From: "Richard F.L.R. Snashall" 
To: atmlist 
Reply-To: "Richard F.L.R. Snashall" 




Bob May wrote:
> I think that you pointed to a wrong lens file as the one I got is just a
> doublet rather than a quadruplet.

Curious... I always get the quad...

> As to things changing over temp, I'd suspect that having the 4 lenses all
> next to each other would end up with less changes due to temp moving the
> elements about as the distances between the elements is so much less.  Then
> again, you can probably move the second set of lenses in a Petzval design
> further before any real errors show up due to the longer length of the
> lightpath making things relatively irrevelant in the length dept.
> You will want to calculate the change in distance for a 100 deg. temp change
> (just to make things even) with each of the elements and spacings and
> replace those numbers in the table and see where things go without
> reoptimizing the lens or even changing the focal length, except for the
> change in length of the lens.

OK.  I finally found out how to change the temperature in OSLO.  Over the
0-20 degree C range, it indicates a change of about 3/8 mm, but, generally,
the correction stays fairly well.

But how does this help me determine if the lens system will get to
temperature well?  Again contrasting it to the double doublet form, I would
think that the double doublet form would tend to act like double pane
windows, insulating the inner lens and taking it longer to cool.  But then
again, the group in the quadruplet form is thick and would take longer for
the temperature to get to the surface.

--
Rick S.
http://users.rcn.com/rflrs

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