115 replies to this topic

[Oberon]

I just slipped mine into my f/4.5 16" and compared it with my Nagler 31. After a quick squiz at Jupiter I spent most of the time in Eta Carina.

Outside of 50% it was pretty hopeless, but every time I put it back in I was surprised how the nebula leapt out at me. In the center was very good.

I also tried with a Paracorr which made a massive improvement. The edges weren't perfect but they were very acceptable. But the Nagler remained better once you started studying detail, and it had a very slightly wider TFOV which I didn't expect. But there isn't much in it, and overall the difference in cost is much greater than the difference in performance.

 

So what does this mean?

A Paracorr would reduce the binocular's 3.5 degree field of view down to 3 degrees, which is the figure I was aiming for, so thats OK and better than the Panoptic's 2.6 degrees. But suddenly with 2 x Paracorr we're talking real money, and a bit of machining to adapt the Paracorr to binocular use and so forth.

 

Maybe I should experiment with a cheaper coma corrector, like the Baader MPCC which would keep the full 3.5 degree TFOV. Any thoughts?

[nicknacknock]

The MPCC would be a good match as a permanent addition to this eyepiece once you find the optimal distance setting. The Edmund is not however threaded for filters.

 

I use a 35mm extender to both reduce the focuser racking out and to thread filters on. This would allow the use of the MPCC and filters as well (with whatever thickness rings are required to get the optimal distance between MPCC and eyepiece).

[Jon Isaacs]

 

 

So what does this mean?

A Paracorr would reduce the binocular's 3.5 degree field of view down to 3 degrees, which is the figure I was aiming for, so thats OK and better than the Panoptic's 2.6 degrees. But suddenly with 2 x Paracorr we're talking real money, and a bit of machining to adapt the Paracorr to binocular use and so forth.

Maybe I should experiment with a cheaper coma corrector, like the Baader MPCC which would keep the full 3.5 degree TFOV. Any thoughts?

 

As I understand it, you're binoculars are refractors, not reflectors. Paracorr's correct the coma by adding coma of the opposite sign and the only improvement the eyepiece's astigmatism is the result of the slight 15% change in the focal ratio.  Used with a refractor, a Paracorr adds unwanted coma.  A simple Barlow might help but honestly.. this is going to be an expense project.  You might find the edge correction provided by the Erfle acceptable but I suspect people willing to spend $5000+ for a binocular are going to want to use eyepieces that offer a reasonably well corrected field of view.  That really does require a modern SWA or UWA design.  

 

Jon

[ArsMachina]

Maybe I should experiment with a cheaper coma corrector, like the Baader MPCC which would keep the full 3.5 degree TFOV. Any thoughts?

 

I also thought about using the Baader MPCC

But I was told that this short two lens unit has a big disadvantage for visual use, it will bring in an undercorrection of around 20%

This is not a problem for photographers, but for visual use it is a big problem.

One can solve this problem with an 115-120% overcorrected mirror, but this mirror would only work with a MPCC then.

 

I decided to go without correctors and stay with a longer focal ratio.

This also saves weight and lenses :-)

 

Jochen

[Mark9473]

 

A simple Barlow might help but honestly.. this is going to be an expense project.  You might find the edge correction provided by the Erfle acceptable but I suspect people willing to spend $5000+ for a binocular are going to want to use eyepieces that offer a reasonably well corrected field of view.  That really does require a modern SWA or UWA design.  

 

Jon

 

 

I agree. Unfortunately there aren't all that many 2" SWA or UWA eyepieces that bring the desired focal length and AFOV into a form factor suitable for bino-viewing.

Personally, I am a huge fan of the 35mm Paragon / AT Titan II ED. I'm not aware of a wider/better corrected eyepiece around that focal length that is still small enough to put two of them side by side. That and the 22mm Nagler T4 would be the backbone of my 2" system.

[ArsMachina]

Hi Mark,

 

I have also been also after a pair of long focal length 2" widefield eyepieces for binoviewing and decided for the Kasai 32mm extra widefield 85°:

 

http://agenaastro.co...piece-32mm.html

 

I do not yet have them in my hands, so I can not tell you how sharp they are at the edge...

