Go Back   Steve's Digicams Forums > Digicam Help > Flash (External)

Reply
 
Thread Tools Search this Thread
Old Apr 22, 2009, 10:29 AM   #1
Junior Member
 
Join Date: Mar 2006
Posts: 26
Default


I'm using a Sony A700, Sony G 70-200 2.8, SONY HVL 56 AM...

Let's say I'm taking a group photo at an event in a relatively dim environment. I am using the flash in a vertical position (pointed toward the ceiling) with the white card pulled out to modify the flash path ( I loathe direct flash lighting). I decide to change from P mode to Aperture prioritymode so that I can set to F8 to gain more depth of field. Though I am set for TTL, my exposure tends not to be predictable, but rather dark, requiring adjustments in either flash compensation or ISO to provide for a decent exposure. I am within the flash range (10-20 feet away from the subjects). Any ideas why I am not getting the proper exposure automatically without adjusting flash compensation or ISO? I thought that Aperture Priority mode was an automatic mode which would not require other adjustments for correct exposure. I appreciate any comments to clarify this issue for me... Thanks...
musicbym is offline   Reply With Quote
Sponsored Links
Old Apr 22, 2009, 11:40 AM   #2
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

musicbym wrote:
Quote:
Any ideas why I am not getting the proper exposure automatically without adjusting flash compensation or ISO? I thought that Aperture Priority mode was an automatic mode which would not require other adjustments for correct exposure.
Not if you're outside of the flash range and you don't increase ISO speed or use Auto ISO (and I'd double check your custom settings to make sure Auto ISO is allowed to go as high as needed). ;-)

Your flash has a GN (guide number) of 183 feet at it's maximum zoom head position using ISO 100.

The maximum flash range for a direct (not bounced or diffused) flash is going to be equal to the GN divided by your Aperture Setting.

For example, if you're using an aperture of f/8, your maximum flash range at ISO 100 for a direct flash would be approximately 23 feet (183 feet divided by your aperture of f/8 )

But, when you bounce a flash, the light must travel to the ceiling, then down to your subject. Because it's being diffused and spread out over a wider area compared to a more focused direct flash, you can lose a *lot* of range. Ceiling height, type/color and more will impact how much range you lose when bouncing.

So, you may need to increase your ISO speed in order to get correct exposure. Each time you double the ISO speed, flash range increases by 1.4x.

JimC is offline   Reply With Quote
Old Apr 22, 2009, 11:45 AM   #3
Junior Member
 
Join Date: Mar 2006
Posts: 26
Default

Thank you for the explanation Jim... very helpful...
musicbym is offline   Reply With Quote
Old Apr 22, 2009, 7:52 PM   #4
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

Please let us know how it works out.

Chance are, when you decided to use f/8 for more depth of field, you probably reduced your flash range enough that you started getting underexposed images compared to when you were shooting in P mode at wider apertures. Increasing ISO speed (or using Auto ISO, making sure it can go as high as needed) will probably solve it for you.

JimC is offline   Reply With Quote
Old Apr 22, 2009, 8:17 PM   #5
Junior Member
 
Join Date: Mar 2006
Posts: 26
Default

I think your analysis is correct. If I increase the ISO all is fine. The problem with using Auto ISO is that the Alpha 700 defaults to the highest ISO setting within the range set in the menu, I assume to maximize battery life and recycle at a faster rate. I would certainly prefer for it to default to the lowest ISO needed for a proper exposure as this would be ideal for me. I really like to keep the noise down as best as possible and run neat image only on the high ISO shots. Thanks...
musicbym is offline   Reply With Quote
Old Aug 11, 2009, 9:43 AM   #6
Junior Member
 
Join Date: Aug 2009
Location: Italy
Posts: 23
Default

Use a more high Iso don't affect very much the battery of a photocamera while use the maximum power of an external flash affect much the consume of the battery (on the flash) and the time of recharge (on the flash) before the next shoot.

If you want lower the Iso for example you could use short focal length because their have more dof .

In general "the standard" is use up to f/4 (at sometimes f/5.6).

On the contrary you need to have very powerful lights ...
alexfoto is offline   Reply With Quote
Old Aug 13, 2009, 11:12 AM   #7
Junior Member
 
TeddyTan's Avatar
 
Join Date: Feb 2009
Location: melbourne
Posts: 26
Default

I agree F/4 is OK for group shots. I personally use F/2.8 but with some careful arrangements and camera angle to make sure everyone is more or less on the same focal plane.
__________________
Wedding Photographer Melbourne Teddy Tan
TeddyTan is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 5:06 PM.