Improving my CaK scans

[Alun_H]

Clouds cleared earlier today so I took advantage to try to improve the images I get when scanning in the CaK wavelength as a majority of them are blurry no matter what slew speed I use to force the scan. Firstly I run with the full aperture of the 72ED,then I reduced the aperture to 50mm,and what a difference,the image is that much clearer and sharper. Also succeeded with stacking four images! Once again comparison images are raw,and the stack has had brightness levels adjustment and orientation correction.

Alun

11_14_28Z_shift=0_72-full.jpg (249.41 KiB) Viewed 1346 times

11_19_51Z_shift=0_72-reduce-to-50.jpg (250.25 KiB) Viewed 1346 times

CaK-stack-of-four-221116.jpg (156.12 KiB) Viewed 1346 times

[thesmiths]

That is a really nice demonstration! The 72ED has a really short focal length, 420mm (f5.8), I believe. Arguably, it might look even better with even a little smaller aperture, at f10.

By the way, if you do stack, I think you really need to do a bit of sharpening (ImPPG or just unsharp mask) or the image will look softer than unstacked. Maybe add a slightly sharpened version of the last image in this post? The result should show lower noise than the unstacked. It looks like the 4 frames you stacked have very good registry.

[christian viladrich]

Nice demonstration indeed !

You can probably push it one step further :
- with a 50 mm aperture, the resolving power is 1.7 arsec,
- with a 40 mm aperture, the resolving power is 2.2 arsec.

Your sampling is about 1.3 arsec/pixel, meaning that your resolving power is at best 2.6 arsec.

I would suggest trying a 40 aperture.

Christian

[Alun_H]

Thank you Douglas.

Yes,the 72 is f/5.8 and with the 50mm aperture the focal ratio is around f/8.4,a reduction to 40mm will bring the scope to f/10.5 so will try that the next clear spell. I used your Version 3.7 to crop square and Autostakkert to stack four out of four images,wish now I had collected more scans but cloud moved in. Here is the stacked version wavelet sharpened in Astrosurface with noise reduction.

Alun

CaK-stack-of-four-221116_proc.jpg (433.24 KiB) Viewed 1334 times

[Alun_H]

Thank you Christian.

I was typing reply to Douglas before I saw your comment, I will try the 40mm mask next clear spell,whenever that will be as rain is forecast for the rest of the week.

Alun

[thesmiths]

The sharpened one is a real beauty!

I try to get at least 6 or 7 frames to stack. More than that doesn't usually improve things. But under normal circumstances, I have to dispose of 25% because of scanning or camera errors. But if atmospheric conditions are good and there are no instrumentation issues, I have occasionally stacked 16/16. But better to not let any really bad frames into the stacking.

In general, I think common telescope optics work best at f10 at the CaK wavelength. So maybe aim for 42mm aperture.

[christian viladrich]

Thank you Christian.

I was typing reply to Douglas before I saw your comment, I will try the 40mm mask next clear spell,whenever that will be as rain is forecast for the rest of the week.

Alun

If you have enough time, and weather permiting, it would be great to have the whole comparison 60 mm vs 50 mm vs 40 mm on the same day.

The processed image is great !!

PS : have you refocused the collimating lens on Ca K ?

[Alun_H]

Thank you Douglas,Christian.

I had to delete a couple or so scans due to the tracking at 16x jumping now and then on the EQ6,I put this down to using the handset and the buttons
on the thing not making electrical contact,need to open it up and clean the contacts. Either that or connect to EQMOD and use the gamepad to slew the mount. The four images I used though were virtually identical with no distortion to the disk,I used Sharpcap this time rather than Firecapture and whether or not that made a difference I don't know. In regards to focusing on CaK,no the collimation lens has been focused on the slit after having focused the camera and 125mm lens on the Moon,all the focusing of the spectrum one end to the other is done by the camera alone.
Comparison of the three apertures is on the to do list

Alun

[marktownley]

Great thread Alun!

Welcome to the world of spherical aberation at 393nm. Your 72mm f6 will be riddled with it at full aperture and will only improve as you stop the aperture down. Aim for 40mm like others say. At this scale you are certainly not losing any resolution by stopping down.

[Alun_H]

Thank you Mark,Am more than happy to reduce to the 40mm for the CaK but at end of day I need to get a short focal length four to six inch Newtonian and rip the coating off the mirror

Alun

[marktownley]

Thank you Mark,Am more than happy to reduce to the 40mm for the CaK but at end of day I need to get a short focal length four to six inch Newtonian and rip the coating off the mirror

Alun

You planning on using the solar newt for higher res CaK?

[Alun_H]

You planning on using the solar newt for higher res CaK?

Along with the Lunt CaK module once I get the filters sorted on it,SHG addiction has put hold on that,but mainly just to rid the refractors and try the Sol'Ex with a solar newt.

Alun

[Montana]

Oh WOW!!!!! jaw dropping images Alun

Alexandra

[Alun_H]

Thank you Alexandra.

Alun