 

Jochen

Edited by ArsMachina, 22 February 2015 - 06:15 PM.

[Jon Isaacs]

The MPCC would be a good match as a permanent addition to this eyepiece once you find the optimal distance setting. The Edmund is not however threaded for filters.

 

I use a 35mm extender to both reduce the focuser racking out and to thread filters on. This would allow the use of the MPCC and filters as well (with whatever thickness rings are required to get the optimal distance between MPCC and eyepiece).

 

 

 

I also thought about using the Baader MPCC
But I was told that this short two lens unit has a big disadvantage for visual use, it will bring in an undercorrection of around 20%
This is not a problem for photographers, but for visual use it is a big problem.

.

 

Again:  Jonathan's objectives are refractive, Coma Correctors are meant for Newtonians that have inherent coma, they add coma of the opposite sign to eliminate the coma.   Refractive optics are typically corrected for coma so adding a coma corrector will add coma.. 

 

In a Newtonian, the MPCC will correct the coma but not address the more serious problem with the 32mm Erfle, the astigmatism. 

 

 

 

I agree. Unfortunately there aren't all that many 2" SWA or UWA eyepieces that bring the desired focal length and AFOV into a form factor suitable for bino-viewing.
Personally, I am a huge fan of the 35mm Paragon / AT Titan II ED. I'm not aware of a wider/better corrected eyepiece around that focal length that is still small enough to put two of them side by side. That and the 22mm Nagler T4 would be the backbone of my 2" system.

 

I have never looked through Paragons.. Those eyepieces arrived on the scene after I pretty much had my eyepiece collection in place.  I started Marcus Ludes, clone of 30mm 80 degree clone of the Widescan II and slowly moved up as I could afford them.  I had that TeleVue 32mm Widefield for some years and then moved up to the 35mm Pan and the 31mm Nagler, last year I added the 41mm Pan. Those eyepieces won't fit unless you're not human.. 

 

If I were building these, I would be tempted to go with the 120mm F/5's, a little more field curvature but eyepieces like the 22mm Nagler would provide a 3.0 degree TFoV and the overall field would be better corrected.  Eyepieces like the Paragons would push that out to about 4 degrees.

 

Jon

[nicknacknock]

Jon,

 

Thanks for the reminder re coma correctors belonging to a reflector    Sometimes a bit more thinking before typing a reply is required.

 

To provide a more accurate description on the 32mm RKE eyepiece, I sketched from memory what I saw:

 

[Oberon]

If I were building these, I would be tempted to go with the 120mm F/5's, a little more field curvature but eyepieces like the 22mm Nagler would provide a 3.0 degree TFoV and the overall field would be better corrected.  Eyepieces like the Paragons would push that out to about 4 degrees.

 

Hi Jon thank you for your advice, its very much appreciated as you can tell I've zero experience with refractors.

Curiously this little exercise started with me looking at buying a couple of Orion 120mm f/5 OTA's here but I thought if I'm going to that much trouble I should look around at doing better than a cheap Chinese achro. Istar seems to get a good wrap for quality and they had a lens pretty close at 127mm f5.5.

 

While we on the subject, what do you know about these objectives from Surplus Shed? The price is right...

[Oberon]

Re. eyepieces, the Ethos 17 is within a whisker of TFOV to the Nagler 22. That has surely got to be the ultimate binocular eyepiece!

[schang]

 

If I were building these, I would be tempted to go with the 120mm F/5's, a little more field curvature but eyepieces like the 22mm Nagler would provide a 3.0 degree TFoV and the overall field would be better corrected.  Eyepieces like the Paragons would push that out to about 4 degrees.

 

Hi Jon thank you for your advice, its very much appreciated as you can tell I've zero experience with refractors.

Curiously this little exercise started with me looking at buying a couple of Orion 120mm f/5 OTA's here but I thought if I'm going to that much trouble I should look around at doing better than a cheap Chinese achro. Istar seems to get a good wrap for quality and they had a lens pretty close at 127mm f5.5.

 

While we on the subject, what do you know about these objectives from Surplus Shed? The price is right...

