DSO imager ventures into planetary space, advice welcome. - Forums

Topic starter

Jul 23, 2021 · Edited: Jul 23, 2021

I started in this hobby about 18months ago - with my primary area of interest being DSOs. I have an Esprit 100 and a GSO RC8.

Last night, I tried out my hand at planetary imaging for the first time, using a 2 x Barlow in my RC8 to give a focal length of 3200mm at f/16.

Here is there picture Jupiter I obtained with my ZWO ASI462MC camera (2.7um pix), running in video model (1024 HD format). Frame times were 50ms and gain 250. I tried other combinations, 420 format, 10ms frame time/gain 380. But all turned out looking pretty much the same. Data was processed in Autostakkert and Registax (great programs). Videos contained from 2000-7000 frames and I used the 10% best. (Also tried 5%, 20% and 50% best - again with little apparent difference, although the 5% best image was a bit noisier.)

I am quite happy with the way my first image at 3200mm focal length turned out, since my site has pretty poor seeing (3-4arcsec) and I suspect the RC is not the best to attempt planetary imaging with.

Notwithstanding that, I was able to get to the resolution limit of the RC (0.57arcsec), corresponding to 3 pix on the detector. Note that I did't drizzle on the basis I was oversampling physics, let alone the seeing! However, I would value any suggestion for imporvement. My image lacks the wow! factor of many out there.

It could be many things

1) the seeing at my site (can't do anything about that)
2) the type/aperture of telescope (that will need to wait)
3) the observing approach
4) the processing

With many thanks in advance

CS Brian

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David Nozadze

Jul 23, 2021

Hi Brian,

I don't have much experience in SSO myself, but one question popped into my mind right away. Did you try imaging without the barlow lense? In my case, it degraded my image quality instead of increasing it. The one I used was rather cheap one, intended for amateur visual observation only and produced horrible chromatic abberation.

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Brian Boyle

Topic starter

Jul 23, 2021

David,
A good point, but I have have now imaged the Moon with and without the Barlow. In this case Barlow doesn't appear to be degrading the image, indeed the sharpness is improved.
CS Brian

astroian

Jul 23, 2021

Hello Brian,

The idea of planetary imaging is to shoot so fast that the seeing is effectively frozen. This means you can get images close to the scopes refraction limit. But to do this your “subs” need to be very short. Even 50ms is considered long for Planetary imaging. One way to reduce that is to reduce the region of interest on the camera, then the data can be downloaded faster and the frame rate can increase.

Cheers,
Ian

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Björn Arnold

Jul 23, 2021

Hi Brian,

I'm not an experienced planetary imager (does solar imaging count?) so this is rather theory than practical experience:
Re freezing the seeing: from your description you said that you went down to 10ms. You should try to push this further down to 2ms, of course without degrading image quality through artifacts due to too high gain and the object shouldn't become too dim. At least for my solar imaging, the 2ms give me much better results than 10ms would (of course, achieving 2ms is easy when the sun is the source).

Re diffraction limit: I am wondering if one can be more aggressive in the calculation of hypothetical resolution. The reasoning: DSO images are extremely stretched and therefore the higher order diffraction maxima (and of course the zero-order maximum) of the Airy pattern are extremely amplified. Since, in comparison, planetary images are close to linear, I'm wondering how one should correctly define the "diffraction limit"? I guess one could calculate with then FWHM of the central diffraction peak or even more restrictive instead of using the first minimum.
(as I said: just a theory from my side)

Re processing: for my solar imaging, my best friend is the high pass filter in Affinity photo which allows me to enhance a lot of detail and to increase contrast.

I'm also planning to image Jupiter these days.

Cheers,
Björn

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SemiPro

IOTD Staff

Jul 23, 2021

Give Winjupos a once over whenever you get a chance. It allows you to combine videos by accounting for the rotation of the planet.

Check out this post to see a test someone did on just how much footage you can combine: https://www.cloudynights.com/topic/625656-winjupos-help/?p=8709416

Also if you are concerned about planetary imaging with an RC, allow me to point you to this gem: https://www.astrobin.com/tfagbj/?nc=collection

That was taken with an RC scope, and only a 6 inch one! Someone can correct me if I am wrong, but the big hang up with RC scopes is a loss of contrast. Thankfully, we have Photoshop. Collimation is super duper critical for planetary, and as an RC owner you know how that goes!

Depending on where you are in the world, you might inquire about an ADC as well.

That's a real solid picture by the way!

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Brian Boyle

Topic starter

Jul 23, 2021

Really helpful input from everyone. Looks like I need to push exposure time down to 2ms or so. I was worried that read noise might dominate with “only” a 200mm scope, but the results from a 150mm scope are impressive. An ADC is also a great suggestion, and i will look into Winjupos.
Thanks so much. It certainly looks like there are more things that i can do or improve on, before i hit the limit of my site, or current rig.
CS Brian

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