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2 inch eyepiece weight on a dob


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Hi All,so i was doing a bit of research the other day on 2 inch ep`s and i came across one ep that the owner said made his 10inch dob nose heavy because of the weight,wow i thought that must weigh like a brick!,now,i have recently bought a StellaLyra 30mm 2inch ep from flo,i like it a lot,it weighs 285 grams and that got me thinking...just what is a safe weight a 2inch ep can reach without upsetting the balance of a dob?...i have a skywatcher 200p ...any thoughts /suggestions?...i would like a few more 2inch ep`s but that discussion will be for another thread soon.

cheers

Mark

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I use a DIY counterweight on the bottom section of my dob because many of my eyepieces are heavy. My tube is aluminum so I use a magnetized kitchen knife rack and a couple of old iron weights for this purpose. If you have a steel tube you can put magnets directly onto the tube. Wrap them in something to stop them scratching the tube.

My eyepieces go up to 1175g in weight.

285g might be OK using the tension handles on each side of the altitude axis. As the tube drops (ie: to observe things lower in the sky) the tendency for the nose of the scope to drop increases.

Edit: I'll just add that the only benefit you get from 2 inch eyepieces is the larger field of view. They don't deliver better performance than 1.25" eyepieces. Most folks have one or two 2 inch eyepieces for low power / wide field observing and then 1.25" eyepieces in the medium to shorter focal lengths.

 

Edited by John
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23 minutes ago, John said:

I use a DIY counterweight on the bottom section of my dob because many of my eyepieces are heavy. My tube is aluminum so I use a magnetized kitchen knife rack and a couple of old iron weights for this purpose. If you have a steel tube you can put magnets directly onto the tube. Wrap them in something to stop them scratching the tube.

My eyepieces go up to 1175g in weight.

285g might be OK using the tension handles on each side of the altitude axis. As the tube drops (ie: to observe things lower in the sky) the tendency for the nose of the scope to drop increases.

Edit: I'll just add that the only benefit you get from 2 inch eyepieces is the larger field of view. They don't deliver better performance than 1.25" eyepieces. Most folks have one or two 2 inch eyepieces for low power / wide field observing and then 1.25" eyepieces in the medium to shorter focal lengths.

 

Thanks John it makes sense now,so i`m ok with just that one 2 inch ep you think? i was worried i`d have to get a whole `range `of `em to match my 1.25`s....phew!!!

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8 minutes ago, starboy71 said:

Thanks John it makes sense now,so i`m ok with just that one 2 inch ep you think? i was worried i`d have to get a whole `range `of `em to match my 1.25`s....phew!!!

It you look at one particular range of EPs, you 'll find a point at which they change to a 2" size. For example, have a look at:
https://www.firstlightoptics.com/explore-scientific-eyepieces/explore-scientific-68-degree-series-eyepieces.html

The widest view you can get with a standard 1.25" EP is, for example, a 32mm Plossl. Lower focal lengths than that if you have a 1.25" EP with a wider field of view than a Plossl.
 

You can get some 1.25" EPs that have a 2" barrel - but that's more for strength/stability due to weight.

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17 minutes ago, starboy71 said:

Thanks John it makes sense now,so i`m ok with just that one 2 inch ep you think? i was worried i`d have to get a whole `range `of `em to match my 1.25`s....phew!!!

I think so. A 30mm 2 inch eyepiece is a good focal length for wide field observing with an 8 inch dobsonian.

 

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My ES 82*/30mm is a grenade of an eyepiece and it sure weighs down on my 12” dob.    I use small sandbags and welders’ magnets to counterbalance.

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1 hour ago, starboy71 said:

just what is a safe weight a 2inch ep can reach without upsetting the balance of a dob?

It really depends on the design of the Dob.  It makes a difference how balanced the moment arm is in front of and behind the pivot point.  The more equal they are, the more resistant the design is to imbalance.  It also makes a difference what materials are used for the bearing surface and the load bearing pads.  The more stiction between the two, the more resistant it is to imbalance.

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I don't have a dob but have an Orion Optic VX8L and wanted it a little higher in the mount so used flat stick on car wheel weights a big box of them is cheap on ebay they may work for you as well

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Hiya,

I've got a 20mm Myriad 2-inch EP, which weights just over a kilo. I use it with my 250PX dob, without a counterweight, though I do have to clamp up the handles pretty tight so it doesn't over balance the tube. The rest of my EPs are 1.25 inch, so I don't tend to swap them and the Myriad around too often. 

Kev

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