Saturn 2019-08-08 21:30 UTC

[Ags]

This is 4 minutes of 50ms frames, taking the 45% best. 1.5 drizzle applied and lightly sharpened in Gimp. I also shot a sequence of 20ms frames but my USB  speed was maxed out at 50ms already, so I gained nothing from shorter frames except noise. Using my Skymax 102 on AZ-GTi as usual.

I have no success using Sharpcap focus assist; the focus quality graph just seems to degenerate into random green and red bars for me. Instead I focussed by watching the sickle negative space between the rings and planet, and optimized the cusps. 

I am really enjoying the combination of the AZ-GTi and the ASI178MM. They both work flawlessly and easily. The freedom find feature is very useful, it lets me center the planet manually then initiate point-and-track on the laptop. If I did not have that feature I would have to move the scope about with a mouse while peering through the eyepiece - not a prospect to relish!

Edited August 9, 2019 by Ags

[vlaiv]

21 minutes ago, Ags said:

I also shot a sequence of 20ms frames but my USB  speed was maxed out at 50ms already, so I gained nothing from shorter frames except noise.

Try using ROI - that will help with frame rate - less data to transfer means better transfer speeds.

Going with shorter exposures does increase noise but it is essential in freezing the seeing - long exposures will average distortions produced by atmosphere and create strong "motion" blur. You can use 30ms exposures only in the best conditions, but if seeing is not good you will need to go shorter than that, often as low as 5-6ms exposures (even if USB link won't provide 200fps at small ROI).

[Ags]

I am using ROI - but i think I selected 1200x1200 instead of 1000x1000 by mistake. Next time I will try a much smaller ROI. I was trying out different frame rates tonight to see if there was a difference - I tried 20, 35, and 50ms. The 50ms sequence seemed to come out best. Here is the 20ms sequence with the same processing applied. I think the added noise loses a bit of contrast in the rings.

Edited August 8, 2019 by Ags

[vlaiv]

1000x1000 is very large ROI for Saturn.

Have a look at ZWO specs for 178 model:

Just as comparison, if you maxed out at 50ms then you were getting somewhere around 20fps. In 4 minutes that is about 4800 frames total. You say you stacked 45% best - that is 2160 subs, or SNR increase over single sub of about ~ x46.

Let's say you used 8bit capture and 6ms exposure on 640x480 ROI with USB3 connection. That would give you around 166fps (limited by exposure time), and in 4 minutes you would collect around 40000 frames. Now take just 15% best of that - it is 6000 subs or SNR increase over baseline of x77. Baseline will have smaller SNR for 6ms exposure, but you will be able to compensate that with higher SNR boost from stacking considerably more frames, even if only using 15% of them.

 

[Pete Presland]

Nice looking Saturn, as @vlaiv said 640x480 is more than enough for Saturn.