 

Just about all of the achromats in refractors and binoculars are made in China, except a few percentage that are made elsewhere.  Call them cheap if you want, though no matter which way you cut it, they are achromats and they can not perform beyond the law of physics about them for low F ratios.  So you if want something special with all of your effort of building it, you might want to think about ED glasses.  The APM offers them, though they are not cheap for a 4" 45 degrees or right angle binocscope, even though they are made in China.  

[Jeff Lee]

I am sure you are all aware of JMI's products: http://www.jimsmobile.com/buy_rb.htm

 

not affiliated with them, just thought they might of interest.

[Jon Isaacs]

 

If I were building these, I would be tempted to go with the 120mm F/5's, a little more field curvature but eyepieces like the 22mm Nagler would provide a 3.0 degree TFoV and the overall field would be better corrected.  Eyepieces like the Paragons would push that out to about 4 degrees.

 

Hi Jon thank you for your advice, its very much appreciated as you can tell I've zero experience with refractors.

Curiously this little exercise started with me looking at buying a couple of Orion 120mm f/5 OTA's here but I thought if I'm going to that much trouble I should look around at doing better than a cheap Chinese achro. Istar seems to get a good wrap for quality and they had a lens pretty close at 127mm f5.5.

 

While we on the subject, what do you know about these objectives from Surplus Shed? The price is right...

 

 

Jonathan:

 

 I don't have any experience with the Surplus shed objectives but people on the ATM forum do.  

 

In my mind, one has to decide the purpose of binoculars like these.  My thinking is that they need to be optimized to do the things they do best.. These are not well suited for planetary viewing or splitting double stars, whether you're using Orion 120mm F/5's or Istar 127mm F/5.5's, these are large, fast acrhomats, that is not what they're about.  

 

Binoculars like this would be all about low power, wide fields of view..  That means a 600mm focal length is more desirable than a 700mm focal length.. And I suggest this as well:

 

Something like this would be best a modular design, design it around the focuser, diagonal, IPD adjustment end of things, design it so the objectives can be swapped without major redesign.  

 

Jon

[Gordon Rayner]

A few posts ago, someone suggested a pentaprism feeding a Porro arrangement ( Porro II preferred).

Consider:

Instead of a pentaprism , a penta mirror composed of two mirrors arranged as are the reflecting surfaces of a pentaprism. ( Not a roofed penta, as in SLR cameras)
Such pentamirrors have been used for many years in rangefinders for ships, armored vehicles, and fixed fortifications.

With a new, shorter, fatter body of plywood and/or aluminum/magnesium sheet/plate, and/or carbon fiber, WW II f/5 20 x 120 Japanese military, or postwar Nikon/Nippon Kogaku or Kowa, or Fuji Meibo/Fujinon/Fujifilm 15 x 80 or 25 x 150 I or II would be right angle viewing, while retaining erect, unreversed images.
Because the very long glass path in the large Porro II prisms, retained, is the same, no readjustment of the objective two elements' spacing between each other , which otherwise is the most convenient variable, would be needed. See Selby "Aberrations of the prism diagonal" in ATM III older version , or in ATM II (?) from Willmann-Bell, for an applicable analysis.




There would , in some /all cases, be the need for shorter IPD bearings. Fuji II 25 x 150 already has very short bearings there, much shorter than the long, heavy ones in the Fuji I 25 x 150.

If for only one person, IPD swivel bearings might be eliminated.


Another approach to the topic of this thread, is( DEJA VU numerous times): Two mirrors arranged as seen in Hopkins in Mil Handbook 141 ( pops up easily in an online search, courtesy of Univ. of Arizona) Replace the Amici II beamprints for a prism by beamprints on mirrors ( which do not need to be ellipses to pass elliptical beamprints).


I wrote a 3D vector program,to handle the compound angles involved, for HP 48 , using the lateral motion of the virtual roof to be half the lateral motion of the one moving eyepiece, for IPD change, ff. WW II CZ Jena 25 x 100, 12 x 60, etc. Various mirror shapes are included in a routine to minimize the intermirror spacing without edge interference. That spacing is fixed. In the Matsumoto approach, the mirrors' axial spacing is varied for IPD change. That change in the "prism" size requires a refocus. In the M-San setup that seems to be between the objective lens and the 'prism'. That seems to eliminate the nose clearance problems with 2 inch barrel oculars and 55-56 mm. IPD.

