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Balance weights

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#1 Manny1

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Posted 08 November 2018 - 06:09 PM

Have a problem, on my 8 inch collapsible when I use a 2 inch eye piece, the scope tends to drop very slowly ,I know I'm going to use weights but what type. Need advisefingertap.gif



#2 Barlowbill

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Posted 08 November 2018 - 06:15 PM

Magnetic.  Orion sells them but you should be able to find in a big box store.  Like refrigerator door magnets, but bigger.   Might need more than one if they aren't too heavy.


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#3 Jond105

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Posted 08 November 2018 - 06:18 PM

https://www.amazon.c...=A3MGZPXAMCF0DM

What I have on my 10" collapsible
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#4 aeajr

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Posted 08 November 2018 - 10:41 PM

I use 8 sets of these.

https://www.harborfr...ocks-98406.html

 

Two sets, about 7 ounces, sit permanently by the mirror of my XT8 since I added a second finder scope.

 

6 sets sit on the pivot of the scope.  Each set is wrapped in duct tape to avoid scratching the tube.    When I drop in a big 2" I might slide a few down to the mirror.   If I add my 2" barlow I might slide the rest to the mirror.   

 

Works great and dirt cheap. 


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#5 stargazer193857

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Posted 09 November 2018 - 05:07 AM

Another plus of steal over aluminum. And a reason I don't do mass produced dobs. My 8" has issues with 1 pound eyepieces at horizon. If you need weights, what about when you take an eyepiece out to change it, especially at horizontal?

My advice is move the alt bearing pads from 90 degrees apart to at least 120 degrees.

My custom scope will already be balanced with proper bearing location for the finders and eyepieces I plan to use, so no counterweights needed.
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#6 Jond105

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Posted 09 November 2018 - 05:45 AM

Another plus of steal over aluminum. And a reason I don't do mass produced dobs. My 8" has issues with 1 pound eyepieces at horizon. If you need weights, what about when you take an eyepiece out to change it, especially at horizontal?

My advice is move the alt bearing pads from 90 degrees apart to at least 120 degrees.

My custom scope will already be balanced with proper bearing location for the finders and eyepieces I plan to use, so no counterweights needed.

That's not a half bad idea. Just not sure if it would work with the goto?

Edited by Jond105, 09 November 2018 - 05:50 AM.

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#7 Jon Isaacs

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Posted 09 November 2018 - 06:28 AM

Another plus of steal over aluminum. And a reason I don't do mass produced dobs. My 8" has issues with 1 pound eyepieces at horizon. If you need weights, what about when you take an eyepiece out to change it, especially at horizontal?

My advice is move the alt bearing pads from 90 degrees apart to at least 120 degrees.

My custom scope will already be balanced with proper bearing location for the finders and eyepieces I plan to use, so no counterweights needed.

 

The problem with commercial Dobs is the bearing are too small. Build a custom Dob, use large diameter bearings, it doesn't increase the friction, it increases the force required to move the scope. Increasing the bearing angle tends to pinch the bearing. I think every premium Dob I've ever seen had large diameter altitude bearings.. 

 

A certain amount of force is desirable for smooth, stiction free tracking, if it's too light, overshoot and jitter result. In my experience, 1 to 2 pounds is about right. 1 pound will allow the use of eyepieces with a range of 0-2 pounds.

 

In any event, magnets are a good solution. The magnets should go on the back side.

 

3912615-Balancing a DOB.jpg

 

Jon


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#8 aeajr

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Posted 09 November 2018 - 07:17 AM

Good approach if you are doing a custom build. For the rest of us the magnets do a good job.
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#9 pregulla

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Posted 09 November 2018 - 10:19 AM

I just use a waist pouch with sand-filled sandwich bag in it on my 8". I simply strap it around the tube. Not the most elegant solution, but gets the job done ;)


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#10 Sarkikos

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Posted 09 November 2018 - 11:49 AM

Good approach if you are doing a custom build. For the rest of us the magnets do a good job.

Exactly.  You can't really rebuild the mount you're stuck with.  But you can improve it.

 

I don't think most amateur astronomers are up to building their own mount from scratch.  And no one should assume they are.

 

Mike


Edited by Sarkikos, 09 November 2018 - 11:53 AM.

