I’ve been working on the webcam telescope on and off for the past week. It took several days to get the inside painted and the outside stained. Today I started the final assembly, calibrated it, and got a so-so test picture (its a typical Pacific Northwest cloudy day).
Here is the completed unit:
I got the idea for this project from Make magazine (Vol 2, pg. 133). However, the original has a very primitive focus system where you just slide the back of the box (which contains the sensor) back and forth until it is in focus. That just seemed like a problem in the making (knowing how much trouble I can have with the simplest of things).
I decided to build course focus and fine focus platforms like this:
The CCD sensor mounts on the front platform. A single bolt lets me move that platform easily large distances and lets me rotate the platform so I can get perfect alignment. I calculated the distance from the lens mount must be 46mm, so this platform lets me get close to that distance.
The 2nd platform is the fine adjustment platform. It is attached to the back of the box with 3 bolts that go into T nuts. This allows me to move the fine adjustment platform back and forth and tilt on either plane as necessary by turning the screws on the back of the box:
To calibrate the unit, I set the lens to focus at 1′ (its closest focus), and slowly adjusted the 3 screws until the image was in focus and aligned fairly well.
Calibration was done using a 28mm lens. That lens was showing quite a bit of enlargement. I was calibrating using the lines of text on an air can and at 1′, I could only see a few words across and 3 lines down.
I then put the 100mm lens on. A little piece of trim on the neighbor’s house 30-40′ away filled the sensor. I wondered just how much magnification I was getting, so I did some math.
Comparing the sensor size to 35mm film size (for which the lens was designed), the sensor is 1/10 the size of a frame of film. So the sensor should enlarge the projected image by 10. If a 50mm lens is pretty close to normal human vision, then I would expect the resulting image to be 10 times larger. The primary lens I am using is 100mm, so I think it should be a power of 20. That is everything it sees should be 20 times larger than what the human eye sees.
Here is the webcam telescope pointed out the window at a park bench:
and here is what the webcam telescope was seeing:
Not too bad!
Of course, I used probably the cheapest Chinese CCD sensor available (I think I paid $4 for the webcam, new on Amazon). Now that I have it working I think I am willing to buy a decent quality webcam with an HD sensor.
Also, I am thinking it would be fun to build a servo controlled mount for it so I can electronically aim the telescope. Trying to move it by hand on the tripod was pretty clumsy. You have to make pretty fine movements.