Re: solar filters
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Just for the record, Al Nagler has stated that there is no problem using their NP scopes for solar viewing with a wedge. The rear elements are far enough forward in the light path that there is no heating problem. I can't comment on others such as those from Takahashi.
From: "'Woody Schlom' woody@... [ap-gto]"
Sent: Wednesday, April 6, 2016 3:13 PM
Subject: RE: [ap-gto] Re: solar filters
I'm curious about your comment to keep the Sun centered to prevent heating up the telescope elements. Unless you've got a 4-element Petzvel design scope where the rear elements are near focus, I don't see two or three elements at the front of the scope where the image is totally unfocused, heating up -- whether centered or not.
I'll admit that my little 80mm triplet doesn't transmit nearly as much light and heat as your big aperture scopes, but I've never heated mine up to the point where the wedge was uncomfortable to touch -- even while imaging continuously for 7 hours with an ambient temperature of 98° F.
And I sure don't understand why keeping the sun centered would decrease heat buildup in the telescope lenses.