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Newbie Q about Dobsonians

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#1 Craven

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Posted 20 October 2020 - 09:10 AM

I noticed on dobs that eyepiece is at 12 o'clock on the tube.  Does that make it difficult for younger / shorter users?   I think I also read that the Explore Scientific dobs are built so that you can rotate the tube to bring that around for shorter users.  Do all dobs do that?  If it is only the ES, then does htat mean its more susceptible to breaking, iyo?   Is this a feature that will bring me more grief in the long run or do they all do that?



#2 SloMoe

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Posted 20 October 2020 - 09:13 AM

Yes, all dobs bring us grief,,,,,,

 

Seriously, most Dobs have the focuser at the 10 o'clock position, and we use either ladders or small step stools for the vertically challenged.


Edited by SloMoe, 20 October 2020 - 09:14 AM.

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#3 SloMoe

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Posted 20 October 2020 - 09:20 AM

I think you're confusing the Dobsonian and the Newtonian designs.

 

Newtonian is the reflector design of the optical tube assembly, Dobsonian's are a design the utilizes a Newtonian reflctor in a particular mount/base.


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#4 Craven

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Posted 20 October 2020 - 09:27 AM

I think you're confusing the Dobsonian and the Newtonian designs.

 

Newtonian is the reflector design of the optical tube assembly, Dobsonian's are a design the utilizes a Newtonian reflctor in a particular mount/base.

I'm not confusing anything.  I was looking at Dobs on the ES scientific website and others and it all appeared that the EP was at the 12 position.  I read that the ES dob tube rotated, which I thought, while convenient, might be constructed in a way that make breakage more likely.


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#5 Lukes1040

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Posted 20 October 2020 - 09:37 AM

Can you share a pic of the one you’re looking at? Almost no dobs have an eyepiece at 12 o’clock.
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#6 Richie2shoes

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Posted 20 October 2020 - 09:39 AM

Typically the dob eyepiece is around the 10 position.  The ES solid tube dobs use rings to hold the alt bearings, so it looks like they could be rotated.  They wouldn't be prone to breaking though, because if you put the tube on an eq mount, you will be rotating the tube frequently.  As Slomoe stated, most people use a step stool or ladder for larger scopes or shorter observers.



#7 sg6

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Posted 20 October 2020 - 09:39 AM

Just looked at the ES USA pages - I assume those are the ones and ES Dobs seem to be photographed with the eye piece mainly at what would be 3 O'Clock or 9 O'Clock.

 

Which seems a little odd as usually they are used with the eyepiece around the 10 O'Clock position.

 

The 8" and I therefore assume the 10" also appear to be on rings. The presumption being the scope come orientated one way 3, 9 or 12 O'Clock and you carefully loosen the rings and rotate the OTA to where you find best and then tighten. The OTA will then mainly get used at that position for some time.

 

I doubt from the pictures that the scope freely rotates, just you loosen the rings, rotate the OTA and clamp back up.

 

The portable version appear to have no option to rotate, understandable from the design.

 

The first small image in the series of the 8" shows the focuser+eyepiece horizontal, the second small image shows it at approximately 45 degrees between horizontal and vertical. Guess someone has lined up a few examples then taken pictures for their site.


Edited by sg6, 20 October 2020 - 09:44 AM.


#8 SloMoe

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Posted 20 October 2020 - 10:05 AM

Ok, so the ES solid tube dob can rotate in it's rings, not going to be easy to do with it pointed up because it might also slide down as you rotate it, so level the scope and position the focuser where ever you need it to be.


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#9 JohnBear

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Posted 20 October 2020 - 10:08 AM

9 out of 10 Dob owners on CN say their eyepieces are located at 10 o'clock.  YMMV


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#10 rowdy388

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Posted 20 October 2020 - 10:08 AM

Also, nothing is prone to breaking on any dob I've ever seen. They are made to be used and anything you

do to them can be undone. 


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#11 Voyageur

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Posted 20 October 2020 - 10:39 AM

The ring assembly looks pretty sturdy and I doubt whether it would be prone to breaking unless misused. 
 

The ability to rotate the tube to place the focuser in a particular position doesn’t seem terribly valuable to me. For a short person, placing the focuser at the 9 o’clock position might make a step stool unnecessary when the scope is pointed close to zenith, but it seems awkward. With the focuser at around the 10 o’clock position, you are looking in and down, bending more or less at the waist and using a step stool as needed, which seems ergonomically favorable to me. With the focuser at 9 o’clock, at lower tube positions, you’d be crouching down to look straight in.
 

And as SloMoe says, it’s not a matter of quickly rotating the tube to a new position as you move the scope up and down in altitude. Once you choose a position, you wouldn’t want to loosen the rings unless the scope was horizontal.

