Location: at home in Tomball, TX
Cloud cover: none
Transparency: above average (4/5)
Seeing: poor (2/5)
Darkness: no moon, city glow
Wind: none
Humidity: 75%
Temperature: 60° F
Start Time: 10:30 pm CDT
End Time: 11:00 pm CDT
OTA: 8″ SC
The Celestron NexImage camera has stopped working. I emailed Celestron customer support, but they have not contacted me, so here I have clear skies and no camera.
I recently found a webcam capture utility for Linux called webstream and decided to try it with the Creative Live web cam I bought on clearance last year. The goal for the evening was just to step through an entire cycle of image capture and stacking to verify that it could be done.
When I first tried using the Creative Live cam last year the I was disappointed and frustrated because the Windows driver would BSOD within a minute or so of operation. I tried it in three different machines with the same result. I hoped the linux driver might work better, and it did. Installing the driver, however, was no picnic. In fact, just locating the driver was no picnic. The camera model was not supported by the standard gspca and uvc linux webcam drivers. After more than an hour of googling I found driver source code, built it, and the world was happy (well, in any case the camera owner was happy). I captured a quick picture from my desktop just to verify that it was waorking correctly with camstream. The first step was successful, but how would it do as a cheap astrophotography camera?
Before mounting the camera to the telescope I removed the tiny webcam lens. It unscrewed easily. I assume that like many webcams the lens had an IR filter, which means that star images captured without the filter will appear brighter than in visible light. Next I used a rubber band to wrap the webcam’s round plastic cover. With the rubber band in place, the camera fit snugly into an old 1.25″ barrel I recycled from one of those useless 4mm eyepieces bundled with a starter scope. Now I was ready to mount it in the telescope!
I set up the scope on the driveway and aimed at Polaris. All the camera adjustments (gamma, brightness, saturation, etc.) were set in the “middle” of the slider range. There are no numeric indicators or fine controls in camstream, so I could only estimate. After the camera was configured I could see Polaris as a bright, flickering disk and I could almost make out Polaris’ brighter companion on screen. I was disappointed that camstream had no shutter speed control, nor could it capture images faster than one per second. I grabbed a few dozen images and shut everything down. The second step was successful, so far so good.
Next I copied the images up to my desktop and opened them with Registax. I recently upgraded to a newer version and I spent a few minutes learning to navigate the new interface. For some reason object tracking was not selected by default. Anyway, it stacked the frames and eliminated the noise. Unfortunately Polaris’ secondary was too dim for Registax to pick it out from the noise. Polaris itself looked a little distorted, but the seeing was poor and the star is only 30° altitude, so I didn’t expect much. As far as I was concerned, the third step and the entire night was a success.
So how does the Creative Live cam compare to the NexImage? Well, they both have a resolution of 640×480, so no big difference there. The sensitivity seems pretty comparable. Last year I imaged the Trapezium with the NexImage and θ1b Orionis (at mag 8.0-8.5) was just barely visible. Various sources list Polaris B between mag 8 and 9, slightly dimmer than θ1b Orionis. The Live cam was able to pick up Polaris B, but at the noise level. The cost difference is pretty big: you can get the Creative Live cam for about $16, but the NexImage is $100. The only advantage I see to the NexImage is that it was designed with the hardware to fit into the 1.25″ focuser. Windows users may have trouble with the driver crashing; I certainly did.
Here’s an idea: maybe the Live cam board will fit inside the NexImage case, then I could use the camera that works in a case that fits the focuser. I’ll have to give that a try.
