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[OM] Re: OT: optics

Subject: [OM] Re: OT: optics
From: Stephen Troy <sctroy@xxxxxxxxx>
Date: Tue, 07 Jun 2005 09:59:02 -0400
At 04:21 PM 06/07/2005 +0300, orava@xxxxxxxx wrote:
>2) And a very off topic question:
>I heard that you could build a telescope using two lenses: one with long
and one
>with short focal lengths. Then you just line up those lenses so that their 
>focal points coincide. I tried this with two of my zuiko lenses and it
really 
>works as a short telescope. But how could I take photos with that kind of
set 
>up? The problem is that I can look through that "telescope" and see the
image 
>sharp at a great range of distances between my eye and the eyepiece (that is 
>the shorter ie. aft lens). This is due to my eye that has a built in
focusing 
>mechanism. But when I tried to connetct that telescope to the camera I
couldn't 
>see a sharp image through my cameras viewfinder. So, how could I connect
that 
>self made telescope to my OM4Ti THEORETICALLY? (If we consider mathematical 
>lens formulas.) What about in REALITY? And is it possible that the image
fills 
>only part of the film (makes a black barrell around a circle shaped image)
or 
>should it fill the whole image?



I just read an article on telescopes in either the June or July issue of
Astronomy magazine.  If I remember it correctly, you can figure out the
power of a telescope built this way by dividing the focal length of the
longer lens by the focal length of the shorter lens.  The example they gave
was a telescope with two lenses with 1000mm and 25mm focal lengths, which
gives a magnification factor of 40x, or a "40-power scope.".

Don't know about mounting to a camera body - I guess you could either use
extension tubes (maybe the zoom tube or a bellows) to try to bring the
image into focus or you could use a reversing ring that screws into a
filter thread to mount one lens "backwards."  Hopefully, someone else will
have a good solution.

Steve Troy, y'all.

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