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[OM] Re: Q for Dr. Flash et al

Subject: [OM] Re: Q for Dr. Flash et al
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Thu, 19 Apr 2007 07:37:09 -0400
AG Schnozz wrote:
> 
> 4b. Auto-flash mode.  This is my preferred setting most of the time. 
> My flashes of choice are the Vivitar 285HVs which have an outstanding
> auto-exposure sensor built-in. They also have three auto-levels and
> four manual-levels to choose from.  Mine lives in Yellow.  Again,
> program the camera with the recommended aperture.  Why I like
> auto-flash is that my background (ambient) light-level always remains
> constant and the flash takes care of my subject.

For those who might be interested, the venerable Vivitar 285 is now back 
on the market after a mysterious disappearance of about one year. 
$89.95 will get you a brand new one from B&H
<http://www.bhphotovideo.com/bnh/controller/home?O=Search&A=details&Q=&sku=61441&is=REG&addedTroughType=search>

I've used a 285HV but never owned one.  I have an OM-1 era Vivitar 283 
with all the trimmings but its trigger voltage is above the safe comfort 
level for the 5D which is only good to 250 volts.  But the A1 will take 
400.  I usually use a Sunpak 422D which has a 5 stop manual range and a 
swivel head.  The 285HV doesn't swivel and has a 4 stop manual range but 
it has larger, more visible and less fiddly controls.  Power output is 
about the same.  Maybe I should get one now that they're back.

> 
> 5. Test to adjust your exposure setting.  Just like the film days
> (see above), you may need to over/under-expose the flash to get the
> results you want.  As a general rule, I choose to overexpose my 285HV
> about 1/2 stop, but that's to match up for my system and my way of
> working.
> 
Actually, I suspect your 1/2 stop over is only accounting for the actual
power output of the flash.  I have never tested a portable hot shoe 
flash that meets the spec'd guide number.  All four of my T-32's measure 
to within 1/3 stop of each other but the average power output is a full 
2/3 stop less than the guide number would indicate.  Both of my Sunpak 
422D's are a full stop less than spec.  Both of my Sunpak 522's are 
about 2/3 stop low.  I've measured a friend's Vivitar 285HV for her.  I 
don't recall the precise value but it too was at least 1/2 stop low if 
not a full stop.  And all of those tests are using extremely fresh 
alkaline batteries or a high voltage pack.  After about 30 shots on a 
set of alkalines you'll be down another 1/3 stop.  If you use NiMH 
batteries the lower voltage (1.2 NiMH vs 1.5 alkaline) will put you down 
1/2 stop from max power even when the batteries are fresh.  But you'll 
get more consistent results since the voltage doesn't drop off so fast.

All flash manufacturers lie about guide number.  I consider a flash 
meter to be an indispensable tool.  I love my Sekonic L-358 which 
reports the percentage of flash compared to ambient since 20-30% flash 
is just right for daylight fill.  Recommended.

Dr. Flash

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