 

In short, having this feature would not really influence my decision to buy the scope either way. 


Edited by Voyageur, 20 October 2020 - 04:56 PM.

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#12 Napp

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Posted 20 October 2020 - 10:45 AM

I have an ES DOB, specifically the 16 inch Gen 2.  There are no rings within which to turn the tube as the scope is a truss tube.  The eyepiece is at 9 o’clock or 3 o’clock depending on how you look at the scope.  The secondary cage can be installed at 12, 3 and 6 o’clock just by the construction of the scope but why anybody would do so is beyond me.  Straight up and straight down eyepiece orientation is not really usable on my scope.  I accidentally installed the secondary 180° to the other side in a hurry one night.  This put the finder below the eyepiece which I did not like.  I have read where someone modified the secondary cage so the focuser would be at 10:30.  I intend to look into that because it would put the eyepiece in a more comfortable position when looking at objects at a low elevation.  This is actually important to me as I regularly go to the Winter Star Party to observe Eta Carina and other far southern objects very low to the horizon.


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#13 Craven

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Posted 20 October 2020 - 12:43 PM

9 out of 10 Dob owners on CN say their eyepieces are located at 10 o'clock.  YMMV

No doubt.  I'm not arguing that point.   What I "saw" was just only that, what I "saw" but I still had the question about rotation.


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#14 clearwaterdave

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Posted 20 October 2020 - 02:08 PM

I didn't look but could it be an optical illusion.,the photos are 2 dimensional.,I put rings on my small tabletop dob and it makes it easier for me.,My 8"Zhumell dob is useable horizon to zenith for me with this office chair at its highest.,20",.A child would need a simple stepstool.,

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#15 aeajr

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Posted 20 October 2020 - 04:17 PM

No doubt.  I'm not arguing that point.   What I "saw" was just only that, what I "saw" but I still had the question about rotation.

If you would post a link to the Dob in question then we would know what you are talking about.   

 

As stated earlier, most Newtonian optical tube assemblies on Dobsonian mounts have the focuser/eyepiece at around 10 o'clock.   I do have an Orion tabletop Dob that has the eyepieces at 12 o'clock, but that is a rare one.   I could not cite another that is set up that way. 

 

Dobsonian Telescopes
https://opticsaide.c...ian-telescopes/

 

As for having shorter people or children reach the eyepiece, well it depends on what you are looking at which will determine how high the tube is pointed.

 

When doing outreach I usually have a step set-up so the kids have something to hold onto.  Something like this:

 https://www.amazon.c...rkle_mcd_asin_0

 

or this

https://www.amazon.c...,aps,303&sr=8-8

 

How old are the children you are talking about?



#16 Tony Flanders

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Posted 20 October 2020 - 07:19 PM

The ability to rotate the tube to place the focuser in a particular position doesn’t seem terribly valuable to me.


Actually, it's really nice, if you can get it.
 
My 7-inch Oak Classic Dob holds the tube in the rocker box by friction, making it fairly easy to rotate the tube. That does indeed allow me to fine-tune the angle to my satisfaction, but it won't necessarily be right for another person. And the rotation isn't something you do casually; it takes a bit of muscle.
 
However, the famous AstroScan and Portaball lines are based on a ball joint, allowing the scope to use just articulation instead of having separate altitude and axis bearings. That design has many benefits, one of which is that you can rotate the tube with your fingertips. It's really handy if you want to share views with someone 6 inches shorter than you are. And it allows you to fine-tune the rotation every time you move to a different object, avoiding any stooping or craning.



#17 Eddgie

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Posted 20 October 2020 - 08:02 PM

I noticed on dobs that eyepiece is at 12 o'clock on the tube.  Does that make it difficult for younger / shorter users?   I think I also read that the Explore Scientific dobs are built so that you can rotate the tube to bring that around for shorter users.  Do all dobs do that?  If it is only the ES, then does htat mean its more susceptible to breaking, iyo?   Is this a feature that will bring me more grief in the long run or do they all do that?

If you look at pictures of Explore Scientific telescopes, you will see that in the ads, they show the eyepiece positioned so that the focuser tube is always parallel to the ground.

 

If you look at pictures from almost all other manufacturers, you see that they have the focuser so that it is angled up when the scope is pointed toward the horizon.

 

Most observers using smaller scopes prefer the latter orientation because as you view closer to the horizon, it would be un-ergonomic if the eyepiece were vertical and in smaller dobs, you would have bend over or sit on the ground to see through the eyepiece.  With the eyepiece angled up, you are in a more natural position.

