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Need help with LXD75's polarscope

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#1 Charles Hall

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Posted 14 January 2013 - 09:27 AM

Can someone explain the screws on the Meade LXD75's polarscope? I'm totally baffled. I've labelled the attached photo:

A - This thumbscrew doesn't seem to tighten anything.
B - This scale can be rotated independently by hand.
C - This scale can also be rotated by hand.
D - This ring with the indicator can be rotated independently.
E - 3 grub screws hold the telescope in. If you loosen them the polarscope comes out.
F - 3 setscrews with pointy ends dig into the threads holding the illuminated reticle to the long polarscope tube.
G - The eyepiece screws in or out to focus.

Which screws align the polarscope? Which control the rotation? Should all those scales be loose to move freely? What's that thumbscrew do?

I thought I generally knew what a polarscope should do, but I don't get this at all. If E and F are tight, the polarscope won't rotate.

Thanks!

Charles Hall
Raleigh, NC

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#2 rmollise

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Posted 14 January 2013 - 11:04 AM

A: That allows (if working properly) for the RA circle to move/not move when the mount is rotated in R.A.

B: Yes, you would need to rotate it to set it.

C: That scale is for the polar scope, but is not very useful.

D: Works with the above; again, not very useful.

E: Yep. Can also adjust its alignment.

F: Can adjust reticle.

G: OK.

You do NOT rotate the polar scope. You rotate the entire RA axis to align the reticle with what's in the sky.

Put the mark for Polaris straight down by rotating in R.A. Set the RA circle to 0. Look up current LST (like with a computer program), rotate in RA until that time is on the RA cirlce pointer. Use altitude and az adjustments to put Polaris on that mark and you are done.

#3 Geo.

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Posted 14 January 2013 - 11:56 AM

Think E or F is a set screw to lock a threaded ring. One of the threaded rings regulates the tension on the hour dial. The ring with the three screws is one that adjusts collimation. Folks often replace the grub screws with longer socket head screws to permit tooless adjustment.

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#4 orion61

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Posted 14 January 2013 - 12:36 PM

F: Can adjust reticle.

G: OK.

Look up current LST (like with a computer program), rotate in RA until that time is on the RA cirlce pointer. Use altitude and az adjustments to put Polaris on that mark and you are done.

Shouldn't that be LMT (Local Mean Time)? that is your exact time compensating for how many minutes W you are from your time zone line. it can be off by 59 minutes.
At least thats how I used to do it with my Vixen non Go To mount, it was very accurate useing the setting circles,
Go-To's may be different.

#5 rmollise

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Posted 14 January 2013 - 01:39 PM

F: Can adjust reticle.

G: OK.

Look up current LST (like with a computer program), rotate in RA until that time is on the RA cirlce pointer. Use altitude and az adjustments to put Polaris on that mark and you are done.

Shouldn't that be LMT (Local Mean Time)? that is your exact time compensating for how many minutes W you are from your time zone line. it can be off by 59 minutes.
At least thats how I used to do it with my Vixen non Go To mount, it was very accurate useing the setting circles,
Go-To's may be different.


Not at all. What you want, and what I meant, is LHA...local hour angle of Polaris. But you are right, I did screw up. :lol:

#6 Cliff Hipsher

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Posted 14 January 2013 - 05:53 PM

There is a much easier way.

Put the mount in the home position with the counter weight bar over the North leg.

Loosen the DEC clutch and rotate the mount 90 degrees in DEC. Set the DEC clutch.

Take RA axis plug out.

Get behind the mount and sight through the PAS.

If necessary, loosen the PAS grub screws and rotate the PAS to line up the "tail" of the center cross with the North leg. Tighten the grub screws.

When you go out to set up, point the mount North loosen the RA clutch and rotate the mount so the counter weight bar lines up with Kocab in Ursa Minor. Now you can use the manual Azimuth and Latitude adjustments to put Polaris where it needs to be in the reticule of the PAS.

Here is a link: http://www.thestarde...Polaralign.html

Works fine, lasts a long time, drains to the bildge. Guaranteed not to chip, fade, rust or rot.

#7 Charles Hall

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Posted 16 January 2013 - 01:21 PM

I'm the original poster, I just wanted to thank everyone for their responses! This is all very, very helpful.

Charles.






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