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New BT series from Oberwerk

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#26 Spikey131

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Posted 26 April 2018 - 09:24 PM

I did stop by the Oberwerk booth at NEAF and had a look at the BT line.

 

I'm no expert, but I thought their quality was excellent and the views (indoor) were clear and bright.  As far as I could tell the prisms were huge and exit pupils round and not truncated.

 

The price is right.  And I think the white one on the walnut tripod would look great in my living room.  Now to convince the other half....


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#27 garret

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Posted 27 April 2018 - 02:07 AM

How is collimation between the two tubes accomplished?

 

Garrett van der Veen, The Netherlands


Edited by garret, 27 April 2018 - 02:14 AM.


#28 OBERWERK

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Posted 27 April 2018 - 08:49 AM

How is collimation between the two tubes accomplished?

 

Garrett van der Veen, The Netherlands

The prisms are non-adjustable.  This does three things- 1) weight reduction, 2) being locked in, they can't slip out of alignment, and 3) no screws to turn so no trouble to get into ;)

Adjustment is by eccentric objective cells, very simple and easy.  As always, I'll set up and test every one, so they'll be "perfect" when they ship.  The cases are our exclusive heavy-duty cases we introduced last year for the Deluxe and Ultra Series, and those will be packed in larger shipping boxes that have cushioning on all 6 sides.  I fully expect that these will survive shipping better than anything that has adjustable prisms.  


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#29 Mr. Bill

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Posted 27 April 2018 - 10:30 AM

Kevin

 

Will a collimation tool be available for the 100mm like APM sells?

 

Bill



#30 OBERWERK

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Posted 27 April 2018 - 11:45 AM

Kevin

 

Will a collimation tool be available for the 100mm like APM sells?

 

Bill

I'll look at that, but a simple optical spanner wrench is all that is needed.  The lock rings loosen with little effort, and the objective cells rotate quite easily.  



#31 Rich V.

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Posted 27 April 2018 - 12:05 PM

Is a single eccentric ring provided on each side like the APMs or double eccentrics like many standard  binos such as Fuji FMTs or Nikons, for example?

 

Rich



#32 OBERWERK

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Posted 27 April 2018 - 12:17 PM

Is a single eccentric ring provided on each side like the APMs or double eccentrics like many standard  binos such as Fuji FMTs or Nikons, for example?

 

Rich

Single eccentric.  



#33 Mad Matt

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Posted 27 April 2018 - 12:45 PM

I recall reading somewhere that since the objectives are fixed (I.e. don’t move when adjusting the IPD) a single eccentric ring is enough.

#34 Mr. Bill

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Posted 27 April 2018 - 12:53 PM

Too bad you didn't have these back when I bought my APMs.....wink.gif

 

I like the fact you supply the new BTs in a case and also the picatinny "rail."


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#35 Rich V.

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Posted 27 April 2018 - 12:57 PM

I recall reading somewhere that since the objectives are fixed (I.e. don’t move when adjusting the IPD) a single eccentric ring is enough.

Since a single ring only allows each optical axis to inscribe an arc, it may likely take moving both sides to get the arcs to intersect at one collimated point.

 

Double eccentric rings allow each optical axis to move within a full circular area of adjustment on each side.  It makes for a larger, bulkier cell, though, so I can understand the use of a simpler, single ring.

 

Rich


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#36 Beg

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Posted 27 April 2018 - 02:14 PM

Congratulations on getting these out there. They look super nice. Excellent to get more choices for us here in the states.


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#37 range88

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Posted 28 April 2018 - 11:20 AM

It seems the listed price of 82xl ($1795) is very close to the actual paying price of the 82sd (euro 1839-vat=euro 1545=$1873).
What do you think?


Edited by range88, 28 April 2018 - 11:25 AM.


#38 Rich V.

