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Wobbly scope - suggestions please?

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#1 Andromeda31

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Posted 24 January 2021 - 09:15 AM

Hello everyone, I've just joined and this is my first post here.  I've had a Skywatcher Evostar 90 with AZ3 tripod for a few years now.  However it's always had a wobble and I don't know if this is to be expected or can be fixed?  I'd describe it as a "looseness" where the telescope tube is attached to the mount (sorry, not sure of the correct terms).  So, the telescope is held by 2 rings which attach to a mounting plate, which is attached to the tripod by a bolt (photo attached).  It's here where the wobble is.  I've tightened the bolt as much as I think I should.  There clearly needs to be some movement as you need to raise and lower the scope, but when I point it at an object manually it drops by a few degrees at the mount, with translates to quite a bit of movement by the end of the tube. It makes it quite hit or miss when trying to locate something as I get it in view but when I take my hands away it's gone!  Otherwise I'd say the scope is solid and the fine adjustment knobs work well.  I've got used to it, but it's a frustration and i wonder if there's something I can do to resolve it? Do I tighten the bolt more, or is there maybe a hidden one I've missed?  I'd enjoy using the telescope much more without it's wobble! Thanks for your thoughts and any suggestions.  

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#2 clearwaterdave

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Posted 24 January 2021 - 09:45 AM

Hello.,You can try moving the scope forward or back depending on which way it moves when you release it.,This issue is common with this style of mount.,It bothered me enough so that I replaced the original mount with pipes.,Now this scope is a treat to use.,good luck.,

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#3 Stellar1

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Posted 24 January 2021 - 09:49 AM

Have you tried tightening  up that nut a bit more? other than that, maybe a thin nylon washer will take up some slack.

If the nut is tight enough and, there’s still wobble then the slack must lie between the two joints on the inside, maybe adding

a thin nylon washer may take up extra play between the two.



#4 clearwaterdave

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Posted 24 January 2021 - 10:02 AM

On my Meade mount.,which looks the same., the play was in the center post of the mount.,where it sat on top of the tripod,,the post is the azimuth "bearing".,but its loose fit.,or "play" is what caused the mount to ( in my case ) drop when released.,It took a bit to figure this out and I did try a few options.,washers.,tape.,.ETC.,but no luck. It either effected the AZ movement or it didn't fix the problem.,



#5 Andromeda31

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Posted 24 January 2021 - 10:04 AM

These are really helpful suggestions, thank you.  I'll try both and let you know.

 

Fly Me To The Moon - love your photo!

 

Thanks to both of you.



#6 Andromeda31

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Posted 24 January 2021 - 10:07 AM

Fly Me To The Moon - mine is the same, the play seems to be inside the outer parts of the mount, where the mounting plate sits inside it. I'll try rebalancing the tube, and a washer may indeed help as Viking1 suggests...now to find one!



#7 c2m2t

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Posted 24 January 2021 - 10:07 AM

Hi Andromeda31!

It is a bit hard to imaging what is causing the telescope to suddenly drop given that you have tightened the pivot bolt to what you believe is the maximum. My first question is, is the telescope balance in the mount...ie, is the weight equal on both sides of the pivot point. This is important for any mount. This mount is not overly well suited to quickly check balance because of the nature of the pivot point which requires quite a bit of tension to keep the scope more or less aligned to your target. Here is what I would suggest...and it would be better to have a second set of hands since one will be dealing with the pivot bolt while the other is ensuring that the scope doesn't suddenly tip. Loosen off the pivot bolt so that the scope can rotate freely. Now loosen off the rings so that you can slide the scope back and forth to find a balance point. Make sure you have an eyepiece in the focuser and the focuser is set for a focused star image. Once you are satisfied with the degree of balance, then tighten up the pivot bolt. This should improve the general movement of the scope but it may not totally eliminate the drop you get.

 

To be honest, this is not  a sturdy mount and in particular for this scope. I have always had a beef with the consumer built  telescope packages because the mounts, for the most part, are inadequate. They are fine for casual use, but if one is trying to encourage the observing hobby, poor equipment is not the way to do it. Unfortunately, good equipment means more cost. There are so many starter scopes collecting dust because the user get frustrated with its operation. It is a bit of a catch-22.

 

I hope that helps. If you want to get serious about the hobby, when the virus clears, get out to some star parties or sidewalk seasons with local astronomy groups, if they are available close by, and kick some tires. I suspect the scope you have is quite a good starter...you just need a steady platform to put it on that holds it firmly without vibration.

