Flash Zoom

[musicaleCA]

Okay, I'm muttering to myself here, feeling rather silly. Just what in the world should I be looking for when I change the zoom of my flash? I've done test shots and changed the zoom setting, but haven't seen a difference. Does zooming the flash to, say, 105mm throw the light farther, or make it harsher or...something? I'm confuddled, and haven't found anything terribly useful in my readings; that and it's annoying that this is the only function on my flash that I don't understand yet.

Oh, and futhermore, whatever zooming the flash does, does using a diffuser or bounce card (or similarly, bouncing the flash) negate the purpose of zooming it in the first place?

 

[Dwig]

...Does zooming the flash to, say, 105mm throw the light farther, or make it harsher or...something? I'm confuddled, ...

Nope, light travels an infinite distance unless it runs into something.

A flash tube puts out a certain quantity of light. The flash's reflector narrows the angle at which the light is emitted from the unit to concentrate the light in a range that approximately matches that of the camera lens. This makes the light more intense in the area photograhed and doesn't "waste" light elsewhere.

When the flash's reflector and lens system is "zoomed" the angle at which the light is emitted is narrowed further increasing the intensity. This effectively raises the brightness of the light and any one distance and, with any given lens aperture, increases the distance at which you can get a proper exposure. That is, if the lens has a narrow enough field of view so that it doesn't "see" anything not lit by the narrow beam of the flash.

Its the same as when you adjust the beam on one of those fancy aluminum flashlights (e.g. MagLight). When the light is spread over a large area, as that seen by a wide angle lens, it is less intense than when concentrated into the narrow field of view of a longer lens.

 

[ANDS!]

Oh, and futhermore, whatever zooming the flash does, does using a diffuser or bounce card (or similarly, bouncing the flash) negate the purpose of zooming it in the first place?

Not necessarily. By zooming the flash head in or out, youre still affecting the direction and apperant size of the light coming out of the flash - even if it is being sent through a diffuser, or bouncing off a surface. A zoomed out flash head is going to bounce over a larger surface than a zoomed in head.

And the above poster has it correct. On auto modes the camera will choose the zoom head position; however if you get into manual mode (as you should. . .you naughty Photography) and control the zoom head position you can create some dramatic shots: wide angle of a friend with only a narrow beam of light hitting their face for example.

 

[musicaleCA]

Dwig[/URL]"]Nope, light travels an infinite distance unless it runs into something.

Evidently. I was thinking more along the lines of the inverse square law. That's all I have to say to that. Bloody semantics. -.-

Thanks for the explanation. I can see why I didn't see any difference in my test shots; I suspect that I would've seen a greater difference if I had been inside a large space like a church or the Chan Centre and bouncing flash in there, or somewhere where I had a lot of wall/ceiling space to bounce it off of.

As for the camera choosing, not really. On my 550EX the zoom is either set to auto on the flash (in which case, yes the camera chooses the zoom based on focal length, but in my case, with EF lenses it'll get it wrong because of the compact frame), or chosen on the flash, separately from the camera, which is where I've always left it (on the flash's manual zoom).

And yes, with flash, I (very nearly; 99% of the time anyway) always shoot manual. ;-) (Though I do love ETTL, mostly as I'm moving a lot outdoors and don't have time to set the flash output manually.)

So here's a situation. Say I'm outside, and want to use my flash for fill to lift the shadows on someone's face. Just to be a stickler, say I use a bounce card too. Would it be best to get the flash zoomed-out (to say, 24mm) to make it softer (taking into account that on ETTL my flash EV will be around -2 to -3 stops)? I'm going to guess, yes. >.>

Thanks again for the explanations.

 

[Dwig]

...say I use a bounce card too. Would it be best to get the flash zoomed-out (to say, 24mm) to make it softer ...

Zooming to a wide setting with a bounce card will not make the lighting any softer unless doing so illuminates a larger area on the bounce card. When using a bounce card, it becomes the light source and its size controls the softness. If zooming wide merely throws light out beside the card then doing so merely wastes the light that misses the card.

 

[musicaleCA]

Duly noted. Thanks.