Saturday Solar 17th August - Celestron Omni CaK testing

[Montana]

Like others have said Saturday afternoon was fairly decent for solar viewing in Cheshire. There were very strong winds and lots of fluffy cumulus floating by but the bits in between were good. Afternoon solar viewing is never good for me as the Sun is directly over a neighbours roof so seeing is always bad but I can't complain as it is the first weekend sunshine for solar in about 3 months!

So the hubby and I decided to dig out his iOptron mount with his Celestron Omni 100mm which we bought for him to view CaK with. He could never focus and gave up about 2 years ago, so with renewed vigour after the CaK wedge repair we blew the dust off and set up. It took him a while to remember how to use the mount but I eventually found the Sun for him. We discovered that the mount seems to have seized up a bit (lack of use) as we had up and down and left movement but no right movement. After a bit of flexing back and forth we got it going but it kept seizing on regular intervals all afternoon which was frustrating.

First out we tested the DMK41 and I took a full disc which consisted of 12 panes although I took 14 but didn't need two. It wasn't too bad and I felt focus was fairly easy. I did not have the contrast I did with the TEC140 stopped to 100mm but I wonder if I stopped the Omni down to 80 or 90mm whether it would improve. Overall I thought it was fine not stopped down.

2019-08-17 CaK full disc f colour by Alexandra Hart, on Flickr

2019-08-17 CaK full disc imp a by Alexandra Hart, on Flickr

Click through to Flickr for a bigger version.

I then tried the 5x powermate and that was daft, there was no way to achieve focus. I don't no whether that was very poor seeing or spherical aberration. But gaps in cloud didn't allow for any other testing. I then tried 2x Barlow and that wasn't too bad.

2019-08-17 16-08-48_f colour by Alexandra Hart, on Flickr

2019-08-17 16-08-48 by Alexandra Hart, on Flickr

but nothing like the TEC, but then conditions were totally different so it isn't really a fair comparison.

I then tested the PGR Chameleon and it was a much better scale for the full disc imaging and the gamma control worked like a dream, however I only managed one panel before the Sun vacated the garden for the evening.

We also tried to test the DMK41 for use with the Hubby's Apple computer but couldn't get it off auto exposure so that is work in progress with James F on Stargazer's Lounge.

So on the whole a good testing session, lots of bugs but overall we are getting there amazing how most of the time the Hubby sat with a G&T while I did all the testing but it was good fun

Alexandra

[xn44]

Good images Alexandra! I want good weather !

[MAURITS]

Good test session Alexandra, nice images.

[eroel]

Alexandra, a very nice testing session.
Best wishes,
Eric.

[krakatoa1883]

Nice discs Alexandra. If the 100mm is the ED version it should be capable of doing much better than that in fine seeing conditions. I have it and in CaK or CaH is really fine at full aperture.

[marktownley]

Nice images Alexandra, glad you got some sunshine.

The TEC at 100mm is always going to work better than the Omni at 100mm, not just the TEC is a mighty fine scope (in comparison to the Omni), but simply down to optics, a lens using its full aperture will show more spherical aberration than one that is stopped down and not running at full aperture. If I was you i'd be using the TEC (stopped down) as often as possible, the Omni only used as a 'grab and go' in between the showers. I find my 100mm Tal stopped down to 80mm will give better results than running at 100mm on all but the best seeing conditions, SA gives a 'haze' across the image that post processing doesn't shift.

Don't ever be afraid to stop down the aperture in CaK to support the seeing, running at an aperture that resolves greater than the seeing will allow is of no benefit and achieves nothing.

Similarly, try running the Omni at 65mm side by side with the lil' Tecnosky 65mm scope you have, I think you will be surprised how much better the Omni will perform compared the smaller scope. If you want to see what spherical aberration looks like this is a good test, the Tecnosky will show it in buckets. My 60mm f6 is diabolical full aperture in CaK, barely acceptable stopped down to 40mm, but even side by side with the coronado 40mm f10 tube looks awful.

Just need more clear skies!

[Carbon60]

Hi Alexandra,

The FDs look pretty darn good to me. I can see you were struggling with the close views, but if your seeing was like mine, it’s no wonder. Getting Sun is one thing, getting ‘quality’ Sun is something else.

Stu.

[ffellah]

A testing session with very good results, Alexandra and hubby

Franco

[allhoest]

Interesting test.
I muss confess that I never came to the idea of stepping down the aperture.
I could never get good results with a x5 barlow.

CS
Alex

[Montana]

Thanks everyone
Honestly the seeing was bad, but it is never good late afternoon for me so I was pleased with these results

Alexandra

[MapleRidge]

Great test session Alexandra and Darren...

The FD's look good, and CaK isn't very forgiving if you try hi res in shoddy seeing...the 2x barlowed images look pretty good in the circumstances. Stopping it down would be a great test next time out.

Brian