 

One final instruction...make sure that you mark the tube so...should you have to remove the telescope to store or to travel, the scope can be placed back into its balanced position.

 

Cheers, Chris.


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#8 clearwaterdave

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Posted 24 January 2021 - 10:13 AM

I am Clearwaterdave.,lol,fly me to the moon is this sites way of labeling us for our time here. You are in the lift off camp.,good luck with the mount.,and thanks,.the pipes doing double duty.,

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#9 LDW47

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Posted 24 January 2021 - 10:35 AM

Hello everyone, I've just joined and this is my first post here.  I've had a Skywatcher Evostar 90 with AZ3 tripod for a few years now.  However it's always had a wobble and I don't know if this is to be expected or can be fixed?  I'd describe it as a "looseness" where the telescope tube is attached to the mount (sorry, not sure of the correct terms).  So, the telescope is held by 2 rings which attach to a mounting plate, which is attached to the tripod by a bolt (photo attached).  It's here where the wobble is.  I've tightened the bolt as much as I think I should.  There clearly needs to be some movement as you need to raise and lower the scope, but when I point it at an object manually it drops by a few degrees at the mount, with translates to quite a bit of movement by the end of the tube. It makes it quite hit or miss when trying to locate something as I get it in view but when I take my hands away it's gone!  Otherwise I'd say the scope is solid and the fine adjustment knobs work well.  I've got used to it, but it's a frustration and i wonder if there's something I can do to resolve it? Do I tighten the bolt more, or is there maybe a hidden one I've missed?  I'd enjoy using the telescope much more without it's wobble! Thanks for your thoughts and any suggestions.  

Get rid of the AZ3 and go to something like a Porta II or if you are short a Twilte I and your concerns will disappear !



#10 LDW47

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Posted 24 January 2021 - 10:43 AM

Hello everyone, I've just joined and this is my first post here.  I've had a Skywatcher Evostar 90 with AZ3 tripod for a few years now.  However it's always had a wobble and I don't know if this is to be expected or can be fixed?  I'd describe it as a "looseness" where the telescope tube is attached to the mount (sorry, not sure of the correct terms).  So, the telescope is held by 2 rings which attach to a mounting plate, which is attached to the tripod by a bolt (photo attached).  It's here where the wobble is.  I've tightened the bolt as much as I think I should.  There clearly needs to be some movement as you need to raise and lower the scope, but when I point it at an object manually it drops by a few degrees at the mount, with translates to quite a bit of movement by the end of the tube. It makes it quite hit or miss when trying to locate something as I get it in view but when I take my hands away it's gone!  Otherwise I'd say the scope is solid and the fine adjustment knobs work well.  I've got used to it, but it's a frustration and i wonder if there's something I can do to resolve it? Do I tighten the bolt more, or is there maybe a hidden one I've missed?  I'd enjoy using the telescope much more without it's wobble! Thanks for your thoughts and any suggestions.  

Two problems with the AZ3 ! 1. You have to practically overtighten the centre bolt to keep the scope from falling back as you get closer to zenith, using a heavy ep, in your viewing angle and 2. The amount of travel on your Alt movement is very limited using your cables, when it reaches the end you have to manually set the travel and keep on going or forget the Alt controls and hand bomb it ! A real pain, a poor design !



#11 Ulmer Spatz

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Posted 24 January 2021 - 11:00 AM

Agree with LDW47 100%. The fundamental problem is that the scope can't be balanced for its entire altitude observing range. Pointing at the horizon, the vertical distance between the nylon nut and the optical tube has no effect on balance. But as you point the scope up, this distance becomes a lever, which increases the force unbalancing it. In short: setting the altitude bearing's preload once and for all is not possible and an exercise in frustration. 

 

One solution is to have a wrench handy (I found a socket wrench  best when doing this in darkness) to tighten or loosen the nut as needed. As clearwaterdave showed, the other one is to get a mount which allows the optical tube's center of mass to be in horizontal alignment with the altitude bearing, like this:  scope>O----I<mount 

 

An equatorial mount will balance an optical tube nicely, even if the tube is mounted above the altitude bearing. That's because the equatorial mount uses a counterweight rather than bearing preload ("friction") to achieve balance.


Edited by Ulmer Spatz, 24 January 2021 - 11:11 AM.

