Sunday, May 29, 2016

 

Issue #495, Here’s Exactly How You Do It: Imaging Jupiter (or Mars or Saturn)…


Jupiter under poor seeing with the setup described herein...
I’ve posted articles concerning planetary imaging more than once in the past, but in them I’ve always given you alternatives, “You can buy software A or software B. You use telescope A or telescope B, you can try camera A or camera B.” But I’ve come to realize people getting started in photographing the solar system may, at first anyway, just want to be told what to do. What exactly can you buy and download to image the worlds of the Sun and how exactly you use it. No choices, just a simple system that works.

So, before you write me to ask, “Well, how come you didn’t mention this telescope or this camera or this software?” I know there are alternatives to the setup I am going to describe. What I am doing is telling about a system that will work, and that you can modify as your experience grows.

One last caveat:  getting good pictures of the planets depends on one thing more than anything else: seeing. Atmospheric steadiness. That trumps telescopes and cameras of the most expensive sort. If you live in an area with constant poor seeing, there’s only so much you can expect. Take heart, though. Most people don’t live in locations like that. Most peoples’ seeing steadies down occasionally at least. Keep an eye out for the sort of weather that will bring steady air, like stagnant high pressure domes, and be prepared to take advantage of it.

How much will it cost to get into planetary imaging? Not much if you already have a suitable telescope and mount. If you don’t, expect to spend as much as 1000 – 1500 bucks for a usable scope and mount, or as little as 300 – 400 for a telescope alone.

OK, let’s get to it. First step is accumulating the gear you need…

Telescope

I don’t make a secret of the fact that I don’t use SCTs as much as I used to, but when I go after the Moon and planets, I go back to them. And specifically the 8-inch Schmidt Cassegrain. It brings one important thing to the table. Lots of focal length. You can get to the 4000mms of  focal length that is where you begin for high resolution Solar System pix with the addition of a simple 2X Barlow. One also has enough light gathering power to make exposures reasonably short, a must if you are to defeat seeing. Finally, a Meade or Celestron 8-inch SCT is short and light and does well on less expensive mounts. Get an 8-inch SCT.

Meade flip mirror on SCT...
Mount

Naturally, you’ll need a driven, tracking mount. You’ll also find goto speeds things up a lot. You wouldn’t think it would be difficult to get Jupiter or Saturn in the field the old fashioned way with a finder, but it is. It’s can be hard even if you have a flip mirror. A modern goto mount can put your quarry on the small chip of a planetary cam every stinking time.

Alt-azimuth or equatorial? A driven alt-azimuth mount is usable, but even if you take pains with the goto alignment (a good goto alignment improves an alt-az mount’s tracking), the tracking will be worse than that of a decently polar aligned GEM. A German equatorial mount makes life easier, so use one. Luckily they are cheap. A goto CG5 style mount, whether the ASGT Celestron CG5 (used only), the newer VX, the Meade LXD-75 (used only), or the new player, the Bresser mount from Explore Scientific, are inexpensive new and very inexpensive used. So, get a CG5 class GEM.

Camera

The requirements for a planetary cam, the basic requirements, are two:  a small chip and small pixels. Quite a few cameras in all price ranges fulfill those requirements, but few do it better than the ZWO Optical ASI120MC. The “C” stands for color, as in one-shot color, which will make your life easier when you are starting out. Just because this camera is inexpensive new, less than 200 dollars, don’t think it is a slouch when it comes to performance. It will deliver up to 100fps, frames per second if you keep the size of those frames small (see below). So, get an ASI120MC.

Barlow

You’ll need to double your SCT’s focal length by placing a Barlow lens ahead of the camera. Which? Luckily, I’ve seen very few poor quality Barlows of late. My choice for you is good, but it is also cheap, the famous Orion Shorty. I’ve used one for years and there is no downside to it.