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Posted 28 April 2018 - 04:19 PM

Effective aperture of the 100XL-ED is 96mm.  19x on the 82mm, and 25x on the 100mm was as low as we needed, therefore 24mm prism aperture was enough.  BTW, no fingernails smile.gif    

Kevin, pardon my persistence but I'd really like to understand BT design philosophies regarding nuisance reflections better. You've been in this business for a long time and have been a driving force in marketing large astro binoculars over the years.  I am assuming you have had some input into the design process of your new BTs so I have some questions.  I'm not intending to put you on the spot or cause some sort of "BT battle"; just to open an honest discussion of what are real design issues that matter to binocular telescope performance and what may not be.  Sadly, I'm not privy to the circle of BT designers/engineers but I'd love to be a "fly on the wall" while they're doing the work.

 

Regarding the "no fingernails" statement, was this a specific design goal? How have these off-axis reflections been removed from the system?  As I pointed out in a post above, I've examined the internals of my Miyauchi BTs and "clones" of these and and there is an aperture stop on the back side of the rhomb turret located midway between it and the Schmidt main prism to prevent off-axis reflections from reaching the rhomb's faces.  It appears Kowa, who you've emulated, also uses this design.  I don't see this baffle design showing obvious signs of vignette to my eyes, nor does it effect full aperture.  These designers thought it was worthwhile.  We've discussed this "fingernail" issue since the APM BTs were introduced.  Some users don't seem to mind and some are bothered by it, depending on their observing style. 

 

Markus has been very insistent on having his APM BTs being optimized for the best illumination of widest field eyepieces.  APM even enlarged the original prism aperture to 28mm from 25mm for this purpose.  On visual inspection there doesn't appear to be any baffles within their prism system as it seems the designers didn't want to contribute to illumination falloff from them either.  The trade-off appears to be these "fingernail" off-axis reflections.  It seems some BT buyers agree (though not necessarily justifiably) that this "fullest illumination" aspect is important in a visual instrument.  Perhaps they are way more sensitive to this than I am.  I actually expect this to be less important for visual use, though, as our eyes are not nearly as sensitive to these differences in illumination as a CCD sensor.

 

I've never seen measurements taken of any standard Porro or roof binoculars that are anywhere close to 100% illuminated to the edge of their field, even premium models. Top performers may have the central 50% of area illuminated by 100% of the objective.  I've never heard anyone complain about the illumination falloff of their Fuji FMTs, Nikon Astroluxes or Tak 22x60s, imperfect as they may be.  FWIW, these standard binos don't show "fingernails" either.  In light of this, what do you think about the quest for fullest illumination? Is this a worthwhile design goal for a visual binocular observer or just a quest for needless "perfection" with unintended consequences?  

 

One other thing; maybe at this point in time we should identify our binos based on the actual effective aperture? It seems long past due industry-wide. Perhaps call the new binos BT-80XL or BT-96XL?  undecided.gif

 

I'd love to hear your perspective on this as someone who has surely given this thought, having been in the binocular industry for years.  All other comments welcome, too, of course!

 

Thanks,

 

Rich


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#39 Mr. Bill

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Posted 28 April 2018 - 04:44 PM

Kevin

 

Markus claims a 6mm fully illuminated image circle (I assume measured at the rear prism aperture) on his APM BTs.....any idea of the size of 100% illumination on your new BTs?

 

:question:



#40 garret

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Posted 29 April 2018 - 03:44 AM

 

APM even enlarged the original prism aperture to 28mm from 25mm for this purpose.

I have the original 2015 version of the APM 100 ED APO binocular, clear aperture of the Rhomboid prism is not 25mm but 23mm.

See my Gallery for images of the Rhomboid and Schmidt prism of the APM 100: https://www.cloudyni...um/9032-images/

 

Garrett


Edited by garret, 29 April 2018 - 03:45 AM.


#41 trener

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Posted 29 April 2018 - 04:42 AM

garret,

 

Prism aperture and clear aperture are two different things.