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#12 LDW47

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Posted 24 January 2021 - 11:05 AM

Agree with LDW47 100%. The fundamental problem is that the scope can't be balanced for its entire altitude observing range. Pointing at the horizon, the distance between the nylon nut and the scope has no effect on balance. But as you point the scope up, this distance becomes a lever, which increases the force unbalancing it. In short: setting the altitude bearing's preload once and for all is not possible and an exercise in frustration. 

 

One solution is to have a wrench handy (I found a socket wrench  best when doing this in darkness) to tighten or loosen the nut as needed. The other one is to get a mount which allows the optical tube's center of mass to be in horizontal alignment with the altitude bearing, like this:  scope>O----I<mount 

 

An equatorial mount will balance an optical tube, even f the tube is mounted above the altitude bearing. That's because the mount uses a counterweight rather than bearing preload ("friction") friction to achieve balance.

I agree with you 98%, lol ! Only because I am not an EQ guy, lol !



#13 DouglasPaul

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Posted 24 January 2021 - 11:22 AM

I am Clearwaterdave.,lol,fly me to the moon is this sites way of labeling us for our time here. You are in the lift off camp.,good luck with the mount.,and thanks,.the pipes doing double duty.,

 

I am Clearwaterdave.,lol,fly me to the moon is this sites way of labeling us for our time here. You are in the lift off camp.,good luck with the mount.,and thanks,.the pipes doing double duty.,

Love that mount, how do those wooden legs do as far as wobble and what did they come off?



#14 Ulmer Spatz

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Posted 24 January 2021 - 12:06 PM

I agree with you 98%, lol ! Only because I am not an EQ guy, lol !

I hear you. I like equatorial mounts. I think the fact that you can balance a scope without resorting to friction is worth putting up with the eyepiece inexplicably pointing to the ground or having to do the dreaded meridian flip.  :-)  


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#15 LDW47

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Posted 24 January 2021 - 12:11 PM

I hear you. I like equatorial mounts. I think the fact that you can balance a scope without resorting to friction is worth putting up with the eyepiece inexplicably pointing to the ground or having to do the dreaded meridian flip.  :-)  

The couple that I have owned do cause you to become a rubber man occasionally, lol ! 


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#16 SeattleScott

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Posted 24 January 2021 - 12:11 PM

Yeah what you are dealing with is backlash, which is common in cheap scopes and not easy to fix. Sometimes you just have to spend money to solve a problem. The AZ3 just really isn’t an adequate mount. It is sometimes sold with beginner scopes because beginners don’t want to pay for a suitable mount. They just want the cheapest thing possible because they aren’t sure yet if the hobby is for them. So they get something that might have a capable telescope tube, but the mount is rubbish and frustrating to use, so they decide stargazing isn’t for them and off to Craigslist the telescope goes.

If you really want to solve the problem without more frustration, buy a $30 dovetail bar and a $200-300 mount. Problem solved. That’s just what it costs to do this hobby right.

Scott

#17 Andromeda31

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Posted 24 January 2021 - 12:15 PM

Clearwaterdave - thanks for pointing out the nomenclature!  

 

And thanks to all for your replies - I know no one else who owns a telescope or has any interest, so I'm kind of figuring this out on my own (and have been for years)!

 

It makes sense that balancing the tube on the horizontal doesn't hold when it's then raised. It's been bothering me for years, and only now am I getting round to asking advice.   I'd love to take it along to our local astronomical group for advice, but that might be a while yet! 

 

I'm glad i'm not the only one that finds the tracking cable things restrictive.  So often I go to use them and they're locked at the end of their track!

 

I had an EQ mount previously, but struggled with the polar alignment and found it counter-intuitive to use, especially for a quick session.  I thought i was doing something wrong when the scope was pointed in unnatural directions! - relieved to see Ulmer Spatz' comment above.   

 

I notice now that there's a tiny crack on the outer washer (you can see it at about 10 o clock on my photo).  Maybe that's not helping?

 

Anyway, I'll consider trying and EQ again, and plod on with this one in the meantime.



#18 SeattleScott

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Posted 24 January 2021 - 12:41 PM

Really the primary issue you are having is backlash. A hallmark feature of substandard mounts. Now maybe the backlash wouldn’t be as big a deal if the scope could balance, but backlash is your main issue. With a small scope and light eyepieces an alt az works fine. Just get a decent one.

