Aug 28 2010

Logitech C510 HD Webcam Hack for Astrophotography

After my first try with webcam astrophotgraphy, I wanted a higher resolution for my next imaging system, and settled on the Logitech C510 HD Webcam. In spite of being marketed as a 8 MP webcam, I am only able to get images of 1600×1200, which is just under 2 MP. I cut right into it even before taking a picture of the undamaged unit. I almost felt bad about destroying the webcam. It is very well made, and the plastics used has a good feel, with nonslip rubber bits.

Start by peeling away the pristine plastic faceplate. The faceplate is a thin sheet of plastic with a high-quality adhesive. Pull it off slowly and it will reveal the screws.

Since I didn’t know how the thing was put together, I tried to pry the plastic shell open, but this did not work until I realized how the plastic faceplate hides the screws. I left a bunch of nicks in the plastic shell from this. Fortunately, the function is more important than the appearance.

Use a jeweler’s phillips screwdriver to remove these four indicated screws. The plastic shell will come apart easily.

Separating the plastic shell halves expose the circuit board. The two screws which attach the circuit board are circled in red. The central thing is obviously the lens assembly threaded into a plastic light shroud. Leave this alone for now to prevent getting dust or dirt onto the CCD element.

On the left is the microphone. I left this alone. To the right of the lens is an LED, which will need either paint or non-conductive tape to prevent the LED from contaminating the image.

On the front-half of the plastic shell is the screw which holds the handy stand. Remove this screw, circled in red, and the stand and its hinge will come right out.

Also note the clear plastic window for the LED. Since this protrudes from the face of the camera, it will have to be removed for a snug fit onto the plastic tube. Cut the black plastic welds off with a knife, these are indicated in the picture by arrows. The window will pop right out. I covered this hole with a piece of electrical tape. I also taped the hole in the plastic shell for the microphone. In fact, I taped up every hole I could find.

Next, unscrew the lens. It has grippy teeth on the outside making it easy to unscrew. The lens is glued into place, but is no match for a simple twist. Be sure every hole is taped up and dark, and then assemble the two halves together with the four screws.

Use a knife to ‘shave’ the lip from the top of the webcam, indicated on the right. This will allow your eyepiece adapter to have a nice flush fit. If there are any other protrusions, shave them as flat as possible. Try not to use a file, as the plastic pieces will get everywhere, and will be nearly impossible to remove from the CCD without damaging it.

The next step is to couple the webcam with whatever optics are chosen. Some folks on the Internet will create a crosshair on paper to align the webcam with their tube. I haven’t seen descriptions of other methods to do this. My alignment method uses an eyepiece to first aim the telescope at an object, swap the eyepiece for a plastic tube, then wiggle the webcam against the plastic tube until the target object was centered in the field of view. I used twisted hair-elastics to hold the webcam in place, as I have shaky keyboard hands. The webcam is then tacked into place with some crazyglue. Be sure not to glue fingers or cables together with the crazyglue, and be careful not to glue the plastic tube into the telescope focuser. After the glue dries, take a second pass to give this part a solid connection. A third step with epoxy, then a wrap in aluminum tape would complete the unit, and block all light from entering the camera.

Lessons learned:

  • A better alignment method is needed. I noticed that when twisting the camera in its focuser bore, the image swings rather than rotates. I suspect this is due to the construction of the focuser, which kinda wiggles in place a bit.
  • The focal plane is near the very bottom of the focuser. Most webcam circuit boards are too small to fit inside the focuser. I would need to cut more of the plastic tube next time, possibly filing it down very close to the end of the flange, about .25-.5cm.
  • The telescope may need to be collimation calibrated specifically for the webcam in a particular orientation. The plastic tube does fit quite snugly in the eyepiece bore, better than the factory-supplied eyepieces, but there is still chromatic aberration in the resulting images. I may need to simply collimate the mirrors in the telescope normally.
  • Hair-ties aren’t all that great for holding the camera in-place, I thought that a piece of copper romex in the shape of a ‘w’ may hold the webcam in-place better.
  • I ended up whittling the tube with an xacto knife, which left a lumpy edge. In hindsight, I probably should have filed the tube flat before I started
  • Using generic spray paint for the inside of the tube works really well. Be sure to use only a light dusting with each pass, let each dusting completely dry before doing it again. Hold the tube up to a light, and see how well the tube absorbs the reflected light. I cut my second tube shorter, which makes it easier to spray the paint along the inside of the tube.

Aug 9 2010

First Image of Space – the nth try

It has taken me a while to put together some images from the telescope, a Celestron 130 SLT. Since the arrival of the unit, I’ve wondered how to get neat pictures. Afocal didn’t work out, as I need additional spacer rings, and other expensive attachments. So I figured I’d go the low-tech prime-focus, using the recording media as the focal plane. I measured the diameter of the telescope’s eyepiece socket with some calipers, and took them to the local hardware store, Keystone. They have a small inventory at Keystone — just the basics, including this sink drain extension tube, for $1.79, which has a beautiful and snug fit inside the 1.25″ eyepiece socket.

drewzhrodague - plumbing extension tube

plumbing extension tube

I was hoping I’d be able to take off the threaded fitting, stuff the webcam in there, and thread it back on. No such luck in this case, and the next course of action is to cut off the wasted end. I did some rough calculations, and cut off all of the wider flanged piece, saving only about 1cm for a nice snug fit. Pipe cutters for copper do not work on flexible plastic, so I crudely whittled it down with a lockblade.

Looking down the tube, I noticed that the inside of the tube was reflective, which would produce some kind of ghosting. I used some discount black spraypaint I had laying around, and gave it several really light dustings down the tube. I could have done a much better job, but it seems to cut down on most of the inside reflections.

Then I popped a 25mm eyepiece into the telescope, and focused on the cell tower in the neighbors yard, a specific bolt to be exact. Then swapped the eyepiece for the tube. I held the webcam on there, fired up cheese, and tried to see something. After fiddling with it for a while, a very unscientific approach, I didn’t think this would work at all, and that I’d missed something. Eventually I realized that it was just out of focus, and I got beautiful orange leaves from the non-orange wisteria — the lack of infrared filter makes the image coloring kinda wonky.

I must have bumped the telescope, because I was no longer pointing to the cell tower. After re-aiming the telescope, I fiddled with the position of the plastic cover over the CCD element, to move the original target into the center of the webcam image. Interestingly, there’s quite a zoom effect when using such a tiny webcam because the element is so tiny, I suspect. Having piano hands, it took a while to get the thing centered enough to superglue the plastic pieces together. It popped off a couple of times, and I had to repeat the procedure until I finally got it.

I was very generous with the superglue, and made sure to wait for it to dry before applying more glue. I didn’t get too much on my fingers, though I did almost glue my hand to the USB cable. Be careful with superglue.

I was able to image Arcturus only, as the tracking was running out of batteries, and not tracking properly anymore. But I am excited about the image, after tuning out the noise it looks quite good for what it is.

Image of Arcturus

Arcturus


Jul 12 2010

Astrophotography – Jupiter

Jupiter

I have been taking the Celestron 130 SLT telescope out on the weekends. Like most first-timers, I am just blown away by the sights in the night sky. Everything except Jupiter and Saturn have been a bright dot or a not-so-bright dot, so no views of galaxies quite yet.

I took this picture of Jupiter, and I’m so tickled to see one of the major cloud bands.