#42 edwincjones

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Posted 29 April 2018 - 07:46 AM

Kevin
 
Markus claims a 6mm fully illuminated image circle (I assume measured at the rear prism aperture) on his APM BTs.....any idea of the size of 100% illumination on your new BTs?
 
question.gif


is not this question asking Kevin to violate the dealer TOS?

but please do not accuse me of being a mod
edj

Edited by edwincjones, 29 April 2018 - 07:46 AM.


#43 Mr. Bill

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Posted 29 April 2018 - 10:39 AM

Don't see how....just another parameter on the spec sheet like 24mm prism aperture.

 

IMO, questions about field illumination drop off are certainly relevant.



#44 Rich V.

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Posted 29 April 2018 - 11:47 AM

Kevin

 

Markus claims a 6mm fully illuminated image circle (I assume measured at the rear prism aperture) on his APM BTs.....any idea of the size of 100% illumination on your new BTs?

 

question.gif

I'm trying to picture how a fully illuminated 6mm image circle relates to an eyepiece with a 27mm field stop that's inserted into the system, for example.  How does this affect the illumination of the exit pupil produced?  How sensitive is our eye/brain system's perception of this illumination profile regarding dimming towards the edge?

 

EdZ used a laser to determine the illumination of the exit pupil of many binoculars; only a few were 100% illuminated in even the central 50% of the exit pupil.  None listed in the link below exceeded 75% illumination at 75% out from center of the objective.  A BT isn't really different than any standard bino; with the right tools and methods, this can be measured.

 

Ed's methodology explained:  https://www.cloudyni...ures/?p=2671239

 

Rich



#45 range88

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Posted 29 April 2018 - 12:22 PM

Don't see how....just another parameter on the spec sheet like 24mm prism aperture.

 

IMO, questions about field illumination drop off are certainly relevant.

Some one told me there is an over 60% illumination drop-off at the edges.



#46 garret

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Posted 29 April 2018 - 12:31 PM

 

I'm trying to picture how a fully illuminated 6mm image circle relates to an eyepiece with a 27mm field stop that's inserted into the system

Image: 22mm Vixen LVW inside the APM 100, the size of the fieldstop of the 22mm is approx. 24.5mm, the exit pupil is very close to the edge of the eyepiece.

Illumination is approx. 70%?

This morning I did this test with my 9mm Delite (fieldstop size 9.6mm) Illumination approx. 85% at the edge.

and with my 5mm Delite (fieldstop 5.3mm) 100% illumination at the edge, not easy to see I had to use a magnifying-glass.

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  • apm-+-22mm-LVW-small.jpg


#47 Mr. Bill

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Posted 29 April 2018 - 02:51 PM

Image: 22mm Vixen LVW inside the APM 100, the size of the fieldstop of the 22mm is approx. 24.5mm, the exit pupil is very close to the edge of the eyepiece.

Illumination is approx. 70%?

This morning I did this test with my 9mm Delite (fieldstop size 9.6mm) Illumination approx. 85% at the edge.

and with my 5mm Delite (fieldstop 5.3mm) 100% illumination at the edge, not easy to see I had to use a magnifying-glass.

I'm getting at least 70% using the 24mm UFFs....



#48 Mr. Bill

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Posted 29 April 2018 - 03:20 PM

When I look down the barrel from the objective end of my 100mm APO with the 24mm UFF in place, very little offset from on axis will begin to show vignetting, in other words a drop off from 100% illumination to 99% on down to 70% at the extreme edge of the fov.

 

So a 6mm diameter of 100% of my 25mm rear aperture diameter would not be unreasonable....

 

The rate (slope) of the dropoff of illumination would seem to be the issue.


Edited by Mr. Bill, 29 April 2018 - 04:43 PM.


#49 Rich V.

