Re: An easier Pasillx N & S Polar Alignment method

Joe Zeglinski

Of course - NOW I see it - thanks Chuck.

In essence, adjusting the "finder set screws" to make it orthogonal, is just like adding shims to the OTA for the same reason. So, if I can't get the mount aligned after a few tries, work on shimming (adjusting set screws) of the finder, and recursively - finally - get the (mount + finder) perfectly orthogonal and all aligned on the pole, tolerating the OTA being left off-centre, in the process.

I see now, that is a lot easier than futzing with brass shims with the (Mount + OTA) alternative.
Of course, the end result is perfect GOTO for the finder, while the OTA field - and thus the camera view are left permanently "off the mark a bit". I can now see why Roland used that procedure, since he might have only been interested in quickly field testing a mount prior to shipment, but that is not something I would desire as a regular "field set up". Although, if the OTA is not that far off, it might be tolerable - just.

By the way, I find adjusting finders in "double ring mounts" a real ain - 6 screws, and possible dents or scratches on the finder tube!

I found a much better method for the tiny 7x finder on my OTA. I removed the front set of 3 screws from the front ring mount, and put a suitably thick O-Ring on the finder front end, so that the finder fit snugly inside the ring mount. This O-Ring then acts like a "pivot bearing" - like on a large machine gun bipod (e.g. Brenn Gun of old) - so all I need to do is adjust the one set of screws at the rear ring mount, which causes the finder to swivel around on the front O-Ring. I get a lot more precise adjustment, quickly and smoothly.

That could be done with similar large OTA ring mounts. You would need to buy something like two huge O-Rings (like those used on "needle work stretch frames" from hobby or sewing centres), spaced an inch apart near the OTA dew shield/corrector, and then a small air inflatable tire tube in the front ring. Fill it with air using a bicycle pump so it grips the OTA in the one inch channel, between the needle work frame O-Rings.
You could probably devise a similar "filler" with rigid foam rubber, or sliced rubber pipe insulation formed into a donut, instead. Now you only need to futz with the rear mount ring screws to get the OTA orthogonal.
Wish somebody would make this a product. Sure beats adding brass shims to the OTA mount rings!
I think that would speed things up if Roland wanted to always have OTA's quickly orthogonal, and tolerate the finder being slightly off centre - which can be squared up with the OTA much easier, upon completion.
Probably not a very common issue for the OTA, but finders on OTA's get bumped and misaligned after almost every trip.


----- Original Message -----
From: "Chuck Hancock" <cdh59@...>
To: <ap-gto@...>
Sent: Sunday, September 21, 2008 10:47 AM
Subject: Re: [ap-gto] Re: An easier Pasillx N & S Polar Alignment method

Hey Joe,
The concept you should know here is that the OTA doesn't need to be
orthogonal. You only need the finder scope orthogonal to the mount (not
the OTA) in order to polar align the mount's RA axis.

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