hamishbarker

Did your Stevick-Paul get completed? I just completed a 160mm f15 version. (I had a very long focus primary, but anyway had to refigure it as it had shocking astigmatism which I only discovered on assembly of the telescope. I made my own convex secondary and concave tertiary. All coatings apart from the quaternary flat are silver, for best reflectivity.

I did some investigation with the OSLO-edu optics software and it appears that tolerances for focal length and spacing along the optical path are actually quite loose. It's just the angles which are a bit more critical. Collimation has gone quite well and i get nice views but at 160mm aperture it's no light bucket. Mine has a tube for the secondary/tertiary/quaternary mirrors and focuser, while the primary is slung below the tube via a hexapod truss allowing both angle and position adjustments. I have a thread over on the ATM section of the big other astronomy forum starting with C.

Yes, I was thinking about that the other day. I guess the internal reflection would be at least 4-6% so no good if one is trying to achieve a decent S/N. I will have a look. I've been concentrating my spare time on finishing the figuring of a big telescope mirror which has been lingering for a couple of years.

Multiple images in the guiding camera are not such a big problem I suppose, especially if they are only faint.

An old thread but perhaps worth a repost: I scavenged some nice front surface mirrors (presumably alu on glass) from an old scanner/printer. There were 5 mirrors!

I tried making reflective slits by cutting the alu lightly with a hobby knife along a straight edge.

Testing with a laser pointer and measuring the diffration pattern indicated that light scoring made a 23um slit, while heavier pressure with a dull tip made about 50um slit.

Looking at the slit under  a magnifier, it looks nice and straight. So will try it in my home built transmission scope (uses old pentax 50mm and 28mm lenses and a piece of 1000lpmm plastic transmission grating but the home made pencil sharpener slit was not even and not reflective)..