Review of 3 Coronado 90's

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mspingy1
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Review of 3 Coronado 90's

Post by mspingy1 »

I've been an owner of some of the finest optical instruments on the market over the last several decades (TEC, Questar, Stellarvue, Spica Eyes reflectors, Optical Techniques, and others), and I wanted to leave some comments regarding several Coronado 90's that I have had the time to evaluate over the last several months. I'm sure many of you have heard some negative comments regarding some of the Coronado's that have been produced by Meade over the last several years. I had recently spent time with the following 3 instruments:

Coronado 90 III DS BF30
Coronado 90 II single stack BF 15
Coronado 90 II DS BF 30 (my current scope)

I have also been an owner of:

2 different Quarks
1 Lunt 80 DS
1 Daystar .6 ATM

Other than the Daystar, I had very poor results with the other 3. The Lunt 80 was even sent back to the company for a tune up and it came back in the same miserable condition. When I contacted Lunt, they said that the scope met company standards! Both quarks had very nonsymmetrical filters; large areas on both filters that did not filter properly. (No wonder these filters are the most sold solar items on Astromart!)

I must say that all 3 Coronado's that I have tested over the last short period of time were all amazing instruments; the double stack units provide the finest views of the sun I have ever encountered.

One aspect of the Coronado's that I absolutely love is the Rich Field tuning knob located on the side of the tube. It's ability to quickly shift the frequency band in seconds to reveal various surface detail is mind blowing. The Lunt is much harder to fine tune the frequency due to the tightness of the pressure tuners. The Coronado was very easy to tune. Following the instructions in the manual, the double stack unit was adjusted first, followed by the tilt tuner, and lastly the Rich field tuner. From this point, all I ever need to do is adjust the Rich Field tuning lever that is conveniently located on the side of the tube in order to emphasize whatever surface detail or prominence detail I want to view. I could not give the Coronado's anything but my highest recommendation. I was very skeptical to buy a Coronado's due to poor reports of some that were manufactured by Meade. I have also had an opportunity to look through our astronomy club's Coronado 40mm, a PST, and a 60mm DS - all performed wonderfully.

Without a doubt, a Coronado instrument would be my first choice if I was to buy another solar instrument in the future.

I currently use a Stellarvue SVX 152 that has a strehl of .993 to view the sun in white light using a APM Hershel wedge, and a 3year old Coronado 90 II DS BF 30 for HA. I have included a photo of my setup on an iOptron 120 mount.
20220917_114127[1].jpg
20220917_114127[1].jpg (7.77 MiB) Viewed 2559 times


Stellarvue 152 mm
APM Hershel Wedge
Coronado II 90 mm BF 30 DS
iOptron 120 mount
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Re: Review of 3 Coronado 90's

Post by marktownley »

Glad the coronados work for you, my personal experience of solar scopes, and I own and have owned a lot! Is that there is huge variability between all of the manufacturers.


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Re: Review of 3 Coronado 90's

Post by Montana »

I agree with Mark, it seems to be a very expensive lottery ticket ;)

I love my PST and would never part with it for a million pounds :)

Alexandra


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Re: Review of 3 Coronado 90's

Post by thesmiths »

I'm also guessing Ca-K filters have quite some variability also; there seems to be quite a range of results, even with those that have not been modded.

I never liked my H-alpha PST that much but I do love my Ca-K PST (I would part with it for a million though :D ).


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Re: Review of 3 Coronado 90's

Post by mspingy1 »

Yes Mark and Alexandra, I agree with both of you. That is the problem with buying a Ha scope - the variability of the performance of the scope. Several years ago, when I was an optician for Celestron, I bought my first Ha product - a .6 ATM. Soon after I bought the filter, I had the pleasure of going out to lunch with Del Woods the designer of Daystar products. I remember asking him how he would create a PE grade filter (the best quality filter he offered at the time). He said it was the luck of the draw. Maybe 1 out of 100 filters that were manufactured met the high quality for the PE series. It was clear from that conversation that Ha solar filters, even though they continue to improve over the years, are probably the hardest astronomical product to produce, therefore, the great potential for companies to cut corners to save money.


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Coronado II 90 mm BF 30 DS
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Re: Review of 3 Coronado 90's

Post by marktownley »

mspingy1 wrote: Sun Sep 18, 2022 10:08 pm Several years ago, when I was an optician for Celestron, I bought my first Ha product - a .6 ATM. Soon after I bought the filter, I had the pleasure of going out to lunch with Del Woods the designer of Daystar products. I remember asking him how he would create a PE grade filter (the best quality filter he offered at the time). He said it was the luck of the draw. Maybe 1 out of 100 filters that were manufactured met the high quality for the PE series.
Interesting to know! Our observations are correct then ;)


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Re: Review of 3 Coronado 90's

Post by Bob Yoesle »

The mica etalon filters are more dependent on the quality of the raw natural material the etalon is made from, it's homogeneity, purity, color, etc. - and then the "luck" of how well a particular mica slice is cleaved and the resultant smoothness of the cleaved surface, and the lack of wedge between the faces. This is where Del's 'one out of one hundred' statement came from.

For the etalons made from manufactured glass materials, these properties are a little more controllable, and polishing smoothness and flatness are qualities that can be perfected with enough time and effort. These etalons will also need good coatings which do not distort the etalon faces, and in the air-spaced etalons, the spacer thickness uniformity is just as important in maintaining the uniformity of the etalon gap. These parameters are where the variability comes in, and the time and effort devoted to getting these right are what results in the variability to produce consistently good etalons.

Tuning methodology and implementation also come into play, with temperature lag, f ratio CWL shifts, variable mechanical pressure variation tuning, and excessive tilt-tuning issues all becoming part of the mix.

