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Re: Dream come true!

Posted: Tue Nov 01, 2016 7:15 pm
by christian viladrich
Thanks a lot Antonello,
You've done a beautifull work and wonderfull design.
Just wondering ... you're using F/6.6 collimating lens on a 150 mm F/10 objective ? Just to be sure.
Best regards
Christian

Re: Dream come true!

Posted: Thu Nov 03, 2016 3:21 am
by Bob Yoesle
Thanks for the OSLO spot diagrams Antonello! This provides confidence that such designs can have very good optical performance, even with a design with a larger sweet spot. Your modular approach is quite nice ;-)
The important thing is that the two lenses are placed exactly as in the drawing above.
Obviously the negative collimator must be the first optic following the objective, followed by the etalon and refocus lens. Are you referring to the plano surface facing outward for each optic? I note this is also the orientation as originally designed for my SM90 internal etalon.

Re: Dream come true!

Posted: Thu Nov 03, 2016 6:15 am
by Valery
Hi Bob,

My congratulations with the success!

Looking for your first imaging session.


Valery

Re: Dream come true!

Posted: Mon Nov 14, 2016 7:04 am
by antonello
Hello Bob

Yes, the two lenses (in a system with a plano concave and a plano convex lens standard) must be placed as in the drawing, with the plano surfaces facing outward for each optic. Only so the quality of the telescope it is maintained.

Hello Christian

Yes the lens has an f: 6.6, but this is the focal ratio of the collimator (needed for marginal beams in a telescope of 200-250 mm of diameter).
The real beam of the my 150 mm telescope (parallel rays of a particular of the Sun on the optical axis) intercepts the collimator (negative lens) at 1078 mm from the objective, where the diameter of the lens used is of 42.2 mm, then the focal ratio of the collimator is 400 / 42.2 = 9.5

For my 150 mm, they would have been sufficient smaller lenses (about 50 mm), but they were available glass disks of BK7 of diameter 65mm and then I did the lenses with this diameter, useful if one day I were to have a telescope 200-250 mm of diameter, which is unlikely, but not impossible :-)

Re: Dream come true!

Posted: Wed Jan 18, 2017 9:46 pm
by Bob Yoesle
Well, it's now going on almost two years since I started this project, and I'm hoping there will soon be "light at the end of the tunnel" - pun intended!

Some of the most recent, and hopefully final, developments:

Back in October when I got some very brief great views before the weather turned bad, I did note a slight degradation of image quality when I used the front SM140 with the internal SM90. I suspected I might have a DERF 160 issue due to the colder fall temperatures, and the securing method I used (black automotive silicone). Sure enough, removing the DERF (still had the internal SM90 EFR in place), solved the problem - I had a much improved hi-contrast view. I consulted with Brian Stephens at Lunt, who agreed stiff silicone was likely the culprit and that most silicone's are not suitable for optical use, and recommended the same Loctite Superflex 575 RTV used to seal the collimator optics and lens cells (hard to find locally, had to order on-line: https://www.zoro.com/loctite-rtv-silico ... lsrc=aw.ds).

First, I removed the old silicone and installed some additional safety retaining bolts and rubber washers; the washers do not actually touch the optic itself:
IMGP4043 SM.jpg
IMGP4043 SM.jpg (371.2 KiB) Viewed 4572 times
I used a syringe and a cut-off 16 gauge IV catheter to squeeze in some blobs of the RTV between the filter and cell wall, similar to how an etalon plate is held in its cell:
IMGP4045 SM.jpg
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IMGP4047 SM.jpg
IMGP4047 SM.jpg (203.98 KiB) Viewed 4572 times
This should hopefully solve the issue of warping of the DERF with changing temperature, while offering a secure hold and prevent the remote chance of a failure from damaging the etalon itself. At some future point I may opt for a completely new DERF filter cell, but for now I hope this will work without untoward effects.

Next up was a better internal ERF and circular polarizer implementation. My original 105 mm B+W Kaesemann filter proved to be too small for the SM90 ERF filter cell I had widened up to 100 mm, as it had an actual OD of only 101 mm. So I acquired another B+W Kaesemann filter, this time the 112 mm, which has an actual filter diameter of 106 mm (almost identical to the Lunt ERF, which is 105 mm in OD)- which was perfect. Both B+W Kaesemann CP filters had to be sent to Schneider Optics in California in order to remove the filter from the filter cell, as there is no easy way to to this yourself without risking breaking the filter.

