Adapting a Canon "point and shoot" camera for astrophotography
I bought a Canon PowerShot A550 camera to use for astrophotography. Previously I had been using a Philips SPC900N webcam. The advantages are huge. The webcam shoots 640 x 480 video and has the capability of 800 x 600 stills, although I was never able to use that for astrophotography. The Canon is a 7.1 Megapixel camera with a resolution of up to 3072 x 2304. It can also do 640 x 480 video, but the pixels are spread out over a much larger area. The larger chip makes it easier to place the image of an object on the chip. This will be especially important when photographing the ISS. It can take full resolution photos at a rate of 1.6 frames per second.
Below is a photo montage I made (using this program) showing the field of view of the two cameras along with a comparison of the size of the two chips. All photos assume the camera being at "Prime focus" which is at the focal point of the telescope with no lens.
The first pair of photos show the coverage with my telescope using the Canon A550 with and without a focal reducer.
The second pair of photos show the coverage of the webcam with and without the focal reducer.
The photos at the bottom show the chip sizes compared to a frame of 35mm film.
It looks like one would need to take about 4 photos with the webcam and paste them together to cover the same area as 1 photo with the Canon A550, although there would be some overlap..
The Canon A550 chip has a 2.5659 times larger area than the one in the Philips. It has 23 times as many pixels.
What prompted me to try this was a program (hat tip to jrlasers) that allows one to expand the capabilities of many Canon cameras. The ability to trip the shutter via a USB cable, to take exposures up to 64 seconds and to manually control the shutter speed are all valuable in astrophotography.
You may have noticed that I said prime focus involves a camera with no lens and realized that point and shoot cameras have a lens. This is where it gets fun.
I experimented with my old Canon A10 first, even though it has little control over exposure. It should work for the Moon though.
The first thing I noticed is that when the camera is turned on, the lens assembly telescopes outward. As luck would have it, the piece on the end is 1 1/4" in diameter, the same as an eyepiece. This make mounting the camera to the telescope as simple as it can get.
. I found that I did not need to disassemble the camera itself. All work could be done from the front of the lens assembly.
I turned on the camera to extend the lens assembly and then removed the batteries which kept the assembly extended.
First I pried off the ring with the lens information using a sharp knife. Then I simply continued prying pieces out until I got down to the lens. If you have any hope whatsoever restoring the automatic dust cap assembly, you should take close up photos of it before removing it and even then, good luck. I abandoned the idea entirely. Once you get down to the lens itself, you will see a thin plastic ring sticking up around the lens. Using a jeweler's screwdriver or knife, break it off around the lens. Then you can pry on the edge of the lens to slide it out. The first lens is a simple glass lens. Under that is a lens assembly with a black ring around it. Under that is one last lens. I had to break that one with a knife to get it out. I should have extended the lens assembly first. I damaged the shutter, but got it working again.
The pieces I removed are shown below in the order I removed them, from left to right.
I got some vignetting with just the lenses removed, so I did some more cutting. I ended up removing the front section completely.
This is what I have left. I inserted the barrel of a 4mm eyepiece to adapt it to eyepiece holder.
No luck at prime focus, at least in a CAT.
I want to try eyepiece projection, but it doesn't want to power up right now.