Accessories

You don’t need too many, but you need some. First and foremost, you need a flip mirror to make initial centering of planets easy, even with goto. This is a special star diagonal with a camera port on its rear and a mirror that can be flipped up and down. Flip it down to center the target in an eyepiece, flip it up to send the images out the rear port to your camera. Flip mirrors can be adjusted so that what’s centered in the eyepiece is centered in the camera, and what’s in focus in the eyepiece is in focus in the camera. Which one? My choice is the SCT specific Meade flip mirror, but it’s apparently no longer being made. That being the case, get this Vixen flip mirror; it will work fine, but it requires the purchase a 2-inch visual back for your SCT if you don’t have one.

Computer

FireCapture
Since planet-cams must be used with a computer, you’ll need one. Any modern PC will do; image acquisition and processing software is much easier on computer horsepower than a modern game like Doom, for example. You’ll either want a Windows PC or a Mac that can run Windows software, and naturally the computer should be a laptop since you’ll be using it outside. My choice is the simple and reliable Toshiba Satellite.

Software

You’ll need to install two programs on that computer. One to operate the camera, and one to process the resulting .avi movies into stacked still frames. For camera control, get FireCapture. It’s free, and while it does tons of stuff, up to and including generating ephemerides and guiding a telescope mount, it is easy to use in simple point and shoot fashion. Its user interface is clean and simple, and it includes a camera simulator so you can play with it indoors. Yeah, get FireCapture.

When you shoot planets, you shoot .avi motion picture files. When done, you stack the (good) individual frames of those movies into finished still pictures and perform processing functions like sharpening the resulting stills and adjusting their histograms (contrast and brightness). The program that will do that is another piece of shareware, Registax. It is mature and easy to use in a basic fashion.

Odds and Ends

You’ll need an IR block filter for a one-shot color camera or images will be way too red, but the filter that comes with the ZWO camera is quite sufficient. All else you’ll need to buy is a longer USB cable, since the one that ships with the camera is a bit too short. Get a 10-foot USB 2.0 AM-BM cable (from your local BestBuy perhaps).

Exposure Controls on FireCapture...
Putting it together

The rest of this is going to be surprisingly short and sweet. To begin, set up the telescope as you normally do, but with the flip mirror on the rear cell instead of the normal diagonal. Use a crosshair eyepiece in the flip mirror, one that will yield a power of about 160x, a 12mm f/l eyepiece, that is. The Barlow goes into the camera port and the camera is inserted into the Barlow via its included 1.25-inch nosepiece. You can hook up the camera’s USB cable now if you like or wait till you are done with the mount alignments. You might also want to connect a serial cable to the mount if you want to be able to adjust the telescope’s aim with the computer.

OK, next you’ll either polar align or goto align. If you are using a Celestron mount, I suggest you do the hand control’s built-in AllStar polar alignment routine to ensure good tracking. To do that, you’ll need to do the goto alignment first. If you are using another brand of mount, you’ll normally do a polar alignment first. That doesn’t need to be a drift alignment, but should at least be a careful alignment with the GEM’s polar scope. If the hand control has a polar alignment routine like Celestron’s, use it.

Acquiring Images

Now, goto Jupiter (or Mars or Saturn or the Moon) and center the image in the flip mirror using the reticle eyepiece. At the computer, bring up FireCapture. There are a heck of a lot of options, but we only want to use the program in the very simplest manner and we’ll mostly be using the Control (exposure) section on the upper part of the sidebar. Adjust the gain slider there until it’s at about 75%; that will prevent images from showing the odd artifacts that can result from lower gain settings. Then, adjust the exposure controls until the planet looks almost bright enough but not quite, so that it looks just slightly underexposed.

All stacked in Registax...
Next, center the planet precisely. If you set up your flip mirror correctly, Jupiter should be in the frame, but probably not centered. Center it either with the HC or with an onscreen HC. If you have ASCOM installed on the laptop, use its virtual HC for centering. Just go to ASCOM in the settings portion of the sidebar by clicking the little ASCOM icon, check “initialize telescope interface,” and select the mount (and check “show hand control”) as per normal with ASCOM. If that sounds too complicated, just use the real HC for centering. An extension cable is helpful for that so you can sit at the computer when using the HC.

