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meade ds-90

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#26 zvaragabor

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Posted 26 January 2011 - 10:06 AM

Thanks scott. You use this scope right? Are you satisfied with it? I'm mostly interested in its optical performance.

#27 ArieSirius123

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Posted 26 January 2011 - 12:00 PM

i have one. its my first scope and i can say that it compares quite nicely to much more expensive scopes ive looked through at star parties. apparently some of them came with .965 eyepiece and some didnt. mine did. and im yet to replace them and even with those eyepieces ive got some awesome views. the goto works pretty good too.

#28 scott m

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Posted 26 January 2011 - 01:51 PM

Optically it's great very little CA on planets and I think I have had my best views of M42 and the double cluster through this scope.

#29 sailor70623

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Posted 26 January 2011 - 02:29 PM

The scope as far as f11 achros goes is fine. Focuser upgrades can help it out a lot. The DS Go-To can work good, but is a bit weak. Make sure it works before you buy. Balance is very important with these units. They do eat batteries. I use my DS Go-Tos with a 12v to 9v adapter and run them off a deep cycle marine 12v battery. The iOptron mounts work a bit better, and the Se mounts from Celestron are much better, but a good working DS mount can be a lot of fun. If you up grade the mount later, these mounts the DS) hold the smaller 60mm scopes just fine. (80mm short tubes too). I have even used them for my 90mm Maks and they work well then too.
The guts on the DS mounts are plastic, and they do break easily. Depending on how much of a DYIer you are, repairs are possible, but not easy. The biggest fown side is that you need power with these mounts. When the batteries are dead, they do not work. Alignment and training and calibration are importabt with these mounts. It can be a challenge for beginners. Once you get the steps down, it's not so bad.

#30 zvaragabor

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Posted 26 January 2011 - 03:34 PM

Thx guys. Sailor, sorry I forgot to mention, it's just the tube I'd like to buy. And the mound would be an eq3. Thank you anyway, useful advice.

#31 sailor70623

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Posted 26 January 2011 - 03:36 PM

Then if it's a good price, go for it.

#32 scott m

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Posted 26 January 2011 - 05:42 PM

I have mine mounted on an EQ3 (Orion AstroView) a little shaky at high power but not bad. I think it has to do with the length of the scope versus the weight of it.

#33 zvaragabor

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Posted 27 January 2011 - 03:44 PM

Bad news, I was late, unfortunately someone took the telescope. :( Now looking for another scope... Thanks for all the help.
Cheers

#34 wagner lip

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Posted 28 January 2011 - 08:19 PM

Last week I bought a DS-90 with the Autostar #494, diagonal and eyepieces are 1.25". I went to pick it up with the seller almost 3 hours from home here in Florida.

I disassembled everything, cleanned everything with warm soappy water and soft brush and cloth as it should. No kidding, disassembled even the main lenses and the guts of the 9mm eyepiece that came along, with extra care, distiled water with small quantity of windex. Fingerprints on the lenses are not a good thing, but I was able to clean everything without compromising the coatings. Ended up pristine clean.

Believe of not, the mount legs were never extended.

The #492 motors units (gears, shafts, photosensor) went through a special care, wash and clean up. Everything was in good shape, but mechanically out of alignment everywhere.

Replaced some washers and nylon retaining nuts on the worm/gear units with brand new ones from Ace Hardware, now they are working like a violin.

I noticed that some people complain about large backlash on DS motors, the problem is mostly adjustment on the worm/gear pressure and worm axial slack movement, easily reduced by the nylon retaining nut adjusment. The worm shaft has a type of conical slug in the opposite side of the nut, if the nut is not correctly tied, the conical slug doesn't go correctly into his bed and the worm ends up with larger distance from the gear... large backlash.

There is a mechanism to fine adjust the distance from the worm to the gear, it is at the nut side of the worm's shaft. It is a kind of bed elevator for the shaft, in the form of a black nylon nut, it pulls the worm's shaft against the gear, adjusted by a tiny alen screw locked by a small nut at 90 degrees to the shaft. The adjustment should be done only after everything else is adjusted (mostly the conical slug in the correct place) and lubed.

A common mistake is to apply grease in the clutch, between the gear and the large locking washers on each side of it. If you do, you will need to apply more force on the knobs to lock the scope (clutch) to the motors. Just wash the gear and the washers in warm or hot soappy water to remove any grease, use a toothbrush to help. After dry, apply a narrow white lithium grease on the gear teeth band and over the worm and that's it. You can apply lithium grease on the support plastic bearings of the worm shaft.

