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Viewers that take two inch eye pieces. How big a diameter can you go

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#1 JohnH

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Posted 26 January 2024 - 02:59 PM

There's a really good older eyepiece, my nagler 20 mm type 2 that I have had a very long time and it's definitely one of my favorite eye pieces to use. It took a bit of getting used to with the fussy eye position and the kidney bean reflections you get with them sometimes.

I recently had the chance to buy another one, so I'm just curious about getting a vinyl viewer to use this on.

But I also realize that the diameter of these eye pieces is quite large and many vital viewers won't be able to accommodate this on some people's eye spacing difference

Edited by JohnH, 26 January 2024 - 03:03 PM.


#2 junomike

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Posted 26 January 2024 - 06:19 PM

I've used 13T1's (1.25")  successfully (and comfortably) however along with size issue (nose, space, merging) there can also  be issues with reaching focus with fixed systems (Newt, Refractor)..

 

Then there's the cost of a BV that accepts 2" eyepieces (as in your case).



#3 Eddgie

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Posted 26 January 2024 - 09:33 PM

There's a really good older eyepiece, my nagler 20 mm type 2 that I have had a very long time and it's definitely one of my favorite eye pieces to use. It took a bit of getting used to with the fussy eye position and the kidney bean reflections you get with them sometimes.

I recently had the chance to buy another one, so I'm just curious about getting a vinyl viewer to use this on.

But I also realize that the diameter of these eye pieces is quite large and many vital viewers won't be able to accommodate this on some people's eye spacing difference

I have not tried it but I can give you my thoughts. 

 

First, they do make binoviewers that take 2" eyepieces. There are two negatives. First, they tend to be pretty expensive, but more important than that, because of the need larger elements to support the field illumination, even though you really don't need it for the 20mm Nagler, the longer light path of the big binoviewer means that it is even harder to get an instrument to reach focus. 

 

For the 20mm Nagler though, since the field stop is only 27.4mm, if you could find a way to convert a conventional binoviewer to accept 2" eyepieces, There really isn't any reason to think it would not work with a large prism BV like the Mark V.

 

Here is the other issue, and it is actually hard to know how it would work out. Many people report that they cannot take in the entire field of a Nagler without kind of turning their head slightly to one side. This is fine if you are using one eye, but if you can't take the entire field with either eye individually without tilting your head left or right, then if you do this with two, when you try to tilt you head to take in one or the other side of the field with one eye, you will lose the exit pupil in the other eye, and vice versa. If you can take the view of the entire field with your head square to the eyepieces, then it should work (if you can solve the other issues) but if you can't without slightly tilting your head one way or the other, then you will likely get kidney bean or dropout in one of the other eyepeice.

 

Again, I have not done this myself, but I do know one person that tried using Naglers and this was his experience. He simply could not roll his eye right or left to get the entire edges of the field in both eyes at once. 


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#4 JohnH

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Posted 17 February 2024 - 02:23 PM

My biggest current telescope is an 8 inch Maksutov with moving mirror for focusing. It never has trouble reaching focus on a lot of things. My Mount is also quite oversized for a scope of this size so weight shouldn't be an issue either. The only possible problem is flex of the light path due to the weight
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#5 denis0007dl

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Posted 17 February 2024 - 02:49 PM

Hi JohnH,

 

I tried Nager 20mm T5 in binoviewer mode using for that time my own Siebert 2" Echelon 40 binoviewer, but never tried Naglers 20mm T2 in bino mode.

 

First about eyepeices: Nagers 20mm T5 re awsome in my experience, I really love them.

 

But there then comes problem: 2" binoviewers use BIG prisms, which casue a TON of false colours and add spherical error to system. That was something I couldnt pass on.

Thus, Echelon have clumzy mechanics, and many pleastic parts, and if oyu using some force and heavy eyepeices, binoviewer starts flexing.

Another thing, overall optical quality is not at great standard as you will get with lets say buying Mark V binoviewer, Denk Binotron etc.

 

I also tried Siebert 2" Elite binoviewer, which have even bigger beamsplitter, and add even more false colours and more spherical error than Echelon 40.

But Elite 45 have better mechanics than Echelon 40.

 

Another BIG issue in all 2" binoviewers, are very long light path taken, which making various problems for any telescope.

 

Another thing, both Echelon 40 and Elite 45 provide for my eyes comparations, dimmer images than any 1.25" binoviewers.

 

For me personally, like for most ppl around, and like for manufacturers, making 2" binoviewers does not have sense at all, otherwise, me personall would using them with same or bigger passion like Im using 1.25" ones, and I can bet, would do many others.

 

Kind regards

Denis


Edited by denis0007dl, 17 February 2024 - 02:53 PM.

