Project Status - 30-cm + mounting


I didn't even mention that I had to fit encoders to the imaging mount! Well, I've now done that job. I've had the encoders for 9 months, just to give you an idea of how slow I am. I had wanted to gear them down in an attempt to get more resolution out of them, but the cost involved seems too much. So now they're just coupled directly to each axis.

I've also finalised the design for the new imaging telescope. A Serrurier truss made of aluminium poles with a centre section of square aluminium. I've bought the material and already cut some of the material for the centre section and mirror cell. The "old" top end has been strengthened but I'm having second thoughts about using it. I think I can do better by utilising the truss poles and top end ring directly rather than having a separate top end as seen on many portable Dobsonians.


This page is working! I'm actually getting things done - slowly.

I've done a pointing test with the equatorial mounting and a provisional model give 0·17 degrees RMS on 32 stars. Polar axis misalignment is less than can be detected with the resolution of the encoders (as expected).

The new imaging telescope is underway. So far the square centre section and two octagonal rings have been welded, and the main mirror cell is almost complete. The octagons are for the top and bottom ends; the truss poles attach to them. In the next few days I should finsish the mirror cell and get it attached to the bottom octagon. Once this is done I'll know the weight of the bottom end. Construction will then commence on the top end. Once that is done I'll know the weight of each end and can then calculate pole lengths for correct balance.


OK! Yesterday the new imaging telescope saw "first light" - a distant tree. Today it met the equatorial mounting. Alas only a partial success - it is just a little heavier than I'd hoped and doesn't quite balance. So I'll need to make a new counterweight for the mounting. This is also bad news as the guide scope isn't attached yet.

Here is a picture of the mounting sitting on the floor showing the general layout and the mirror cell. While here it is attached to the mounting, also with the CCD attached. The secondary mirror is not attached in either picture, and the second picture shows a small weight hung from the secondary holder as the balance isn't right - the baffling has yet to be installed.

Still lots more work to do on it, but it's getting there. Can't wait to look at some stars with it.


I've actually done some imaging with the telescope although things weren't really ready. This was due to my comet discovery and wanting to get some astrometry done, and as I'd removed the 20-cm I simply had to use the 30-cm. The optics lined up easily and the mirror cell seems to work well. I've just hung some extra weight on the end of the existing weights and placed a small baffle opposite the focuser to block the direct sky from the CCD.

I've mounted the finder and guidescope, and run an extension cable from the focuser to my CCD desk (which also combines the motor drive and encoder into the one line for convenience). The cables are just tied to the truss tubes at the moment which looks a bit untidy - but will probably remain that way.

What remains to be done is a proper job of the baffling, an extra counterweight on the dec. axis, and a general tidy up. Unfortunately, the re-location of the declination axis meant that the encoder had to be removed. The final job will be to replace it.


I think I can call the telescope finished now. I've added a baffle tube made from 0·8mm thick polycarbonate to keep out the dust, dew and light. I've just painted the spider which I forgot to do earlier. And finally I've written it up on my telescopes page.

There will always be some fiddling done to the telescope and mounting, but the system is back to being useful again so it is as finished as it needs to be...

Page last updated 1999/05/25
Steven Lee