Coronado SM40 and Solarmax II 60mm working great, but why?

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twinship
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Coronado SM40 and Solarmax II 60mm working great, but why?

Post by twinship » Mon Jul 10, 2017 6:11 pm

Sorry I haven't posted in awhile, but better Ohio weather has me out observing much more. I have a new SolarMax II 60mm DS scope which has had unacceptably low contrast (BF15) and quite an old (but good) SM40 SS (BF5) that has always worked well. I tried various adjustments in tuning the SM60, with no results. More or less in desperation I tried switching the BF15 with the BF5 on the 60mm scope. Well, now the 60mm seems to be working very well--excellent contrast and detail--with the BF5. An additional benefit, the SM40 with the BF15 is now working noticeably better than before. Believe me, I'm not complaining, but what did I do?

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Re: Coronado SM40 and Solarmax II 60mm working great, but why?

Post by marktownley » Mon Jul 10, 2017 7:36 pm

Sounds like the blocker is rusted to me!
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Re: Coronado SM40 and Solarmax II 60mm working great, but why?

Post by twinship » Mon Jul 10, 2017 7:57 pm

Which one? I can believe it with the 60mm BF15, since contrast was so low, but it isn't low when used with the 40mm. The BF5 seems to be working very well with the 60 mm. The BF5 is 17 years old, the BF15 brand new. Je ne comprend pas, at least not yet. I don't think I see, if I'm looking in the right places as suggested by other posts, any rust on either scope.

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Re: Coronado SM40 and Solarmax II 60mm working great, but why?

Post by Montana » Tue Jul 11, 2017 7:06 am

All blocking filters are slightly different and all etalons are slightly different. The blocking filter has to perfectly match the etalon. Remember the etalon produces light in waves, like a comb shape. The blocking filter has to fit exactly over the 656 peak and block all the other peaks. If it isn't a snug fit then contrast will be low (leakage of continuum light from the next comb peak).
When Ken from Solarscope came to my garden he had quite a few blocking filters in his bag and we looked through them all. Some were amazing contrast and others were not. This is why Ken tests all his etalons and matches the perfect blocking filter to the etalon. Commercial runs will just churn out blocking filters and pop them in the box at random. You have now established your perfect combination.

Alexandra

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Re: Coronado SM40 and Solarmax II 60mm working great, but why?

Post by twinship » Tue Jul 11, 2017 4:36 pm

I hope you're right, Alexandra. It certainly wasn't anything I did on purpose! I guess this is cosmic compensation for having destroyed a previous SM60 II when it slid out of the mount on to a concrete sidewalk, breaking all (and I mean ALL) of the optical elements. What a horrible sight!

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Re: Coronado SM40 and Solarmax II 60mm working great, but why?

Post by Live_Steam_Mad » Sun Jul 23, 2017 6:53 pm

Montana wrote:
Tue Jul 11, 2017 7:06 am
All blocking filters are slightly different and all etalons are slightly different. The blocking filter has to perfectly match the etalon. Remember the etalon produces light in waves, like a comb shape. The blocking filter has to fit exactly over the 656 peak and block all the other peaks. If it isn't a snug fit then contrast will be low (leakage of continuum light from the next comb peak).
When Ken from Solarscope came to my garden he had quite a few blocking filters in his bag and we looked through them all. Some were amazing contrast and others were not. This is why Ken tests all his etalons and matches the perfect blocking filter to the etalon. Commercial runs will just churn out blocking filters and pop them in the box at random. You have now established your perfect combination.

Alexandra
...but surely you can tune your Etalon to match the Blocking Filter? If performance is still poor when tuning is tried, is the Blocking Filter simply then "out of band" i.e. poorly "quality" of the Blocking Filter? i.e. BF not to spec, frequency is wrong for the BF? Just trying to figure out why some of these solar scopes are such poor performers.

Regards,

Alistair G.

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Re: Coronado SM40 and Solarmax II 60mm working great, but why?

Post by Montana » Mon Jul 24, 2017 7:13 am

I think it is the fact that making these items is an art, not a pure exact science. Ken said all the coatings on the blocking filters are ever so slightly different (this is fractional remember). Also every etalon tuning and wavelength is different due to using thin slivers of naturally occurring mica as spacers - it is a natural material and so random. Perhaps you have an etalon with a wide band (broad shoulders at the base of the curve - this is different to the FWHM) and the blocking filter is slightly wider than normal, then the result will be a bad contrast (continuum leakage) but put that same blocking filter on a tight peaked etalon (no broad shoulders at the base) and the result will be a nice contrast as the wideness of the bad blocking filter doesn't matter. Then vice versa, say you had a bad etalon (wide shoulders at base of peak) but a tight narrow blocking filter then immediately you get good contrast as the wide base is being chopped out, but then a good etalon and tight blocking filter will also give a good end result. This is very basic but hopefully you will understand and why Ken used to match his good and bad blocking filters to match the etalon.
Alexandra

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