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#11 Sarkikos

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Posted 09 November 2018 - 11:50 AM

I just use a waist pouch with sand-filled sandwich bag in it on my 8". I simply strap it around the tube. Not the most elegant solution, but gets the job done wink.gif

Good idea.  It's what I do.  But I put bags of lead shot in the pouch.  Lead shot takes up less space than sand.

 

Mike


Edited by Sarkikos, 09 November 2018 - 11:50 AM.

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#12 Sarkikos

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Posted 09 November 2018 - 11:55 AM

My custom scope will already be balanced with proper bearing location for the finders and eyepieces I plan to use, so no counterweights needed.

Yes, that will work until you decide you want different finders and eyepieces.

 

:grin:

Mike


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#13 Sarkikos

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Posted 09 November 2018 - 11:59 AM

A warning about magnetic weights:  If you observe at very dewy sites - like I do - you'll probably find those magnetic weights sliding down the OTA during the course of the night.  Dew is a good lubricant.

 

My solution was to put Velcro on the weights and a patch of Velcro on the OTA where you will place the weights.  

 

For instance, I have a small patch of Velcro beside the focuser on my 10" Dob.  When I switch from a heavy eyepiece to a light one, I place a weight on the Velcro patch to compensate.

 

Mike


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#14 brentknight

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Posted 09 November 2018 - 02:31 PM

It does get tricky though, when you use a large wide-field "target" eyepiece to find something, then replace it with a smaller, high power to take a closer look.  Often the process of switching eyepieces will cause the scope to dive up or down...  My scope has sliding bearings, but that does not help when just switching eyepieces.  I'll be trying the magnets on the mirror cell method next time the clouds clear out...



#15 Sarkikos

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Posted 09 November 2018 - 02:45 PM

It does get tricky though, when you use a large wide-field "target" eyepiece to find something, then replace it with a smaller, high power to take a closer look.  Often the process of switching eyepieces will cause the scope to dive up or down...  My scope has sliding bearings, but that does not help when just switching eyepieces.  I'll be trying the magnets on the mirror cell method next time the clouds clear out...

One way to eliminate that particular problem is to not use a wide-field as a "target" eyepiece.  Use a finderscope.  

 

And use zoom eyepieces more often.

 

But you will still be switching eyepieces at some time or another.  It can't be helped.

 

Mike


Edited by Sarkikos, 09 November 2018 - 02:46 PM.


#16 aeajr

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Posted 09 November 2018 - 03:54 PM

One way to eliminate that particular problem is to not use a wide-field as a "target" eyepiece.  Use a finderscope.  

 

And use zoom eyepieces more often.

 

But you will still be switching eyepieces at some time or another.  It can't be helped.

 

Mike

 I have two finders on my Dob, a 9X50 RACI and a RDF or Laser.    But in my very light polluted sky I often can't see the guide stars or the target in these.  So a 2" 38 mm is my next level up finder eyepiece.    I can use this in the scope by tightening down on the Alt bearing or adding a few magnets by the mirror, or a combination.   

 

Removing that big eyepiece and going to a heavier or lighter one has never been a problem.  Adjusting the balance or the friction dial happens easily.  But should the scope move because I was clumsy changing the eyepiece, it is just a matter of lifting it slightly till I regain the target.  Not a big deal. 

 

I usually confirm the target or some other reference in my finder scope so, should I lose it I can get it back quickly after the change. 

 

naturally I don't have this issue with my GoTo scopes. 

 

Naturally your smileage may vary. 


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#17 stargazer193857

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Posted 09 November 2018 - 04:05 PM

Yeah, but what is the minimum low power view your main scope should have? I'm thinking 1.25 degrees.

As for pinch issues, maybe wider or longer pads with the right curvature.

#18 aeajr

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Posted 09 November 2018 - 04:28 PM

That is a matter of choice.   

 

Since the OP has an 8" Dob, probably around F6/1200 mm FL, a 32 mm Plossl would, in my opinion, be the minimum requirement for a low power wide view eyepiece.    37.5X and 1.3 degree FOV.   

 

2" 68 or wider would be better, but the 32 Plossl can get the job done if that is all you can afford.   Mine is 38 mm 70 degree for 31X/2.2 degree.  


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#19 brentknight

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Posted 09 November 2018 - 09:11 PM

Of course it's cloudy this evening - probably all weekend too... but I did get three pairs of those Harbor Freight magnets (very easy investment) and did some testing.

