Dobson design

[Richard N]

Why is the focusser on one side and not the other and why is it at an angle to horizontal? Guessing there are good engineering reasons?

Edited August 15, 2023 by Richard N

[Mandy D]

32 minutes ago, Richard N said:

Why is the focusser on one side and not the other and why is it at an angle to horizontal? Guessing there are good engineering reasons?

The focuser is at an angle to horizontal for convenience in viewing. You would have to bend to some uncomfortable angles if it were parallel to the ground, so instead it is rotated about 45° to the horizontal. Why it is on one side and not the other, I guess is a judgement call or maybe more convenient for right handed people. I can see no particular reason for that.

Incidentally, when my 200P OTA is mounted on a Skytee mount on a tripod, I have the focuser parallel to the ground, as it is sat so much higher than when it is Dobsonian mounted.

Edited August 15, 2023 by Mandy D
Dang typos!

[vlaiv]

48 minutes ago, Richard N said:

Why is the focusser on one side and not the other

For very large dobs where observer must climb a ladder to observe - it is usually on the opposite side.

Rationale being - less chance of accidental fall. We are more likely to go out of balance and fall if we "chase" the focuser rather than if it "presses" into us as we track the sky. We can lean forward but most people get uncomfortable when leaning back very quickly and there is more chance we will notice that we must change ladder position.

On the ground - I guess there is more "viewing" time if we lean somewhat forward before we adjust our chair.

[Peter Drew]

My 30" Dob requires a tall step ladder.  The focuser is on the E side so it's a push away action.  Either side or action has its problems in the dark, there is little difference between the telescope moving away from you and the sensation of falling backwards.  Smoothness of movement is critical, a jerky movement can easily unbalance an observer.  No clear advantage over E-W focuser.     🙂     

[Second Time Around]

I like the eyepiece on the left hand side of the tube looking up from the main mirror end.  This is because my left eye is my dominant one.  This means that the heat from my body doesn't waft in front of the open tube and cause turbulence and so degrade the image. 

[Louis D]

9 hours ago, Second Time Around said:

I like the eyepiece on the left hand side of the tube looking up from the main mirror end.  This is because my left eye is my dominant one.  This means that the heat from my body doesn't waft in front of the open tube and cause turbulence and so degrade the image. 

I'm having difficulty diagramming this in my mind's eye.  Doesn't your entire body sit to one side or the other of a Dob when observing?  None it is in front of (below for big Dobs?) the tube when observing in my experience.  Could you explain a bit more how your body heat ends up wafting up in front of the open end of the tube?

FWIW, I'm also left eye dominant, so I feel your pain when using DSLRs and other devices that assume right eye dominance.  My DSLR's rear screen has all sorts of nose grease imprinted on it because of this.

[Second Time Around]

If I'm on the other side then my head and body will be some 2 1/2 inches to the right (the distance between my eyes), and thus part of my body will be past the end of my tube.

 

[Piero]

Well, both my 12" and 16" home made dobsons have the focuser to the West when the telescope points to the South (north emisphere).

The primary reason is pulling instead of pushing when tracking manually.

The second reason is that I slightly prefer this configuration. My dominant eye is left and it is slightly closer to the telescope when aiming with the Rigel or telrad.

My 8" f6 solid tube dobson has the focuser installed to the left like most of commercial dobsons. It's usable just fine although I prefer the other way around.

 

12" and 16" dobs:

 

8" f6 dob (focuser and eyepiece sold years ago..)

Edited August 16, 2023 by Piero

[Mr Spock]

Mine is at 45 on the E side. Absolutely hate it. When viewing vertically I’m almost climbing over the tube to reach the focusser. I’m a left eye viewer and would much prefer if the tube could rotate. 

[Louis D]

I'd never given it much thought, but all of my Dobs have the focuser on the right (E side) as seen from the primary end.  Thus, I pull as I track when viewing south, my typical viewing arrangement.

[bosun21]

Mine is also on the east side when pointing south. I don’t think I would be too perturbed if it suddenly changed to the west side. To me it all depends on what you have grown accustomed to over the years and for you that has become fine.

[John]

My 12 inch dob was in tube rings so I could have the focuser at whatever angle I liked. After some experimentation I went for this:

I observe standing using my left eye and I am left handed. 

I got the finders and focuser positioned so that I could shift between them with minimal head movement.

It worked well for the 10 years that I owned the scope.

 

 

 

[Louis D]

6 hours ago, John said:

My 12 inch dob was in tube rings so I could have the focuser at whatever angle I liked. After some experimentation I went for this:

I observe standing using my left eye and I am left handed. 

I got the finders and focuser positioned so that I could shift between them with minimal head movement.

It worked well for the 10 years that I owned the scope.

Beautiful scope.  It really looks like a yard cannon with those giant altitude trunnions in black contrasting against a white OTA.  😉

I hope the current owner is making good use of it.