Thursday, September 23, 2010

Project updates

I'm at various stages of four astronomy DIY projects.  Projects 2 and 3 are linked in that the eyepiece will have narrow usable field of view, and hence will benefit from the equatorial table.

1. Digital setting circles: I bought a bluetooth-based module that can communicate with encoders.  Unfortunately, I can't get the magnetic encoder to work with it.  I think an oscilloscope might be needed to figure it out.  So I may just need to save up for two optical encoders (360 cpr, and then attached via a 1:4 timing pulley setup).

2. Equatorial table: I had routed the sectors, but it turns out that I had miscalculated the center of mass of the telescope, so the cut radii weren't good.  I've been procrastinating recutting them.  Need to get back to that.

3. Hastings triplet eyepiece: Today I ordered a super-cheap (about $1.80 shipped) ebay 30X triplet loupe.  I think it should be a 8.3mm Hastings triplet.  If it works, I hope to drill out a 1.25" wood dowel and mount it inside as a nice planetary 8.3mm eyepiece.  If it works really well, I might try to sell them for $15-20 each.

4. Laser collimator: This is for a friend.  I still need to print and cut out a collimation target, and then collimate the collimator.


  1. The alleged triplet came, and it's only 10X. Eek. Looking at Amazon reviews, I get the feeling there are two cheap magnifiers out there labeled "30X21mm". Some of them are genuine 30X triplets and some are closer to 10X. There seems to be a bit of a pattern. Those that also have "TRIPLET" stamped on them seem to be really 30X (and some people complain the magnification is high and eye-relief is low, which is exactly what you'd expect for 30X) and those that just have "30X21mm" are the 10X ones.

    I tried the magnifier with my 8" F/4. Used as a hand-held eyepiece, it seems to have a similar magnification to my 30mm Rini eyepiece, which would make it about 8X-10X (I sometimes suspect the Rini is a bit shorter FL than 30mm) in magnifier language (apparently the magnification of a magnifier is 250mm/FL). It shows chromatic aberration on Jupiter, but the tiny Jupiter did in fact show a cloud belt at least, so it's not completely unusable. Turned to the Double Cluster it gave a good image, but with much smaller AFOV than my 30mm Rini. Maybe the AFOV was 30 degrees.

    Given that there do seem to be cheap genuine 30X units (which should be 8.3mm FL), I think I will try again. But I still want to try to make sure I source the cheapest possible unit that does the job, as I may want to make a bunch of eyepieces, e.g., to give them out at star parties to volunteers.

  2. I've given up on the DSC encoders, and sold off my most expensive component. Just decided I don't really need this project.

    And the Hastings project fell through, too. The cheap magnifiers aren't Hastings.