SharpCap Forums

By now I presume it's known that I do like to experiment with things. I just try things and see if it works.
So of course I had to try my new TeleVue 2" Powermate 4x on a deep sky object with my Zwo ASI071MC Pro camera. The combination is far from perfect, the camera has smaller pixels and will give big stars then.
Decided on M13. It was not in the perfect backfocus of the OTA, so the result is f/35 (FL 6992mm), a FOV of 0,1936 x 0,1286 degrees.

And I was not disappointed: of course the stars were big but I could really go deep into the core without any overblown stars. But the smaller stars were not showing, so it was a bit "empty".
Decided then to merge it with my f/10 data (see viewtopic.php?t=5366 ) by blowing that up and merging it with the f/35 data.
Now more is showing. Still big stars but it's more complete now and in the core there are many visible, individual (and round ) stars.

And that gave this result. The "propeller" is also there and it gives a good reference to what the scale is.
It's in grey scale because the colors did not work well with merging.
The big 4890 x 3226px version is here: https://i.ibb.co/M6F25Gy/M13-f35-deep.jpg

Menno




Meade LX200 8" f/10 ACF
Ioptron CEM25EC mount
TeleVue 2" PowerMate 4x
Zwo ASI071MC Pro camera
Baader IR/UV Cut filter

SharpCap Pro
42 x 30sec / Gain 200 / Offset 10
20 darks, 50 (dark)flats.

Stacked with DeepSkyStacker

Merged this with f/10 data in Photoshop.

Menno,

It's great to have a large aperture. Your 200mm scope is able to resolve the tightly packed faint stars near the core while my 71mm scope only shows a glowing mass. It just illustrates the importance of proper telescope and camera selection for the task at hand.

Brian

HI Brian

Yep, but it takes some "playing" though. I have my initial settings (which are based on gut feeling ), I then make a few captures and then stack those and (if needed) I adjust the settings. But with objects like M31 it's always a trade off: do I want to show it in it's full glory with the faintest stars visible or do I want to see the stars in the core. When in full glory, I also have a blown out core.
But of course with 200mm and long FL it's easier than with a 71mm.
And yes, camera / scope combi is important. Now that I have a Zwo ASI482MC, I can do better planetary nebulae for instance (not with the Powermate). That camera has big pixels (5.8µm) which suits the long FL way better.
So, more than enough to experiment with

Menno

Hi Menno,

Re "Glory vs Blowout": If the core blows out in a single frame then lower the exposure until it doesn't. Stack, stack, and stack some more until 20th magnitude stars are clearly visible having little to no noise. Once you've achieved a high dynamic range stack that brings out the "glory", then use post-processing tools to compress the dynamic range so that it "fits" within the DR of most monitors which generally have poor DR. If you don't do that step then all of your integration time is wasted. Star clusters need to be treated differently than galaxies and nebulae due to their huge DR.

Brian

Menno

Nice images and write-up. M13 - another 'easy' object which turns out to be quite tricky to capture and process.

Dave

Hi Menno,

Agree with comments above. M13 is actually pretty difficult - showing the fainter stars, resolving the core, fitting the whole picture into a dynamic range that works -- and getting the colour right. M3 and M94 are arguably more difficult though because they have tighter cores --M3 I think some stars only 1.2-1.5 arc sec apart? I hope to have another go later in the month -- I think these are targets where deconvolution might also be a useful tool to try?

Tim