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Planetary Imaging (Mars)


TerriZ
(@terriz)
Member Moderator
Joined: 2 years ago
Posts: 40
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Some things I've learned since embarking on planetary imaging with the opposition of Mars this past October.

I am using an 11" Celestron EDGE HD SCT for imaging.   I am also using a 2X powermate putting the scope at F20 and 5600mm focal length.

First thing you need to do is polar align, align your finder scope (really well), and align coordinates to mount because Mars is small and if you want to find Mars in the small camera frame you need good alignment.  

The best free capture software I've tried is called FireCapture.  It's free and works with most major camera.   I am using a ASI224MC with 3.75um pixels.

For Mars I'm using a fairly fast exposure of 2.5ms at 230 frames/sec.   I exposed for approximately 80% histogram, but I've found some areas are overexposed.  I think it should be in the 60-70% range.   I am capturing 4 minute videos on Mars.

I've captured at both 16bits and 8 bits.  16bit files are enormous   I'm going to be going with 8 bits until I determine it's not sufficient.   Chris Go uses 8bit files exclusively, which should be good enough for me.

Debayer should be turned off for capture.  Debayer, while capturing, will result in 3X image sizes.

Gamma should be turned off while capturing.   Gamma will effect imaging capture contrast to no value other than ending up with overly contrasty images.

I believe I should be using a UV-cut filter with a color camera.   Next imaging session I will be using a UV-CUT

I should be using an atmospheric dispersion corrector, I have the ZWO version.    

Will update as I refine my process.


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Eben Gay
(@eben-gay)
New Member
Joined: 6 months ago
Posts: 3
 

Terri,

I am just starting in with an 8" SCT trying to get my first planetary pictures.  I'd like to hear how your experience progressed.

Thanks

Eben


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TerriZ
(@terriz)
Member Moderator
Joined: 2 years ago
Posts: 40
Topic starter  

Hi Eben, nice to hear from you.   

So you can see some of my experience from above.   I think one of the most difficult things, is keeping the object centered at high magnification.  You'll be at 4000mm and F20 (2000mm scope with 2X barlow I assume) and probably a small chip camera..  The planets are so bright, you'll still use medium gain and fast exposures.    You can't underestimate the job of keeping the planet centered.    Do the very best alignment that you can.    Now for an alt-az mount, that's different from a polar alignment, but still, tracking will depend on how accurately you set up and synchronize software to the sky.

When I first started, I'd put an eyepiece in there, do the centering, and then pop in my camera (which was a philips webcam toucam) and take a couple thousand frames..  but it was a chore.    It's easier if you have a computer connected up and watching the planet, as well as a sky map, on the screen and making adjustments as necessary.     The skymap is giving you an idea where your frame is versus the planet, so if you loose it, you know how to skew so you don't go too far from the object.    

The program I recommended above also does some automatic centering of the planet in the camera view, which I've never used, but next time we have good planetary views, I'm going to try it.   To me one of the biggest chores.    The next thing is focus.   I used a bhatinov mask on a bright star, then skewed to the planet.   And my focus was on the computer screen.    Firecapture provides some focus aid but I found the bhatinov mask best.   

My planetary A-P experience was limited to a couple of images 10 years ago of mars and Saturn, and then recently with Mars and the Sun... Really not much and I'm still learning.   I did mostly deep sky with my 8" SCT, with wedge, then moved on to various refractors on equatorial mounts.   There are a couple of really good youtube videos on-line about planetary imaging. The Chris Go video's are really good.    Why don't you share what the rest of your system is so I have an idea of what you're working with.   Just remember I am no super-expert but happy to help with what I've learned.

 

Terri

 

 


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Eben Gay
(@eben-gay)
New Member
Joined: 6 months ago
Posts: 3
 

Terri,

This is my current kit:

A Celestron EdgeHD (2000mm, flat image edge to edge)

The Evolution Alt/Az mount on a DIY equatorial wedge.  This is probably the weakest link in my system at the moment.  I'm still working on removing sources of error.

An Olympus micro four thirds camera (OM-D E-M1 mk II) with a 20 MP sensor that can take up to 60fps in short bursts.

Until recently I've been connecting my camera directly to the back of the telescope with an adapter.

I just got an adapter that connects the camera in place of the eyepiece and can take the 13mm eyepiece in-line for 16x increase in magnification.  I used this for the first time last night.

Usually I use SkyPortal on my phone to direct the mount and Olympus Capture on my computer to run the camera.

I also have a 600mm equivalent f/4 lens for the camera that mounts to the Evolution mount in place of the telescope.  I have a 1.4x teleconverter that pushes it to 840mm equivalent at f5.6.  This lens does very nicely on larger deep sky objects.

I live in a condo in the center of Burlington and have been doing most of my observing off my porch with a fairly high level of light pollution.  I just tried a light pollution filter on the 600mm lens last night and got a decent image of the Orion Nebula.  A couple of weeks a year I visit the island of Vinalhaven in Maine which has very dark sky.


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TerriZ
(@terriz)
Member Moderator
Joined: 2 years ago
Posts: 40
Topic starter  

The good thing about planetary imaging, is that light pollution matters a lot less.  For deep sky, light pollution means longer overall integration time for the same quality photo as someone at a dark sky site... this is to get equivalent signal to noise (SNR).   So you'll end up having to take more and shorter exposures versus if you were at a dark site (min light pollution) where you can take longer and less overall integration for the same SNR. SNR is the goal in deep sky.    Back to planetary:    For planetary you need focal length, so you don't want reducers, you want barlows (2-3X) or extenders (power-mate 2-5X).    So the Olympus 4/3 sensors are really nice (I think panasonic).  I have a mono version ASI1600 which is a darling of the deep sky community right now.   The question is, what frame rate can you get on that camera?   And to get a decent rate, you will need to restrict the field of view (no high frame rate for 16mp), how much of the sensor is being read?   I am not that familiar with those cameras for high frame rate and what options you have.    So a great camera for deep sky, but not clear on what it can do for planetary.   For planetary you want high frame rate, e.g. 1000s or 10's of 1000s of frames of frames in a couple of minutes.   Would it work with Firecapture which will help with both taking images as well as keeping the object centered?   I would not worry about a flat field for planetary.. the image is so small that field curve over the area is insignificant.   Firecapture is free, so you can try it inside just connected to your camera.    

I have an 11" Edge, that I've only done visual and planetary imaging with so far. 

The other thing about planetary, and why you want lots and lots of frames, is because you live under the jetstream here in vermont.    It's fact of life that your planetary views will be like watching water boil much/most of the time.  There will be fleeting moments of good seeing that you'll have a higher probability of capturing if you're capturing at a high frame rate.   

If your camera can't do a decent frame rate, then the good thing about planetary is that the small cameras that do this well, are really cheap.   ASI120MC, ASI224MC (I have this one).  You want one that does USB3 communication to get a fast rate.  

 

 


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