The magic starts in getting the focal length of your set up to match up with the camera pixel size to get Jupiter across at least 120 pixels. In nearly every case, between a 1.5 - 3x Barlow will get you there with most telescopes. The one you use can be calculated by using this formula:
- Just insert the Barlow on your telescope, then the camera into the Barlow.
- For the capture session, get your telescope out for at least 30 minutes to get it equalized with the outside temperature.
- Use a regular eyepiece if that is easier and get a decent 2-star or polar alignment depending on your mount.
- If your camera comes with driver and capture software follow the "Read Me" instructions and install both. Once you connect the camera via USB and run the software you should be able to connect to the camera.
- With your software running, adjust the exposure and gain to see stars by adjusting the focus. Then move to a bright star near Jupiter. There take your time to get your focus as best you can then move the scope to Jupiter. Due to atmospherics Jupiter will still look a bit out of focus but if you got a good star focus you will be fine.
- Your alignment will drift over time, not to worry, just use your manual or electronic controller to keep it centered as best you can. An occasional move will not hurt your data capturing several frames per second.
- Adjust the gain and exposure time as to not saturate Jupiter. Should be bright enough to see the bands especially when it captures an occasional good still (not so disturbed by atmospherics) image.
- Your camera should save the images as an AVI or SER video file or sequentially numbered JPG images. Run a short capture then go to your default folder and check to make sure all is working. If all looks good, run the capture for as long as you can. You can break it up in to blocks of several minutes.
- Imaging through thin clouds, haze, and near the Moon shouldn't be an issue and there is still plenty of good data captured. The impact detection software is much more forgiving than regular astrophotography.
- Once you have the data, you will upload it to the folder Dr. Kunio Sayanagi has created and can run the DeTeCt software locally and forward the report.
- There are plenty of YouTube videos out there that will walk you through all of this in more detail depending on the camera and mount you have.
- If you have any issues you can utilize our club's Yahoo Group for further guidance. Clear skies.
Oversampling Seeing– The atmosphere that you see and image through is turbulent. In order to capture sufficient detail it is recommended to oversample by imaging at 3 times the seeing conditions. With a good night of seeing rated at 1.5 arc-seconds that gives a target of 1.5 / 3 = 0.5 arc-seconds.
Image at least 0.50 arc-seconds per pixel due to seeing conditions.
Frames Per Second - Seeing through the turbulent atmosphere can be momentarily clear and stopped in time by a fast picture, called “Lucky Imaging”. By using high speed imagery or video capture quantified in Frames per Second (FPS), several images can be taken at the moment of clear or calm seeing. Capturing at 30+ FPS is desired since the majority of the frames captured will be blurry and this should provide a few acceptable frames within the 1 second impact capture window
Image at 30+ FPS is a good target.
Resolving Power is all about the Aperture and we all know Aperture rules and getting the biggest Light Bucket you can is a motto in the astronomy community. Here is why; Resolving Power has to do with the diffraction of light as it enters your telescope. The opening edge causes interference light waves to be created that prevents a point of light from coming in to perfect focus. Instead it produces a pattern called an Airy Disk which has several rings around the central image. This blurring limits the fine Resolving Power of a telescope. Oversampling the images at 2 times the Resolving Power of your telescope is the recommendation.
The Resolving Power (arc-seconds) = 120 / Telescope Aperture (mm).
So let’s take a look at some examples:
The image scale is the angular dimension that each pixel on the camera sensor captures. This scale is depended on the width of each pixel on the camera sensor in microns and the focal length of the telescope. It will be the determining factor on how much resolution you will be able to capture.
Image Scale (arc-second/pixel)=Camera Pixel size (um)/Telescope Focal length (mm)*206.265
So now let’s take a look at the camera.
Dr Kunio has two Celestron 4” Nexstar GOTO telescope that he can loan out. Pair this up with a ZWO ASI120MC camera above will provide:
This configuration will work but could benefit with a 2X magnifying Barlow ($50) providing 0.29 arc-sec/pixel (0.58 / 2) producing a 156 pixel wide (78 x 2) image of Jupiter.
You can also use a different camera such as the ZWO ASI178MC (color) camera ($369) with smaller 2.4 um pixels:
Taking it up a notch using a Celestron 11 inch at prime f/10 with a ZWO ASI120MC camera:
Pro-Amateur Astronomers routinely image around 0.20 arc-seconds per pixel. They tend to use larger 14” telescopes (2 times oversample = 0.17 arc-sec) and image in locations that provide great 1 arc-second seeing conditions (3 times oversample =0 .33 arc-sec).
You can see how these two factors form book ends to what you can best do depending on your scope and seeing conditions and ultimately drive the camera selection.
Using a large telescope with a matched high speed camera and imaging in excellent seeing conditions will provide the most and best resolution imagery thus increasing the impact detection odds. But after running the number the great news is:
There are many image capture software available to interface with and control cameras. FireCapture is highly recommended. It saves the images in a SER or AVI video format. SER format is the preferred format. Make sure you activate the log function as it is read by DeTeCt impact detection software to get the maximum timing information.
If you are using a Canon DSLR camera, use the Live View as it captures at 1:1 pixel resolution at 5-10x magnification. I have found the 10X works best. A software package that interfaces with DSLRs like Astro Photography Tool or BackyardEOS saves the images as a JPG in a sequential numbering format.
A simple USB webcam will create an AVI video file and a cell phone will create a MPEG video file.
The good news is that all of these image formats are acceptable for the impact detection software and even a 4 inch telescope with an inexpensive WebCam in average seeing conditions will provide research grade data and a chance to capture an elusive Jupiter asteroid impact!
First in general: The usual imaging acquisition setup is fine, when you run DeTeCt afterwards on the videos. This way gives you minimum additional work: you go out for imaging normally, and just run DeTeCt on them afterwards, checking the generated detection images generated (*_dtc_max.jpg images) in search for a possible impact. If something is suspect, please contact me and send me the detection images and the DeTeCt.log. If nothing is suspect, please send me the DeTeCt.log nonetheless, non-detection are very important for the project.
1) Mono or color, is one any better than the other?
2) Ideal CCD imaging scale (arc-seconds/pixel)?
3) Minimum A to D converter bits, 8, 10, 12, 14, or 16?
4) Minimum frames per second?
5) Are all of the frames submitted or just the best X%?
6) No-filter or filter (Red, Dark Red, IR, or IR-Band Pass) to improve sharpness and contrast?
7) Best image or video file format to use?
8) Imaging camera manufacturer and model that you have seen that has worked best?