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Need advice on best camera choice for Mars

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#1 excaliburlives

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Posted 12 July 2018 - 11:00 PM

  Can someone tell me what my best 3 choices are to shoot Mars with? I have a CPC1100 and was wondering which camera is best suited for my scope. Should i use a barlow to capture Mars also? Thanks for any advice i can get .

  Thank you



#2 OleCuss

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Posted 12 July 2018 - 11:28 PM

If I wanted a camera specifically for OSC planetary imaging and finding and tracking the planet is not a concern?  No question, it would be the ASI224MC with USB3.  Great SNR1 with a very fast frame rate.

 

Second unto that would be the ASI385.  It has the same great SNR1 but the frame rate may be just a little slower (but still very good and you may be able to define a smaller ROI and get the same frame rate as the ASI224?).

 

If I had the budget for it, however, I'd compromise just a little bit and get the ASI294 Pro.  The frame rate will be a bit slower even if you define a small ROI (but still very good) and the SNR1 is just a little worse than what you get with the IMX224 and IMX385 cameras.  But you have the option of using the entirety of the much larger sensor if you want (with a slower frame rate) and since this gives you a much larger FOV this can make it much easier to find the planet and your tracking doesn't need to be quite so good.

 

So with the ASI294 camera you might start out using the entire sensor to locate the planet.  Then you select a much smaller Region Of Interest so that you have a much faster frame rate and are not collecting useless data (when imaging planets we don't usually want a big FOV - it just means more processing without benefit).

 

But that bigger sensor is also very nice for DSO imaging!  This means that the ASI294 will do a good job for both planets and for DSOs.

 

Whether you choose to use something like a Barlow or a Powermate is certainly up to you.  But most I think would choose to use one.  But with a CPC1100 you have pretty good focal length even without a Barlow and tracking gets more tricky with more effective focal length.  My recommendation would be to try adding the Barlow (or the better Powermate) and see if you like it and if your tracking is good enough and your sensor big enough for that effective focal length.  If you don't like the Barlow you can go right back to imaging without.


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#3 james7ca

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Posted 13 July 2018 - 12:43 AM

With the range of CMOS cameras that are available today it's really hard to say that any one (or two) is the best choice. If you are looking for maximum resolution (i.e. critical sampling) and assuming that you have the seeing conditions that will allow reaching the potential of your CPC1100 (and that's a big maybe) then you should really be looking at the image scale that you can get given your effective focal length and the pixel size of the camera.

 

For planetary imaging, the general rule for a mono camera is that you want to work with a focal length that is given at the f-ratio as calculated by five times the pixel size in microns (um) of the camera. For a one-shot-color camera you probably want a little more magnification, so perhaps seven or eight times the pixel size (a factor of maybe 7.5X).

 

Thus, for the ASI224MC camera recommended by OleCuss that has a pixel size of 3.75um you'd need to achieve a focal length given by the following f-ratio, 7.5 x 3.75um ≈ f/28. So, something between a 2.5X and 3X barlow with you CPC1100 (which has a standard f-ratio of f/10).

 

Some might suggest that you can use a Bayer drizzle to compensate for the resolution differences between a mono and color camera of a given pixel size. But (IMO), that only compensates for part of the difference when switching between a mono camera and a one-shot-color version that has a resolution-reducing Bayer pattern. Basically, you can't regain that resolution (by drizzling) without compromising something else (and in this case that something else might be signal-to-noise, or the exposure level, or the number of frames that must be captured to produce a "clean" looking image). This situation isn't particularly dire, however, so that's why you probably need only a little more magnification and/or a little longer capture sequence to make up the difference (if you use a Bayer drizzle, otherwise increase the multiplication factor from the 5X used for a mono camera, or try a combination of both factors, drizzle with a small increase in the multiplication factor).

 

All that said, I'd probably recommend using a one-shot-color camera because it makes capturing a full-color image easier than when using a mono camera with three filters (separate red, green, and blue). However, a mono camera will work more effectively if you decide to do something like imaging in the near IR (which might help with the dust storms that are currently happening on Mars).

 

You can look at a range of potential cameras and if you don't plan on making it a multi-use camera (for planetary, lunar, solar, and DSOs) then you probably don't need to worry too much about the size of the sensor (in physical area).

 

So, some good color cameras would be:

 

ASI178MC, ASI224MC, ASI290MC, ASI385, QHY5III178C, QHY5III224C, and QHY5III290C.

 

If you have an interest in lunar and solar imaging then you might also want to consider the ASI174MC or the QHY5III174C (but for planetary work, both of these cameras would require working at a significantly longer focal length). Note also that near IR imaging on the moon can help overcome problems you might have with less-than-good seeing, although in that case you probably want to be using a mono camera (like the mono ASI174MM, ASI178MM, ASI290MM, or the similar offerings from QHY).

 

Lastly, don't just assume that a larger sensor will give you a wider field of view for planetary or lunar/solar work. A larger sensor will give you a wider field at any given focal length, but it may NOT give you a wider field at any given image scale.

 

Here is a link that will demonstrate that behavior (review post #23 and #24):

 

 https://www.cloudyni...a/#entry7590925


Edited by james7ca, 13 July 2018 - 05:29 AM.

