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Sb 25, f numbers and iso.

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Lee dann photography says:

I have been using the nikon CLS system for a couple of years and love its simplicity, but know it has its limitations.

Decided to get into abit of manual flash using triggers etc. I have just bought a used sb 25 and am a little confused about the f/number and iso settings. I thought you put the flash into manual mode and used the 1/1 1/2 1/4 settings and so on. What part do the f and iso settings play. do i ignore them??? what do i set them too???

I understand a little about studio flashes and how you take light readings and set the f/numbers accordingly.
7:59AM, 10 April 2012 PDT (permalink)

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Low Res says:

The 1, 1/2, 1/4... are power settings, relative to the maximum output of your flash. They're set to increments of 1/2 power so that they align to the variables you're used to in photography in Stops; ISO, Aperture, Shutter Speed. Open your aperture ("f stop") one stop and you can reduce your flash output one stop, for the same exposure.

The "f and iso settings" play the same role as they do with the sun, the difference with flash is that it's nearly instantaneous so shutter speed doesn't play a role if you're below your sync speed.
67 months ago (permalink)

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Lee dann photography says:

Ok think i have that, Watched all the david hobby dvd's, unless i missed it, but doesn't he only talk about f/stops and iso as they relate to the camera and not the flash???

so the aperture controls the subject light and the shutter speed controls the background??

I have two sb600's that i have been using prior to getting the sb25, they dont seem to have the f/number or iso and seem alot easy to control.
67 months ago (permalink)

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Low Res says:

I haven't seen the vids, but I'd assume it was mentioned in some form or another. You may have missed it because it was brief, as there's not much to say on it. Aperture and ISO affect flash the same as any other lighting. If you light a scene totally by flash and set it to expose properly, and then close your aperture one stop the picture will then be underexposed by a full stop.

The neat thing about flash is that it isn't affected by shutter speed, so it lets you separate those previously dependent variables. You can move your shutter speed up and completely block out the ambient light, or back it off and let some through. In that respect yes, the shutter speed controls the background, but I wouldn't think about it that way. The shutter speed controls the ambient/continuous light, what you choose to do with it is up to you.

No, the aperture doesn't "control the subject light". The aperture affects how the camera sees all light, equally. Ambient, continuous lights, flash - everything.
Originally posted 67 months ago. (permalink)
Low Res edited this topic 67 months ago.

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brownie114 says:

On most older SB flashes when used in manual mode, the unit will display an f-stop, ISO value and distance when a particular power is chosen. This is just a handy calculator that helps to make a good exposure. The only thing you need to worry about is the power setting.
67 months ago (permalink)

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Lee dann photography says:

Thanks for the help guys, think I got it now.
67 months ago (permalink)

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Mr. Speedlight says:

The ISO, distance and f/stop on older Nikon speedlights is for manual flash calculation when the flash is mounted on a manual exposure, non-TTL camera, e.g. a Nikon F. You can completely ignore these if using your speedlight off camera. If you use light modifiers the manual flash calculators won't work anyway.

If using your flash raw, that is without modifiers, you could use the manual flash calculator as a guide when setting up off camera flash. You can use your histogram as a sort of flash meter and the review image with blinkies as a Polaroid. If you want accuracy and repeatability then you want a flash meter. You can buy used like a Minolta Flash Meter IV or III if your budget is tight.

Anyway when using a speedlight like the Nikon SB-24 and later off camera, most will totally ignore the manual flash calculator.

Dave Hartman

PS: The last time I remember setting ISO and f/stop on a speedlight is when using my SB-24 in Auto Mode with my D2H while I saved for an SB-800.

I've found most speedlights are under exposing by 1 stop when using the manual flash calculator. I note this from my first Vivitar 283 though my SB-24. It's something about the standard test conditions makers use.

Originally posted 67 months ago. (permalink)
Mr. Speedlight edited this topic 67 months ago.

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Lee dann photography says:

Thanks for the help....feel a little more confident in using the sb25 over the easier to use sb600.
67 months ago (permalink)

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alohadave says:

The ISO, distance and f/stop on older Nikon speedlights is for manual flash calculation when the flash is mounted on a manual exposure, non-TTL camera, e.g. a Nikon F. You can completely ignore these if using your speedlight off camera. If you use light modifiers the manual flash calculators won't work anyway.

I use the calculator as a guide when using the flash off camera as well. It tells you what is good exposure for a given flash-subject distance, it works whether the flash is on-camera or not. And if you assume about 1-2 stops reduction through mot modifiers, you'll get in the ballpark easy enough.
67 months ago (permalink)

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