lacey_smith1

well, some semantics here, but it looks as though folks getting down to similar conclusions. My two cents worth - dof oas defined by accetpable circle of confusion is settled by lens focal length, aperture, magnification -- not by film format, as optics doesn't care how much wasted negative space is around a little dot. However, magnification does come back into play when you MUST ALSO INCLUDE ANTICIPATED VIEWING. If both 35 and 6x7 are to be enlarged to only 8x10 (or any other fixed comparison size), then the 6x7 can tolerate a larger circle of confusion, and thus the calculations of dof are not as strenuous as for 35, --- dof of a normal lens MAY only be slightly less than a normal lens on the 35, though one be 50 mm and the other 90. However, if your 35s are enlarged to only 5x7, and your 6x7 to 16x20, the size of that circle of confusion becomes progressively more important for the larger format.

Unless you have access to some equipment that you consider physics-lab quality light metering, you may be stuck with only comparison capabilties. I've a couple of modern digital meters, and they register flash 1/2 - 2/3 stop differently. Part of overall calibrate and know your own equipment -- all that stuff about needing to know your equipment better than the manufacturer, etc. Req'd for optimal Zone system work.

 

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Here's a comparison method, though - assuming you have one piece of automatic equipment you trust (you like the rasults and consistency) --- it can be a TTL SLR (with film), or a trusted, tried-and-true non-TTL (but auto) flash, Place the meter to be tested on a 18% grey equivalent, ready to read a flash, and fire the auto or TTL flash, set at f5.6 or whatever. Your auto flash/TTL camera will limit the flash at what it thinks is f5.6. Then simply see how close the reading on the meter is, and adjust accordingly. I'd suggest a set of readings, minimum three, perhaps more with different ambient surroundings. (actually, even a manual flash with trustworthy GN would work, at precise distances, but I don't trust manufacturer's guide numbers). Try the same with 2 or 3 of your tried-and-true flashes, and you'll find they vary a slight bit too.

 

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None of this establishes "correct". That you have to do for yourself, say, off extensive Zone-testing or color transparencies to your taste -- but this does establish relative readings. You can establish your own "correct" meter values without ever knowing meter calibration - just accept the meter, and bracket in both directions, then adjust ISO setting to compensate for your best choice (doable in 1 roll of film, though I would use various ambient situations, bracketing each). Assuming consitency of readings, you should eventually have a calibrated system. However, meter consistency is another issue.

 

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Incidentally, until modern electronic wonders (and even some of them), shutter & diaphragm variations of 1/3-1/2 stop were not uncommon.