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Tuning my Coronado 90DS

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#1 Mike I. Jones

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Posted 04 July 2020 - 05:53 PM

Got my new C90DS in and temporarily mounted on an old Orion EQ mount (because it's the only one I had with a Vixen dovetail).  I sweltered in the Texas sun learning how to use the finder, and I am definitely going to improve on that!  I got the sun in the FOV of the 25mm Cemax eyepiece, and figured out how much I had to pull out the focuser to reach focus (it's way back there).  I saw a disk but couldn't see any detail on it, partly because of the sun blazing onto my head and viewing eye.  Definitely have to make some sort of hat-brim shield to keep the sun off of me while viewing.


I turned the etalon to each end of its limit trying to see either disk or limb details and saw neither.  So I have some questions:

1.  As seen from the eyepiece looking forward, which way do I turn the etalon for proms?  To the right or left?

2.  How quickly does the visibility of either proms or disk come into view?  Is it very quickly, like barely a 1/10 turn, before winking out, or is the rotation range larger?


I am waiting on my ZWO mono camera to get here, then I can set the scope out in the sun and view the image on my laptop in the shade.  But for now I'm trying to enjoy it visually, without much luck so far.


Thanks to all experienced Coronado users for any help!


C90DS has arrived June 30 2020.jpg

#2 bigdob24



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Posted 04 July 2020 - 10:31 PM

I’ve got a DS Lunt and I take off the DS and tune the scope with the SS then put the DS on and tune it for the best view.

Im sure some Coronado users will post.

You need to make a sun shield to attach to the scope , here’s a pic of mine to give you an idea.

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#3 BYoesle


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Posted 05 July 2020 - 09:16 AM

Hi Mike,


I'd forget about imaging until you get a bit of experience with visual observation. Try "imaging" via drawing the activity you see, and you'll gain a lot more appreciation of the subtle details and their minute-by-minute changes you can witness in H alpha. By the time activity picks up in a year or so, you'll be ready to move on to electronic imaging.


H alpha 3 16 1978 drawing adj sm.jpg


Until you get experienced with what a true on-band H alpha disc surface looks like, tuning with little solar activity is more difficult, so don't get discouraged. Prominences can be seen at a wide range of tuning settings, so when present, getting filaments darkest is generally the easiest way to determine when you are exactly on-band:


P Zetner SHS H alpha crop SM.jpg

Peter Zetner (click for larger)


I'd also suggest the tune-each-etalon-separately technique until you get "muscle memory" for the tuning process. Remember tilt is generally bad for etalons, and using the rich-view mechanical pressure tuning with as little tilt as possible is better for the primary etalon. But this can be tricky depending on your particular etalon and elevation. Too much tilt will create "banding," and too much rich-view pressure will create uneven contrast, and risks cracking the ERF! So start out with little to no tilt or rich-view pressure and go from there. With a single etalon the image may be a bit bright to see subtle surface detail, so use some ND filtering (or sunglasses cool.gif ) to reduce the image brightness if necessary. It also helps to eliminate any stray light coming in from the side of the eyepiece, so rubber eye-guards, cupped hands around the eyepiece, etc. are your friend (along with a good solar hat). The shield on the scope is good idea as well, especially for solar outreach and events, but can act as a sail and affect image steadiness even with a small breeze unless your mount is massive. 


SM140 90 w Bob sm2.jpg


Once you have the primary etalon tuned, add the secondary etalon and then tilt the secondary etalon just enough to get any secondary ghost reflections off the main image. Remove both etalons and use just the secondary etalon - keeping the tilt unchanged - and use only rich-view tuning to get it on band again. Then reassemble the double stack. The best view is when both etalons are tuned exactly to 656.28 nm. Once you become proficient at knowing what-does-what with tilt verses rich-view, it will become easier.


Hope this helps waytogo.gif

Edited by BYoesle, 05 July 2020 - 12:44 PM.

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#4 Mike I. Jones

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Posted 07 July 2020 - 03:12 PM

Thank you so much for the detailed reply, Bob, very helpful!!!  Weatherman predicts a few days in a row of clear skies here in Fort Worth, so I will give all you say a try.  I like the sunscreen posted above to keep the heat and light off me, plus your "solar hat" looks great.  I need to understand more about the Coronado filter stack operation.  I got my ZWO ASI1600MM camera in today, loaded up all the software and it works fine, so maybe I'll plunge into imaging a little sooner.  

Gonna hold off posting images for a while, the pictures here are simply marvelous!



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