Flash, ISO and background exposure

Posted: 10th July 2007 by Jacky Yong in Photography

Flashing is undeniably one of the toughest variable to control in photography. Being a newbie handling a flash unit, I encounter a lot of obstacles and errors, resulting in very bad pictures, from a technical point of view.

If you remember one of my earlier posts, I did mention that dialing a high ISO in a flash filled picture will brighten up the background considerably. I might not have the samples to prove my point at that time, but now I have them. And I will be showing them to you here.

Take a look at this photos. Any comments on the background lighting?

ISO : 100, exposure 1/60s, f4.0, focal length 30 mm.

ISO : 200, exposure 1/60s, f4.5, focal length 31 mm.

This is a bit extreme. I was barely 3 metres away from him. I used bounce flash with my DIY diffuser:
ISO : 100, exposure 1/60s, f5.6, focal length 55 mm.

The effect is horrible! The background is so dark, and his face totally overblown! *Tsk tsk tsk!*
ISO : 100, exposure 1/60s, f5.0, focal length 43 mm.

BTW, if you still remember, this is the picture of my DIY diffuser I made earlier.

I was frustrated at the very PnS looking result, and I was determined to find out why. I even dialed the flash compensation to the maximum and still could not get the result that I wanted. I then accidentally bumped into the ISO setting.
ISO : 1600, exposure 1/15s, f5.6, focal length 37 mm. A bit blur, probably because of the slow shutter speed.

ISO : 800, exposure 1/60s, f5.6, focal length 40 mm.

Everything is much clearer now. But to be fair, I used a more intermediate ISO and see the different result:
ISO : 400, exposure 1/60s, f5.6, focal length 41 mm.

ISO : 400, exposure 1/60s, f5.6, focal length 55 mm.

So the conclusion that I get, use high ISO to include more background light. No noise is immediately discernible in light areas anyway. Please comment and correct me if I’m wrong.

Note: This post has been posted in LensaMalaysia and ShutterAsia previously. To view the original post and the replies posted in the respective forums.