High quality and consistency comes at a high price in etalons. When consumer demand is for more inexpensive products at high sales volumes, consistency and quality become much more of a random "luck" proposition. Other than a rather meaningless generic FWHM "bandpass" specification which takes an actual spectroscopic level evaluation to determine, the average customer has no definitive way to evaluate any particular etalon other than their own subjective evaluation based on experience. In most cases there is no individual etalon test report with finesse and transmission plots, etc. to go by. You just get what you get and hope it works well -- and that you're the lucky one who gets a more randomly good example.

Unfortunately, since MEADE took over Coronado, I have found they generally have poorer sample-to-sample consistency, compounded by excessively high CWL's and richview tuning issues.

Bob


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Re: Review of 3 Coronado 90's

Post by mspingy1 »

Bob, what are excessively high CWL's?


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Re: Review of 3 Coronado 90's

Post by Bob Yoesle »

These are etalons which have a tuning with a central wavelength that requires excessive tilt and/or richview mechanical pressure tuning to be brought on band. This can produce uneven contrast across the solar disc. Almost every MEADE etalon I have viewed through requires significant tilting to come on band.

Additionally, in my limited experience with the larger non-PST richview tuned etalons, it only applies mechanical pressure to the central spacer, which deforms the etalon gap and widens the etalon bandpass. Ideally pressure would be applied evenly to both the central and peripheral spacers, but there is no pressure whatsoever applied at the periphery of the SMII and SMIII richview etalons.

The richview tuning would only be suitable if the etalon already was nearly on-band with a CWL just slightly high, and needed a minimal amount of pressure to get on-band, and thereby not creating significant etalon gap non-uniformity. But then again if this were the case, tilt tuning alone would be sufficient more often than not.

Richview tuning originated with the David Lunt era Coronado Tucson internal etalons (and the PST), and these were made with more exacting CWL standards that were very close to being on-band to begin with, but could not be tilted easily due to their internal placement within a collimator system.

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Re: Review of 3 Coronado 90's

Post by DeepSolar64 »

I am really glad to hear your very positive experience with Meade Coronado. I have a double stacked SMII60 and a double stacked SMII90. I have overall really enjoyed my scopes, especially visually and the SMII90 does wonderfully on prominences. I have however had some experiences that leave me wondering. I do often have trouble getting the entire disc evenly on band and evenly illuminated. This is especially noticeable during imaging. Visually the scope can be moved to show all the details visible in a " sweet spot " but this often spoils an image. I usually think it's most likely something I am doing wrong since I am relatively new to Ha solar observing and especially to imaging but despite other's advice and three years of practice I still find tuning and getting an evenly illuminated field difficult. And like Bob has stated I have noticed that it does often take a considerable amount of tilt to get mine on band. I also find tuning much easier, especially for imaging, in single stack.

Whether it's me or my scopes or both I do get frustrated while imaging sometimes but I can get around it often with very satisfactory results while visually observing through the scopes. And like I said before the performance with proms in single stack with the 90 is impressive. I don't seem to have trouble tuning in on those, visually or imaging.

It sucks that the manufacturing of etalons is so variable. There should be a set standard and not a low minimum standard either. They could at least be honest and state some thing like " suitable for visual but not for imaging ". Pedro Re' comes to mind with his small SolarScope saying it's good for visual but not so much for imaging. I found that surprising because SolarScope has a good reputation for high quality etalons. But I guess again it falls to variability issues in materials and manufacturing.

Though I get frustrated sometimes. I get I don't bitch too much. Overall the Coronados do their job. I can see all the solar features in Ha and it has been and still is a learning experience. Those scopes have been an eye-opener on the Sun for me. I still recommend them.

Would flats help in evenly illuminating the field for imaging work? I know it has no effect on tuning.

James


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Orion 70mm Solar Telescope
Celestron AstroMaster Alt/Az Mount
Meade Coronado SolarMax II 60 DS
Meade Coronado SolarMax II 90 DS
Meade Coronado AZS Alt/Az Mount
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Losmandy AZ8 Alt/Az Mount
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Re: Review of 3 Coronado 90's

Post by Montana »

Yes James, I use flats all the time with the Solarscope

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Re: Review of 3 Coronado 90's

Post by DeepSolar64 »

Montana wrote: Tue Oct 18, 2022 10:56 am Yes James, I use flats all the time with the Solarscope

Alexandra
I need to learn to do that. Can you use flats with short video files? I doubt you can with single frame captures.

JP


Lunt 8x32 SUNoculars
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Celestron NexStar 102GT with Altair solar wedge
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Re: Review of 3 Coronado 90's

Post by Montana »

Usually it is part of the stacking process in Autostakkert James

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Re: Review of 3 Coronado 90's

Post by DeepSolar64 »

Montana wrote: Tue Oct 18, 2022 4:07 pm Usually it is part of the stacking process in Autostakkert James

Alexandra
Ok. I thought so. AVIstack has a place for flats as well.


Lunt 8x32 SUNoculars
Orion 70mm Solar Telescope
Celestron AstroMaster Alt/Az Mount
Meade Coronado SolarMax II 60 DS
Meade Coronado SolarMax II 90 DS
Meade Coronado AZS Alt/Az Mount
Astro-Tech AT72EDII with Altair solar wedge
Celestron NexStar 102GT with Altair solar wedge
Losmandy AZ8 Alt/Az Mount
Sky-Watcher AZGTI Alt-Az GoTo mount
Cameras: ZWO ASI178MM, PGR Grasshopper, PGR Flea
Lunt, Coronado, TeleVue, Orion and Meade eyepieces

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