Scott

#19 f74265a

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Posted 24 January 2021 - 12:44 PM

Years ago I used— for a long time— a photo tripod with a panning alt/az head for a telescope mount. It had a significant, but predictable, rebound problem so you had to adjust your aim to account for it. It was tolerable at lower power bc of the wider field. I couldn’t afford an upgrade so I lived with it as it was way better than nothing. Today I use a porta ii on a wooden berlebach tripod and it works light years better.

#20 LDW47

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Posted 24 January 2021 - 01:42 PM

Really the primary issue you are having is backlash. A hallmark feature of substandard mounts. Now maybe the backlash wouldn’t be as big a deal if the scope could balance, but backlash is your main issue. With a small scope and light eyepieces an alt az works fine. Just get a decent one.

Scott

The backlash on an AZ3 is exceptionally bad but the limited travel on the Alt. movement is the killer ! Have you ever used one over a period of time, 99% say the same thing ! I had 2-3 of them, all the same !



#21 Ulmer Spatz

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Posted 24 January 2021 - 02:04 PM

Anyway, I'll consider trying and EQ again, and plod on with this one in the meantime.

Just to be clear: a good alt-azimuth mount also allows you to balance the optical tube by weight shift. With the tube horizontally in line with the altitude bearing (not perched above it), you move the the tube forward and rearward in relation to the bearing to balance it. And the azimuth rotation needs no balancing act.


Edited by Ulmer Spatz, 24 January 2021 - 03:22 PM.


#22 clearwaterdave

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Posted 24 January 2021 - 03:41 PM

Love that mount, how do those wooden legs do as far as wobble and what did they come off?

The tripod is nice. Plenty stable., It came with the Meade,.It had the same slo-mo set up as the OP's.,most frustrating.,To change over to the pipemount was easy and well worth it.,The whole thing is heavier but it's still a quick out the door ready to use set up.,

   For the mount the wood pieces were scrap and the pipe pieces added up to about $35.,I made it push-to as well.,Works all good.,

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#23 SeattleScott

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Posted 24 January 2021 - 03:49 PM

The backlash on an AZ3 is exceptionally bad but the limited travel on the Alt. movement is the killer ! Have you ever used one over a period of time, 99% say the same thing ! I had 2-3 of them, all the same !

No I haven’t used the mount. I was just going off the OP’s description. I will take your word for it all the more reason to replace it with something suitable.

Scott
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#24 JohnnyBGood

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Posted 25 January 2021 - 09:52 AM

I think the key problem is balance. Because the scope isn't balanced in the Y direction you need a lot of what my old Physics professor called "sticktion" to hold it in place. I've seen pictures of older AZ3 mounts that included a counterweight and I think the current version of the mount can probably be modified to have one. I've also seen photos where people have used springs to counterbalance their telescopes on AZ3 mounts.

 

I bought my father an Infinity 102 a few year ago and there were enough nights of the two of us struggling with the mount that when the StarPro series came out I bought a StarPro102 and traded him (the StarPro mount is *much* better). I haven't gotten around to it yet (because someone wanted to borrow the scope) but I plan to disassemble the Infinity 102's mount head and flip around the piece where the panhandle attaches so I can try putting a threaded rod in its place, bending it, and figuring out how to attach a counterweight to it. That would allow me to loosen the friction nut and should make the scope smoother to move with less backlash. That's the hypothesis, at least. We'll see how well it works when I finally get the scope back and get around to tinkering with it.



#25 LDW47

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Posted 25 January 2021 - 10:32 AM

I think the key problem is balance. Because the scope isn't balanced in the Y direction you need a lot of what my old Physics professor called "sticktion" to hold it in place. I've seen pictures of older AZ3 mounts that included a counterweight and I think the current version of the mount can probably be modified to have one. I've also seen photos where people have used springs to counterbalance their telescopes on AZ3 mounts.

 

I bought my father an Infinity 102 a few year ago and there were enough nights of the two of us struggling with the mount that when the StarPro series came out I bought a StarPro102 and traded him (the StarPro mount is *much* better). I haven't gotten around to it yet (because someone wanted to borrow the scope) but I plan to disassemble the Infinity 102's mount head and flip around the piece where the panhandle attaches so I can try putting a threaded rod in its place, bending it, and figuring out how to attach a counterweight to it. That would allow me to loosen the friction nut and should make the scope smoother to move with less backlash. That's the hypothesis, at least. We'll see how well it works when I finally get the scope back and get around to tinkering with it.

Springs ? Weights ? On an AZ3 ? Really ?    ???


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