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Re: next up: polar alignment tutorial

 

JMD:

You posed this puzzle:

? ?How to eliminate or minimize the variation in polar alignment when you loosen and re-tighten the AZ and EL locking bolts.??

_______

Here is what I did to help minimize this problem:

When you loosen the AZ bolts, the only mechanical element holding the vertical axis firm is a large center bolt under the bottom of the RA axis.? I think this is 3/8-16 thread on the G11 and GM8 and GM811.? This must be loose to allow the AZ to be rotated.

1. I install one or more heavy Belleville spring washers under that bolt head.? The compressed Belleville washers provided a constant force on the AZ axis.? ?

2. I also put a pair of face to face Belleville spring washers surrounded by flat stainless steel washers on each of the AZ and EL bolts.

4. I put either Black or (better for dim lighting) color (Red or Yellow) T handle bolts that are slightly longer, to accommodate the needed vertical space.

When you then slightly loosen the AZ or EL locks, the springs keep these AZ and EL axes under a constant force that is easily adjustable.? Then the polar axis adjustments have less play.? ?Perhaps you will see near zero play....depending on your scope FL.??

Here are photos...

I have these parts, for a modest fee.? I will make up the bolts in the color T handle you prefer (or you can just use your existing T handles of course).? Contact me if interested, and let me know your mount type.??

Best,
Michael





On Sat, May 22, 2021, 7:43 AM Les Niles <les@...> wrote:
It¡¯s complicated.? Because refraction varies continuously across the sky, there is no combination of polar alignment and tracking rate that will give perfect tracking everywhere.? In fact, there is no combination that will given perfect tracking of any single object as it moves across the sky, though it¡¯s possible to get close by aligning on the refracted pole and using a drive with a proper adaptive King rate.? At least in the middle latitudes, aligning to the refracted pole actually works better than trying to align to the true pole.? There¡¯s a detailed discussion at?, including formulae and spreadsheets to calculate the theoretical drift, which you could compare with what you¡¯re actually seeing. ?

The bottom line is that guiding is always going to be necessary.? The purpose of polar alignment is to get close enough that guiding is smooth and field rotation is not significant. ??

? -Les



On 22 May 2021, at 6:13, alan137 <acfang137@...> wrote:

What I would like to see some day is: Polar Alignment, part 2 - very accurate polar alignment

I can get extremely precise PA with sharpcap, but the accuracy seems to be a bit off since I still get a very slow RA drift.? I dunno it's either due to refracted vs real pole, king rate, equipment flex, etc.? I think I'd need to do some kind of a drift alignment to trim to the final value, or just cheat and adjust the RA divisor rate.

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