Camera lens as a telescope

[Terry Scope]

Just thought I would tell you of my attempts to turn a webcam, pentax body and lenses into a telescope.

The web cam I used was the Philips SPC880/900 from Morgan computing. I obtained a Pentax P30 body for nothing off Freecycle and I already had 80-200 and 80-320mm pentax lenses as well as a few primes (50, 110 etc).

I removed the shutter from the P30. Nothing sophisticated. A pair of pliers and brute force. Stick the mirror up with tape.

Dismantled the webcam and found it had two mounting holes top and bottom of the sensor board. Took off the mic. Pliers again and disabled the on LED (cut track). Offered up the sensor board to the body and lo and behold the sensor was just in front of the film plane. Drilled two holes near the film guides in the middle of the shutter aperture and with a little insulation tape (to prevent the pcb shorting to the body) attached the sensor board to the camera body.

Connect up the webcam, put body on tripod and attach 80-200 lens.

The same night I tried it out. At 200mm with the small sensor size the moon filled 80% of the screen image. Great I thought. However, I couldn't get a sharp image even though the lens focus ring allowed adjustment on either side of best focus.

Tried the 80-320mm and the moons image more than filled the frame but still couldn't get a really sharp image.

I puzzled over this for a few days until I found out that film lenses were able to focus an image equivalent to 55 lines per mm. I worked out knowing the dimensions of the sensor in relation to a 35mm negative and knowing the number of pixels in the sensor that at 55 lines per mm each line would span 3 or 4 pixels.

I concluded that camera lenses were just not good enough so bought a telescope instead.