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12-17-2014, 08:18 AM   #16
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Perhaps a flash meter would solve your problems.

12-30-2014, 09:23 PM   #17
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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.
12-31-2014, 04:29 PM   #18
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QuoteOriginally posted by Not a Number Quote
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.
... snip...

A flash meter would not do what this does. That is set up the lights and ratios of light without actually firing the flash(s) individually and in concert. This would assist a meter to get the ratios correct, and then a reasonably accurate first set. Someone who has used a flash set up over years, will have guesstimated a set up and then refined it by trial and error, then that prior knowledge would do be the basis for setup. Without that prior knowledge, it's a setup, test, setup test setup test situation. Whether that test is with a meter or polaroid or digital, the process is setup and test and retest until the setup works. The calculator can reduce that retest cycle considerably.


QuoteOriginally posted by Not a Number Quote
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.
I REALLY like your rings!! The only reason I am going with a slider is that allows me to use a log-log on the reverse to add up the photons.

I don't think dropping the ISO designation is a good idea at all. If I am shooting paper negs at ISO 3, then the calculator should let me designate that I am using ISO 3, not +5 EV from zero.
I looked at your rings and saw that my own setup requires an added step and conversion factor. Your rings require a rotating index. I reconfigured to allow a single slide and a static index. I had the fstop indexed with the GN, and setting the distance indexed with GN solves that extra step and conversion.

Thanks for your input!!
12-31-2014, 06:11 PM - 1 Like   #19
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This is the GN slider part, I need to build the reverse side for the log-log side, and then the cutting folding marks. but it is useable as it is if you cut out the blue area, and cut the grey area out on the FAR outside line, (giving you a way to move the slider easily under the cut out top part.
http://www.45ink.com/gallery/images/demo/Flash-guide-slider.pdf

12-31-2014, 06:27 PM   #20
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"This would assist a meter to get the ratios correct, and then a reasonably accurate first set. Someone who has used a flash set up over years, will have guesstimated a set up and then refined it by trial and error, then that prior knowledge would do be the basis for setup. Without that prior knowledge, it's a setup, test, setup test setup test situation. Whether that test is with a meter or polaroid or digital, the process is setup and test and retest until the setup works. The calculator can reduce that retest cycle considerably. " And thats exactly what a flash meter does!
12-31-2014, 08:09 PM   #21
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QuoteOriginally posted by T Evergreen Quote
"The calculator can reduce that retest cycle considerably. " And thats exactly what a flash meter does!
sigh.

Please really think about what a set up would require using several flash units with different guide numbers.
How would you set up the ratios?
Assume your biggest flash will be your main. set that main, and fire it on the meter.
Now guess where to set a fill, for 1/4 ratio, set it, fire that flash on the meter. Is that flash set to 1/4 ratio? No? then change it and reflash the meter. Is it right yet? No? Retest until it is.
Now add a hair light, set it and test it with meter, keep adjusting and testing until it is right.
Now flash the whole setup, on the meter, and set up your camera, take a test shot. chimp.

Then, consider the problem I posed in my original post, are you certain that a meter will answer that correctly?

With the calculator, you set the main light at the distance and power calculated, set the fill light at the calculated distance and power for 3 stops down, set your hair light, test shot, chimp.

Just saved about 6 steps and numerous test flashes.

I get it, that some people have no use for this calculator. However I have seen other people request this, and I was looking for one myself, and no one had made one.
So I made it myself, and I am giving it away for people who might want it.
I am ok, with you not wanting it.

If people can afford to buy a $300 flash meter, then fine, they are welcome to it.
For those who just want a flash GN calculator, I built one.
http://45ink.com/gallery/images/demo/Flash-guide-slider.pdf
12-31-2014, 09:26 PM   #22
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QuoteOriginally posted by 45 Mike Quote
Please really think about what a set up would require using several flash units with different guide numbers.
A high-tech solution would be to use Cactus V6 triggers with the transmitter unit using "absolute" mode.

Then you can specify a desired light output for a flash and the receivers will make sure their flashes produce this amount of light, independently of the guide number of the individual flashes.

You still have to deal with varying distances, but it is a nice way of getting rid of the dependency of the fractional power system (1/2, 1/4, etc.) on the maximum power of the flash.
01-02-2015, 02:21 PM - 2 Likes   #23
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QuoteOriginally posted by 45 Mike Quote
ssume your biggest flash will be your main. set that main, and fire it on the meter.
Now guess where to set a fill, for 1/4 ratio, set it, fire that flash on the meter. Is that flash set to 1/4 ratio? No? then change it and reflash the meter. Is it right yet? No? Retest until it is.
You're making it way too complicated, there isn't a big retesting cycle. You've set your main. You guess on the fill. It tests at a 1/2 ratio. Drop the power down 1 stop. Done, no need to retest. Move to the next light, etc. Take one reading of the entire setup at the end and you're ready to shoot.

QuoteOriginally posted by 45 Mike Quote
With the calculator, you set the main light at the distance and power calculated, set the fill light at the calculated distance and power for 3 stops down, set your hair light, test shot, chimp.
My biggest problem with using guide numbers is sucking at estimating distances in real life and I find a flash meter much quicker to use than a tape measure.

I don't mean this as a criticism though, people will work in different ways and I'm sure your calculator will be a useful tool for some.

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