Focus up precisely. Again, if you set up the flip mirror correctly, Jupiter should be close to being in focus, but probably not exactly in focus. One help here is Motofocus. I had JMI’s Motofocus motor on my old Ultima C8, Celeste, and what a joy it was to sit at the PC and watch the display while focusing with a remote control. Otherwise, trot to the scope, adjust focus a bit, squint at the computer, and repeat as needed till Jupe is as sharp as you can get him (if there’s a Galilean Moon in the field, that’s a great focusing “tool”).

Finally, decide if you want to use FireCapture’s ROI, “Region of Interest” feature or not. If you engage this by clicking ROI in the “Image” portion of the sidebar (very top), and have selected “Jupiter” in the exposure section, Firecapture will crop the frame to a size just big enough to contain Jupe. That will allow the program to deliver much higher frame rates than you’d get at the ZWO’s full resolution. As long as tracking is good enough to keep Jupiter in the field for a minute to a minute and a half, use ROI.

Wavelets...
There are  two other settings you need to check. Make sure “debayer” is NOT checked in the Options section of the sidebar. As you may know, one-shot color cameras use red, green, and blue filtered pixels to produce color images. Normally, these pixels are combined on the fly to make a color image, they are “debayered” as you shoot. FireCapture, however, allows you to forego debayering, to shoot the avis as, basically, black and white images, and debayer them, convert them to color, later. This saves computer processing power and allows for a higher frame-rate. Also, check in the capture section to make sure "avi" is selected as the file type.

That’s the preliminaries. Now, just click the record button in the Capture section of the sidebar, and record some Jupiter movies. How long? About 1-minute is pretty good, especially if you are using ROI. That will give you plenty of frames to play with but not result in huge files that can be a problem. Shoot plenty more sequences, aiming for getting footage during the best seeing (best circumstances are shortly after dark with the planet above 30-degrees). When you’ve got some sequences that appear to capture the planet when it’s steady, you are done.

Processing

Next morning, the first task is to convert the .avi movies to color. Do that using the Debayer app in the FireCapture directory (put a shortcut to it on your desktop, since you will use it frequently). Open the little program, leave all its settings at their defaults, and select and then debayer all the .avi files. Debayer will place color versions of the .avis in the capture directory of FireCapture (you can specify the directory in FireCapture’s setup section before you do your captures).

Now comes stacking the best frames from the sequences with Registax. You will more than likely be a little daunted when you open the program for the first time. Don’t be. There are lots of options and adjustments, but you really only need to perform a very few actions to use the program in the most basic fashion:
And that is all. All of the foundation you will build upon as you become more experienced and interested in Solar System imaging. Even if you never go beyond this, I guarantee the above will still allow you to take pictures of the Moon and planets that will flat-out freaking amaze you.

Comments:
This is exactly what I've needed - an actual checklist of the basics for venturing into AP. Thanks!
 
An expensive addition would be starizona's adaptive optics rig.
 
Expensive and not really much help. Shooting .avis and stacking the best frames really does the same thing, and Registax is free. ;)
 
I suggest testing the use of free software AS! 2. Very easy stacking, so Registax can only be used to sharpen the image in the wavelet filters. In the extamente I do like you and want to check my work here is the page: http://www.astrobin.com/users/astroavani/
Best Regards
Avani Soares
 
Sorry to be late to the party. It's the end of the school year and we just finished with teacher outservice.

Uncle Rod, thank you for this post! It's perfect. Funny enough, I had just purchased a "new to me" ZWO ASI120-MC-S off of eBay the weekend before you posted this. I was reading your post just as I was getting it ready to take out for the first night. Great timing!

As always, your tips and advice are spot on. I've bookmarked this and have reviewed it while at my 'scope both times I've used this amazing little camera.

Thanks again.
 
Rod, this is great, just what I needed. Thanks so much, Phil, UK.
 
Avani, I've used that software very successfully and like it. That was not the point here, though. Rather than alternatives, the point was to talk about a simple system that works. Once a novice is familiar with their camera and process, those alternatives can be explored. :)
 
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