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Broken Coronado Solarmax II afocal adapter lens

solar optics
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#1 MoBacon

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Posted 18 September 2019 - 10:37 AM

Hello all. I got my old SolarMax II 60 out a couple of weeks ago and got excited about solar imaging. Ordered a double stack second etalon. And new ITF filter. And moonlight focuser....

 

And then I found that I had a nice Y-shaped crack in the "negative collimator (afocal) lens with the attached "richview tuning" pressure bolt," to quote Bob (user BYoesle on CloudyNights--so much good info about these scopes from Bob and others on CN!) I am attaching a pic. I am pretty sure I know the answer but just hoping:

 

Does anyone know of a way to get a replacement?

 

I have called Meade, and I don't mind the $150 minimum repair fee--I guess it could go higher. But I do mind losing the scope for 6-8 weeks minimum. That's the estimate on repair.

 

If anyone knows of a replacement or of a used scope they are parting out or selling, I would be interested. Thank you!

 

(Post here or direct message)

Attached Thumbnails

  • Coronado60.jpg

Edited by MoBacon, 18 September 2019 - 10:41 AM.


#2 MalVeauX

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Posted 18 September 2019 - 10:45 AM

Heya,

 

Yea, there's no way to repair that DIY without the parts and the know-how with the right tools. It will be significant to repair, way more than $150 from Meade. I would be curious too to find out what they charge to basically give you a new scope (nothing else in the SM2 is expensive, not like the front element is anything special either, and definitely doesn't have a good focuser to worry about). Short of buying a new single stack SM2 scope as they're on sale and being discontinued and all that... a repair, hopefully they even have parts if that's even an option.

 

Any idea how the break happened?

 

Very best,



#3 vincentv

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Posted 18 September 2019 - 11:05 AM

Ask beloptik, a user in another thread reported they can find/manufacture the lens. 

In the meantime you can use the front etalon and blocking filter with another scope.



#4 MoBacon

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Posted 19 September 2019 - 02:28 PM

 

Yea, there's no way to repair that DIY without the parts and the know-how with the right tools. It will be significant to repair, way more than $150 from Meade. I would be curious too to find out what they charge to basically give you a new scope (nothing else in the SM2 is expensive, not like the front element is anything special either, and definitely doesn't have a good focuser to worry about). Short of buying a new single stack SM2 scope as they're on sale and being discontinued and all that... a repair, hopefully they even have parts if that's even an option.

 

Any idea how the break happened?

That is what I am afraid of. I think I probably overtightened it in the past trying to make the sun look better when it was probably a bad ITF filter. My fault.



#5 MoBacon

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Posted 19 September 2019 - 02:28 PM

Ask beloptik, a user in another thread reported they can find/manufacture the lens. 

In the meantime you can use the front etalon and blocking filter with another scope.

Thank you very much. I will ask!



#6 MoBacon

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Posted 19 September 2019 - 10:54 PM

UPDATE: As vincentv posted above, the lens is a simple glass lens that you can source from anyone that makes lenses (it may be coated but I a not sure and I am not sure if that coating would be required except to maybe correct some chromatic aberration). And another very helpful Astronomics poster gave me a source for a plano-convex lens since my posting there seemed to imply this lens was behind the etalon. 

 

However, I took it out and measured it. It's 38.1 mm in diameter, but plano-concave (like Bob had posted before, it's a negative collimating lens) because this lens is actually in front of the etalon. I wasn't sure if maybe I was just not understanding and was scared I was going to fry my eyes. So I started reading more, and actually, the way it works is pretty "simple"--once you have some very smart people break it down. (And the smart engineers who figured all this out to use a smaller, cheaper etalon. And Galileo, Newton, et. al, who originally figured some of this astronomy lens stuff out, which is pretty incredible.) If you already know this stuff, great, but I thought other beginners may be interested. NOTE: I am not suggesting anyone try to disassemble or work on your own solar scope. This is for information only. I may or may not try fixing my scope but I am not an expert and I have no advice for fixing anything like this. It's just interesting and I learned something new and wanted to share it.

 

The below diagram is of an internal etalon scope like Meade's and I think Lunt's and it is from a very helpful article by Ian Morrison:

 

http://www.ianmoriso...ion-and-survey/

 

The etalon needs the incoming light to be approximately parallel to the principle axis of the etalon. If the etalon was in front of the objective, nothing would have to be done to alter the path before entering the etalon. But since the Coronado has a convex lens up front like other refractors, the light leaves that lens converging towards a point (the focal point of the lens). The smart people realized that they could put a concave lens in front of the etalon to return the light waved to parallel to each other and the lens axis. Then behind the etalon, use another convex lens to bring the light back to a focal point where we can focus and use eyepieces, etc. 

 

So I took the etalon out, and sure enough, there is a plano-convex lens behind the etalon. The two lenses are basically the exact opposites of each other. in fact, if you look at something through both, no divergence or convergence occurs--just like looking through a plate glass window. The plano-covex fits neatly into the concave and together they become a flat piece of glass. You can separate them a few cm (where the etalon would go) and its still the same. I am sure you could measure some divergence with small separation with better equipment than my eyes, but it's close. 

 

The diagram and article help make this much clearer. Also the article explains what the etalon and the blocking filter do in a little more detail than I had read before starting this and why the ITF filter is so important in more detail, too. And how there is no magic in these telescopes, just basic, good optical engineering. A very good read.

 

Anyway, I hope this is interesting to someone here and helpful--I have learned much from CN just in the past few weeks and wanted to contribute what I had found. There is an amazing amount of info on here. Thanks everyone for reading and trying to help out.

 

Clear Skies to all.

 

 

 

Attached Thumbnails

  • Optics.jpg

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