 

As the scopes get much larger (20" or so) you start to see the eyepiece sometimes horizontal.  This is because larger scopes cans sometimes require a ladder or step to reach the eyepiece when viewing high in the sky and having it stick right out of the side keeps the base from interfering with the ladder or step stool.

 

Explore Scientific truss scopes do allow the owner to change the position from that shown in the picture and most do change it.

 

The Costco version does not have this capability out of the box, but I know of at least on CN member that drilled new holes in the secondary cage wall so that he could rotate the focuser to a more comfortable position. 

 

So, the answer is simple.. It is ergonomics.  Why ES shows their truss dob with the eyepiece in an un-ergonomic position. Most people would not want their smaller dobs configured this way.


Edited by Eddgie, 20 October 2020 - 08:03 PM.


#18 kfiscus

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Posted 20 October 2020 - 08:15 PM

My Z12 is at 10:30 (?) and my 16 Lightbridge is at 9 o'clock (horizontal).

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#19 MellonLake

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Posted 20 October 2020 - 08:37 PM

Dobs work great for kids. They are rugged and the eyepiece is never too high or to low (at least up to 10" f/5). My kids and cousins kids have looked through mine many times (kids as young as 5) with no issues.

I am more confident letting kids use the Dob than the AZ or EQ mounts.

#20 Voyageur

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Posted 21 October 2020 - 08:47 AM

Actually, it's really nice, if you can get it.
 
My 7-inch Oak Classic Dob holds the tube in the rocker box by friction, making it fairly easy to rotate the tube. That does indeed allow me to fine-tune the angle to my satisfaction, but it won't necessarily be right for another person. And the rotation isn't something you do casually; it takes a bit of muscle.
 
However, the famous AstroScan and Portaball lines are based on a ball joint, allowing the scope to use just articulation instead of having separate altitude and axis bearings. That design has many benefits, one of which is that you can rotate the tube with your fingertips. It's really handy if you want to share views with someone 6 inches shorter than you are. And it allows you to fine-tune the rotation every time you move to a different object, avoiding any stooping or craning.

Being able to rotate the tube "on the fly" would make this feature better than I first thought, and it might work out well for multiple users of different heights.

 

It just struck me more as a hassle than otherwise, but I have been wrong before about such things. When I replaced my old Ford van with a newer Chevy, I thought strongly that I would not like having passenger doors on both sides of the vehicle (due to my custom interior setup). I ended up really liking the two-sided doors. I was made fun of for my about-face...

 

Bottom line, you wouldn't have to use the rotating rings if you didn't care to, and there would be no reason to believe that they would make the scope more vulnerable to damage.

 

Actually, the real bottom line is finding the scope in stock.undecided.gif  



#21 Asbytec

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Posted 21 October 2020 - 09:01 AM

The rotating rings on the ES firstlight do rotate. Not freely, you have to loosen the clamps and rotate the tube to suit you. It also allows some freedom of movement higher or lower in the saddle for balance. The bearings are the strong point, as well as fairly sturdy construction. Unlike others, my focuser is at 2 O'clock. :lol:

#22 spaceoddity

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Posted 21 October 2020 - 05:00 PM

9 out of 10 Dob owners on CN say their eyepieces are located at 10 o'clock.  YMMV

Could be 2 o'clock if you're standing in front of the tube. I would guess the ES dobs have rings on the OTA in case you wanted to rotate it to the other side(left eye viewing?) or maybe if you wanted to put the OTA on a tripod mount. I use my left eye but I still prefer the eyepiece on the left(10 o'clock) side. 


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#23 icomet

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Posted 24 October 2020 - 12:08 PM

Clam system

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#24 Avgvstvs

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Posted 25 October 2020 - 02:32 AM

Too much pontificating, just get a Dob!



#25 Jon Isaacs

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Posted 25 October 2020 - 03:31 AM

No doubt.  I'm not arguing that point.   What I "saw" was just only that, what I "saw" but I still had the question about rotation.

waytogo.gif

 

Some Dobs allow for tube rotation but most don't.  Generally rotation is something you experiment with and the leave it set.  If you try to do it while observing an object, you'll probably lose the object.  

 

I like my focusers somewhere between about 30 degrees (2 oclock) and 45 degrees (1:30).  This lets me look down into the eyepiece when I am viewing near the hortizon and it's still comfortable viewing the zenith. 

 

As was mentioned, with large scopes, particularly ones the require a ladder, the focuser is typically horizontal, it needs to be as close as possible so you are not leaning over too much from the ladder. 

 

4474488-Obsession and Jon at Jewel Valley.jpg

 

StellarVue finder on 22 inch.jpg

 

Jon




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