There's some computation on this page regarding red eye avoidance
<http://research.microsoft.com/users/alexeib/_private_protected_/p0418.htm>
showing a 7 degree angle from the center of the retina to the edge of a
mostly dark adapted pupil of 6mm diameter (but note that 7mm is possible
if completely dark adapted). There's also some argument (mostly
unjustified IMHO) that 5 degrees is a reasonable working value. In any
case, whether 5 or 7 you need to keep the flash separated by at least
that number of degrees from the center of the lens... a tough job at
40-50 feet. The tangent of 5 degrees is 0.088 and 7 degrees is 0.123.
Multiplying each tangent value by 50 feet yields a flash separation of
4.4 feet at 5 degrees or 6.2 feet at 7 degrees. Clearly impossible
using a flash bracket.
Your best bet is to put the flash on a light stand if you can and keep
yourself about 8 feet away from it. I would use a cheap ebay radio
transmitter to fire the flash such as this 16 channel RD616
<http://cgi.ebay.com/RD616-Wireless-Radio-Slave-Flash-Trigger-16-Channel-New_W0QQitemZ250284156012QQihZ015QQcategoryZ30086QQssPageNameZWDVWQQrdZ1QQcmdZViewItem>
I don't know this seller but he has good feedback and this is the lowest
price ($21.61) including shipping. You're unlikely to get the
advertised 100 foot range (although some do) but you'll probably get
30-40 feet OK. That also means you could place the flash much closer as
long as you can keep it out of your field of view. Keeping it far away,
however, will result in some harsher shadows but also keep exposure very
even across the field of view and, perhaps more importantly, also front
to back.
You won't get any TTL control using the transmitter but if you're
shooting digital you shouldn't need any. With the flash in a fixed
location, and flash and camera in manual mode, the exposure will not
change. Taking and chimping 2-3 test shots should give you much better
exposure control than any TTL system.
ps: If 'twere me I'd use multiple flash units and large diffusers if
possible.
Dr. Flash
Jez Cunningham wrote:
> I have to do some theatre photography soon for friends - nothing too
> challenging, just at dress rehersal.
> Previously I've had to use flash - on-camera so I could move around - and
> with a long (200mm) lens. Red-eye was inevitable.
>
> What distance would I have to get the flash away from the lens to avoid it?
> (Assume camera-subject distance about 40-50feet.)
> I'm just wondering if 6" (on a bracket) would be enough or if it's gotta be
> a few feet (with an assistant and a long cord)?
>
> thanks for any advice
> jez
>
>
> ==============================================
> List usage info: http://www.zuikoholic.com
> List nannies: olympusadmin@xxxxxxxxxx
> ==============================================
>
>
> No virus found in this incoming message.
> Checked by AVG - http://www.avg.com
> Version: 8.0.138 / Virus Database: 270.6.6/1627 - Release Date: 8/22/2008
> 6:48 AM
>
>
>
==============================================
List usage info: http://www.zuikoholic.com
List nannies: olympusadmin@xxxxxxxxxx
==============================================
|