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RE: [OM] Focusing Screens

Subject: RE: [OM] Focusing Screens
From: "daniel" <danrich@xxxxxxxxxxxxx>
Date: Fri, 30 May 2003 16:21:38 -1000
Ahhhhhh! Thanks you mister wizard sir :)
Dan

-----Original Message-----
From: owner-olympus@xxxxxxxxxxxxxxx
[mailto:owner-olympus@xxxxxxxxxxxxxxx] On Behalf Of Julian Davies
Sent: Friday, May 30, 2003 4:16 PM
To: olympus@xxxxxxxxxxxxxxx
Subject: Re: [OM] Focusing Screens

It's the heat wot does it....

When the lens gets hot, it expands, and the elements move away from the
film. This is the same as focusing closer, so you need to be able to
shorten
the lens a little more than usual to get to infinity. At normal
temperatures, this translates into 'beyond' infinity.
The alternative is to paint the lens white instead of black.

Julian


----- Original Message ----- 
From: "daniel" <danrich@xxxxxxxxxxxxx>
To: <olympus@xxxxxxxxxxxxxxx>
Sent: Saturday, May 31, 2003 3:11 AM
Subject: RE: [OM] Focusing Screens


> How dose the cold cause the lens to focus differently?
> Dan
>
> Pop Photo had an article a month or two back about zooms and
super-teles
> that focus _slightly_ past infinity at desert temperatures
> so they will +barely+ reach infinity at arctic temperatures.
>
> If the infinity mark lines up next to a "L" shaped index mark, instead
> of a purely vertical "|" one, it's a common way to display
> the idea it's been designed that way.
>
> While a 180 / 2.5 is neither a zoom, nor a super-tele, I just thought
> I'd mention it.  Maybe it's so darned fast it has the same
> kind of variablity with temperature?
>
> Lama
>
>
> > Tamron 180 2.5
> > It will go just a bit past infinity in focus, after reaching it, I
can
> > still go a little more noticing the focus screen split image shift.
>
>
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