The DS-90 tube is heavy, large mass, the #492 motors are not that strong for this brute, lacks muscle, so tube balance should be pristine. Because of the mass of the scope, the motors will consume more power than most of the other DS scopes. For that I don't use regular AA batteries. I use a power adapter (12V @ 2A) or a 12V@7A Powersonic Lead Sealed battery underneath the mount, or tied to a tripod leg.

Found the plastic encasing the worm/gear underneath the mount base with 3 to 4mm of slack to the base (horrible backlash), like if it was with loosen screews, even so the 3 screws that hold it underneath the mount base where tied. Removed everything, clean, glued a thin silicon band (rubber band should do the trick) in the grove (on the plastic case) that touches the underneath of the mount base. Upon assembly it is now solid. It should had a "O-Ring" or some grooves to avoid it being only hold the plastic case by the tiny screws. With the constant force of the motors back and forth, and friction, the screws openned a wider hole in the plastic, causing the problem. The silicon/rubber band will solve it for years.

The Autostar Computer Controller #494 was telling me some motor problems upon power up. Google told me it could be several things, including bad connection on the coiled cable. Measuring continuity between the RJ31 connector and the inside connector of the #494, found the green wire (pin #4 or #5 on the RJ31) with no contact. Just use the RJ45 crimp tool to recrimp the RJ31, and bam! working like a charm.

The output gear of one #492 motor has one tooth with a small damage. From time to time it skips a step. I am already shopping for a gear replacement. As a matter of fact I am requesting 2 extra #492 motors for safe future, Meade is not manufacturing those any longer.

The DS-90 has fantastic optics, simple, clean, clear and easy, nice light. The viewpiece of 9mm gives around 110x magnification, you can see an orange vertical band on Jupiter, and Saturn is like a little white bird sliding in the black sky, will be stuck in my mind forever.

Aperture of 90mm (3.5") is not that much, but make wonders. This kind of scope really needs a TELRAD urgently. The viewscope that comes with it is a total waste of time.

The AutoStar unit works very well in this unit.

You *MUST* setup the AutoStar controller with your correct Lat/Long (or city), and perfect Date/Time (and DayLight Savings info). Date and Time is required at each power off/on.

Then you need to do the inicial physical setup, very nice horizontal alignment with the tripod and scope. Use a couple of good round (360 degrees) bubble levels, one for the mount and legs, another for the scope itself, then point everything (horizontally) the best you can to the sideral north. Then proceed with the two stars alignment. After that, things works very nice most of the time.

The original focuser has some small vertical slack, but not a problem if you use the #494 and motors to fine adjustment of position.

I have severe back pain. It seems that all refractor scopes are no good for people like me. As the pivot point of the mount goes in the middle of this 40 inches scope, any lateral or vertical move will require you to do the same on the eyepiece. After 90 minutes of playing outside, my back was killing me. I am not that athletic anymore.

I will hate to depart from this DS-90 unit, but it seems the obvious path for my back sake.

The DS-90 is an impressive unit, it is not small, it has personallity and size. People look at it and say "wowa, for sure this is not a toy".

This week I was able to find a ETX-90EC with lots of bells and whistles. With much less movement on my side, my back is already thanking me.

Of course I am still waiting HayNeedle to deliver the second box of my brand new CPC800. The scope itself is in the box here waiting the mount and power bucket that are on backorder from Celestron.

In some way I need two scopes, this way I am trying to have my teen-18-ager boy along me on those Saturday cold nights. Yeah right! At least after he returns home late night!

#35 rdandrea

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Posted 28 January 2011 - 08:39 PM

Good, thorough post. Thank you.

#36 mexjon

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Posted 28 January 2011 - 09:14 PM

Wagner- Very informative post! Now that you have that ETX90 EC, make sure you do the same good cleaning job to the right friction clutch so yours doesn't end up broken like mine. Apparently previous owner(s) had over-tightened instead of cleaning and sanding the right tube adapter as they should have. Probably had a lot of grease preventing friction, and they just kept tightening away. By the time I got it, most of the damage was done and it soon broke on both sides of the clutch.

Thanks for your thorough report on your DS. I enjoyed learning about it.

Cheers

#37 wagner lip

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Posted 31 January 2011 - 02:56 PM

John, yesterday I disassembled the ETC90-EC, clean, sand, adjust, lube. It was a nice task. I am posting the work in a new thread, including some pictures of the fork motor noise reduction trick and sealed lead acid battery support.

