Sunday Sunshine - Seeing and Sampling June 26th

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Sunday Sunshine - Seeing and Sampling June 26th

Post by marktownley »

Sunday dawned clear at sunrise, but by 6am when I was getting setup to observe there was cloud starting to bubble up. I setup first in the back yard with the solarquest mount on the portable pier for my dose of Ha. Using the double stacked 50mm Lunt etalons on the 60mm f6 refractor, a 2x cemax barlow and the ZWO183mm using 2x binning I ran off a full disk.

ImageHa-FD-DS50-2x-cemax-zwo183mm-2x-binning-bw by Mark Townley, on Flickr

ImageHa-FD-DS50-2x-cemax-zwo183mm-2x-binning-colour by Mark Townley, on Flickr

After capturing the files I ran them through AS3 while I setup the Bresser 127L on the permanent pier round the other side of the house. This is on the western side an so sits in the shadow of the house for an hour or so after I can observe with the portable solarquest, anyways, gives me time to setup. There were clouds scudding by and meteoblue was giving seeing at around 1.6", which, wasn't far off. I masked the scope down to 120mm to give me f10, then putting the Airylab 2.7x telecentric ahead of the filter I thought I would try the zwo183mm with 2x binning. The view on the screen was boiling away but I figured if I shot enough frames something would come out. I got the following image and viewing full size you can just about start to resolve the penumbral fibrils, which, in ideal conditions is possible around 80mm in CaK. Reverse granulation is visible but there is a certain softness to the image.

Imagear13040-CaK-120mm-f27-zwo183mm-2x-binning-bw by Mark Townley, on Flickr

Imagear13040-CaK-120mm-f27-zwo183mm-2x-binning-colour by Mark Townley, on Flickr

I did try AR13038 on the limb with this combo, but the results really were mush...

So, ever the one for an experiment, I decided to do away with the telecentric, not use 2x binning with the 183mm and stop the scope down to 80mm which corresponds to a seeing value of 1.2" (120mm is 0.8") - I figured, as with the image above if I captured enough frames I should get a result. It would also give a similar image scale with both setups.

You would expect the images from the larger aperture to produce better results with more resolution? Wrong. The 80mm setup is the winner hands down. Double click to view full size in flickr, there is more detail in the penumbral fibrils and the image is not as soft. The quality values in AS3 are much higher for the 80mm images.

Imagear13040-CaK-80mm-f15-zwo183mm-bw by Mark Townley, on Flickr

Imagear13040-CaK-80mm-f15-zwo183mm-colour by Mark Townley, on Flickr

Capturing AR13038 in the limb was also much easier producing a decent result.

Imagear13038-CaK-80mm-f15-zwo183mm-bw by Mark Townley, on Flickr

Imagear13038-CaK-80mm-f15-zwo183mm-colour by Mark Townley, on Flickr

Seeing remained the same throughout the session. The Airylab telecentric is not the culprit here either, this is a great piece of glass in CaK wavelengths and when the aperture does match the seeing I have got excellent results with it (that are not soft). Moral of the story is match the aperture to the conditions, and then make sure it is critically sampled!

Cloud then became the dominant force, and I decided to pack up, jobs to do, I may get a CaK disk later on if i'm lucky to complete the set but I suspect clouds and showers will prevail.

Hope you like these and hope your skies are bluer than mine!

Mark


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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by marktownley »

And a side by side comparison to make easier to see.

Imagear13040-CaK-Comparison by Mark Townley, on Flickr

Notice the light bridge that is forming in the active region is seen easier with the 80mm setup.


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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by rigel123 »

Great results Mark, really big difference in the CaK images comparing 120 to 80mm. I would assume you should get more resolution when you are not binning since you would have more pixels per mm or am I off base?


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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by marktownley »

Thanks Warren, given it was 2x binning and pretty much 2x the focal length you would expect (for the same aperture) things to be equal in terms of resolution. If seeing wasn't capped the bigger aperture should show more detail. The other element in this was exposure time, and with the 80mm it was quite a bit shorter (less glass soaking up light?) - so maybe that is it? Or, maybe the seeing was marginally better for the 80mm images?

Either way, f15 seems to be a synergy point with my CaK filter and the zwo183mm. I'm quite tempted to pick up one of the Bresser AR-102L/1350 scopes https://www.teleskop-express.de/shop/pr ... Tubus.html I could stop it down to 90mm to get f15. I think I would be in trouble with Mrs T though for buying another scope :roll:


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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by MapleRidge »

Excellent captures all round Mark :bow

The CaK comparison certainly speaks for itself!

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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by marktownley »

Thanks Brian!

So after I did this run of images it clouded over, so I went back into the house to do some chores and grab a shower, and at this point there were some breaks so I decided to grab a few more images. First off the CaK full disk, the 100/800 APM stopped down to 53mm so the filter sees f15:

ImageCaK-FD-50mm-f15-zwo183mm-bw by Mark Townley, on Flickr

ImageCaK-FD-50mm-f15-zwo183mm-colour by Mark Townley, on Flickr

And while I was getting the full disk my Quark was warming up, so popped it on the 100/800, double stacking with the PST etalon. I took a lot of files as the clouds were interrupting every run, and they were all junk apart from this one which worked. Camera was the PGR Grasshopper with the IMX174 sensor.

ImageAR13040-Ha-DSQ-100mm-f8-imx174-bw by Mark Townley, on Flickr

ImageAR13040-Ha-DSQ-100mm-f8-imx174-colour by Mark Townley, on Flickr

Quite pleased with the haul i've had over the weekend, fingers crossed the mornings before work next week offer some pickings.

Hope you like these, and hope is sunny where you are...

