Aperture while in i-TTL

AlexW

AlexW

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Alexander
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Hello all,

Quick question on Nikon CLS. Taking photo's of some graphic design work, catalogues, packaging etc... Work positioned on table on white card. SB600 on tripod fired at white ceiling. Manual settings for camera, flash on i-TTL.

When I adjusted the aperture the exposure was affected even though it's on i-TTL. Is this because the flash fires at the beginning of the exposure, setting it correctly, and then the ambient comes in and over exposes it? Assume setting to rear sync stops this?
 
Good question. I'm not sure what difference rear curtain sync would make. If you set your shutter speed high enough, you can control the ambient light. And to control the flash exposure, just stop down. I'd rather have the camera on a tripod for product shooting rather than the flash. The flash can sit on it's own mini-stand can't it? Or any other flat surface for that matter.

Edit: Scratch that - I think that applies when you have the flash on manual... it's late :)
 
Changing the aperture changes the flash power required to get the same shot - Aperture has no effect on the ambient light which is controlled by the shutter speed.
 
Doesn't sound right to me. If you change the aperture, iTTL should compensate and maintain correct exposure. Even if you have loads of ambient light coming in, iTTL should compensate for that too. First curtain or second curtain sync won't make any difference.

How high is your ceiling? Are you running out of flash power? What are your camera settings? Can you post a picture?
 
I'm on way to work now so can't post picture, will do tonight though. Settings would have been iso 200 I think. Shutter speed 1/125 (to remove abient without going into HSS) then apertures between f2 and say f5.6 to get different DoF effects. Ceiling is normal hight (8 feet?) flash on tripod at about headhight.

Edit: here's a link to a couple of the shots: http://www.thedesignery.co.uk/decor.html
 
The white background is possibly upsetting things - flash metering works just like ambient metering and will be fooled by a predominently white background.

In a situation like that it's better to establish correct exposure with the gun locked on manual power.
 
Thanks Richard. That's a good call I think. I guess there's no reason to be using TTL in a situation like this.

Is there any chance I would be pushing the power limit of the SB600 at these settings - ISO 200, f5.6 bounced off a close ceiling? I wouldn't have thought so.
 
AlexW said:
Thanks Richard. That's a good call I think. I guess there's no reason to be using TTL in a situation like this.

Is there any chance I would be pushing the power limit of the SB600 at these settings - ISO 200, f5.6 bounced off a close ceiling? I wouldn't have thought so.
Click to expand...

If you've got a little time to set up manual is better. You just know where you are and the exposure is locked unless you change something.

I wouldn't have thought you run out of power in that situation, but switching to manual will soon confirm that.

This thread might be helpful - similar sort of shot I think
http://www.talkphotography.co.uk/forums/showthread.php?p=2319878#post2319878
 
HoppyUK said:
The white background is possibly upsetting things - flash metering works just like ambient metering and will be fooled by a predominently white background.

In a situation like that it's better to establish correct exposure with the gun locked on manual power.
Click to expand...

Yes in ETTL flash metering would be fooled. A light meter would solve the problem and as you say - shoot with the flash in Manual.
 
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