 

The magnets solved my problem with the 2" eyepieces causing a nose-dive.  I mostly use 1.25" ep's with filters and a barlow, so I set the balance point on the side bearning to balance with any 1.25" ep combination or without any ep.  I only need the extra weight when I use the 2" ep's (it took 6 magnets attached to the mirror cell bolt on the outside of the tube to balance the ES30).  I still had the problem of the tube flying up when I change 2" ep's or when I switch back to 1.25" because the extra weight had messed up the normal tube balance.

 

Most of you seem to be able to solve that problem because you are able to adjust the tension on the side bearing.  I don't have that option as there is no additional tension on my bearing other than that provided by the teflon.  I "think" I've got that problem solved though.  I have a wire punch tool I used back when I pulled network cables.  When I'm ready to change the ep configuration, I can just wedge that punch tool into the gap between the side bearing and the rocker box till it clicks.  The tube is then prevented from moving up and I can pull the weights off and the eyepiece out without losing my view.  That's the theory anyway - maybe one evening I'll get the chance to test it...



#20 aeajr

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Posted 09 November 2018 - 09:28 PM

sitting next to the Dob, place your leg under the tube, slide the magnets up, pull the eyepiece.

Easy peasy

#21 brentknight

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Posted 09 November 2018 - 09:41 PM

One way to eliminate that particular problem is to not use a wide-field as a "target" eyepiece.  Use a finderscope.  

 

Mike

Thanks Mike...

 

I'm finding more and more that from my orange front yard, I can't see quite enough in my finder.  Maybe it's the weird way of looking down to find something above me, or maybe I'm having a little extra trouble identifying the field using my SkySafari.  It just seems to cause me more frustration than anything else when I'm "looking" for something.  At a darker site I think it would be much more useful.

 

Right now I find using a pair of binoculars and a green laser much easier to get the scope to the correct field.  That method will usually get the object in the field of my target eyepiece.  I can use the finder then to "confirm" the correct field.  My next iteration in finding methodology is going to be adding an AZ circle to my angle gauge and seeing how that works. But then again the goal there is to get the object in a wide-field eyepiece.



#22 brentknight

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Posted 09 November 2018 - 09:56 PM

sitting next to the Dob, place your leg under the tube, slide the magnets up, pull the eyepiece.

Easy peasy

Easy for you... for me... very difficult.

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#23 25585

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Posted 10 November 2018 - 09:53 AM

That is a matter of choice.   

 

Since the OP has an 8" Dob, probably around F6/1200 mm FL, a 32 mm Plossl would, in my opinion, be the minimum requirement for a low power wide view eyepiece.    37.5X and 1.3 degree FOV.   

 

2" 68 or wider would be better, but the 32 Plossl can get the job done if that is all you can afford.   Mine is 38 mm 70 degree for 31X/2.2 degree.  

For a finder eyepiece, with that as its main reason, the widest TFoV and brightest images the better. You're only looking for stuff, not studying it.

 

As an example, M57 in a 40mm will glow out as a tiny ring between gamma and beta Lyrae, rather than larger and fainter, with dimmer stars in your FOV.


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#24 aeajr

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Posted 10 November 2018 - 10:56 AM

Easy for you... for me... very difficult.

Ahhh, I see.  Very long scope.   I would just add a push stick to the magnets so I could manipulate them more easily from the focuser.  A wood dowel would work well.  Include it in the duct tape wrap around the magnets grouped in whatever number you find convenient.  One dowel per group. 

 

Not trying to convince you of anything, but that is how I would do it. 



#25 stargazer193857

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Posted 10 November 2018 - 11:30 AM

Easy for you... for me... very difficult.


I see the metal corner brackets you use. That is what I would expect on such a base. The rear top of the base is susceptible to side to side bending. Also, the large bearings apply a 45 degree sideways force to it. They are ok on a short box, but bend a tall one.

My rear base will slant forward, so less leverage can bend it. Also my smaller bearings will apply force tangent to the wall, only pushing nearly straight back, the direction it is strongest.

The steeper pad angles will provide the needed friction, and I'll widen them and curve and bevel them and use thin depth to avoid pinching issues. Pinching is more of an issue for heavier scopes.


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