2 inches is 50.8 mm . 56mm/2 minus 50.8mm/2 equals 5mm/2, =2.5mm wall thickness available, about 0.10 inch for a male threaded tube to hold the eyepiece, together with a female threaded mate whose exterior touches, or is very close to, the nose. This is
a very tight construction problem and use situation for someone with a 56mm IPD. (I am 65mm), if the focuser surrounds the eyepiece. Two inch eyepiece barrels waste valuable space.
It would be possible to move both eyepieces laterally, still using the invariant "prism" approach I chose, but that is more complex . It would have no effect on nose clearance.

The invariant "prism" approach eliminates the possibility of image rotation which might occur in the variable "prism" (Matsumoto-San) method.

In these 2-mirror erect and unreversed image "prism" designs, the line of sight can be chosen and fixed to deviate from perhaps 60 deg ( long, narrow beamprints) to 180 degrees. At 180 degrees , the angles are simple, not compound, and the beamprint is the familiar 1.41 major/minor axes ratio Newtonian diagonal shape.

Edited by Gordon Rayner, 26 February 2015 - 01:36 PM.

[Oberon]

 

 

If I were building these, I would be tempted to go with the 120mm F/5's, a little more field curvature but eyepieces like the 22mm Nagler would provide a 3.0 degree TFoV and the overall field would be better corrected.  Eyepieces like the Paragons would push that out to about 4 degrees.

 

Hi Jon thank you for your advice, its very much appreciated as you can tell I've zero experience with refractors.

Curiously this little exercise started with me looking at buying a couple of Orion 120mm f/5 OTA's here but I thought if I'm going to that much trouble I should look around at doing better than a cheap Chinese achro. Istar seems to get a good wrap for quality and they had a lens pretty close at 127mm f5.5.

 

While we on the subject, what do you know about these objectives from Surplus Shed? The price is right...

 

 

Jonathan:

 

 I don't have any experience with the Surplus shed objectives but people on the ATM forum do.  

 

In my mind, one has to decide the purpose of binoculars like these.  My thinking is that they need to be optimized to do the things they do best.. These are not well suited for planetary viewing or splitting double stars, whether you're using Orion 120mm F/5's or Istar 127mm F/5.5's, these are large, fast acrhomats, that is not what they're about.  

 

Binoculars like this would be all about low power, wide fields of view..  That means a 600mm focal length is more desirable than a 700mm focal length.. And I suggest this as well:

 

Something like this would be best a modular design, design it around the focuser, diagonal, IPD adjustment end of things, design it so the objectives can be swapped without major redesign.  

 

Jon

 

 

Yes, that is exactly what I have in mind. The focuser, diagonals, IPD adjustments etc are all fixed and able to deliver for a range of objectives and eyepieces, maybe even a camera. The initial driver was rich field but the ability to swap objectives and focal lengths easily makes it a uniquely flexible platform for expansion and customization. I'm trying to find the most practical and desirable extremes available in objectives and eyepieces so as to identify the sweetest most effective spot for engineering this thing.

Edited by Oberon, 24 February 2015 - 08:42 PM.

[ArsMachina]

I finished my Borg today :-)

 

 

 

Jochen

[schang]

This looks impressive, Jochen.  Did you order the visual back from Mr. Matsumoto?  How much does it cost, may I ask?

 

How do you collimate these two scopes together? Do they stay collimated for extended use? Thanks.

[Mark9473]

Very impressive, Jochen. I take it this instrument is built for a single IPD?

[ArsMachina]

Hi Shien,

 

yes I ordered the EMS-UXL units from Mr. Matsumoto they arrived just yesterday :-)

You can find the prices at his Website.

 

I mounted the dovetail rails directly to the telescope tubes, so I saved weight and could be sure that they are exactly parallel to the tubes.

As the central mound with the big bearing is also exactly parallel no further collimation is needed.

 

The right EMS unit has two collimation screws to merge the images and when the images are merged these collimation screws are in their default position.

This means that the two telescope tubes are exactly parallel.

