Solar images 27th May 2021

[Carbon60]

Mark T recently reminded me to take 'critical' image scale into account, matching focal ratio and camera pixel size to achieve the best overall degree of resolution. Taking this onboard for calcium K-line imaging I made a 40mm mask for my 72mm Altair Astro Lightwave with a native focal ratio of f/6.

Objective Mask by Stuart Green, on Flickr

The idea of taking a 72mm objective and reducing it to a 40 mm might seem a waste of glass, but Mark pointed out the additional benefit of reduced spherical aberration.

What a difference!

Here's the result (at 40mm).
20210527_CaK_FD_40mm by Stuart Green, on Flickr

Compare this image taken at 72mm (all processing the same as the 40).
20210527_CaK_FD_72mm by Stuart Green, on Flickr

...and this one which is the same 72mm image with 'optimised' sharpening.

20210527_CaK2_FD_72mm by Stuart Green, on Flickr

Neither of these at 72mm match the 'resolution' of the image taken with the mask when you zoom into the detail. Thanks Mark.

Here it is in colour:

20210527_CaK_FD_40mm_Colour by Stuart Green, on Flickr

I should add that the conditions were average to poor as these were all captured late this afternoon.

I also managed to capture a WL image of the two active regions on my Tecnosky 125.

20210527_WL_FD by Stuart Green, on Flickr

...and in the morning (first thing) I even managed to capture an image of this same region in Ha on the 250mm RCT. Not ideal with the conditions and I failed to take a flat, leaving some residual 'texture' in the background from the camera.

20210527_Ha_RCT_AR2824_AR2826 by Stuart Green, on Flickr

The weekend is looking good weather wise, but of course these active regions are rotating out of view.

Thanks for looking.

Stu.

[MAURITS]

Very sharp images Stu.

[DeepSolar64]

All of these look really nice Stu. That 40mm mask works!

[arnedanielsen]

Very good images and an interesting topic, Stu!

Thanks for sharing!

Best regards,
Arne

[Stardust5858]

Lovely captures Stu, yes, it's interesting how masking the objective make's a difference, I couldn't get my head around it at first but the results speak for themselves. Thanks for sharing.

[Ivan]

Hi Stu

This diaphragm works great. The difference was obvious even on the small screen of the phone I was looking at.

Ivan

[EGRAY_OBSERVATORY]

Thanks Stu for your excellent captures of the action today.

Terry

[p_zetner]

Nice captures, Stu, and an interesting result of the aperture study in Ca. It makes quite a difference.
Cheers.
Peter

[Astrophil]

Very good images, Stu. The results from the reduced aperture test surprised me. Makes sense to me now but does this mean that we should listen to Mark?

Phil

[H-Alpha]

Excellent work and mask comparison Stu!!!
Thanks a lot for sharing.
I am struggling with mask-no mask the last days, and did not have the time to make a comparison. (130 mm --> 100 mm).
I will soon after your very useful example!
Best wishes,
Alexandros

[Montana]

Am I missing something? when I zoom in I see much nicer detail in the 72mm vs 40mm?

That's a beautiful Halpha

Alexandra

[MapleRidge]

Very nice set of images Stu...great captures

Brian

[Carbon60]

Very good images, Stu. The results from the reduced aperture test surprised me. Makes sense to me now but does this mean that we should listen to Mark?

Phil

Ha....ha....Yes, I guess so.

[Martin_S]

Very good imaging Stu the 40mm aperture stop makes a real difference.

Martin

[Carbon60]

Am I missing something? when I zoom in I see much nicer detail in the 72mm vs 40mm?

That's a beautiful Halpha

Alexandra

Many thanks, Alexandra.

Under these conditions and with this processing it appears that the masked image has more of a 'cauliflower' texture whereas the images taken at 72mm are less well defined, even a bit 'dotty'. Will it be the same result under better seeing conditions or with further micro-tweaking of the ImPPG parameters, I'm not sure and it remains to be seen, but I was surprised at the improvement I saw in this example.

Stu.