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New member with an old model DS-90 refractor


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#1 mellowgeorge

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Posted 10 October 2012 - 07:09 PM

I acquired a lightly used Meade DS-90 refractor (white tube) with the older Autostar mount on Craigslist.

The telescope optics looks clean and clear. I disassembled, cleaned, and regreased the gears that turn the mount.

This telescope, unfortunately, suffers from a really cheap, low-quality focuser. The drawtube is plastic with a lot of wiggle and play. I did my best to clean the focusing gear and replaced the felt pads inside the focuser with slick tape. Now it's a snug and smooth when I draw the tube out but suffers from a significant backlash in the opposite direction.

I'm probably going to replace the focuser with a better made rack and pinion focuser (perhaps a Crayford in the future).

Just wanted to say hello and hopefully I can meet other fellow owners of this particular scope / mount.
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Meade DS-90 (white tube) refractor on an Autostar mount with 494 controller
Orion Spaceprobe 3 on an Alt-Az mount
Celestron 15x70 binoculars

Meade DSI

#2 MistrBadgr

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Posted 10 October 2012 - 08:40 PM

Hello MelloGeorge!

Welcome to the Meade 4m Community Forum!

I have a DS-2090 and a DS-2102 that I have put together from various parts from different origins. My mounts and optical tubes are newer versions than yours. For whatever it is worth, you can probably pick up a new focuser, if you want one, from Telescope-Warehouse and maybe a few other places on eBay.

I am not sure just how your focuser is configured. But, on mine, about the last two inches of what would normally be the metal tube is actually part of the plastic focuser. I have thought about having a part machined to take the place of that two inches and then insert a crayford. I have found it simply easier to live with the old focuser. As the do wear out and start getting a lot of back lash in them, the likelihood of shelling out gear teeth gets higher.

You might want to stick a cheshire eyepiece in your telescope and make sure things are still lined up. Putting a little more of the slick tape you have or felt on one side or the other can shift things around to get collimation spot on.

These are fun scopes to tinker with as well as use.

Best Regards,

Bill Steen

#3 mellowgeorge

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Posted 11 October 2012 - 02:42 AM

Bill,

I do enjoy the fact that these older scopes are so open to tinkering. :)

Good suggestion re: collimating the focuser. I'll do that once i get a hold of a cheshire eyepiece. The only collimating eyepiece that I have is the one that came with my small Newtonian reflector. It looks like an end cap with a hole in the middle. Will that work on refractors?

The objective cell on the DS-90 is fixed and I haven't done a star test yet.
===
Meade DS-90 (white tube) refractor on an Autostar mount with 494 controller
Orion Spaceprobe 3 on an Alt-Az mount
Celestron 15x70 binoculars

Meade DSI

#4 MistrBadgr

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Posted 11 October 2012 - 03:44 AM

George,

If you can use the circle of the inner end of the focuser to center the the circle of the objective in, then it should work. If the circles are too far apart, then the cross-hairs in a cheshire will help.

I also use a laser collimator. The collimator is a bit heavy for the focuser. The fix for me has been to point the scope vertical. I cut out a circle of paper that will just fit inside the objective retaining ring, put a small black dot in the center, then insert the collimator and turn it on. The red dot of the collimator should shine on the black dot. I have also found that quite a bit of light will bounce back to the collimator and I can see a widened red dot on the collimator screen. However, I am not sure a laser collimator bouncing a red dot back off the back side of the objective is a definitive way to do this and is really necessary.

The only time I have found an objective lens off was when the actual optical tube was slightly bent. I put a long aluminum "yard stick" along side the tube and then hold the tube up and look at a ceiling light shining through the tiny gap between the tube and the yard stick. I work my way around the tube, looking for differences. With the tube that was bent, which was a DS-2102 that showed a lot of purple in its image, I gently worked the tube over my knee and thigh. It took a lot of little bumps and re-measurement, along with a sore leg, But, it eventually came back in line.

I will also check out the objective itself and blacken the edge of the lens with a regular size "Sharpie." I use the side of the cone tip and even blacken the little bevel in the glass. This seems to really help with contrast. Check around the little lip of plastic inside the housing that the lens sits on with your finger nail, and make sure there are not any little bumps along the way.

I have written some posts on taking apart an NG-70 and working it over to get the best image out of it. I give a description about taking the lens apart and getting it back together. So far, the DS 90 and 102 mm refractors have the two lenses cemented together, rather than having an air gap between the two, like an NG scope. This makes life simpler.

If this does not make sense to you, holler back with any questions.

Best Regards,

Bill Steen




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