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07-20-2009, 08:04 AM   #1
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Need flash manual or guide number

I just recently acquired a (very lightly used) Sunpak GX8R ringlight with accessories and original packaging. The unit works perfectly, however it did not contain any instruction manual.
Can anyone tell me where I can get (even a photocopy) the instruction manual or know what the guide number is for this flash?
Thanks in advance!

07-20-2009, 09:00 AM   #2
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Hello,
I found an owner in a (Dutch) forum, who states the guidenumber= 11
Good luck, Jan
07-21-2009, 06:18 PM   #3
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Be sure and check the trigger voltage. Some older flashes can damage modern DSLRs.
07-21-2009, 06:57 PM   #4
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I've got this flash. The 8 indicates that the guide number is 8 (in meters), comes to about 25 (in feet).

Any of the Sunpak ringflashes uses the number as the guide number.

07-22-2009, 07:50 AM   #5
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I'm not sure we're using the same meaning for "guide number" ... If the guide number you're speaking of 8 (meters) or 25 ft, what would be the f/stop used at that distance for 100 speed film?
07-22-2009, 11:30 AM   #6
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Explanation
07-23-2009, 02:12 AM   #7
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QuoteOriginally posted by hillerby Quote
I'm not sure we're using the same meaning for "guide number" ... If the guide number you're speaking of 8 (meters) or 25 ft, what would be the f/stop used at that distance for 100 speed film?
Divide the flash-subject distance into the guide number to get your shooting aperture. (Camera-subject distance is irrelevant, although if the flash is on the camera it is the same thing, of course).

Guide numbers are always given in terms of feet or meters and for a value of 100 speed film.

For example:

GN is 60 (feet) and your subject is 15 feet from the flash: 60 divided by 15 equals 4, so your shooting aperture is f4. If using 200 speed film, adjust aperture accordingly to f5.6. If using 400 speed film, adjust to f8, etc etc.

If using digital, you have the advantage of being able to review the shot and make a fine adjustment on the aperture to brighten or darken the shot as necessary. It isn't necessary to be overly anal about the math; eyeballing the distance and doing some minor rounding on the numbers is fine.


Last edited by Mike Cash; 07-24-2009 at 04:29 PM. Reason: typo
07-23-2009, 06:16 AM   #8
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Mike,
I've got it now! You're response above was what I was trying to get to. I guess I didn't explain in the original post that I need the GN for 100 film. I can remember dividing the distance into the GN to obtain the f/stop back. I learned to do that using flashbulbs! I'd forgotten however, that the GN changes dpending on the film speed used.
At any rate, THANKS to all for your response and "jogging my memory" on this subject.
07-24-2009, 08:50 PM   #9
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QuoteOriginally posted by hillerby Quote
Mike,
I've got it now! You're response above was what I was trying to get to. I guess I didn't explain in the original post that I need the GN for 100 film. I can remember dividing the distance into the GN to obtain the f/stop back. I learned to do that using flashbulbs! I'd forgotten however, that the GN changes dpending on the film speed used.
At any rate, THANKS to all for your response and "jogging my memory" on this subject.
Right. Typically, the advertised guide number is for ISO/ASA 100, in feet or meters. But not always. Some less scrupulous companies used to "fudge" their guide numbers by advertising the ISO/ASA 200 guide number, without specifying, leading unsuspecting consumers to think it was more powerful than the competition, who used ISO/ASA 100.
07-24-2009, 11:55 PM   #10
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Hey Bob,

I assume you will be using a macro lens with your new ring flash.

Note that at close focusing distance, the effective f-stop of the lens is not the same as the setting on the aperture ring.

In general, the setting on the aperture ring is correct to about 1:10 magnification. From 1:4 to 1:2, you need to add 1 stop (e.g. 5.6 setting on the aperture ring is F/8 effective). From 1:2 to 1:1, you need to add another stop.
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