Baby steps in imaging the gas giants.....

[Steve Reed]

So I have myself an ASI 120 MC which I am using with an Explorer 200p. My first efforts at imaging Jupiter and Saturn were surprisingly decent, more by luck that judgement I suspect. Last night I had another session, Jupiter was less impressive (although GRS showing up this time) but Saturn was overexposed and lacking detail.

I have used the camera directly plugged into the scope which gives a small image but I have yet to get good focus with a 2x barlow. I will persevere with this. 

I am using ASICap and adjusting exposure until I get some details on the planet on screen. This seems a bit unscientific. I have no idea what I am doing with gain! I am using a resolution of 1280*960, this is the default and not sure if this is the best to use. I am not tracking so I record for about 2 minutes, using the fine controls to keep the planet in the centre of the view. 

Can anyone please advise me on:

Exposure - how do I get it right?

Gain - do I need to adjust it?

Resolution - is 1280*960 optimal?

Video recording - is 1.5 - 2 min about right?

Any hints of getting focus when using a 2x barlow?

Thanks in advance!

Steve

 

 

 

[dark knight]

Could try using a Bhatinov mask for focus, slew to nearby bright star, put mask on end of telescope and focus, take off mask and slew back to planet. I'm sure there will be other suggestions available too, maybe setting up a parfocal eyepiece

[Elp]

No need for bahtinov, keep your exposure relatively high so the planet is a bright dot 1-2 seconds should be okay you want it fast enough so any focus change and dampening of the tripod is quick to update so you can see the focus changes, then adjust your focus until the planet is as small as possible, it should also when the turbulence settles seem sharp around the circumference. Then you can lower the exposure until you can see planet surface details and try to get them as sharp as possible via very minor focus adjustment (note at this point your focus turns will be imperceptible almost to the point you're not adjusting it at all).

You then want to settle on an exposure where you can see some surface detail but not too bright (as the detail will oversaturate and trend towards the white, you can always brighten an image if it's not too dim but if it's too bright the detail is lost) and not too dark (as per previous comment), we're talking milliseconds here.

Gain I find doesn't really have much of an impact for planetary but as a general rule for astro cameras higher gain = less sensor read noise, less dynamic range, lower full well depth, for planetary I tend to keep it low to midpoint.

Resolution is fine, if you make it smaller via ROI region of interest, your frame rate will be faster so you can capture more frames per second which is beneficial for planetary.

Short videos are okay and better for file management, personally I tend to capture raw (tif or fits) images instead as they're normally a higher lossless quality format, video usually compresses the data unless you're specifically saving as lossless format, and if anything happens mid capture the file won't corrupt as the captured images will have already been written to disk. Each set of captures I do until there's been significant drift or time/number of frames (too much drift from start to finish and the post processing software won't stack each set so well). So around 1-2 minutes or around 1000-2000 frames per set.

Barlow focusing is the same as normal focusing, the higher power you use the more difficult it will be and the dimmer the view.

Most of the work is fighting with the atmosphere, try imaging when they're higher up (less atmosphere to shoot through) and try to avoid shooting above warm buildings/roofs if possible.

Edited August 20, 2022 by Elp

[Steve Reed]

Great advice! Many thanks.

 

St6eve

[newbie alert]

There's loads of info out there on advanced planetary imaging, exposure/ gain has a massive contribution to frame rate... 

With planetary imaging combination of focus, collimation ( if needed) exposure and gain , alongside a decent Jetstream position and clear skies... Try not to shoot above rooftops and thermal distortion will effect capture..

It all needs to come together all at once