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Re: [OM] Zoom lens and OM4T

Subject: Re: [OM] Zoom lens and OM4T
From: "Parzival Herzog" <parz@xxxxxxxx>
Date: Mon, 9 Jul 2001 13:59:00 -0500
----- Original Message -----
From: "Terry and Tracey" <foxcroft@xxxxxxxxxxx>
> How much light was coming in the back of the viewfinder? I just experiemnted
> a similar thing with a just purchased 35-105. Light from the viewfinder
> caused a noticable error.

No I wasn't using an eyecup, and yes, using a makeshift eyecup (a black tape 
spool)
creates about a 1/3 to 1/2 stop difference in E.V. (interior lighting).

Wow. I didn't  know that!


----- Original Message -----
From: "C.H.Ling" <chling@xxxxxxxxxxxx>
> Just tested the newer 35-105 setting at F8, point to a plain wall. My OM-1n, 
> 2n and 4
> all read 1/2s (with the 2n read very little below 1/2s, I think it was less 
> than 1/3
> stop). There is no different between 35 to 105mm on my OM4.

The actual difference from f3.5 to f4.5 is log(4.5/3.5)/log(1.4142) = 0.73 f 
stops.
You should be getting 3/4 stop difference (unless new model lens is different,
mine is the flat rear element model).

I coupled the lens to my Sekonic meter at the focal plane (using plumbing!).
The Sekonic showed 3/4 stop change as I zoomed the lens. This is exactly
the expected value.

So, now comes the kicker - I had originally installed new silver oxide batteries
in the OM4T (replacing the LiMn battery.) Now I took the (what I thought were
pretty new) siver oxide batteries out of the OM2N, and replaced them with the
(very new) batteries in the OM4T.

Lo and behold! 2 stops increase in absolute E.V. on the OM2n, and the change
due to zoom (with "eyecup T") was now over 1/2 stop (my estimate is 0.6
stops). This is within the measurement error as far as I'm concerned.

I thank everyone in the list for their thougtful responses. I certainly
learned more than I expected from the exercise of a little neurosis about
my new (used) OM4T!

So, what about those "new" AgO2 batteries? I guess I'll have to be neurotic
about those now!

Now I want 2 eyecups. Anyone got some kicking around?

- Parzival



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