 

Best wishes Jochen

[ArsMachina]

No Mark, if you look closely there are big helicals between the EMS units, so you can change the IPD from around 62mm up to 72mm

Below 62mm is not possible because of the diameter of the 2" helical eyepiece focusers at the top of the EMS units.

 

I have chosen this way instead of a parallel platform mount to change the IPD because of the weight and size.

The weight of this binoscope is just 8 Kilogramm ;-)

I wanted a small and lightweight package which you can break down very easily by just taking the two tubes out at their dovetail rails.

 

Jochen

[Mark9473]

That's a very ingenious solution for IPD adjustment.

What's the widest FOV you'll be able to reach in this instrument, you think?

I know the theoretical maximum is about 3.3° but do you have an eyepiece pair giving this FOV and still fitting within the IPD?

[ArsMachina]

Hi Mark,

 

I just bought a pair of 32mm Kasai 85° eyepieces, these should give me 3,4° of field with an exit pupil of 5mm and they will work with 62mm IPD.

But I do not know how good they will be at the edges ...

Below these I will work with Ethos 17, Ethos 13, Nikon NAV 10, Nikon NAV 7 and Nikon NAV 5

 

You can easily balance different eyepiece weights by just moving the two tubes with their dovetail rails in the central mount.

So you always have a perfectly balanced scope.

 

Jochen

Edited by ArsMachina, 25 February 2015 - 05:40 PM.

[Gordon Rayner]

The IPD is variable via the helical threaded spacing adjuster between the two mirrors. M-San originally used a Pentax 67 accessory there. An IPD change requires a refocus. That focuser can be between the rear of the telescope tube and the entrance to the 2-mirror Amici 2 'prism'. That position relieves the eyepiece region of a focusing function, thus helping nose relief at low IPD.


I was writing just as the responses from Jochen were incoming. So, it appears that the focus is at the eyepiece, and not at the rear of the telescope tube. Why?
The 62mm lower IPD may also involve the mirror housing of the second mirror in the M-San EMS setup.

Edited by Gordon Rayner, 26 February 2015 - 01:15 PM.

[ArsMachina]

Hi Gordon,

 

I do not have a focuser between the telescope tubes and the EMS units as this is usually.

Two big (Feather Touch) fucusers are way to heavy for my taste.

I decided for lightweight helical focusers which are also my eyepiece holders.

 

Jochen

[TheBigEye]

Wow - this is a fascinating thread!  I think the OP was asking about the market for binoscopes and what price purchasers might be willing to pay.  I don't mean to sound discouraging, but I think this is not only a "niche" market, but there are already 120mm and 150mm binocular-telescopes out there that can be purchased.  I had a pair of Oberwerk 120mm binocs (they no longer sell them). Achromats, Chinese origin, built like a tank, and pretty good optically.  I don't remember the f/ratio.  Anyway, these 120mm binocs accepted any 2" eyepieces, had 45-degree angled diagonals for comfortable viewing, and an erect image.  Cost?  $2150 at the time.  I eventually sold the Oberwerks and bought a pair of Garrett 150mm binocs.  These had 150mm triplet objectives at f/5.5 and accepted 2" eyepieces.  The views through those binocs were amazing - I had Nagler pairs at 20mm, 16mm, and 11mm. The left tube had a bit of astigmatism but the right tube showed very sharp views of Saturn and its moons.  The was some CA, but only on the moon and bright planets.  A Minus Violet filter cleaned that right up. Deep sky viewing was what I really bought them for and these binocs did not disappoint.  Garrett is no longer in business, but these 150mm binocs can still be purchased directly from China - at Runderoptics.com.  In January 2015, cost delivered to the USA via DHL/Air was $2950.  (Garrett sold them for about $4500 as I recall).  Includes a very nice aluminum case and 6 really decent wide-field eyepieces.  Even if you could successfully produce a binoscope in sufficient quantity to have a self-sustaining business, I'm not sure how you could compete with pricing like that.  Apparently, Garrett couldn't sustain it. And Oberwerk isn't selling the "big boys" either. Of course there will always be the innovators, like the ones in this thread, who turn out specialized top quality equipment and use premium components.  But, those instruments will never be found in the mass market - only in the hands of people industrious and talented enough to build them.  Good luck to you all!