In order to have tilted filter components, I also ordered a Lunt 100 mm filter ERF cover, and had it machined to fit within the internal etalon mount front ring. I attached the SM90 ERF cell to the rear of this ring, and was careful to align both ERF filter cells so that they would have opposite tilts to minimize any chances of unwanted reflections:
IMGP4037 SM.jpg
IMGP4037 SM.jpg (244.11 KiB) Viewed 4572 times
The completed ERF and CP equipped front etalon ring. The ERF precedes the CP in the optical path in order to protect the CP from excessive heat and possible damage when used in single stack mode.
IMGP4039 SM.jpg
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The completed internal etalon assembly, with ERF and CP, minus the vacuum assembly:
IMGP4042 SM.jpg
IMGP4042 SM.jpg (234.56 KiB) Viewed 4572 times
So at this point, I'm hoping I've done just about all that I can to optimize the filter system and telescope's performance. It should now be completely suitable for both for single and double stack use. Time will tell, as now I have to wait for suitable weather conditions. Current temperatures are well below freezing, and I have a couple of feet of snow to contend with in the path to the observatory... This may be the only sun I see fore awhile ;-)
IMGP4012 SM.JPG
IMGP4012 SM.JPG (304.78 KiB) Viewed 4572 times
Either that, or an exploratory trip to visit California when the weather improves there. In the meantime, maybe this thread needs to be moved to the "solar scope modifications" category!

Re: Dream come true!

Posted: Thu Jan 19, 2017 6:25 am
by marktownley
Always very interesting to read the developments here Bob. You should hopefully be having some good fun with it this year. Interesting gems to keep for future reference regards the B+W filter and the silicone seal used.

Re: Dream come true!

Posted: Thu Jan 19, 2017 1:15 pm
by GUS
Hi Bob, I'm not sure if you mentioned this before, but how do you know which side of the Lunt ERF faces the sun. I have the 100 and 75mm ERF's and there is nothing to indicate which side to point to the sun. I've been told that there should be an arrow on the edge, but can't see any on either ERF.
And thanks for posting this thread Bob, it's been interesting to following your progress.

Ivan.

Re: Dream come true!

Posted: Fri Jan 20, 2017 8:19 am
by Bob Yoesle
Thank you Mark and Ivan, I hope some of what I've learned will be of use to others.

Ivan, the Lunt ERF's don't have an arrow (the thicker Baader DERF's do). The lunt ERF's do have a sunward side, which can be discerned by tilting the ERF at about 45 degrees or more to a bright light source. It then will have a bright metallic rose-pink appearance. You can see some of this brighter reflected light falling on the etalon module ring in the photo above:
IMGP4037 SM 2.jpg
IMGP4037 SM 2.jpg (222.16 KiB) Viewed 4487 times
So while from near normal angles the RG630 looks very deep transparent red, when tilted at 45 degrees or more you will see this bright metallic rose-pink reflective coating:
Lunt ERF.jpg
Lunt ERF.jpg (292.95 KiB) Viewed 4320 times
The other side has a standard anti-reflection coating and will not have such a bright reflective coating. Hope this helps.

Re: Dream come true!

Posted: Fri Jul 07, 2017 6:16 am
by Bob Yoesle
Still working on DERF issues, but there has not been much activity lately. So when a hot day with no wind appeared, I hefted the the heavy double stacked scope with the Lunt internal ERF and a B+W circular polarizer installed onto the Losmandy G11, and I discovered AR 2665 on July 5th:
IMGP3926 SM crp.jpg
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140DS 1200mm_050717_225627.jpg
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140DS 2400mm_050717_174300.jpg
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140DS 2400mm_050717_174129.jpg
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The internal etalon required only - 1.5 PSI to be on-band, and contrast uniformity is excellent! Seeing was only average, so it appears I will have to wait for some excellent seeing to get the most out of this scope, but after a long journey I'm quite pleased with these results ;-)

Re: Dream come true!

Posted: Fri Jul 07, 2017 7:04 am
by Montana
Well done Bob!! :hamster: :hamster: :hamster:

Alexandra

Re: Dream come true!

Posted: Fri Jul 07, 2017 9:05 pm
by Roman
Wow! I just finished reading this thread and I must say - hands down. What am I complaining about :D? This was real torture you just came through, but as I see, it was really worth it. That images are incredible right now. Can't wait what you post here when the weather will cooperate :).

Re: Dream come true!

Posted: Sat Jul 08, 2017 2:56 pm
by marktownley
Really quite excellent results there Bob, i'm glad this project is working out for you :)

Re: Dream come true!

Posted: Sun Jul 09, 2017 6:56 pm
by Bob Yoesle
Thank you very much Alexandra, Roman, and Mark!

Re: Dream come true!

Posted: Sat Aug 12, 2017 9:51 am
by Solar B
Superb images and Update on the beasties performance .... love it.


Brian