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Best mount type for zenith views

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#1 ScottW

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Posted 01 May 2011 - 05:48 AM

This might be a strange question but I have to ask, which mount is the most comfortable and easy to use for straight overhead? Is it the same type for both reflectors and refractors?
My homemade Dob just doesn't do the trick.

Scott

#2 Jim7728

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Posted 01 May 2011 - 06:30 AM

Hi Scott,

Why doe's your dob(reflector?) have trouble pointing to zenith?

This is usually not a problem for dobsonians, unless there's a balance or clearance issue. Otherwise, dobs are the best, simplest design for pointing a reflector ota to zenith.

As far as GEM and alt/az mount designs, as long as the the ota is mounted high enough for comfortable viewing position and does not interfere with the tripod legs, then either will work fine for pointing at or near zenith.

#3 DaveJ

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Posted 01 May 2011 - 08:31 AM

My homemade Dob just doesn't do the trick.


Hi Scott,

They don't call it "Dobson's Hole" for nothing. Alt/Az motions are quite difficult at Zenith, as you've discovered. Generally, a GEM is the ticket. The GEM has the same "hole" if pointed near the NCP, but fortunately, there isn't much to look at there. :grin:

#4 Jim7728

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Posted 01 May 2011 - 09:21 AM

Funny, for me the "dobson's hole" effect was never more than a short term inconvenience, if that. YMMV. ;)

#5 Eddgie

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Posted 01 May 2011 - 09:25 AM

To answer your question (the others seem to be assuming that your concern is Gimble Lock, but you did not say specifically that this was the case) please describe in which way the mount is uncomfortable to use?

Is it the height of the eyepeice? A good observer's chair will often correct this unless the eyepeice is too high for that and you are using a ladder. This was one of my chief issues with Dobs. I don't like standing, and I don't like sitting on a ladder rung.

Is it the inteference of the Dob base itself, making it difficult because you are constantly having to shift the position of your chair/ladder? This is because on the dob (and refractors), for a given area of sky, the eyepeice moves through a far longer arc to get from one side of the area to the other. You start with your head in a comfortable position but now you move the scope a few degrees and you find that you have to once again dismount and move your chair/ladder so that you are once again in a comfortable position?

If you explained your specific concerns, I think it would be easier to answer.

In general though Refractors and Newts tend to be the most difficult to use at zenith.

SCTs and small refractors on a GEM mount (for me anyway) by far and away the most comfrotable of all telescopes to use.

Larger refractors though chan have the same problem of Newts. The arc of eyepiece motion for a given area of sky necissitates more chair movment.

With My C14, I can sit at normal height and view a great deal of the sky around zenith and move the chair very little. With my 6" APO, I have to move the chair and adjust the height constantly. No big deal, but still, the SCT is by far and away a more productive and comfortable viewing configuration.

#6 ScottW

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Posted 01 May 2011 - 09:30 AM

Jim,

It,s just a thrown together home made one. It's not all that smooth in either axis and I have to get on the ground to aim it.
I was thinking about maybe using an alt/alt mount I saw a while back. But then again if you just tip one end of it upward you have something similar to an English yolk mount.

Thanks for you input.

Scott






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