Nikon SB800/900 real GN value ...

Started Apr 2, 2014 | Discussions thread
Ferguson Senior Member • Posts: 1,298
Re: Too complicated, very non-scientific and totally wrong...

olyflyer wrote:

Ferguson wrote:

olyflyer wrote:

Arnaud M wrote:

It-s not a specific way to measure the GN, it's just the way to use the incident light meters.

Yes, when you want to take images. I know that very well, but I am not so sure it is the same as measuring the maximum output from the flash. Did you try both ways?

I just checked the manual, and it does not describe how to measure flash output, so I guess we are in the blind here.

If you want to confirm your measurement of guide numbers, I'd suggest something more controlled but like I did -- a specific lens and distance, a grey card if you have one, get a camera-measured-non-flash shot of it so you know the specific converted value of that grey card, and compare to the flash-output-only value of that grey card when exposed according to the guide number. In something like lightroom you can then see how many stops (or fraction) you need to raise or lower it to match the camera's "right" exposure.

If it comes out correct, then the output matches the guide number, regardless of what the light meter says.

Or conversely, if they match, you'll have evidence that the technique you're using is either right, or off the same amount as the flash.

That's not a flash GN measurement. If you want to measure the GN all you need is s light meter. If you involve a lens and a camera then you test the camera meter, the lens and the exposure accuracy of that camera, not the guide number of the flash. Involving a software and a raw development process makes your measurement even less scientific...

All you need is a light meter that is calibrated and known good, and known correct technique.  Sounded to me as though there were questions about all those things.

-- hide signature --

Comments welcomed on photos:

Post (hide subjects) Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow