Flash and ISO

MohaimenK · Oct 4, 2010

I had some issues this weekend while doing the wedding indoor. Seemed like even with Flash, I couldn't get the subject bright enough. Well, there was another issue becuse the guy was really dark so he was the main problem, but his wife came out much better.

Should I not go over certain amount of ISO while using external flash? Or how should I have it so its just perfect? Please explain. I googled ISO and Flash and it's all computer related nothing to do photography.

Hardrock · Oct 4, 2010

MohaimenK said:
I had some issues this weekend while doing the wedding indoor. Seemed like even with Flash, I couldn't get the subject bright enough. Well, there was another issue becuse the guy was really dark so he was the main problem, but his wife came out much better.

Should I not go over certain amount of ISO while using external flash? Or how should I have it so its just perfect? Please explain. I googled ISO and Flash and it's all computer related nothing to do photography.

Good question. Looking forward to see what others say. It seems the only options you would have would be to open up the aperture more , add more flash or raise ISO.

Village Idiot · Oct 4, 2010

When shooting a flash, you can use your ISO to increase the flashes power in an exposure.

What flashes are you using that aren't powerful enough? That shouldn't be an issue unless you're shooting outside.

MohaimenK · Oct 4, 2010

I am using the Canon 580EX I. The ISO was in the 2000 range I believe

MohaimenK · Oct 4, 2010

Someone said the higher the ISO is the less the flash is trying to work so it doesn't fire as much? Is this true?

Village Idiot · Oct 4, 2010

MohaimenK said:
Someone said the higher the ISO is the less the flash is trying to work so it doesn't fire as much? Is this true?

Raising the ISO is like using a wider aperture, but instead of getting less DOF, you get more grain.

It'll cause the exposure from the ambient and the flash to both be brighter, meaning you can turn down the flash's power.

ababysean · Oct 4, 2010

I am begging for darker toned skinned to shoot. I am looking through all my photos and all I have are Caucasian faces. I'm wondering if shooting the dark skin hubby, against the lighter wife is a challenge within itself.

ababysean · Oct 4, 2010

P.S.
You have some hot gear!

Big Mike · Oct 4, 2010

Raising the ISO, just allows you to get an exposure with less light. So yes, if all else is equal, you will require less output from the flash as your ISO goes up.

If you are shooting with auto flash metering (E-TTL) then you won't change the flash exposure by adjusting the ISO, the flash will just use less power and give you the same exposure.
But if your flash is in manual mode, the flash exposure will increase as your turn the ISO up (or open the aperture).

So what mode was your flash in? How were you metering? Where was the flash and where was it pointed?

MohaimenK · Oct 4, 2010

I used ETTL and I had it facing up but used a lightsphere. I think I should get a reflector when I think about it because the lights go all direction. I should put something inside so none of the lights spill backward so all the lights go forward.

It was an issue when the subjects were clsoe to me with darker outfits, such as the brides made. And their dresses were highly reflective. I wonder if that played a role?

Big Mike · Oct 4, 2010

And their dresses were highly reflective. I wonder if that played a role?

Bingo.

ETTL is an automatic metering system. It works by reading the light reflected from the pre-flash. So if you have a reflective subject, it will reflect a lot of light, making the camera think that it doesn't need a lot of light. The result is that you end up with less light that you want.

Just like your camera's ambient meter, you may need to override it when it doesn't give you the results that you want.

This is where FEC, Flash exposure compensation, comes in.