How to judge/control amount of light from a flash

[guitar_j]

When using a flash (I hope to get a wireless flash for my Maxxum this

christmas) how can one judge or control how much light from the flash

actually falls on the subject. for example, if I have something,

we'll say a coffee cup, that I want to photograph (I like to do

macro) how can I best tell how far/where to place the flash from the

subject to prevent uneven lighting such as a bright spot on the

glossy surface of a coffee cup?

 

I know that diffusers and softboxes are an option, but again, how do

I know where to place the light?

 

I suppose I'm unsure of flash technologies. Do some flashes put out

different amounts of light depending on how much added light is

needed? if so what is this technology? or do they all just blast away

and leave it to the photographer to control the light?

 

thanks for reading (and hopefully responding to) my noob question.

[gary evans]

In short, the answer to your question is Yes.

 

Almost all newer flashes (not familiar with Maxxum) have what is called TTL, or Through-The-Lens capabilities. In short, how this works on a film camera is that the shutter opens as the flash is putting out light. The camera reads the reflection of the light hitting the film and passes this information to the flash so the flash knows when to extinguish the light. Bingo, perfect exposure every time. At least, every time you are photographing something that is approximately of 18% reflectance (middle grey).

 

For lighter objects, such as your white mug, you may want to dial in some + flash compensation. If the mug was non-reflective and black, you might need to dial in some - flash compensation. Most cameras do not control flash compensation and you must do this on the flash itself.

 

But most flashes also have a manual mode, whereby you can tell the flash your ISO, your focal length, and what power level you want the flash to be (1/1, 1/2, 1/4, 1/8, 1/16,...).

 

In your situation, studio setup with unmoving subject, a flash meter would be invaluable, think about picking one up.

 

Oh, and TTL works on digital cameras in a different way than film cameras since on digital cameras, there is no film plane to read the light's reflection from. So flashes that have TTL for digital cameras do so with very short (can't see with naked eye, least I don't think you can) bursts from the flash so the camera/flash can tell what output level the flash need to be at.

 

And as far as where to place the light, what angle to you want the lighting to be from for your photo? How soft do you want the light to be? It's very difficult to get soft lighting from a speedlight, some would say impossible, but you can soften it with a mini-softbox, like Lumiquest, or using a lightstand and umbrella, and moving the diffused flash closer to your subject.

 

Browse through the Lighting Forum here on Photo.net. TONS of GREAT information there!

[garry edwards]

Josh,

 

Gary Evans has given you a good answer, what he says is right for flashguns that fit on to cameras.

 

For studio flash units though, the flash doesn't do any 'thinking' for itself and the photographer makes all the decisions.

 

If you want to avoid bright spots you need to make the light big in relation to the size of your subject. The easiest way to do this is to use an umbrella or a softbox, very close to the subject but there are other ways too, for example a diffusing material such as translucent white plastic could be placed near the subject and the flash fired through it. In effect, the diffusing material becomes the light source.

 

The info on the lighting forum is filed under 'administration'

 

Hope this helps