Experienced Photographers - What Does This Mean

[Uncreative]

I am looking at a bounce flash for my camera and noticed this statement in the description of a bounce flash that fits into a hot shoe.

"It features a powerful Guide Number of 148'/45 m at 85mm, and features a power-zoom flash head that covers a focal range from 24mm to 85mm."

Does that mean that you should not use that flash with a zoom lens above 85mm or does that just mean that beyone 148' the flash will be ineffective with an 85mm lens and I would guess at progressively shorter distances as the focal range decreases towards 24mm?

Example: You are taking a picture 10' away from a subject and have zoomed in to 135mm is that okay to do?

[life-is-plastic]

... when you bounce you flash against a ceiling or wall those numbers won't count, as they're only correct with the flash directly on your subject. With modern cameras things will be taking into account by all the electronics (TTL/ Thru The Lens). Bouncing will 'reduce' the flash's output as on the way light is absorbed ... so the lighter the bounce surface, the better. Also be careful with colored walls/ceilings! Your bounced light will get the same color ...

... bouncing your light will scatter the light much more which is nice, as this gives much softer shadows. You could counter too much loss by using a slightly narrower beam (manually) ... e.g. you're taking pictures with a standard 50mm on a Fullframe dSLR, you can easily bounce via a wall/ceiling with the flash-zoom set to 70mm or 85 mm ... it's often just a case of experimention. Btw: depending on the bounce-surface you often might need to use flash-compensation ... you can dial that in on your camera, providing you're using TTL on a (d)SLR ... just check the pictures you get on the screen (too dark, dial in a +compensation / too light, dial in a -compensation).

Hope this helps you a bit

[Dollarhyde]

That's a great explanation Life-Is-Plastic personally I don't bother with the numbers since the flash I use is generally bounced into an reflective umbrella depending upon the type of look that I'm after. Shadows etc.

[midiman]

I use a continuous light kit so I can see what I'm getting before I click the shutter.

Also helps me sweat off a few pounds during a lengthy session, which suits my wife fine

I was wondering what all that stuff meant though. Thanks for starting the thread. Not enough technical threads here

[life-is-plastic]

... the guidenumber is a reference to the power (or amount of light) your flash is producing ... and in the olden days it was used to calculate exposure: GN = distance × f-number ( http://en.wikipedia.org/wiki/Guide_number ) ... nowadays it's mostly used to compare different flashguns, although it needs to be said that overal this performance should be mentioned with the zoomhead in the 50mm position ... the number mentioned in the first post was at 85mm, which is a more concentrate lightbeam, and therefore more powerful, thus kinda misrepresenting things ...

... btw: for studio-flashes Watts/sec (W/s) are used to compare output ...

[cosycottage]

personally I don't bother with the numbers since the flash I use is generally bounced into an reflective umbrella depending upon the type of look that I'm after. Shadows etc.

...like picking up special infra-red film for nocturnal shots at the zoo