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Built in eyepieces

Binoculars Eyepieces Optics Lens Making
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#1 mati93

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Posted 13 May 2024 - 11:24 AM

Hi, recently I bought some binoculars to watch the sky, landscapes, birds, etc. Back then when I was researching a bit, I was only interested in just magnifying the image, and I would not have been able to distinguish the view from a budget binoculars to a high end one. But then I have gained an interest in how they work and why more expensive ones are "better", what aberrations, defects and compromises there are. This led me to get better binoculars than what I had.

 

I thought that by looking at the optical designs one could get an idea about what the binocular is good at. For instance, if the objectives are complex designs, the binocular could be good at correcting CA. The problem is that manufacturers are very obscure about the binoculars specifications like optical design, strehl ratios, etc. And also about performance numbers, other than the common characteristics in the specification lists.
There are just a handful of modern binocular "cutaway" pictures, where you can actually see their guts.
In particular I am very interested about the eyepiece designs, what kind of eyepieces are there in binoculars? Are they typical designs, or specific to the model?

 

The Swarovsky Habichts have relatively few lenses, which let you have amazing transparency and contrast, but poor edges and narrow FOV. On the other hand, I have a Nikon EII 8x30, and I know that the eyepiece is quite complex with 6 elements in 3 or 4 groups, which seems to be more than the norm. One could think it should be very well corrected off axis, but this is not really true, although the field is wide, it is very sharp up to the 50% of the AFOV. My Nikon Monarch HG has a wider sweet spot (although a bit smaller total AFOV), but I don't know how many elements are there, I doubt it is more than 6 (maybe some aspherics lens?) What are the extra lenses in the EII doing? I guess if you remove the field stops, any binocular can have wide AFOV with fuzzy edges.

The new Sky Rover Apo, do we know anything about their design? It manages to have an even wider FOV with fully sharp AFOV, is it magic?
I am puzzled by this, I think by knowing the designs we should be able to predict or explain the binoculars performance, features and defects, to a certain extent. Anyone could shed a light on this?
Thanks for reading!



#2 jrazz

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Posted 13 May 2024 - 11:42 AM

Yes and no. 

 

Knowing the optical design, materials and arrangement can give you clues to performance but there is a lot more that isn't readily visible that can and does affect performance. Things like baffeling, blackening, polish level, figure accuracy and coating quality all affect the view and does not show up on the design.

 

There's also the observing conditions which might favor one design over another. What you are looking at can make a difference. Astronomy is different than birding. Even in astronomy doubles, clusters, nebulae, planets and DSO's are all different. 

 

Finally and perhaps most importantly is the observer. One set might work with one observer and not with another. I know that I have my preferences that are different from others. 

 

At the end of the day the binocular/observer/conditions/object system is really complex and while knowing the design can give you clues the only way to really **** performance is to look through them.


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#3 TOMDEY

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Posted 13 May 2024 - 11:43 AM

Very expensive binoculars are almost universally superior in all the ways that matter. Very cheap binos necessarily are loaded with compromises to pull the price down. Merlitz covers all of this in his expansive tome, a great read and will answer all of your questions and observations.    Tom

Attached Thumbnails

  • 118 The Binocular Handbook.jpg

Edited by TOMDEY, 13 May 2024 - 11:46 AM.

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#4 fftulip

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Posted 13 May 2024 - 11:58 AM

Just one aspect of binocular eyepiece designs is that because of the very short focal ratio, the image plane is going to be very curved.  So even if you have a "good" eyepiece design like on the Nikon, it probably doesn't correct for field flatness very well.  It's easy to check for this by varying the focus and the edge will be well corrected but not the center and vice versa.   I've only seen a few binoculars touting field flatteners in the design and they're expensive (extra elements).  For most people, a wide FOV with fuzzy edges is acceptable because you're focusing on the center of field.


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#5 mati93

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Posted 13 May 2024 - 12:47 PM

Very expensive binoculars are almost universally superior in all the ways that matter. Very cheap binos necessarily are loaded with compromises to pull the price down. Merlitz covers all of this in his expansive tome, a great read and will answer all of your questions and observations.    Tom

Yes that's it, I need to get the book.
 

 

Just one aspect of binocular eyepiece designs is that because of the very short focal ratio, the image plane is going to be very curved.  So even if you have a "good" eyepiece design like on the Nikon, it probably doesn't correct for field flatness very well.  It's easy to check for this by varying the focus and the edge will be well corrected but not the center and vice versa.   I've only seen a few binoculars touting field flatteners in the design and they're expensive (extra elements).  For most people, a wide FOV with fuzzy edges is acceptable because you're focusing on the center of field.

It makes sense, perhaps a good way to test it would be to compare it with the EII 10x35 version, which uses the same eyepiece. The latter should have a less curved field, and thus wider sweet spot



#6 TOMDEY

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Posted 13 May 2024 - 02:33 PM

Just one aspect of binocular eyepiece designs is that because of the very short focal ratio, the image plane is going to be very curved.  So even if you have a "good" eyepiece design like on the Nikon, it probably doesn't correct for field flatness very well.  It's easy to check for this by varying the focus and the edge will be well corrected but not the center and vice versa.   I've only seen a few binoculars touting field flatteners in the design and they're expensive (extra elements).  For most people, a wide FOV with fuzzy edges is acceptable because you're focusing on the center of field.

Nikon WX sharp across the entire ultra-wide field --- because the entire optical train is optimized in combination and no skimping on the optics.    Tom



#7 sevenofnine

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Posted 13 May 2024 - 02:54 PM

Nikon's Reference Binocular:

 

https://www.bhphotov..._binocular.html.

 

A standard where cost is no object moneyeyes.gif




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