Arie's Dobsonian Telescopes

Optics and performance

Optics

Mike Lockwood made the two 13 inch f/5.0 mirrors. Communication with Mike was very pleasant and very professional. He kept me informed of any significant step in the process and delivered the mirrors within the promised time.

An essential feature of the two mirrors is that they must have almost identical focal lengths. If not, the different magnifications will give you a headache. 1-1.5% difference in focal length of the entire system (so including eyepieces etc) is all the brain can handle. Mike asserted that he could not detect any difference in focal lengths between the mirrors. Also that he could not detect any astigmatism in the mirrors. This really shows, the optics are really impressive! Stars are pinpoint sharp throughout the entire field up to the highest magnifications. The individual images, produced by each mirror are spendid as well. This shows, for instance, when used in the 13 inch mono-telescope (see the section on that) And that certainly has to do with the outstanding quality of Mike's optics!

Performance
Overall the binoscope is easy to set up and a pleasure to use.
• The binoscope itself works splendidly and is very stable, that is, with hardly any vibrations.
• Fusing of the images is no problem, there is hardly any adjustment needed during the night.
• Good collimation during the entire observation session.

As can be seen in the picture below, I installed the Argo Navis/ ServoCAT system on the binoscope. It all works like a charm, very stable and accurate, with impeccable ServoCAT tracking. With a short, initial TPAS session the pointing accuracy is very good, all night long.

Body heat and how to get rid of it

One fundamental drawback of a binoscope is that you are sitting below the optical paths of the system. Uprising body heat will inevitably enter the lightpath, potentially creating constant bad seeing conditions. How to avoid that? Dressing properly to reduce outgoing body heat has been suggested, but I also use a lightshroud around the binoscope to keep warmth out of the lightpaths (see below).

A further solution was to place dewshields on top of the secondary cages (picture below). I made these with the flocking material from Protostar. This is on the inside coated with a kind of non-reflective velvet material and is rather light weight. It helps to control the upward stream of warmed air better.

So to wrap it up.....overall, I'm pretty satisfied with the binoscope and think it was worth the trouble making it!

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