18 replies to this topic

[Bearcub]

I found this but for binos and it seems very practical. So why not for telescopes? I dont understand why they dont include vixen mount railing.

[Tony Flanders]

Larry Patriarca, owner of Universal Astronomics, told me that he tried marketing his UniMount p-mount for refractors, but hardly anybody bought one.

 

I think the fundamental problem is that a p-mount needs to be much heavier than a traditional mount that's rigidly attached to the tripod to provide any given degree of stability. That's not too much of a problem with conventional binoculars, which tend to be light, and are only used at ultralow magnifications (by telescopic standards). It's much more of a problem with telescopes, which are expected to operate smoothly well above 100X.

[Bearcub]

Larry Patriarca, owner of Universal Astronomics, told me that he tried marketing his UniMount p-mount for refractors, but hardly anybody bought one.

 

I think the fundamental problem is that a p-mount needs to be much heavier than a traditional mount that's rigidly attached to the tripod to provide any given degree of stability. That's not too much of a problem with conventional binoculars, which tend to be light, and are only used at ultralow magnifications (by telescopic standards). It's much more of a problem with telescopes, which are expected to operate smoothly well above 100X.

But ive seen binos that are 10 or 12kg. Which is far heavier than many sct..

[SeattleScott]

But ive seen binos that are 10 or 12kg. Which is far heavier than many sct..

How many binoculars have you seen that big? Probably not many. It isn’t that no one wanted the parallelogram for telescopes. But it sold poorly. It’s hard to make a successful business marketing to 0.5% of the population.

Typically binoculars that big aren’t on parallelogram mounts for that matter.

[Napp]

Are you looking at binocular telescopes?  They are heavy but usually have the eyepieces at 45° or 90° angles to the barrels.   The  angled eyepieces allow using them at high angles while seated in a chair.

 

I have 25X100 binoculars that weigh about 10lbs.  I had to rebuild my parallelogram to hold them steady.  My setup went from something easy to move around to something that’s a real chore to move.

[Jon Isaacs]

Bearcub, on 21 Jul 2024 - 03:00 AM, said:

But ive seen binos that are 10 or 12kg. Which is far heavier than many sct..

It's not the weight as much as it's the steadiness. Parallelogram mounts work OK with binoculars because they're used at low magnifications. At more normal magnifications they're shaky.

If you look at a parallelogram mount and compare it to a GEM or Alt-az mount, they're flimsy.

Jon

[Bearcub]

It's not the weight as much as it's the steadiness. Parallelogram mounts work OK with binoculars because they're used at low magnifications. At more normal magnifications they're shaky.

If you look at a parallelogram mount and compare it to a GEM or Alt-az mount, they're flimsy.

Jon

Hmm.. so dob is the steadiest mount? I never had opportunity for any other mount besides pressing buttons on automatic tripod which is to be honest not my favourite for visual use!

[Starman1]

Hmm.. so dob is the steadiest mount? I never had opportunity for any other mount besides pressing buttons on automatic tripod which is to be honest not my favourite for visual use!

A dob is the steadiest portable mount, BUT:

--getting smooth motion without backlash seems to be a major problem for most of the commercial Chinese dobsonian scopes.

   A little work on the bearings is often necessary.  Lots of threads about that here on CN.

--full-tubed scopes have high centers of gravity, so the rocker box sides are tall.

   Many, if not most, commercial dobs would benefit from buttresses on the side panels, like this one:

   https://octelescope....dobsonian-22471

   They can be added by the owner with access to a drill and some screws.

--truss tube dobs have a lower center of gravity and lower rocker box sides, so tend to shimmy less:

   https://telescopes.n...hRoC3d4QAvD_BwE

Edited by Starman1, 21 July 2024 - 03:28 PM.

[Sebastian_Sajaroff]

But ive seen binos that are 10 or 12kg. Which is far heavier than many sct..

Steadiness is the main issue.

Getting a steady view at 250x (typical telescope) is not easy on a parallelogram (which are used with 15x-30x binoculars) 

[kfiscus]

I saw a photo of a super-cool parallelogram mount that a club made for an 8" SCT to accommodate wheelchair viewing.  The mount was bolted/welded onto a small trailer.  The mount itself must have weighed 200 pounds.

[zizzapnia]

I experimented with putting a 60mm refractor OTA on my homemade parallelogram mount/tripod, which was a heavy monstrosity made with oak, so quite stable. Even so, the 60mm oscillated slowly at the slightest touch and was quite jittery. 

[Jon Isaacs]

 

A dob is the steadiest portable mount, BUT:

--getting smooth motion without backlash seems to be a major problem for most of the commercial Chinese dobsonian scopes.

   A little work on the bearings is often necessary.  Lots of threads about that here on CN.

--full-tubed scopes have high centers of gravity, so the rocker box sides are tall.

   Many, if not most, commercial dobs would benefit from buttresses on the side panels, like this one:

   https://octelescope....dobsonian-22471

   They can be added by the owner with access to a drill and some screws.

