Camera Labs

On the polar finder, tonight I had a go at collimating it. My conclusion, I think I messed it up beyond repair.

To cut a long story short, I can't keep the main barrel on the correct optical axis relative to the mount.

I now know more about how it is built than I ever wanted to know... on the tip is a cemented doublet. It fell out as I disassembled it, and thankfully one side was dirty enough for me to tell it was the one facing outside!

The main barrel is a plastic tube with thread on both ends, the other end screws into the section holding the image overlay and light source. A mistake I made in the past is that there is a screw holding the barrel in place. When I last dropped it, I unscrewed and rescrewed it in without touching that screw, which stripped off a lot of thread on the plastic barrel. The thread on both ends of the barrel appears the same, but even if I reverse it to use the other good end, it screws in very loosely that even with the screw tightened, it wobbles.

Inside the assembly is the insert which has the overlay. That is held in place with three screws which you can adjust to collimate it, assuming you didn't mess up the rest as badly as I did. Finally is the rear section holding a lens assembly of relatively short focal length. This overall seems to produce a basic telescope with inverting image. I think the image overlay should sit at the common focal point in order for everything to be in focus.

I think right now, my best bet might be to try replacing the plastic barrel with something else more sturdy, but I'd need to get the thread and diameter exact. That'll be tough I think. The alternative is to buy a replacement polar finder. I wouldn't get the same one again, but I'm not sure if any other model would be mechanically compatible or would otherwise be easily modified as such.

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Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.

Hi popo,

What a shame. No chance of a free replacement due to a manufacturing defect I suppose?

My guess, without ever having seen an AstroTrac in the flesh, is that while you could no doubt find polar finders that would fit through the mounting hole you would probably have to get someone with a lathe to make an adaptor to fix it in place. Or maybe you could adapt an AC602 Polarmate but they aren't exactly cheap. Or could you interest Astro Engineering in developing a version specifically for the AstroTrac and becoming a beta tester in return for a freebie! Sounds unlikely but if you don't ask....

Bob.

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OM-D E-M5 + ED 12-50mm, H-PS14042E, H-F007014E, L-RS014150E, M.ZUIKO DIGITAL 45mm 1:1.8.
Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.

The earlier dropping of it leading to it going badly out of alignment was entirely my fault, although thinking more I can try asking them if I can just purchase the long plastic section and have another go replacing it myself. Asking for a repair might be another option but I doubt that would be economic compared to re-buying new. I'm concerned I might also have damaged the bit the long bit screws into.

I have seen a relatively cheap Skywatcher but it's a bit lacking in detail as to what it offers.

_________________
Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.