Megrez 72 FD questions

[flyingbarron]

Hello,
I'm the happy owner of a 2nd hand Megrez. Judging by the clouds which it has summoned - it must be a fantastic scope!

In the meantime, I have a few questions...

I want to purchase and attach a finderscope.
1. The scope has a finderscope screw which I can unscrew and place a WO finder base. Are there other finder bases which have the same standard screw? Is this standard?
2. I've got an AZ4 tripod which means that the scope is rotated 90 degrees to get the mounting plate into the tripod head. This pivots the finder to the side too. Could I use any of the 3 screws behind the lock screw for this?
What are they for, anyway?
I've attached a picture - I'm asking about the screws circled in blue.

The focuser seems fine, unless I pivot the telescope too high up and then it can "zoom out" and turning the focus knob won't pull it up - even when the only weight is only a diagonal + eyepiece.
I see that there's a way to tighten the focus mechanism underneath the tube. Would this be likely enough to solve the problem or might I be looking at something more serious? I need to go out and buy an Allen tool that matches anyway.

I hope there are some people here familiar enough with this old scope!
Thanks in advance,

Robert.

[vlaiv]

I'm not familiar with this particular model, but I'll venture a guess here on questions you asked.

2 hours ago, flyingbarron said:

1. The scope has a finderscope screw which I can unscrew and place a WO finder base. Are there other finder bases which have the same standard screw? Is this standard?

"Standard" Vixen finder shoe often uses two screws to secure it in place - like this one here:

https://www.firstlightoptics.com/finders/astro-essentials-finder-shoe.html

Although technically - you could secure it in place with just one screw.

2 hours ago, flyingbarron said:

2. I've got an AZ4 tripod which means that the scope is rotated 90 degrees to get the mounting plate into the tripod head. This pivots the finder to the side too. Could I use any of the 3 screws behind the lock screw for this?
What are they for, anyway?

My guess is that two larger wholes - one marked for finder scope and other of same diameter that you circled in blue are for same purpose - attaching finder scope shoe.

Difference between the two is that it allows you to decide if you want your finder to rotate with the focuser or not. In your case - you want it to rotate to properly mount the scope on AZ4. There are cases when you don't want it to rotate - like when imaging - you rotate focuser to frame the subject - but have guide scope attached at fixed finder shoe - you don't want to rotate that as it messes up with guide calibration.

I suspect that two smaller holes contain grub screws that are used to adjust the tension / play on rotation mechanism.

As for slipping focuser - I suspect that focuser is crayford type and that you should have screws on the bottom side - used to adjust the tension of focuser itself. There should also be focuser lock screw down there.

I'm sure there are online tutorials that show how to adjust tension on such crayford focuser.

There are threads like these:

https://www.cloudynights.com/topic/651495-crayford-focuser-tension-adjustment-help/

for example.

HTH

[Louis D]

Don't mess with the three grub screws around the perimeter of the focuser.  Those control focuser rotation tension as vlaiv says above.

It is the larger holes you want to use as vlaiv says above.  One for fixed orientation, one for rotation with the focuser.

I have no idea why you would want to put a finder scope on it.  Get a 2" diagonal and a 35mm to 40mm widest field 2" eyepiece, and you've got an 11x to 12x, 6+ degree finder scope built in.

I do use one of the two holes to attach a Rigel QuikFinder foot to it.  That does make sense.

I have the Astro-Tech AT72ED version of that scope.  I've attached the manual for it below.

Astro-Tech 72ED.pdf

Edited March 25, 2021 by Louis D

[flyingbarron]

Ok, thank you both.

I bought an Allen tool for the screw and the focuser is much "grippier" now.

Yes, I meant a Red Dot Finder, not a finderscope and now that I look again, one of the blue screws is bigger than the others. The Astro-Tech manual makes it much clearer!

 

 

[KP82]

I had a Megrez 90 before which came with a similar focuser to your 72. The larger grub screw closest to the WO swan logo can actually be un-screwed and replaced with a standard M5 bolt for attaching a finder base. The other two however are used to control the rotation of the focuser unit, so leave them alone. Most standard Synta finder shoes require 2x M4 or M5 bolts, but they can still work with just one. Alternatively grab yourself a Baader universal finder base instead.

Edited March 26, 2021 by KP82

[Louis D]

You may need to put silicone bumper feet on your finder base's corners to keep it from rocking on the small diameter focuser.  I had to do this with my QuikFinder base.

Edited March 26, 2021 by Louis D