Canon ST-2 and flash Zoom setting

kdog

Trying to get savvy on my new ST-2 and flash in general...

I've noticed that using the ST-2 that the flash units zoom factor doesn't change with the lens focal length. Instead, it stays on 24mm. Then it occurred to me that since the flash isn't mounted to the camera, it's probably a moot point, because the flash is a fixed-distance from the subject. So is it ok to leave it at 24? Or do folks have some sort of heuristic for setting it otherwise?

Any words of wisdom would be appreciated. :bow

pathfinder

Why would the flash need to zoom to different focal lengths when used off camera? I can see that you might want to zoom the flash to concentrate the light, but this is a function of the flash to subject distance, which has nothing to do with the camera to subject distance.

You might be shooting with a 24mm focal length or a 300mm focal length, and the only thing that the flash zoom needs to do is cover the subject area with sufficient light, right?

Set the flash's zoom setting when you set up the flash at the beginning, sufficient to cover the area that needs lighting, and you should be good to go.

kdog

Thanks, Jim. Note that I said in my original post "Then it occurred to me that since the flash isn't mounted to the camera, it's probably a moot point, because the flash is a fixed-distance from the subject."

So you've confirmed that as well as given me the heuristic: "Set the flash's zoom setting when you set up the flash at the beginning, sufficient to cover the area that needs lighting, and you should be good to go." Sounds logical enough. I guess I just needed some reassurance.

Cheers,
-joel

kdog

Ok, here's a related question. Using a longer focal length on the flash will cause a narrower light dispersion. In that case, will the flash act like a more powerful flash and be able to light from a further distance than using shorter focal length with a wider beam?

Thanks,
-joel

pathfinder

Within limits, certainly. When the flash is diffused out to cover a 24mm focal length it is not as intense as when it is concentrated in the area covered by a 105mm lens.

That is the logic behind the Better Beamer, which is an external positive Fresnel lens to help collimate the flash beam to add fill flash to wildlife at a distance of up to 60 feet or better.

The new Nikon SB900 will zoom out for a 200mm lens, and this helps focus the light to an even smaller area, just as adding a snoot does, but the snoot does not concentrate the light light as a positive lens does.

I hope the next iteration of the Canon flash also allows more zoom than the present 105mm.

Despite the limitations of the ST-E2, it is a very useful device that I always carry in my bag, if I think I will need flash.

kdog

Thank you again, Jim. I was hoping it worked like that. I'm slooowly starting to figure out this flash stuff, but still have a ways to go.

Cheers,
-joel