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#6 havasman

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Posted 17 February 2024 - 07:10 PM

My biggest current telescope is an 8 inch Maksutov with moving mirror for focusing. It never has trouble reaching focus on a lot of things. My Mount is also quite oversized for a scope of this size so weight shouldn't be an issue either. The only possible problem is flex of the light path due to the weight

I'd say hanging over 2 pounds of Naglers off the end of a small telescope would cause all kinds of problems in addition to those Denis points out. Hard to imagine the manufacturer put a stout enough focuser/visual back on your scope to keep that load stable. And any binoviewer I ever used had a failure mode whereby the body of the binoviewer could unthread from the nose piece if not sufficiently torqued in place and kept at the angle that encourages tightening instead of loosening. That much weight would amplify that mode.


Edited by havasman, 17 February 2024 - 07:11 PM.


#7 RAKing

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Posted 18 February 2024 - 07:26 PM

John,

 

From a pure mathematical view, the biggest diameter eyepiece anyone can handle is equal to, or slightly less than, their Inter Pupillary Distance (IPD).  Each of those eyepiece's radius would be half the distance, so putting the two eyepieces side-by-side would match your IPD - and that would be the only way anyone could capture both exit pupils for viewing.

 

My IPD is 62mm, so I am limited to eyepieces 2.44" in diameter or less.  In reality, the largest eyepieces I ever used in my BV were a pair of 8mm TV Ethos (2.1" diameter, each).  The view was very nice, but having two of those big expensive eyepieces was not in my plans, so I returned one of them to its proper owner and have been very happy with my pairs of T6 Naglers.

 

My .02,

 

Ron


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#8 DRodrigues

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Posted 19 February 2024 - 05:49 PM

...

 

But there then comes problem: 2" binoviewers use BIG prisms, which casue a TON of false colours and add spherical error to system.

...

Denis,

 

You still didn't tested your supercharged 30mm BVs with 2" eps?



#9 denis0007dl

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Posted 20 February 2024 - 03:39 AM

Denis,

 

You still didn't tested your supercharged 30mm BVs with 2" eps?

Hi David,

 

I dont like added false colors which 30mm prisms binoviewers provide.

 

Also, using 2" eyepieces for me does not make any sense.

 

Kind regards

Denis



#10 noisejammer

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Posted 20 February 2024 - 01:23 PM

I went through this thought process years back. The part I missed was "What could 2" binoviewers do that 1.25" binoviewers cannot?"

 

My experience is that I don't have binocular vision over a field much larger than about 70°. This means that I might usefully use wide angle eyepieces with effective field stops that  are ~29mm diameter or larger and have a notional field of (say) 40°-70°.

 

Consider the optical path length. The 45 Elite has a 45mm clear aperture but its ~10" path length (184mm for binoviewers + 70mm for an attached diagonal) means that there is significant vignetting. I get that at f/12 you are only going to have ~25mm diameter fully illuminated. It's less worse if you use a larger diagonal, but this costs optical path length. Can your scope locate its focus 10.5" behind the exhaust pipe?

 

Next thoughts - How large is your MCT's secondary mirror? It may not even illuminate the 45mm clear aperture. Another factor is that its optical performance will be significantly degraded if you push the mirror 1.5" up the tube to achieve focus.

 

Finally, there's the weight - or more accurately the moment on the focuser. I have a FTF3545 which carries 2kg fine but absent a way to attach the diagonal directly to the rear surface, I can't see this working with a moving-mirror MCT.

 

Ultimately, I realised that Cassegrain optics are not well suited to wide fields. It turned out that a 1.25" binoviewer (I picked the Baader Mk V) allows me a true field of 2.1° with my 4" and 1.5° with my 6" refractorS. This is entirely sufficient.


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#11 DRodrigues

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Posted 22 February 2024 - 03:15 PM

Hi David,

 

I dont like added false colors which 30mm prisms binoviewers provide.

 

Also, using 2" eyepieces for me does not make any sense.

 

Kind regards

Denis

Hi Denis,

 

Different uses and/or priorities/sensibilities, result on different preferences. For me using 2" eps (with the Baader MK V supercharged by you...waytogo.gif), makes sense to get wider TFOVs - see https://www.cloudyni.../#entry11124843

On my day-light use and with my combo material http://www.pt-ducks....#CR-binoviewing there are no false colours that bothers me... wink.gif 
 


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#12 denis0007dl

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Posted 23 February 2024 - 04:12 AM

Hi David,

 

absolutely agree about personal preferences.

 

Glad you enjoy, and that is main point of everything.

 

Denis



#13 Astroyesmer

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Posted 23 February 2024 - 04:38 AM

I would not use a 2" BV with a telescope smaller than about 14/16 inches. At least up to 12 inches a 1.25" BV should be the way to go... Aside from weight and light path issues, there would be really no benefit I can think of unless you are absolutely dying to use an ultra wide field for focal lenghts above 16mm...


Edited by Astroyesmer, 23 February 2024 - 04:39 AM.



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