guide number on flash what does it mean: guide number of flash what does that mean. :) I just figured it out how to add a smiley face by accident. I was never to bright to begin with...

roy4711 Loc: Spring Valley IL.

guide number of flash what does that mean. :) I just figured it out how to add a smiley face by accident. I was never to bright to begin with so this a great accomplishment for me. :) :-P

emmons267 Loc: Arizona, Valley of the Sun

http://en.wikipedia.org/wiki/Guide_number

marki3rd Loc: Columbus, Indiana

roy4711 wrote:

guide number of flash what does that mean. :) I just figured it out how to add a smiley face by accident. I was never to bright to begin with so this a great accomplishment for me. :) :-P

Lets make it simple. Use the following formula to calculate manual flash exposures as opposed to automatic TTL exposures.

F stop # = GN/distance

i.e. divide the specified Guide Number by the distance from flash to subject to obtain the correct f stop setting.

roy4711 Loc: Spring Valley IL.

with a automatic TTL flash does flash set everything for you? lets say you are to far away from subject will the flash fire or not. thanks

marki3rd Loc: Columbus, Indiana

roy4711 wrote:

with a automatic TTL flash does flash set everything for you? lets say you are to far away from subject will the flash fire or not. thanks

With TTL Flash, the camera communicates with the flash and tells the flash what flash power to use. The camera determines the exposure and sets the aperture (the shutter speed is of coarse set to the sync speed of the camera). The camera then tells the flash what flash power level to use. Of coarse, the flash used has to be TTL capable and compatible with the specific camera in order for this to work.

If you do not have a TTL capable camera/flash combination there are two possible methods to obtain correct exposure. The easiest way is to use the Guide Number and formula above. The other way is to own a light meter with incident flash measurement ability to actually measure the amount of light hitting the subject from the flash and then set the aperture accordingly.

amehta Loc: Boston

marki3rd wrote:

roy4711 wrote:

guide number of flash what does that mean. :) I just figured it out how to add a smiley face by accident. I was never to bright to begin with so this a great accomplishment for me. :) :-P

Lets make it simple. Use the following formula to calculate manual flash exposures as opposed to automatic TTL exposures.

F stop # = GN/distance

i.e. divide the specified Guide Number by the distance from flash to subject to obtain the correct f stop setting.

The GN is quoted with a specific ISO, usually ISO 100. Every two stop increase in ISO (100 --> 400 --> 1600) doubles the GN, as used in the above formula.

amehta Loc: Boston

roy4711 wrote:

guide number of flash what does that mean. :) I just figured it out how to add a smiley face by accident. I was never to bright to begin with so this a great accomplishment for me. :) :-P

In the simplest term, it tells you how powerful your flash is. Even if you are shooting in TTL, it helps to know if your subject is too far before you try to take the picture and the camera refuses. :-)

SharpShooter Loc: NorCal

roy4711 wrote:

guide number of flash what does that mean. :) I just figured it out how to add a smiley face by accident. I was never to bright to begin with so this a great accomplishment for me. :) :-P

Roy, as you know the number represents how far the flash will reach. Unfortunately, you will never get to that range. Most, and probably all flashes, are tested using f1.0. Most of us don't have an F1.0 lens laying around to use with the flash.
But, the higher the number, the more power. GN 66 is usually 66 meters or about 200 feet. ;-)
SS

amehta Loc: Boston

amehta wrote:

The GN is quoted with a specific ISO, usually ISO 100. Every two stop increase in ISO (100 --> 400 --> 1600) doubles the GN, as used in the above formula.

The GN will also specify if it is in feet or meters, and that is the unit that you should use for the distance.

jerryc41 Loc: Catskill Mts of NY

roy4711 wrote:

guide number of flash what does that mean. :) I just figured it out how to add a smiley face by accident. I was never to bright to begin with so this a great accomplishment for me. :) :-P

Yeah, it's funny how those emoticons can appear by themselves. When I type certain combinations of letters and characters, an emoticon will appear, even in emails.

marki3rd Loc: Columbus, Indiana

amehta wrote:

The GN is quoted with a specific ISO, usually ISO 100. Every two stop increase in ISO (100 --> 400 --> 1600) doubles the GN, as used in the above formula.

Yes the GN is specified for a reference ISO, you are correct. I didn't mention it becuse when you check the GN for a flash it always states the ISO (as you said, usually ISO 100) as part of the specification. After I posted the thought crossed my mind that possibly I should have mentioned the ISO relationship but didn't bother to go back and elaborate.

amehta Loc: Boston

marki3rd wrote:

Yes the GN is specified for a reference ISO, you are correct. I didn't mention it becuse when you check the GN for a flash it always states the ISO (as you said, usually ISO 100) as part of the specification. After I posted the thought crossed my mind that possibly I should have mentioned the ISO relationship but didn't bother to go back and elaborate.

I did the same thing regarding feet/meters. There are so many times when we "fill in the blanks", I forget that someone who isn't familiar with this already doesn't know how to fill them in. :-)

roy4711 Loc: Spring Valley IL.

The guide number on my flash is 58 at ISO 100 I would think that would be a powerful flash after reading some of the replies correct me if I am wrong in my thinking. :roll: :roll: :roll: :roll:

amehta Loc: Boston

roy4711 wrote:

The guide number on my flash is 58 at ISO 100 I would think that would be a powerful flash after reading some of the replies correct me if I am wrong in my thinking. :roll: :roll: :roll: :roll:

If it is 58 in ft, then it is a mid-level flash in power. The powerful Nikon and Canon flashes tend to have guide numbers around 120-150, though they also zoom to increase that at higher "focal lengths".

Most P&S flashes tend to be below 40, and the Nikon D5200 flash is 39' (ISO 100), so yours does significantly better than those.