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Alignment marks in/on OTA.

 

To follow up on an earlier post, took the corrector off the C14.? Noted where the alignment mark was on the edge of the corrector...there was an etching that said "alignment".? This was in about +/- the 4 o'clock position.? I made a small "dot" with a sharpie on the edge of the inside of the tube so it could go back where it started.? Now this is interesting.? There is a black sharpie mark on the inside edge of the primary (I can see it clearly with a dental mirror).? This was off quite a bit from the mark on the corrector AND the mark on the secondary.? So now everything is rotationally aligned(ish), within say 1/4" of rotation.? Mark on the primary aligns with the mark on the corrector and this aligns with the mark on the secondary mirror, at about +/- the 5 o'clock position.? My understanding is that the alignment is traditionally set at 3 o'clock position from a set position (don't remember what that is), that does not seem to be the case with this OTA.? Clock references are me facing the OTA, dovetail on my left 9 o'clock position.

Also, not only did this OTA have a possible centration issue, it was an optical dog.? Images were never really sharp, and there was a fair amount of astigmatism.? I have a Takahashi Mewlon 250 that blows it out of the water optically and I use the Tak for planetary work.? We'll see if this made any difference.

Mike
 

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Mike you might find this interesting..

From: [email protected] <[email protected]> on behalf of Mike Shade via groups.io <mshade@...>
Sent: Saturday, December 30, 2023 2:22 PM
To: [email protected] <[email protected]>
Subject: [C14EdgeHD] Alignment marks in/on OTA.
?
To follow up on an earlier post, took the corrector off the C14.? Noted where the alignment mark was on the edge of the corrector...there was an etching that said "alignment".? This was in about +/- the 4 o'clock position.? I made a small "dot" with a sharpie on the edge of the inside of the tube so it could go back where it started.? Now this is interesting.? There is a black sharpie mark on the inside edge of the primary (I can see it clearly with a dental mirror).? This was off quite a bit from the mark on the corrector AND the mark on the secondary.? So now everything is rotationally aligned(ish), within say 1/4" of rotation.? Mark on the primary aligns with the mark on the corrector and this aligns with the mark on the secondary mirror, at about +/- the 5 o'clock position.? My understanding is that the alignment is traditionally set at 3 o'clock position from a set position (don't remember what that is), that does not seem to be the case with this OTA.? Clock references are me facing the OTA, dovetail on my left 9 o'clock position.

Also, not only did this OTA have a possible centration issue, it was an optical dog.? Images were never really sharp, and there was a fair amount of astigmatism.? I have a Takahashi Mewlon 250 that blows it out of the water optically and I use the Tak for planetary work.? We'll see if this made any difference.

Mike

 

There have been various opinions about whether the marks on the optical components even mean anything as the production process doesn't create astigmatic components with a high degree of confidence. There's a second theory that since the corrector is cored after being figured on the master block, the core is at the optical center which may not necessarily be the physical center. Trying to physically center the corrector may cause optical decentering and result in astigmatism.

Another possibility is that the corrector is not well seated or maybe even reversed, or the baffle tube is not square.?

If you can Roddier test the scope, that could show the dominant aberrations.?

My own C14HD was phenomenally sharp and would easily outperform a Mewlon 250 (I owned both but not simultaneously). Sadly, it was a bear to cool down in our climate so I sold it to a happy owner in a better climate.?

On Sat, Dec 30, 2023, 11:22?AM Mike Shade via <mshade=[email protected]> wrote:
To follow up on an earlier post, took the corrector off the C14.? Noted where the alignment mark was on the edge of the corrector...there was an etching that said "alignment".? This was in about +/- the 4 o'clock position.? I made a small "dot" with a sharpie on the edge of the inside of the tube so it could go back where it started.? Now this is interesting.? There is a black sharpie mark on the inside edge of the primary (I can see it clearly with a dental mirror).? This was off quite a bit from the mark on the corrector AND the mark on the secondary.? So now everything is rotationally aligned(ish), within say 1/4" of rotation.? Mark on the primary aligns with the mark on the corrector and this aligns with the mark on the secondary mirror, at about +/- the 5 o'clock position.? My understanding is that the alignment is traditionally set at 3 o'clock position from a set position (don't remember what that is), that does not seem to be the case with this OTA.? Clock references are me facing the OTA, dovetail on my left 9 o'clock position.

Also, not only did this OTA have a possible centration issue, it was an optical dog.? Images were never really sharp, and there was a fair amount of astigmatism.? I have a Takahashi Mewlon 250 that blows it out of the water optically and I use the Tak for planetary work.? We'll see if this made any difference.

Mike

 

From what I understand the marks are at least in theory supposed to matter, if they do in reality is another matter entirely.? The secondary is centered, I center dotted it and laser aligned it yesterday.? The corrector is rotationally aligned with the primary, it was way off prior to this.? When I get clear skies I can collimate and test.? Other than this, not sure what I might do with it.? Getting any sort of optical testing done on it is going to be impossible: I am very rural New Mexico, there is nowhere within 3 + hours.? Really not going to put the effort and expense into it.? It could also be the corrector lens group on the back end.?

If I might ask, where were you and where did you sell the Mewlon to?? I was in SE Arizona, bought it from a guy there and he got it from a guy in I "think" Virginia.? He sold it as he had a line on a Mewlon 300.

Hopefully my puttering around with it will help, as I offered it was an optical dog.? I generally have very good seeing here, 1" or better according to the seeing monitor on the observatory.? This scope would mush through focus, never "snapping" into focus.? Lack of planetary detail.? I used it as a visual scope only for poking around, I have bigger equipment doing variable star photometry.

Thanks, Mike??
 

"Burdbeen" did you not try the Starizona EDGE cooling fan that goes in place of the secondary mirror? Or wrap the optical tube in Reflectix material to aid in thermal equilibrium??

Fernando

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