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Posted 29 April 2018 - 03:51 PM

We know that all binos vignette to some degree.  The question is how much does this vignette really affect our views and what is the best compromise of illumination vs. minimizing off-axis reflections that is acceptable to us?  Some of us hate off-axis reflections and some don't mind.  I don't know if I can tell the difference between views with the APM 70mm ED BT at 16x and the MS ED 16x70s regarding illumination but I know for a fact the MS EDs show a lot less ghosting.   shrug.gif

 

Will we ever see a perfect 100% illuminated bino that also has 100% elimination of all reflections/ghosting?  I doubt it, but remain hopeful.

 

Rich



#50 OBERWERK

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Posted 29 April 2018 - 06:39 PM

Kevin, pardon my persistence but I'd really like to understand BT design philosophies regarding nuisance reflections better. You've been in this business for a long time and have been a driving force in marketing large astro binoculars over the years.  I am assuming you have had some input into the design process of your new BTs so I have some questions.  I'm not intending to put you on the spot or cause some sort of "BT battle"; just to open an honest discussion of what are real design issues that matter to binocular telescope performance and what may not be.  Sadly, I'm not privy to the circle of BT designers/engineers but I'd love to be a "fly on the wall" while they're doing the work.

 

Regarding the "no fingernails" statement, was this a specific design goal? How have these off-axis reflections been removed from the system?  As I pointed out in a post above, I've examined the internals of my Miyauchi BTs and "clones" of these and and there is an aperture stop on the back side of the rhomb turret located midway between it and the Schmidt main prism to prevent off-axis reflections from reaching the rhomb's faces.  It appears Kowa, who you've emulated, also uses this design.  I don't see this baffle design showing obvious signs of vignette to my eyes, nor does it effect full aperture.  These designers thought it was worthwhile.  We've discussed this "fingernail" issue since the APM BTs were introduced.  Some users don't seem to mind and some are bothered by it, depending on their observing style. 

 

Markus has been very insistent on having his APM BTs being optimized for the best illumination of widest field eyepieces.  APM even enlarged the original prism aperture to 28mm from 25mm for this purpose.  On visual inspection there doesn't appear to be any baffles within their prism system as it seems the designers didn't want to contribute to illumination falloff from them either.  The trade-off appears to be these "fingernail" off-axis reflections.  It seems some BT buyers agree (though not necessarily justifiably) that this "fullest illumination" aspect is important in a visual instrument.  Perhaps they are way more sensitive to this than I am.  I actually expect this to be less important for visual use, though, as our eyes are not nearly as sensitive to these differences in illumination as a CCD sensor.

 

I've never seen measurements taken of any standard Porro or roof binoculars that are anywhere close to 100% illuminated to the edge of their field, even premium models. Top performers may have the central 50% of area illuminated by 100% of the objective.  I've never heard anyone complain about the illumination falloff of their Fuji FMTs, Nikon Astroluxes or Tak 22x60s, imperfect as they may be.  FWIW, these standard binos don't show "fingernails" either.  In light of this, what do you think about the quest for fullest illumination? Is this a worthwhile design goal for a visual binocular observer or just a quest for needless "perfection" with unintended consequences?  

 

One other thing; maybe at this point in time we should identify our binos based on the actual effective aperture? It seems long past due industry-wide. Perhaps call the new binos BT-80XL or BT-96XL?  undecided.gif

 

I'd love to hear your perspective on this as someone who has surely given this thought, having been in the binocular industry for years.  All other comments welcome, too, of course!

 

Thanks,

 

Rich

Well, probably can't address all of that without violating TOS. There are a number of things we were trying to achieve, such as effective aperture as close as possible to objective size, minimal reflections, etc., knowing there were going to have to be some compromises.  Support for low magnifications (>24mm) was deemed not a priority if everything else was good.  Took much more time, and cost more, than I could have imagined- but I'm finally very pleased with the results.  Even the non-ED 82XL is surprisingly-good- very minimal CA when viewing the moon at 56x (8mm's).  I think for this forum, it's best for me to drop out, and let owner reviews (which should be coming soon) speak for themselves.  




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