1025/16th (64 1/16th seconds). You need to factor in the cumulative aspect of multiple exposure, meaning that you will be about a stop out per "band" after the initial 1/16th one.
You are absolutely correct that the shutter speed/f-stop setting is repeated for the second exposure otherwise the doubling sequence doesn't come out right. It is what I do.
Also, I doubt that running shots past 1 second will be of much value for working out EI for most films due to reciprocity failure skewing results. It is fine once you have EI worked out, but only to ascertain reciprocity compensation for a given EI. You would be best served by shooting the first two "bands" of film at your fastest available shutter speed (light permitting).
I try not to go past 1 second but more from concerns about lack of consistency in manually timed exposures compared to mechanical timing rather than worries about reciprocity failure. For daylight exposures the problem doesn't really come up. For example 32x times Zone V exposure for a 100 speed film comes out at about 1/2sec@ f16. Actual testing of reciprocity failure is a tedious business but my results indicate that the film manufacturer's tables are often madly pessimistic. I suspect film makers don't bother to test but offer generic tables with a big "safety" margin thrown in.
It would also be very useful to have a calibration of shutter speeds done prior to doing any testing in order to know if you are actually giving the exposure at the stated shutter speed…
Yes, I have a millisecond resolution shutter tester and actual shutter speeds are known and allowed for. And you are right about the imperative to do this for sensible results.
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Laboratory style film testing is best done with step wedges but I've convinced myself that results I get by in-camera exposures translate better to actual shooting conditions because lens flare and camera-body flare are automatically incorporated in the results. Both paths to knowledge work but mine, I reckon, is quicker if dirtier.