I am surprised this post has gone 3 hours without
more replies...
It is curious, but my experience is very much what
you might have predicted. I've seen 2 air-spaced
triplets that would pinch below 32F. The manufacture
was very good about it, and did a little extra
machining and it has been perfect ever since. I have
also seen 2 other air-spaced triplets that were
perfect -- no problems at all.
I also have one oil-spaced triplet by very respected
maker where the elements have moved side-ways over
the years and now the collimation is very bad.
I have yet to see if it can be fixed, but I am not
so sure it can be separated without breaking anything.
The scope has been well treated, but was carry-on
baggage on many flights (you might say it has
Traveled a lot), and saw many nights of freezing
temperatures in the desert or mountain peaks.
But I also have other oil-spaced lenses by the same
company and they are fine (though their travel
is extremely limited). So triplets are somewhat
hit-and-miss, perhaps due to added complexity.
Maybe 30% or 40% with some issue, at least in my
humble experience.
Petzvals are another rough spot. My data there
are four scopes, three of which had collimation
issues. Two were sent to maker and came back
in near-perfect collimation for some nominal fee.
So they are fixable.
I have never had a doublet with problems either
at low temperatures or spontaneously lose
collimation, and I have much more data on these
than triplets. I have even been able to take some
of them apart and re-space and make even better
than factory -- something I would not do with a
triplet.
I should add I am a serious star tester -- for
me scopes need to have perfect symmetrical rings
on both sides of focus, etc. Perfect Airy pattern
at best focus. Nothing else will do.
So doublets are batting 100%, triplets 60% to 70%,
and Petzvals 25%. Rather supports your conjecture.
Though indeed nearly all the scopes were fixable after
some effort. Question: so is the added trouble of
the Petzvals and triplets worth it? I would say
a definit "yes" for the added color correction.
But if I needed a scope to work 100% of the time
without factory service for say 50 years -- I think
one would have to give a nod to the doublets. I
could be happy with Vixen Fluorite for a long time.
I suppose one could wonder if exposed Fluorite and
ED elements in the doublets (as opposed to protected in
the center of a triplet) will age well, but so far there
are no problems.
OK, I will now head for the bomb shelter. See you
in a couple half-lifes. :S
more replies...
It is curious, but my experience is very much what
you might have predicted. I've seen 2 air-spaced
triplets that would pinch below 32F. The manufacture
was very good about it, and did a little extra
machining and it has been perfect ever since. I have
also seen 2 other air-spaced triplets that were
perfect -- no problems at all.
I also have one oil-spaced triplet by very respected
maker where the elements have moved side-ways over
the years and now the collimation is very bad.
I have yet to see if it can be fixed, but I am not
so sure it can be separated without breaking anything.
The scope has been well treated, but was carry-on
baggage on many flights (you might say it has
Traveled a lot), and saw many nights of freezing
temperatures in the desert or mountain peaks.
But I also have other oil-spaced lenses by the same
company and they are fine (though their travel
is extremely limited). So triplets are somewhat
hit-and-miss, perhaps due to added complexity.
Maybe 30% or 40% with some issue, at least in my
humble experience.
Petzvals are another rough spot. My data there
are four scopes, three of which had collimation
issues. Two were sent to maker and came back
in near-perfect collimation for some nominal fee.
So they are fixable.
I have never had a doublet with problems either
at low temperatures or spontaneously lose
collimation, and I have much more data on these
than triplets. I have even been able to take some
of them apart and re-space and make even better
than factory -- something I would not do with a
triplet.
I should add I am a serious star tester -- for
me scopes need to have perfect symmetrical rings
on both sides of focus, etc. Perfect Airy pattern
at best focus. Nothing else will do.
So doublets are batting 100%, triplets 60% to 70%,
and Petzvals 25%. Rather supports your conjecture.
Though indeed nearly all the scopes were fixable after
some effort. Question: so is the added trouble of
the Petzvals and triplets worth it? I would say
a definit "yes" for the added color correction.
But if I needed a scope to work 100% of the time
without factory service for say 50 years -- I think
one would have to give a nod to the doublets. I
could be happy with Vixen Fluorite for a long time.
I suppose one could wonder if exposed Fluorite and
ED elements in the doublets (as opposed to protected in
the center of a triplet) will age well, but so far there
are no problems.
OK, I will now head for the bomb shelter. See you
in a couple half-lifes. :S
