I finally updated my planetary camera from the once popular Philips ToUcam 740K to ZWO’s ASI120MM. This was after reading a number of positive reviews and seeing plenty of amazing photos produced by the ASI120MM. During my second night out with this camera, I realized it would push my imaging results to a much higher level. The detail in Jupiter’s cloud belts and the clarity of the Great Red Spot on my laptop screen was much better than I had ever seen before.
This article is a review of the ZWO ASI120MM camera with a basic tutorial of the methods I used to capture the footage of Jupiter and process it into a detailed composite image in Registax and PhotoShop. All of this is based on my second night out with the camera so I should improve my skills as I use it more. I will make more posts here on AstroPhotography Tonight to share what I learn.
Below is a comparison of my best work on Jupiter with the ToUcam Pro 740K (back in 2005) vs. my second imaging session with the ZWO ASI120MM. I realize there are more factors involved than just different cameras. For one, my 2005 telescope was an 8″ Celestron SCT and my current scope is a Celestron 9.25″ SCT. There may have been differences in sky conditions and how close Jupiter was during the imaging sessions. Still, the difference in the amount detail I obtained from each camera is significant. This really is a testament to the advancements in imaging devices.
|Jupiter May 15th, 2005||Jupiter December 1st, 2013|
|This represents my best work the Philips ToUcam Pro 740K and 8″ Celestron SCT.||This image is from my second imaging session with the ZWO ASI120MM and Celestron 9.25″ SCT.|
ZWO’s ASI120MM Details
Here are some of the main features and spec’s:
- Sensor (monochrome): 1/3″ CMOS MT9M034 1280 X 960 @ 35 FPS
- Resolution: 1.2 Mega Pixels 1280×960
- Pixel Size: 3.75 µm
- Exposure Range: 64µs-1000s (62 millionths of a second – 16.7 minutes)
- Interface: USB 2.0
- Dimension: 62mm X 28mm
- Weight: 100 grams
- Anti-reflective coating on sensor protection window
- Full aluminum housing with standard 2″ interface
- Integrated ST4 autoguider port allows the ASI120MM to be used as an autoguiding camera
- Wide exposure range allows camera to be used for planets, Moon, Sun, and deep space objects
- Can be used as an all-sky camera with the 150º wide angle lens attachment that is included
- 35 FPS at full resolution of 1280 X 960 / 215 FPS at lowest resolution of 320 x 240
- Threaded screw ports on back housing for installing thermoelectric cooler
Here is all of the main equipment I used to image Jupiter.
|ZWO ASI120MM Camera||ZWO Color Filter Wheel||ZWO LRGB Filter Set||Orion 12.5mm Illuminated Reticule Eyepiece|
|Celestron 9.25″ on CGEM||Zhumell SCT Dual Speed Focuser||TeleVue 2.5x Powermate 1-1/4 Inch||Rigel QuikFinder Compact Reflex Site|
Here is an image showing how the components of the optical train are attached. Click on image to see it full size.
Basic Method for Capturing Jupiter with ZWO’s ASI120MM
Here are the overall steps I took to image Jupiter. The telescope used was a 9.25″ Celestron SCT on CGEM mount.
1. First I balanced my optical tube with the ASI120MM installed. Adjustments were made to the counterweights and optical tube position in the saddle to get everything in perfect balance. This helps minimize the stress on the mount’s gears while tracking and allows smooth operation of the scope.
2. Next I removed the ASI120MM and inserted an Orion 12mm Illuminated reticule eyepiece and performed a good drift alignment. This is important for keeping the planet in the field of view (i.e. on the computer screen) while taking the video of it.
3. After the drift alignment, I collimated the SCT. Optical alignment is super important when imaging the planets. I started out with the ASI120MM installed so I could see the defocused star on the screen (using Firecapture software. More on this later). I tweaked the 3 adjustment screws for the secondary mirror until the shadow of the secondary mirror was centered as good as I could get it. Then I removed the ASI120MM and inserted a 25mm eyepiece to fine tune it. The eyepiece provided a crisper view of the defocused star. Next time I’ll probably just use the eyepiece.
4. Since Jupiter is bright and easy to find, I didn’t bother with goto. I slewed the scope to Jupiter and centered it in the eyepiece. Once centered, I removed the eyepiece and inserted the ASI120MM / color filter wheel into the eyepiece holder.
5. Now it was time to focus. Jupiter was very much out of focus so I adjusted the SCT focusing knob to get it close. Since this causes image shift, I had to keep re-centering Jupiter after making small adjustments. But then I was able to use my Zhumell SCT Dual Speed Focuser which is nice for making fine adjustments. Plus, it’s a zero image-shift type of focuser so there was no need to re-center Jupiter after focusing. I spent a LOT of time trying to get the focus a good as possible.
6. Once I got Jupiter focused, it was finally time to capture some video! This was done using FireCapture software which is a nice program with lots of features. FireCapture free download here. Screenshot of FireCapture:
7. Since the ASI120MM is a monochrome camera (rather than a color camera), the videos must be taken through Red, Green, and Blue (RGB) color filters. The videos of each color are combined later to obtain a color image. More on this in the processing section below. With FireCapture, you select the filter (from the drop down menu) for the color you are about to image through. This was the first thing I set in FireCapture.
8. Next, I selected the resolution, gain, exposure time (Exp. ms), and gamma for the red channel. Then, I selected the recording time for the video of 60 seconds. Since Jupiter has a very short rotational period, the total time (for recording all three color channels) shouldn’t go much past three minutes. Thus, I selected 60 second videos for each color channel. I took several videos of Jupiter using different settings to see which combinations turned out the best. Below are the settings for the videos (of each color channel) that were used for my best photo from that night. Note that these are not necessarily the best settings since I didn’t have a lot of experience with the camera. In fact, I figured out during the wavelet processing in Registax that the gain for the green channel should have been higher. It produced a bad “onion ring” effect which I couldn’t remove. This limited the amount of detail I could bring out in the green channel. The gain should probably be closer to 50 from what I have read.
|Resolution||512 X 440||512 X 440||512 X 440|
|Exposure Time (ms)||13.65||12.49||5.0|
|Video Duration (sec)||60||60||60|
9. Now it was time to capture the AVI video. I made sure the red filter was selected in the color filter wheel and also re-centered Jupiter in the field of view on the computer screen. Then I recorded the 60-second video. This process was repeated for the green and blue filter.
This was the method I used to capture the videos with the ASI120MM. It was quite exciting to see Jupiter looking so clear on the screen! It helped that the seeing was better than normal. The stars were hardly twinkling that night which was a good sign of a very stable atmosphere. I remember thinking that I needed to take advantage of the clear skies. It was hard to pack it up for the night. In fact, I stayed up until 4:00am taking my last video for the session!
Basic Processing Method
I processed the AVI’s in Registax 6 and then PhotoShop CS3. Fortunately, I found an excellent video tutorial produced by David Rankin of Rankin Studio for complete processing of Jupiter. David has produced superb images of Jupiter with the ASI120mm. Click here to view his astrophotography gallery which includes Jupiter and number of other solar system photos as well as deep space work. Thank you David for letting me use your video tutorial in this article! I followed this video very closely for processing Jupiter in Registax and PhotoShop.
I am very excited about the potential with the ASI120MM! I continue to see outstanding work posted by other imagers who are using this camera. I know I need more time with it to perfect my methods, but my goal is to produce images that are close to the spectacular work of others. I know it’s achievable based on my second session with the camera. I plan to share my experience as I go along and at some point, post a more thorough review. I hope this article is useful and please feel free to provide feedback in the comments section below.