MArk


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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by ffellah »

Beautiful double set of images, Mark. What you say about aperture, masking and seeing makes a lot of sense. Lovely results !

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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by torsinadoc »

Great set of images!


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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by arnedanielsen »

Beautiful work, Mark and a very good example of the importance to match aperture and sampling to the seeing!

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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by SolarHans »

Great images Mark! For a newbie like me it is good to see experiments with focal ratio/camera type like this to get a better understanding.

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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by Martin_S »

Great presentation Mark, thanks for all the extra information on sampling etc.
Last edited by Martin_S on Sun Jun 26, 2022 8:22 pm, edited 1 time in total.


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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by Rusted »

Great stuff Mark! :bow


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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by marktownley »

Thanks everyone for all your kind words!


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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by MapleRidge »

Superb results form that session Mark :bow

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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by DeepSolar64 »

Mark,
The 80mm wins hands down!! You had a very good run of images today. Congratulations!! I had nothing but clouds. You are really good at imaging.

Did your furry alarm clocks wake you up this morning? :lol:

James

P.S. Did you notice the tiny filament with the bright area under it in the NW quad in your Ha full discs? I wonder if I could have seen that visually.


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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by marktownley »

Thanks guys, cloud and rain here this monday morning.


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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by Carbon60 »

Hi Mark,
A scientific approach wins the day. This is a really nice demonstration of the balance to be struck between some important factors determining the ability to resolve detail. My approach is to try to set up each of my scope/Barlow/camera (pixel size) combinations to operate under ‘critical sampling’ conditions and then hope for the best on the day that the seeing will cooperate and provide a few excellent frames required for stacking. Your approach is to modify the scope (by masking) to match its resolving power to those of the prevailing seeing conditions and modify the rear elements, such as adding a Barlow (or not) and changing out the camera (pixel size) and/or binning to optimise the ‘sampling’ configuration in accordance with the modified scope.

We know there are other factors at play as well (exposure time per frame, number of frames captured, duration of the video capture, gain and gamma settings and so forth) all of which impact the final result, so it can be a real juggling act to bring all elements together optimally.

I imagine your approach improves the odds of capturing good frames (improving your luck with ‘lucky imaging’) given the relationship between aperture and seeing conditions. On any given day, if there are no periods of excellent seeing (allowing the larger aperture scope to image at its full resolving power), even brief ones, then the final result won’t generally be as good as that from a smaller scope (or masked scope) better matched to the conditions. I think this is what you are demonstrating, which is a really useful lesson to all of us…..that simply and blindly relying on a larger aperture to achieve maximum resolution is too simplistic and often wrong if the seeing conditions don’t allow the scope to operate at its diffraction limit.

Stu.


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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by vineyard »

That is a v interesting (illuminating? :lol:) comparison on the CaK - encouraging to see that less can indeed be more. And btw that last Ha closeup is real nice too!


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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by Montana »

You were lucky to get some sunshine Mark, great images and very interesting :bow :hamster:

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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by marktownley »

Carbon60 wrote: Mon Jun 27, 2022 7:32 am Hi Mark,
A scientific approach wins the day. This is a really nice demonstration of the balance to be struck between some important factors determining the ability to resolve detail. My approach is to try to set up each of my scope/Barlow/camera (pixel size) combinations to operate under ‘critical sampling’ conditions and then hope for the best on the day that the seeing will cooperate and provide a few excellent frames required for stacking. Your approach is to modify the scope (by masking) to match its resolving power to those of the prevailing seeing conditions and modify the rear elements, such as adding a Barlow (or not) and changing out the camera (pixel size) and/or binning to optimise the ‘sampling’ configuration in accordance with the modified scope.

We know there are other factors at play as well (exposure time per frame, number of frames captured, duration of the video capture, gain and gamma settings and so forth) all of which impact the final result, so it can be a real juggling act to bring all elements together optimally.

I imagine your approach improves the odds of capturing good frames (improving your luck with ‘lucky imaging’) given the relationship between aperture and seeing conditions. On any given day, if there are no periods of excellent seeing (allowing the larger aperture scope to image at its full resolving power), even brief ones, then the final result won’t generally be as good as that from a smaller scope (or masked scope) better matched to the conditions. I think this is what you are demonstrating, which is a really useful lesson to all of us…..that simply and blindly relying on a larger aperture to achieve maximum resolution is too simplistic and often wrong if the seeing conditions don’t allow the scope to operate at its diffraction limit.

Stu.
Thanks Stu, I like the way you put this :)


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Re: Sunday Sunshine - Seeing and Sampling June 26th

Post by MapleRidge »

Hi Stuart...

I agree with all you have posted!

It is a juggling act to make the most of the conditions, but if an effort is made to consciously attempt to make the most of the conditions/equipment then excellent results can be had.

Brian


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Photos: https://www.flickr.com/photos/185395281@N08/albums

10'x15 Roll-off Roof Observatory
Takahashi EM400 Mount carrying:
C14 + Lunt 80ED
Deep Sky Work - ASI294MM Pro+EFW 7x36/Canon 60D (Ha mod), ONAG
Planetary Work - SBIG CFW10, ASI462MM

2.2m Diameter Dome
iOptron CEM70G Mount carrying:
Orion EON 130ED, f7 OTA for Day & Night Use
Ha Setup: Lunt LS80PT/LS75FHa/B1200Ha + Home Brew Lunt Double Stack/B1800Ha on the Orion OTA + Daystar Quantum
WL, G-Band & CaK Setup: Lunt Wedge & Lunt B1800CaK, Baader K-Line and Altair 2nm G-Band filter
ASI1600MM, ASI432MM, ASI294MM Pro, ASI174MM, ASI462MM
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