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Use of 0.7 x video conversion lenses with binoculars

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#1 Chomatic Aberrant

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Posted 12 October 2019 - 06:50 PM

Hello-

Thought someone out there would find this arrangement interesting, if not useful. 

I use two 0.7 X conversion lenses for temporarily attaching over the objectives of a set of 7x35 mm wide angle binoculars. The best ones binos I have now, ones which afford generous eye relief is a vintage set of Jason 11.5 degree Statesman. (Today I was outbid on two pairs of Rangemasters.)   The 0.7 X converters reduce the Statesman down to 4.9 power, perfect for seeing the entire stage from my seat in the nose bleed upper balcony of the Lyric Opera here in Chicago. Last week with monopod attached I saw The Barber of Seville. The best opera experience I have ever had. Obsolesces and eBay have made such conversion optics affordable. True, I can’t call this arrangement, a sort of a reverse barlow, ideal. Eye placement is tricky until you get the hang of it. I have not tried the fixed focus Bushnell 5 X binos. My guess is I would not like them. And I doubt their FOV would be wide enough.

Here are two pictures of my setup with 0.7 X converters. I don't trust the velcro completely. A plastic cable tie (not shown) goes around the end of the straps to surround each converter. The groves in the velcro pads shows where the cables were.  I admit this is a very crude arrangement. If I had the skill, a machine shop or a 3 D printer, I might come up with something better.

I also push glass and star gaze.   Yet I have not tested this optical pairing on stellar sources. I don’t expect perfection. But for the opera it seems sharp enough. 

 
Chomatic Aberrant

Attached Thumbnails

  • Jason 7x35 Statesman W.A. with 0.7X adapters 1 sm.jpg
  • Jason 7x35 Statesman W.A. with 0.7X adapters sm.jpg

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#2 Chomatic Aberrant

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Posted 12 October 2019 - 07:24 PM

It's me again.  Forgot to mention. These 0.7 X conversion units were made to fit over the main lens of older, big clunky amateur video cameras.  Often you will see these paired with a magnifying booster lens.  Many are available on eBay, with 49mm and 52mm thread mounts.  There may be other sizes.  Step-up rings and step-down rings can be used to get the I.D. of the adapter to a close match with the O.D. of the objective of a 7 x 35 or other size bino. 

 

Chomatic Aberrant


Edited by Chomatic Aberrant, 12 October 2019 - 07:25 PM.


#3 PEterW

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Posted 13 October 2019 - 02:09 AM

Could you post an example ebay or other link so we know which type of lens to look for. Do you get vignetting or other degradation of the field. Those wide field 7x35 have 70+ degree apparent field of view, quite often soft edges and little eye relief. What’s the effect of the reducer on these.
Wonder how this arrangement would stack up against the 5x25 visionking, which is a good wide binocular for kids.

Interesting find!
PEter

#4 Mark9473

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Posted 13 October 2019 - 08:27 AM

Is it as simple as thinking that with 0.7x the magnification you get 1.43x the FOV?



#5 Chomatic Aberrant

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Posted 13 October 2019 - 09:17 AM

Hi Peter-    Thank you for bringing 5x25 visionking to my attention.  Had I known about them I might have forgone this adapter project.  Reviews on the Amazon seem very good although one poster says they will not give you the full FOV with glasses. Unless I can modify them that's a non-starter for me.

 

Here is a link to the Baypage for wide angle conversion lenses. 

 

https://www.ebay.com...verter&_sacat=0

 

Apparently conversion lenses are available in different demagnifications and thread sizes.  Prices are all over the place.  You need a matched pair for binos, of course.  Some sellers are offering more than one of the same kind. But with so many postings it would not be hard to fine two sellers fencing the same unit.  Your local eBay might be a better source since some sellers I know on the US Bay will not ship internationally.   C.A.

 

s-l1600.jpg

s-l1602.jpg


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#6 Chomatic Aberrant

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Posted 13 October 2019 - 09:26 AM

Hi Mark.  Sure.  It's that old square root of 2 thing again.  C.A.



#7 Swedpat

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Posted 13 October 2019 - 11:18 AM

Visionking 5x25 is definitely a good buy for the ~$50 I got them for. The sweet spot is pretty narrow but on-axis sharpness very good. The eye relief is short and without eyeglasses I have the eyecups almost in the lowest position for best view.

I just wonder about the result with 0,7 or 0,5x conversion lens used with binoculars with sharp image to the edges, will the image remain sharp over the entire field? 

Also I wonder: with conversion lens attached to the objectives, will the exit pupil remain the same or increase?


Edited by Swedpat, 13 October 2019 - 11:21 AM.


#8 Chomatic Aberrant

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Posted 13 October 2019 - 01:58 PM

Comparing with the binos alone, the sharpness does seem to take a slight hit, even in the center, with the converters.  Adding more glass naturally you might expect this. With the wide angle 7x35s I am only familiar with the older 1950-1970s mainline brands like Binolux, Jason, Sans and Steiffe, Tasco, Mayflower, etc. (and not their high end models). They all lose sharpness and exhibit rectilinear distortion toward the edges. Many variants of conversion optics can be found online and with a huge price range.  Someone out there might have done some comparing.  You would think that those from the major makers might be better.  The only ones I have tried are Kenko and Sony and they perform about the same.  As for exit pupil I would think it should only increase since the power is reduced and the aperture is set the diameter of the bino's objective (35mm) which is smaller then the converter.  Eye placement seems more critical. That could tell us something.  I might add that my setup (ver. 1.0) needs some tweaking. Alignment is a bit sloppy as the converters shift around a bit in use.  Bicycle tires as rubber bands with velcro isn't ideal. But hey, I'm not a member of the Zeiss / Leitz / Swarovski crowd.  At least not yet.

 

Chomatic Aberrant


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#9 PEterW

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Posted 13 October 2019 - 03:43 PM

Looks like a simple 3D printed pushfit job could hold the alignment and your bungee cords stop them falling off. Just need some reasonable measurements.

Peter

#10 Chomatic Aberrant

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Posted 13 October 2019 - 04:11 PM

Good idea.  I do work for a college.  I am sure the engineering department must have a 3-d printer.

 

I could do a drawing of what I need with the dimensions.  Someone over there can get me started with a CAD-type program and I can put in the specs making a digital file to feed the printer.  (I really know nothing about this.  But I have friends.)  

 

Thanks for your suggestion, Peter.   
C.A.




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