Clavius, 2-panel mosaic, 2x Barlow - reprocessed

[turfpit]

Captured 21/04/2021 @ 23:00. Reprocessed with lessons learned over the last year. A 2-panel mosaic captured with a 2x Barlow.

Celestron AVX mount, Celstron C8 SCT, Celestron 2x Barlow, Skyris 618m CCD camera, UV/IR-cut /L filter.
Each panel 2700 frames @ 45fps. SER, MONO8, 640x480, gain=300, exposure=12ms.
Sharpcap 4, Autostakkert!3, Microsoft Image Composite Editor, Registax 6.
Stack best 9% with drizzle 1.5. Registax sharpening layer 1 2 3, gamma, contrast, brightness.

Clavius_2-panel-mosaic_2x-Barlow.jpg (264.91 KiB) Viewed 728 times

Lesson learnt - stack less frames based on Quality Graph in AS!3 to achieve a better image.

Note: I did try image stabilisation with PIPP but there was no improvement. Success with a Barlow really needs the best seeing. When playing the captured video in SER Player the image varies rapidly from very clear to blurred - all caused by the atmospheric turbulence which is magnified by the Barlow.

Dave

[Menno555]

Nice capture Dave!
Your equipment combi has a very small FOV when this is 2 part panel?

Menno

[timh]

Very nice Dave. I have a similar question to Menno I think. Was it deliberate to do this in two panels...because - technically - it works better that way? i.e. the smaller the FOV then the higher the probability of a moment of good seeing that spans across the entire area - so it is better to break big views up into small pieces and then stich them together. Or is this just overthinking it -- and the tight FOV is just a consequence of the sensor size and very long focal length using the Barlow?
Tim

[turfpit]

Menno, Tim

Thanks for the comments.

The camera sensor is 640x480, the C8 SCT has a focal length of 2032mm (2 x 2032mm with the 2x Barlow in the optical train)- resulting in a small FOV. Hence the need for the mosaic when using the Barlow. Without the Barlow, Clavius will fit a single image.

618m_C8_2x-barlow_FOV.JPG (64.12 KiB) Viewed 677 times

The Celestron Skyris 618M is really an Imaging Source DMK23U618 CCD camera in a different case. https://www.theimagingsource.com/produc ... dmk23u618/

The camera was £499 when first released. I picked mine up for £80 in an Astronomy365 clear out of unfashionable/obsolete gear (thanks Robin). Not a bad price for a 120fps USB3 camera. A review of the camera family by Damian Peach can be found here https://s3.amazonaws.com/celestron-site ... ams_AN.pdf.

Without the Barlow, I can image at 120fps using exposures around 2ms. With the Barlow attached, the exposure has to be increased to around 12ms with a resultant reduction to 45fps.

I think the camera's larger 5.6um pixel size helps. I tend to use it with a 0.63x reducer. Given unlimited funds, I would probably go for a ZWO ASI174M which has a 1900x1200 sensor.

Dave

[Menno555]

Ah okay, the 640x480 is the culprit
I really was wondering because with my ASI482MC (1920 x 1080 and 5,8µm) and 4x Barlow, I'm still bigger. Well, not me but the FOV
I wanted to experiment with that and stack my Televue Powermate 2,5x on the Powermate 4x but the clouds were ruining it and now the moon is too low for me.

Menno

[turfpit]

Menno

Yes it is the sensor size that meant I had to use a mosaic with the Barlow - I don't see lunar mosaics as a problem having had plenty of practise. The sensor is a handy size for planetary imaging. I have been running through and reprocessing old lunar data and have concluded that my pre 2019 lunar data probably needs erasing from the disk - poor focus and incorrect exposure (histogram) being the main culprits.

Dave