Saturn RGB - 17 June 2017

[geoflewis]

Here is my 1st Saturn of 2017 and also the 1st time I imaged it using a mono CCD camera with RGB filters.

I was hoping to catch the Seeliger (ring brightening) effect around opposition on 15th, but the skies would not give to me that night (nor 14th/16th), so a couple of days after opposition I'm note sure if it was still in play. I captured AVIs using my usual RRR, GGG, BBB methodology for Jupiter, but being so low the planet was much dimmer with capture rates much slower fps. The good seeing for the reds deteriated as I captured the greens and was very poor by the time I got on the blues (and I was down to <5fps for blues), with only one AVI usable (and that poor quality).

Anyway, it was good to get this in the bag from such a low altitude (13-15 degrees).

The composite image shows the varying quality of the RGB data that comprised the final RGB.

 

[michael.h.f.wilkinson]

Very nice, especially with Saturn so low in the sky

[geoflewis]

Just now, michael.h.f.wilkinson said:

Very nice, especially with Saturn so low in the sky

Thanks Michael, it certainly is a challenging target right now. I tried again last night, but the conditions were worse, so I gave up after 2 hours of mixed seeing. I'd get a reasonable red, but greens and blues would not sharpen....

[michael.h.f.wilkinson]

1 minute ago, geoflewis said:

Thanks Michael, it certainly is a challenging target right now. I tried again last night, but the conditions were worse, so I gave up after 2 hours of mixed seeing. I'd get a reasonable red, but greens and blues would not sharpen....

I have had endless trouble with poor seeing in blue, even when Saturn was WAY higher. can't imagine what it will look like now

[geoflewis]

1 minute ago, michael.h.f.wilkinson said:

I have had endless trouble with poor seeing in blue, even when Saturn was WAY higher. can't imagine what it will look like now

Yes, the blues are always the worst, but you can get away with that if there are decent R&G to add as luminence. I used the x3 R stack as luminence in the above image which made a big difference. I've today ordered an Astronimic Pro IR 742nm filter as that should help cut through the seeing for sharper ring details, which may be an even better L layer option.

[morimarty]

Still some nice detail captured despite the blues not playing ball. the drop in frame rates was an eye opener for me too!

[geoflewis]

23 minutes ago, morimarty said:

Still some nice detail captured despite the blues not playing ball. the drop in frame rates was an eye opener for me too!

Thanks Martyn, I'll push the gain up next time, but I still think that with my rig (incl laptop) the frame rate for blue will not be much >5 fps. If seeing is really good I might get 20fps for red and 15fps for green. The ASI120 is a good camera, but doesn't have the fast rates of more recent zwo versions.

[Pete Presland]

Nice end result, the rings do look quite bright. Maybe you have captured the seeliger effect?

[geoflewis]

Thanks Pete, I think I may have, but I'm hoping to get another run at it soon to see what difference there is now. My planetary imaging mentor down in Bucks says that 2 nights ago the rings were noticibly fainter, being about the same brightness as the planet's disc, but I haven't had a decent run for several nights, so no comparitor yet. My IR742nm arrived a couple of days ago, so I'm hoping that will cut through poor seeing better than the RGB and provide a good luminence to sharpen the final image. Regards, Geof

[knobby]

Please excuse me if I'm asking a silly question but did you refocus after each filter change ?

I'm a pure colour imager with no mono experience but I've read about refocusing somewhere ...

Lovely image anyway.

[geoflewis]

3 minutes ago, knobby said:

Please excuse me if I'm asking a silly question but did you refocus after each filter change ?

Hi, no I don't refocus when changing filters. In my experience it makes no difference for planetary, at least not from the UK, as focus is changing all the time due to atmospherics acting like an lens/prism. The point of 'lucky imaging' using video and tools like Autostakkert or Registax, is that they will grade the frames allowing you to select and stack the sharpest, 'in focus' frames. Typically I'm shooting 4000 frames at around 50fps per channel for Reds and Blues and 3000 frames at 30fps for the darker blues. I then stack the best 15%-33% of each channel (more if seeing is really good, which is proving very rare currently), then derotate and stack in WinJupos for the final image. Refocusing DSOs for each filter is of course best practice, but planetary and DSO imaging are completely different arts....

Others may disagree, but that is what I do, so hope it helps.

[geoflewis]

14 minutes ago, knobby said:

Lovely image anyway.

I meant to say thanks too, sorry. Your feedback is much appreciated. Geof