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#4 RedLionNJ

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Posted 13 July 2018 - 12:10 PM

If this is your first foray into planetary (hi-res) imaging and you live in New England, there are other questions which should likely be asked first, else you're destined for frustration and disappointment.

 

It's not all about the camera. Or even the scope. An 11-inch SCT is perfectly fine for this purpose.  So, for that matter, is any old webcam (literally) giving a decent image scale. This could be as simple and archaic as a ToUCam at 15fps.

 

Too many people obsess over the merits (or demerits) of the latest planetary cams when almost anything would produce similar quality results. If all the pieces for the game are not present, nobody wins. So:

 

Mars will be at an extremely low altitude (elevation) this summer. This means looking through a lot of atmosphere. In order to get good images, the entire atmosphere (from your camera sensor all the way out to the edge of the earth's atmosphere at, say, 100,000 feet) has to be very steady (all at much the same temperature with only a steady, slight gradient of temperature/density). If you're imaging with Mars at, say, 20 degrees altitude, that path through the atmosphere is going to be about 425,000 feet (80 miles), as opposed to the 20 or so miles it would if Mars was overhead. That 80 mile path might lay over towns, cities, rivers, highways, airports, whatever - this (seeing) can be THE major challenge for a planetary imager.

 

On the same vein - low altitude increases atmospheric dispersion - the spreading out of some colors of light more than others. This causes "fringing" and a rainbow/blurring effect on objects lower than about 50 degrees. It becomes VERY noticeable down around 20 degrees or so.  There is a tool to offset this, in use for many years by seasoned planetary imagers - the Atmospheric Dispersion Corrector.

 

Focusing. You have no idea how tough it is to achieve good focus with an SCT on a planet until you've tried and failed a few times. As soon as you touch the scope, you need additional settling time to assess the new focus. And sometimes (with an SCT), focusing will move the orientation of the primary mirror just enough to throw off collimation AND move the target off the sensor.  Best to use an aftermarket, Crayford-style focuser with remote control. No primary mirror movement, no telescope shake to settle down. Better still, a focuser with a digital readout in microns, so focal positions are reproducible.

 

Focal ratio - as indicated above, there are focal ratios considered optimal for critical sampling. But there's also no point in trying to sample finer than the seeing will allow. It's usually a trade-off. Depending on the camera you choose to use, you may find you're best suited by even less than a 2x amplification. Perhaps 1.5 o 1.7x.  These are a lot harder to come by and you may need one custom-made.

 

Guiding - if you're imaging at something like 5 meters focal length with a tiny imaging sensor, it's pretty important to first put the target on the chip, then keep it there.

 

Processing - a whole other story if you're unfamiliar with hi-resolution imaging.

 

 

But, if your goal is only to select a planetary camera based on modern technology, you won't go far wrong with any USB3-based cam, including all those listed above and adding in the imx183-based cams.

 

 

Good luck!


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#5 excaliburlives

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Posted 17 July 2018 - 04:44 PM

Wow, that is some great advice guys. I'm leaning towards the ASI294MC Pro. I like the fact that i can do DSO as well as Planetary. My tree line is around 30 degrees so i won't be able too see mars. I planned on going to the beach so i wouldn't get and light pollution there. 

 

  Redline gave me something to think about with that crayford focuser. I bought a Feather touch focuser (didn't install it yet) to get better focusing out of my scope. I really hate the mirror flop of this sct. I didn't know i could put a crayford on it, i will look into that. 

 

   Should i get a 2X powermate or a 2.5x?



#6 RandallK

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Posted 19 July 2018 - 10:09 PM

The ASI120MCS Colour One Shot CMOS is an excellent planetary imaging camera. I used my second scope that I bought, a SkyWatcher 127mm  MAK along with the ASI120MC-s.

 

Here are images from 2 nights ago....(No Barlow either)

 

Saturn 0630.jpg

 

 

Mars 0950.jpg

 

The 120MCS is stil in production. The US Price is around $200.00 or less. (Make sure it is the USB3 version...there were apparently issues with the USB2 version) 

 

On Mars, with a region of interest of about 1024 X 768 I get just over 100 Frames per Second. On a 90 second video of Mars i get over 8,000 frames to run through Autostakkert.

 

Hope this helps and Clear Skies!

 

 


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#7 RedLionNJ

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Posted 20 July 2018 - 03:20 PM

 

On Mars, with a region of interest of about 1024 X 768 I get just over 100 Frames per Second. On a 90 second video of Mars i get over 8,000 frames to run through Autostakkert.

 

 

1024 x 768 is a HUGE ROI for Mars, which subtends less than half an arcmin.  You might get an even better frame rate (and smaller per-frame file size) by trimming the ROI down to around 200 x 200. Mars should still easily fit inside this for most scope/cam combos.

 

And, er ....  if you're at over 100 fps, then a 90-second recording should yield over 9,000 frames, right?



#8 RandallK

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Posted 20 July 2018 - 07:23 PM

Yep..that's right. I did cut the ROI down and my frames were in the 9,000's. I can stack a 90 second .ser file in about 2 - 3 minutes. 



#9 excaliburlives

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Posted 20 July 2018 - 07:30 PM

Nice pics Randal. I think Redlion is right. I don't think i'll great shots due to how low Mars will be. With only a few weeks left for any decent shots, i will have to use my Neximage5 for now.




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