Jupiter and Saturn 1 Oct 2021 - Can you give me some advice ?

[GrahamD]

Jupiter and Saturn from Friday night.

Still very much a work in progress, both were shot with the Celestron C8 with 2.5x Powermate. ASI 462MC Camera, controlled through Firecapture.

I still can't work out why I'm not getting them sharp, I think they are in focus, and I think I've successfully Collimated the scope on a Star (Altair), so it's either "seeing" or, as I'm beginning to suspect the heat coming off the roof? - Any thoughts ? - I'm imaging from my back garden in West Sussex.

Also with regards to heat coming off roofs or conservatories, does anyone know how high above the roof does the heat rising cancel itself out with the general atmosphere ?

Jupiter 3007 frames captured, stacked the best 50% 10.45ms, Gain 301

Saturn 21985 frames captured, best 50% stacked in AS3, Exposure 29ms, gain 339

Graham

[PeterCPC]

"I think I've successfully Collimated the scope"

Do you not know? Have you got the concentric rings with equal spacings? Assuming collimation is ok I would think that the seeing is the issue. The heat rising off the roof may make the image wobbly but I don't think that's the issue.

[Nik271]

In this cooler weather, I expect roof tiles will be near ambient temperature within 1 hour of sunset. Chimneys and flutes venting heat plumes from gas heating in the cold season are also responsible for poor seeing. 

A C8 should produce better images than these, but only in good seeing. Yesterday (Friday) was ok in Oxford, but nothing special there was quite a lot of wind.

At F25 the images look oversampled, try a faster focal ratio for better sampling rate, I recommend something like F15 (x1.5 barlow) or even the native F10 rather than F25. It will give a smaller image but it will be cleaner and easier to focus.

Also exposure time of 29ms seems too long to be able to freeze the seeing, aim for under 10ms, this is where the faster focal ratio will come useful, with more light you can get faster shutter speeds and take more images to stack.

 

Edited October 2, 2021 by Nik271

[dweller25]

You have three things working against you - low planetary altitude, poor seeing at the moment and a roof possibly radiating heat - so given all that your images are quite good.

 Can you reposition your scope to avoid building heat ?

[vlaiv]

Way too low frame count for Jupiter.

You want to capture x10 as much and stack only 5-10% of the best. Use USB 3.0 and ROI (say 640x480). Your camera is capable of 300FPS at these resolutions and with 5ms exposure length you should get at least 180-190FPS. With 4 minute of recording that will give you 4 * 60 * 180 = 43200 frames total.

Use Gain 334 with your camera, and use F/11.3 for ASI462mc camera (2.9µm pixel size) - which in your case means, loose the barlow altogether or maybe find a model that will give you x1.2 at most (which means just barlow element mounted real close to sensor).

Sub duration needs to be around 5ms or so if you expect to freeze the seeing.

Lookup optimizing planetary views on google for tips on how to get good planetary visual and then apply the same for imaging (especially thermal management where you avoid houses and large bodies of water, waiting for scope to cool down and so on).

[GrahamD]

8 hours ago, PeterCPC said:

"I think I've successfully Collimated the scope"

Do you not know? Have you got the concentric rings with equal spacings? Assuming collimation is ok I would think that the seeing is the issue. The heat rising off the roof may make the image wobbly but I don't think that's the issue.

Thanks Peter, I did get the concentric rings so it would have been collimated, I also checked inside and outside focus and get the same result.  I know there is always more you can do to improve though.  The star was “on fire” so maybe it was the seeing.

Graham

[GrahamD]

7 hours ago, Nik271 said:

In this cooler weather, I expect roof tiles will be near ambient temperature within 1 hour of sunset. Chimneys and flutes venting heat plumes from gas heating in the cold season are also responsible for poor seeing. 

A C8 should produce better images than these, but only in good seeing. Yesterday (Friday) was ok in Oxford, but nothing special there was quite a lot of wind.

At F25 the images look oversampled, try a faster focal ratio for better sampling rate, I recommend something like F15 (x1.5 barlow) or even the native F10 rather than F25. It will give a smaller image but it will be cleaner and easier to focus.

Also exposure time of 29ms seems too long to be able to freeze the seeing, aim for under 10ms, this is where the faster focal ratio will come useful, with more light you can get faster shutter speeds and take more images to stack.

 

Thank you for your thoughts, Ill try that next time we get a clear night.  I may also fit the .63 reducer, accepting the smaller image to see what that produces, and to reduce the exposure time.

Graham

[GrahamD]

7 hours ago, dweller25 said:

You have three things working against you - low planetary altitude, poor seeing at the moment and a roof possibly radiating heat - so given all that your images are quite good.

 Can you reposition your scope to avoid building heat ?

Thanks for your reply, the garden is North facing, but I could move further back, giving me more separation from the roof, or of course find a more remote location.  It’s also been quite windy recently, and I haven’t looked in the last couple of days to see where the Jet Stream is !

Graham

[GrahamD]

6 hours ago, vlaiv said:

Way too low frame count for Jupiter.

You want to capture x10 as much and stack only 5-10% of the best. Use USB 3.0 and ROI (say 640x480). Your camera is capable of 300FPS at these resolutions and with 5ms exposure length you should get at least 180-190FPS. With 4 minute of recording that will give you 4 * 60 * 180 = 43200 frames total.

Use Gain 334 with your camera, and use F/11.3 for ASI462mc camera (2.9µm pixel size) - which in your case means, loose the barlow altogether or maybe find a model that will give you x1.2 at most (which means just barlow element mounted real close to sensor).

Sub duration needs to be around 5ms or so if you expect to freeze the seeing.

Lookup optimizing planetary views on google for tips on how to get good planetary visual and then apply the same for imaging (especially thermal management where you avoid houses and large bodies of water, waiting for scope to cool down and so on).

Many thanks for your reply, I’ll work on your suggestions !

Graham

[Pete Presland]

Some nice detail visible, as has been said more frames need for Jupiter and some better seeing coniditions.