#38 mexjon

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Posted 31 January 2011 - 03:23 PM

John, yesterday I disassembled the ETC90-EC, clean, sand, adjust, lube. It was a nice task. I am posting the work in a new thread, including some pictures of the fork motor noise reduction trick and sealed lead acid battery support.


Very good. Avoiding a major problem by getting all that done. Hope you enjoy it.

#39 artao

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Posted 01 February 2011 - 07:53 AM

@Wagner -- thanks for all that info, i'll have to take mine apart and check those adjustments. I do have a backlash problem on both axes, which seems to exist IN the mount, not the gearpack. I've read of "the leather washer fix", but am having difficulty re-locating that info. Do you, or anyone one else, know anything about this??
Also, regarding your disassembly and cleaning of the main optics ... how difficult was it to maintain collimation? Is the lens assembly sensitive to rotational collimation as well?
:D :D

#40 mexjon

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Posted 01 February 2011 - 03:27 PM

@Wagner -- thanks for all that info, i'll have to take mine apart and check those adjustments. I do have a backlash problem on both axes, which seems to exist IN the mount, not the gearpack. I've read of "the leather washer fix", but am having difficulty re-locating that info. Do you, or anyone one else, know anything about this??
Also, regarding your disassembly and cleaning of the main optics ... how difficult was it to maintain collimation? Is the lens assembly sensitive to rotational collimation as well?
:D :D


I read on Google that the leather washer info is on the Yahoo DS Group.

#41 wagner lip

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Posted 01 February 2011 - 07:09 PM

Artao, I removed 3 screws on the front DS-90 lens black lens tube, it came out with lenses.

Put some pencil marks on the black plastic lens tube and white tube.

Then with small force I was able to unscrew a large ring in front of the lenses. This ring hold the two lenses in place.

Now slowly I insert a clean microfibre cloth inside and against the lenses, turn it upside down and "pourred" the two lenses over my hand, marking each lens in the border with pencil (Lens #1 arrow to front, up, same for lens #2).

For a more permanent marks you can use the "house owner's" nail polisher (at the edge of the lenses) and wait it to dry.

After cleanning the lenses very well (distiled water, few drops of windex, I use microfibre cloth, clean perfectly), observe the lenses against a strong light, initially it is never clean. Be carefull to not clean the pencil marks.

Then wait it to be really dry and here comes the tricky part, holding the lenses together and insert it back into the lens tube.

After you find it out, it is easy. Use a clean cloth (microfiber) over the top open of a regular tall water drinking glass and deposit the lenses aligned over the cloth, over the glass. The glass will serve as a temporary tall support, and it must have a smaller diameter than the lenses.

Now slowly cover the lenses with the black plastic lenses tube, following the alignment marks done previously by pencil.

After the tube is down in place, hold everything together, tube, lenses, cloth and cup with some pressure, and turn it upside down, remove the glass cup and cloth, screw back the large front black plastic ring.

Insert all the unit in front of the telescope tube, align with marks, with holes, screws. That's it. There is no ajustments to be done.

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#42 ducatirob

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Posted 02 February 2011 - 04:19 AM

Here's the web address showing the leather washer fix; http://jjacobso0.tri...ds90ec/id4.html
I've owned my DS 90 for around 10 years. It Still gets alot use, Hpoe this helps you.
Rob

#43 artao

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Posted 02 February 2011 - 10:51 AM

Thank you all three for the info. I had tried googling, but only found references to the washer fix, not the actual "how-to", and my older links were mostly broken ... I eventually found the link ducatirob posted.
@wagner - Very Thank You! for the in-depth description. My optics could use some TLC, but I've been kinda afraid of screwing them up ... this is my only scope, so I don't want to destroy it, obviously ... I've got a lens-cleaning kit, including lens-solution and disposable lens-paper, as well as a microfiber cloth, that I can use. It's just that condensation has left various dirt spots on the lenses where I'd have to take 'em apart to get to.
Now I'm not quite so scared :D :D

#44 ArieSirius123

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Posted 03 February 2011 - 03:30 AM

good link ducatirob, was able to fix the clamp on one of the legs. thanks.

#45 zvaragabor

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Posted 29 November 2012 - 10:48 AM

Do anyone know the inside diameter for the tube? Or could someone measure it?
Thanks!

#46 zvaragabor

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Posted 26 January 2013 - 11:44 AM

Finally I managed to buy a second-hand Meade ds-90 OTA. I'm so happy! :) It will be my double-star hunter. I found that the only coated side of the lens is the concave len. Is that the case with eveyone else's ds-90?






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