--truss tube dobs have a lower center of gravity and lower rocker box sides, so tend to shimmy less:

   https://telescopes.n...dobsonian.html?

 

I have measured the center of the altitude pivot bearings of a number of Dobs.. This corresponds to the center gravity of the OTA.  

 

What I found was they are all about 24-26 inches.. It's somewhat surprising...  But my 22 inch which has an eyepiece height at the zenith of 8 feet and my 10 inch GSO Dob are within a couple of inches of each other.. 

 

The sides are taller on commercial Dobs because the bearings are smaller.. 

 

This photo shows 4 Dobs ranging from 12.5 inches to 25 inches, you can just about draw a horizontal line through the center of rotation of the altitude bearings.

 

 

Jon

Edited by Jon Isaacs, 25 July 2024 - 07:14 AM.

[Echolight]

I don't even want to use one with binoculars, much less a telescope.

[Starman1]

I have measured the center of the altitude pivot bearings of a number of Dobs.. This corresponds to the center gravity of the OTA.  

 

What I found was they are all about 24-26 inches.. It's somewhat surprising...  But my 22 inch which has an eyepiece height at the zenith of 8 feet and my 10 inch GSO Dob are within a couple of inches of each other.. 

 

The sides are taller on commercial Dobs because the bearings are smaller.. 

 

This photo shows 4 Dobs ranging from 12.5 inches to 25 inches, you can just about draw a horizontal line through the center of rotation of the altitude bearings.

 

 

 

Jon

And if that 25" had a tube, the altitude axis would be about the level of your heart.

 

This scope has large trunnions and still has a high center of gravity:

https://www.explores...ht-10-dobsonian

It is because a tube adds so much additional mass above the altitude axis.

 

Compare it with the 10" truss tube from the same company:

https://www.explores...ts/10-dobsonian

Similar size trunnions, but much lower center of gravity.

[WillR]

And if that 25" had a tube, the altitude axis would be about the level of your heart.

 

This scope has large trunnions and still has a high center of gravity:

https://www.explores...ht-10-dobsonian

It is because a tube adds so much additional mass above the altitude axis.

 

Compare it with the 10" truss tube from the same company:

https://www.explores...ts/10-dobsonian

Similar size trunnions, but much lower center of gravity.

Yes, those mirror boxes on the small truss dobs have a lot of counterweight built in that the tube dobs don’t. I have the ES hybrid ( admittedly the UTA is heavier on this) but it still has 4 large counterweights in the mirror box and I still have to add a chain and a magnetic weight. 

Edited by WillR, 25 July 2024 - 03:21 PM.

[csrlice12]

Doesn't Clearwater Dave's Frankenmount work similarly?

[Bearcub]

A dob is the steadiest portable mount, BUT:

--getting smooth motion without backlash seems to be a major problem for most of the commercial Chinese dobsonian scopes.

   A little work on the bearings is often necessary.  Lots of threads about that here on CN.

--full-tubed scopes have high centers of gravity, so the rocker box sides are tall.

   Many, if not most, commercial dobs would benefit from buttresses on the side panels, like this one:

   https://octelescope....dobsonian-22471

   They can be added by the owner with access to a drill and some screws.

--truss tube dobs have a lower center of gravity and lower rocker box sides, so tend to shimmy less:

   https://telescopes.n...hRoC3d4QAvD_BwE

Is there any mount that i could use manually with my maksutov? I want something that is really simple but high quality. I thought parallelogram mount would be most practical for my mak. Anything i could take a look?

[Starman1]

Is there any mount that i could use manually with my maksutov? I want something that is really simple but high quality. I thought parallelogram mount would be most practical for my mak. Anything i could take a look?

Ask Vic at Stellarvue if the Stellarvue M2C mount is viable with that much weight and that long a focal length.

If so, it is an incredibly easy mount to use, and you can even add Digital Setting Circles to it to make it even more advanced.

[Jon Isaacs]

And if that 25" had a tube, the altitude axis would be about the level of your heart.

 

This scope has large trunnions and still has a high center of gravity:

https://www.explores...ht-10-dobsonian

It is because a tube adds so much additional mass above the altitude axis.

 

Compare it with the 10" truss tube from the same company:

https://www.explores...ts/10-dobsonian

Similar size trunnions, but much lower center of gravity.

 

I get that..

 

I just measured the height of the center of the altitude bearing of the 10 inch F/5 GSO Dob, it's 23 inches. 

 

I wonder what the center of the altitude bearing is with both those scopes. I wonder how much counterweight is needed in the ES 10 inch Truss.

 

I once bought a custom made 8 inch F/6 truss style Dob. I looked it over. It was clean, it had a Parks mirror, a Protostar secondary and spider, a JMI focuser. It was $200, what could go wrong?

 

I bought it and the seller asked me if I wanted some help loading it in the car. That seemed like a strange question until I realized it had 30 pounds of steel plates stacked under the mirror cell to make it balance..

 

But I'm not sure how parallelogram mounts for telescopes morphed into discussions of Dobs?

 

Jon