Re: [Utah-astronomy] HELP!!!
You dodged a bullet! It's actually rare to find cemented achromats in larger sizes, because differential expansion of the two glass types will generate stress and deform the glass- sometimes enough to pop them apart and damage them. Over about 70mm, most of the quality objectives are air-spaced. One other thing to note is that there should be registration marks on the edge of both elements, so you can re-align them in the correct radial orientation. It's sometimes just a pencil mark, so hopefully you didn't remove it with your cleaning. Not all makers use indelible ink for such registration marks. Often it's just a pencil line drawn simultaneously through the edge of both elements. Also not all makers even bother. Only the higher-quality achromats will have them. On Jan 4, 2008 1:27 PM, Rob Ratkowski Photography <ratkwski@hawaii.rr.com> wrote:
Follow up
the Burgess 127 doublet is air spaced. I was about to use mineral spirits to separate the elements when I noticed a space and then remembered the 3 clear tabs. It popped apart easily and w/ some fine surgical gauze and mineral spirits, clean up began.
The TEC scopes are all oil spaced so we should learn from Rob not to mess around near the objective. The Takahashi are air spaced but I would strongly advice against disassembling one of their cells. The tolerances are tight and even the Texas Nautical techs have had problems with disassembly. It is easy to chip an element when trying to reassemble the lens cell. -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Chuck Hards Sent: Friday, January 04, 2008 2:52 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] HELP!!! You dodged a bullet! It's actually rare to find cemented achromats in larger sizes, because differential expansion of the two glass types will generate stress and deform the glass- sometimes enough to pop them apart and damage them. Over about 70mm, most of the quality objectives are air-spaced. One other thing to note is that there should be registration marks on the edge of both elements, so you can re-align them in the correct radial orientation. It's sometimes just a pencil mark, so hopefully you didn't remove it with your cleaning. Not all makers use indelible ink for such registration marks. Often it's just a pencil line drawn simultaneously through the edge of both elements. Also not all makers even bother. Only the higher-quality achromats will have them. On Jan 4, 2008 1:27 PM, Rob Ratkowski Photography <ratkwski@hawaii.rr.com> wrote:
Follow up
the Burgess 127 doublet is air spaced. I was about to use mineral spirits to separate the elements when I noticed a space and then remembered the 3 clear tabs. It popped apart easily and w/ some fine surgical gauze and mineral spirits, clean up began.
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Don, you'll pardon me if I exclude myself from your "we". But you're advice is sound. Don't mess with something that you're not qualified to handle. On Jan 4, 2008 3:27 PM, Don J. Colton <djcolton@piol.com> wrote:
The TEC scopes are all oil spaced so we should learn from Rob not to mess around near the objective. The Takahashi are air spaced but I would strongly advice against disassembling one of their cells. The tolerances are tight and even the Texas Nautical techs have had problems with disassembly. It is easy to chip an element when trying to reassemble the lens cell.
AMEN I did dodge a bullet but also learned lots about the Burgess 127mm. I had painted over the registration pencil marks BUT got my diamond engraver bit and marked the alignment before I separated the elements. I have taken the scope completely apart as well as the new Moonlight Tri-Knob focuser, I'm optimizing the scope for solar work and there are many things that I can do to improve the contrast and the only way to do this, is take it apart. I have found the Burgess 127mm to be solidly built, well made and very crisp w/ minor color fringing for being an achromat. As soon as the microfiber cloths dry, I'll put it all back together and not touch the lens cell for a year PROMISE!! Needless to say, I was really down when this happened I usually don't make big mistakes. Aloha Rob
participants (3)
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Chuck Hards -
Don J. Colton -
Rob Ratkowski Photography