[tempestwizz (Brian)]

Now that I have fabricated an acceptable environmental housing to shield my permanently set up mount and scope from the heat and wild weather of Laos while not observing, I am moving on to the next stage of set up.

Now trying to set up a Tak EM200 mount on my pier, and match it to my TOA130. The OTA is attached with the standard Tak clamshell.

This is the first time I’ve considered the cone angle with this arrangement.

What I have noted however, I have found confusing.

In my alignment process: (with the luxury of being in the northern hemisphere)

1. I have adjusted the EM200 so that the polar scope is centred on Polaris.
1a. I have confirmed that as I rotate the mount, Polaris remains in the centre.

2. With the mount at top dead centre, I have inserted shims as necessary in the clamshell to bring the scope to point to Polaris. ( with dec trim as required to centre )

3. Now for the problem! (I’m using a 12mm illuminated reticle eyepiece.)

When I rotate the mount 90° to the right, Polaris appears to be too high, ie, about half way from centre, to the edge of view on the RHS.

When I rotate back to TDC, Polaris is centred as before.

When I rotate the mount 90° to the left, Polaris again appears to be too high, ie about half way from centre to the edge of view on the LHS.

At TDC, Polaris is centred!
That cannot be, to my reckoning.

I have repeated this process several times with the same result. I cannot understand the mechanics of how this can be.
Hopefully someone smarter than me may be able to explain?

It suggests there may be a bow in the axis of rotation.

Maybe if I crank the gears so that I make a 90° shift in the mechanical shaft position of my current TDC, it would change?

I’m at a loss.

Brian