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Forum: Flashes, Lighting, and Studio
12-30-2014, 09:23 PM
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A flash meter would be the best solution.
As for the GN calculator I think you are expecting too much and over engineering the device. After all an analog device isn't going to give you digital precision. A lot of interpolation and extrapolation is required (guesstimating). I used slide rules in high school and my freshman year in college. After that they started to allow the use of pocket calculators during exams.
So here are examples using the dial calculator from a Vivitar 285 GN=120ft at ISO 100, a Sunpak 433D (same GN as the Vivitar) and a quick and dirty dial whipped up in about 20 minutes with the help of a compass and protractor left over from my middle and high school days. I tried fiddling around with Adobe Illustrator but it was too difficult to do with my non-existent Illustrator skills. It would have been simple to do in Corel Draw.
Vivitar 285
set for GN 120 @ ISO 100 (you can see some "fudging" was engineered in)
set for GN 80 @ ISO 100
set for GN 160 @ ISO 100
Sunkpak 433D
set for GN=120 @ ISO 100
set for GN=80 @ ISO 100
set for GN=160 @ ISO 100
Paper dial calculator - outer ring - GN and Feet. Inner ring - f-stop and ISO
set to GN=120ft @ ISO 100
Set to GN=200ft @ ISO 100
Now how about the same flash at ISO 1600 (ignore the label, for my reference only)
Now to take the example of the Holga with a listed GN of 72 @ ISO 100
Want to switch to ISO 400? (label for my reference)
Rather than ISO that ring perhaps be better as EV +/- with zero being where I have ISO 100. The increments are in 1/3rds since ISO is in 1/3rd stops. Meters can easily be added on. Since the dial uses f-stops which are based on the inverse square law the full stop increments on GN and feet are a factor of the square root of two (1.414). As this was just a rough proof of concept no particular care was taken in the spacing or rounding of any of the markings.
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Forum: Flashes, Lighting, and Studio
12-16-2014, 01:42 PM
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If I still had Corel Draw installed on I could make a dial calculator. Should not be too hard to put both meters and feet on it. Print out on card stock, and laminate it (or not) and rivet together.
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Forum: Flashes, Lighting, and Studio
12-10-2014, 04:58 PM
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Why not just find like an old Vivitar flash from the 80s or early that has a dial calculator and use that? I remember the two cell thyristor flashes often had a calculator on them. All you would need to doe is cut of the part of casing with the dial. Shave off any stops on the dial so you can set it any where you want ignoring the ISO/ASA. Example - a flash with a GN of 60 in feet at ISO 100. Turn the dial until about f6 is lined up with the 10 foot mark. You're set to go.
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Forum: Flashes, Lighting, and Studio
12-10-2014, 11:46 AM
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You can easily create a spreadsheet. I did one for macro work. All you need to know is that there is a factor of 1.414 per f-stop change. I have it calculate by power output level too: 1x, 1/2, 1/4...1/256. It also calculates the extension factor by magnification.
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