Flash, ISO and background exposure

[jackyyong]

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.

I have experienced before that dialing a high ISO in a flash filled picture will brighten up the background considerably. Allow me to prove my point here.

Take a look at these photos. Any comments on the background exposure?

http://lh3.google.com/jackyyong/RpMdYzRsekI/AAAAAAAAGMI/pjCBwnWJXkE/s800/_MG_2550.jpg
ISO : 100, exposure 1/60s, f4.0, focal length 30 mm.

http://lh4.google.com/jackyyong/RpMdYDRseiI/AAAAAAAAGL4/2gh1HpEnDSU/s800/_MG_2546.jpg
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
http://lh6.google.com/jackyyong/RpMcyjRsdGI/AAAAAAAAGAY/JCoBk-QzwNI/s800/_MG_2288.jpg
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!*
http://lh6.google.com/jackyyong/RpMczjRsdJI/AAAAAAAAGAw/KRW4SI_WISg/s800/_MG_2291.jpg
ISO : 100, exposure 1/60s, f5.0, focal length 43 mm.

*All pictures taken with a 1.6x body. Photos not cropped, only resized.

[jackyyong]

I was frustrated at the very PnS looking result, and I was determined to find out why. I even dialled the flash compensation to the maximum and still could not get the result that I wanted. I then accidently bumped into the ISO setting.

http://lh5.google.com/jackyyong/RpMdbTRseoI/AAAAAAAAGMo/MNg80xedpYM/s800/_MG_2568.jpg
ISO : 1600, exposure 1/15s, f5.6, focal length 37 mm. A bit blur, probably because of the slow shutter speed.

http://lh3.google.com/jackyyong/RpMdbzRsepI/AAAAAAAAGMw/n6d7xGL95P4/s800/_MG_2571.jpg
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:

http://lh6.google.com/jackyyong/RpMdcjRserI/AAAAAAAAGNA/j6ZWyNtNdos/s800/_MG_2589.jpg
ISO : 400, exposure 1/60s, f5.6, focal length 41 mm.

http://lh3.google.com/jackyyong/RpMdczRsesI/AAAAAAAAGNI/rssFBmNqCGI/s800/_MG_2590.jpg
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 discernable in light areas anyway. Please comment and correct me if I'm wrong.

[ShaolinTiger]

You are correct, using higher ISO gives the same effect as using a longer shutter speed with flash photography.

It gives you more exposure to the ambient light or background light.

This stops you from getting those horrible black backgrounds which take all the feel away from the pictures.

Try and use a lower shutter speed too, you should be able to handhold down to 1/15 or 1/30 with ISO 400 or 560 you should get nicely exposed pictures with good background light.

A faster lens helps too something with f/2.8 or a cheap 50mm f/1.8 prime at around f/2.2

[zool1956]

First of all, your ISO is quite low hense your CCD could not be sensitive enough to pix up the low lighting condition. I would prefer to choose a much higher ISO such as 200 or 400. Second, your shutter speed is too fast hense there is no ambient lighting in view.

Try using a dome on your flash light which you can be purchase at any photo store. With this you have an overall lighting condition. But if creativity photography is in mind, shadows does have an important part.

Happy shooting!

[mobbes]

curious, are you shooting ttl flash or manual?

[jackyyong]

Thanks for the very informative tips ShaolinTiger and zool1956. Definitely need more practice here. Your tips will come in handy! I do have the 50 mm 1.8 prime, but a wedding reception like this needs me to snap group photos, which would be quite a challenge on this lens. Nevertheless, I still interchange with the 50 mm lens whenever the need arises.

mobbes, I believe I was using e-TTL at that time. (I'm using the 430EX, if you're familiar with it). But I do not know if the e-TTL will be disabled when I point it any other directions than straight ahead. :?

[hotdrive]

What if we do not have a fast lens and a tripod, what other settings that we can use? I'm curious as well, cos' i faced the same problem on a few occasions..

[raclette]

what i do all the time when using direct flash (as in no ceiling/wall bounce) is try to keep the shutter open long enough for the background to be properly lit and short enough so that you could hold the camera without shaking ( a tripod is a plus) . And yeah, dont forget to tell the person not to move before the shutter closed or they will appear transparent :D

[andythology]

Jacky, that hall cannot use bounce light. It is more than 30 feet tall.
1/50 will do.. i guess..

[Alan]

Bumping up the ISO also has a number of other useful shooting benefits when you are using flash:

1) Longer flash range - could be doubled or more if you are careful
2) Save batteries and as a result, gives you more shots per set of batteries
3) Faster recycling time. This is crucial in weddings if you want to get ready for the next shot. You also get more shots before your flash goes completely flat and needs time to fully recharge.

You gotta a bit hard-cored to shoot weddings with ISO 100. ;)

[chuah406]

Bumping up the ISO also has a number of other useful shooting benefits when you are using flash:



How high an ISO do you go up to ? And still usable quality......

[andythology]

in times, I do go up to 1600 too.

[Alan]

How high an ISO do you go up to ? And still usable quality......

I am still new with my D80 and have so far shot at 800 and experimented up to 1600. Noise, yes but since my previous digital experience is only a pns, that's pretty decent and usable. Still beats the heck out of ISO 200 and 400 films that I used to use.

[sinister]

I've used 1600 on mine many times already... :D

[william68]

Tried ISO3200 on a averagely lit hall with f2.8 so far still acceptable but with a flash head will be a lot better.

I did that coz I don't have a flash head.