Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 (Tek) 9/28/84 based on 9/17/84; site hammer.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!bellcore!decvax!decwrl!pyramid!hplabs!tektronix!orca!hammer!seifert
From: seifert@hammer.UUCP (Snoopy)
Newsgroups: net.rec.photo
Subject: Re: Flashes and telephoto lenses
Message-ID: <1881@hammer.UUCP>
Date: Wed, 19-Mar-86 10:16:26 EST
Article-I.D.: hammer.1881
Posted: Wed Mar 19 10:16:26 1986
Date-Received: Sat, 22-Mar-86 05:05:38 EST
References: <1587@watmath.UUCP> <263@noscvax.UUCP> <633@mhuxl.UUCP>
Reply-To: tekecs!doghouse.TEK!snoopy (Snoopy)
Organization: The Daisy Hill Puppy Farm
Lines: 23

In article <1587@watmath.UUCP>, rayazwinski@watmath.UUCP (Yazwinski) writes:
> I have heard that when using a flash and, say a 135mm lens you have to
> change your f-stop to allow for the light loss through the extra glass.
> I have also heard that f4.5 is f4.5 no matter which lens you use.

[ various followups about T-stops and the number of elements in various
lenses ]

Isn't anyone going to point out the obvious?  You need a tele-lens on the
flash to concentrate the light on the area covered by the lens.
Some flashes have various focal length lenses available for this purpose.
The more important case is when you're using a wide angle, otherwise
the center will be overexposed and the edges underexposed.

{not to ignore 'T-stops' and the number of elements in a lens, as
this could be significant in some cases.  If it is significant, it will
also be significant if you use an external (non-TTL) light meter.
I would think that TTL flash *should* compensate for this.}

Snoopy (an "available darkness" photographer)
tektronix!tekecs!doghouse.TEK!snoopy

(That's TTL = Through-the-lens metering, not transistor-transistor-logic)