FNS 120 Binocular Spotter Scope (1 Viewer)

Has anyone tried it? looks good!



- Scope length without binocular unit and lenses – 18 inches
- Scope length with binocular unit and 25mm lenses – 22 inches
- Total weight of lenses, scope and case – 18 pounds
- 120mm (4.7 inch) objective lens
- Field of view 20x 155 feet at 1000 yards, 30x 110 feet at 1000 yards
- Telescoping sunshade and quick detach front lens cover
- Ambidexterous Focusing knobs
- Fitted hard case (20 ⅛ x 8 ⅛ x 11 ½) with inner soft case

http://www.tactical-life.com/gear/the-fns-120-binocular-spotter-scope/

http://bulletin.accurateshooter.com/2008/07/new-binocular-spotting-scope/

I like the idea/concept of this optics. Binoviewers have been around for a years but, if I am not mistaken, there was always an issue of reaching focus at various distances when used in conjunction with a spotting scope. This optic seems to have remedied the issue by having the binoviewer built into the spotting scope itself.

Looking at the specs I noted only a couple of interesting issues...

1) At 18 pounds it is a bear! Most of the heavier, reasonably priced, 80 mm class scopes only 5 pounds or so. Even with a second eyepiece and the binoviewer attachment I can't imagine why it would increase the weight by 13 lbs.

2) The field of view at 20x seems reasonably wide. Not anything special but not porthole-effect oriented either.

One thing that got me twisted. Many of you read usually cloudy nights, right?

There's one member (Edz) who explian that, for example this case, a 120 BV is like using a 85 binocular ... probably is more my poor english than the maths, but i can't understand:

A binoviewer is a beam splitter. If it is working as it is designed to do, and at 100% efficiency, then it splits the light exactly one half to each eye.

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Ok, Half of something is 50% , or x divided by 2... so 120/2= 60 mm aperture

And here comes where i get lost

A 120mm scope has an area of 120x120 = 14400 sqmm
That gets split, half to each eye, therefore 14400/2 = 7200
That's like getting light from two 85mm apertures
So a 120mm scope with a binoviewer is like a 85mm binocular.

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Emmm, sooo , well ... i mean? what??? :brains:

http://www.cloudynights.com/ubbarch...=collapsed&sb=5&o=all&fpart=1&vc=1&PHPSESSID=

I am sure there is some reasonable explanation for EdZ's comments.

However, I am right there with you in terms of the math.

Ed's math is correct. I may not be able to make things any clearer, but I'll try.

The light gathering power of a lens is determined by its surface area, not its diameter. The easy way to compare the surface areas of different sized lenses is to simply square the diameters (not really correct for a circular area, but fine for comparisons). So, a 60mm lens has a surface area of 3600 square millimeters and a 120mm lens has a surface area of 14,400 square millimeters; four times more, not two times more.

A beam splitter divides the light of the 14,400 sqmm surface area of a 120mm lens into two light cones, each containing half the light that originally struck the lens surface. So, each cone contains an amount of light equivalent to what would strike a lens with a surface area of 7,200 sqmm. The square root of 7,200 is about 85, so the amount of light that reaches each eye is equivalent to what would strike the surface area of an 85mm lens, not a 60mm lens.

The binoviewer approach has some advantages. A 120mm scope with a binoviewer retains the full resolving power of the 120mm aperture, so all things being equal, it will show smaller details at high magnification than an 85mm binocular. The problems of collimation are also eliminated.

I wouldn't be much tempted by a contraption like the FNS 120. I think you could do much better for the same money by purchasing an astronomical refractor, binoviewer and eyepieces separately.

henry link said:

I wouldn't be much tempted by a contraption like the FNS 120. I think you could do much better for the same money by purchasing an astronomical refractor, binoviewer and eyepieces separately.

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But there is a problem Henry, all 120 refractors a i know are from 900 f/l ... maybe a 110 (wich is gone below) that is 750 ... put the corrector, the BV ... it goes to a very long focal lenght, the one here is 750, still allows you to use some medium mags with a decent FOV ...

The big issue of the scope with binoviewer is the image quality. Still didn't read any real review of it.
Some time ago I found a similar solution http://olivonmanufacturing.com/spotting-scopes/t-9090ed-spotting-scope but still didn't found if is the binoviewer that have special details or the scope that has large focus range. Also never read a review of this scope with the bionoviewer...

I want one with 30X or 50X mag eyepieces. That would be an absolute dream for Skua watching off the cliffs (and various other sea birds).

Yes, yes I do.

Click on the Google images here to find other examples of this item:

http://www.google.com/search?q=bino...OMyAGP64C4Dw&ved=0CAoQ_AUoAg&biw=1669&bih=895

Essentially the same Chinese scope with different sized objectives has appeared under several brand names. I agree with David that the true quality of any of these is unknown, but I suspect they're cobbled together from bins of generic parts to fit whatever a client specifies. I can't seem to find an example that is still currently available.

henry link said:

Click on the Google images here to find other examples of this item:

http://www.google.com/search?q=bino...OMyAGP64C4Dw&ved=0CAoQ_AUoAg&biw=1669&bih=895

Essentially the same Chinese scope with different sized objectives has appeared under several brand names. I agree with David that the true quality of any of these is unknown, but I suspect they're cobbled together from bins of generic parts to fit whatever a client specifies. I can't seem to find an example that is still currently available.

Click to expand...

From outside its seems like you say, the prism unit has in the outside all the brands those three relieved lines, the internal features are unkowed. And the BV unit i bet is exactly the same in all. The lens in the model we are talking about are APO four color corrected, as is described in the link. Lets asume its true, the only thing to care about are the prism and the BV. It looks like the celestron model or the TS, probably is a generic piece too selled by diferent brands.

I wouldn't take the APO claim too seriously. No real information about the objective design, glass types or performance is supplied. The importer seems to be mainly a gun dealer, with this one scope (now discontinued?) as a side line.

Given the long train of prisms involved I would be surprised if it's a true APO or if the clear aperture is really 120mm. The front prism acting as an aperture stop is probable in a design like this. If you're really interested I would proceed with caution. Be sure you can return it if it's not quite up to what's claimed for it.

henry link said:

Be sure you can return it if it's not quite up to what's claimed for it.

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No thanks. I already read enough :king: