How would one measure area? (of a irregular shape like the opening of an aperture with five blades?)
Would it not suffice to get a pretty good estimate of some linear dimension? I'm thinking of someting roughly equivalent to the diameter....
How would one measure area? (of a irregular shape like the opening of an aperture with five blades?)
Would it not suffice to get a pretty good estimate of some linear dimension? I'm thinking of someting roughly equivalent to the diameter....
If by "measuring the sides" you mean the exposed length of each aperture leaf, then you may want to consider that measuring the "diameter" directly might be easier to do accurately. The length of the exposed edges of the leaves can be very small and measurement error with calipers can become significant. Also, you might find that there is significant variation in length from leaf to leaf.
In measuring the diameter directly, if the shutter has an odd number of leaves then you will be measuring from the center of the exposed edge of one leaf to the apex where two join on the opposite side. You could probably use this as a good estimate of effective diameter. Alternately, if the leaves are straight it would be easy enough to calculate the area of the polygon from the "diameter" measurement.
In your situation, I would probably physically measure the diameters to set the new scale and use the light meter only to confirm that I did it all correctly.
"I would probably physically measure the diameters to set the new scale and use the light meter only to confirm that I did it all correctly."
Then it would be much easier to just use the meter in the first place. And, much faster!
ok, measuring isn't the hardest part. The hard part is to find the area of copal shutter. The copal shutter has 7 leaves, however, it doesn't form a perfect heptagon (in between the heptagon and the circle that contains the heptagon). So the area of the opening is a bit off. The leaves in the prontor shutter forms a perfect pentagon, and area calculated is very accurate. Luckily, the lens I tried to mount has 5.6 at max opening, that saves me a lot of trouble.
technically, I just need to establish the linear relation between the side(I use the long diagonal) of the pentagon and heptagon. I don't have to worry about the area. Anyway, it was a fun project.
Just a few thoughts, in practice, if we set the aperture at the left or the right side of the mark, maybe we can get 1/10 step off?
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