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False claims about Binoculars?

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#1 Oakie

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Posted 14 October 2020 - 02:20 PM

As far as I understand this man [it won'tallow the youtube link] is saying the 20x50 are really only 10x50.He says in a comment it is "just for cheating"

 

Is that possible to have it 10x rather than 20x? How could one tell?. How do I know my 12x32 are 12 times closer. I was looking at these in a shopbut the person did not know the IPD and the exit pupil is smallish isn't it and the eye relief is only 9mm


Edited by Oakie, 14 October 2020 - 02:21 PM.


#2 sg6

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Posted 14 October 2020 - 02:29 PM

Greater chance they are 20x but not really 50mm.

Trick is to put poor 50mm objectives in, then to reduce aberrations put a stop inside to reduce the effective aperture so cut out the poor edges.

You read 20x and go Oooh, you see 50mm and go Oooh, sell me a pair.

 

Also they could have undersized prisms in there as a cost reduction measure.


Edited by sg6, 14 October 2020 - 02:30 PM.

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#3 Rich V.

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Posted 14 October 2020 - 02:59 PM

You can actually figure quite precisely what the true aperture and true magnification are but you have to geek out some and measure the effective aperture of the bino with a light projection technique and then measure the exit pupil diameter with a caliper at the eyepiece.  Once you know those two measurements, you can simply calculate the magnification.  Your "20x50" may very well end up being something like 18x45 instead.

 

Some unscrupulous vendors sell junk binos with wildly strange numbers on them that nobody can decipher as to what their real magnification and aperture are.   tongue2.gif   Here's a "100x180" bino that also suggests in the specs as being 10x with 25-29mm objectives. confused1.gif

 

100x180 bino

 

Quality binoculars will end up being much closer to the stated spec than the inexpensive junk ones.  You usually get what you pay for.

 

Rich

 

 


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#4 hallelujah

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Posted 14 October 2020 - 04:05 PM

In over 14 years of using & purchasing binoculars I have yet to encounter a quality binocular in a 20x50 configuration.

Actually, I have never even seen any kind of a 20x50 binocular in person.

 

Once I purchased a used Omega 30x50 Porro binocular.

Looking through it I could not discern any obvious magnification whatsoever.

I ended up selling it to someone who wanted it just for parts.

 

Stan


Edited by hallelujah, 14 October 2020 - 04:07 PM.


#5 KennyJ

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Posted 14 October 2020 - 05:03 PM

A number of Cloudy Nights binocular forum regulars of yesteryear used to send me surprise little gifts in the post all the way from the USA.

 

One of these little gifts was a very simple but ever so useful device which could be used both for measuring ( or at least estimating to within 0.5mm, exit-pupils and eye pupil dilation.

 

It was basically just a rectangular piece of plastic measuring approximately 5 inches x 3 inches, with 20 perfectly round holes drilled through it in every size from 0.5mm to 10.0mm. with the size indicators neatly printed below each one.

 

By simply holding binoculars up to a light source with one hand ( or mounted ) to see the exit - pupils, it was just a case of holding up the device and carefully moving it around until the small discs of light were matched in size.

 

It's very surprising how easy it is to spot a difference of only 0.5mm -- so easy I reckon it would be virtually impossible for anyone with reasonable eyesight to make a mistake.

 

I use the past tense because somewhere along the line I appear to have misplaced ( or lost ) it, probably during a slightly crazy period which ended up with using four or five different hard padded cases for carrying around eyepieces, barlow lenses, erecting prisms, tripod adaptors, red dot finders, lens caps, objective masks, spare lanyards, test cards and all sorts of paraphernalia every time I went away to our static caravan with binoculars, spotting scopes and tripods, which for around 6 years in the "naughties" was almost every weekend.

 

Estimating magnification is a little trickier but by no means rocket science.

 

I found a couple of spare sheets of plywood, each about 1.5 metres square ( 5x5 feet ).

 

On the first sheet, I simply drew a series of 10 circles in a vertical line from top to bottom down the left hand side of the plywood sheet, each 1cm in diameter.

 

Then to the right of those, another vertical line of circles, this one ranging from 1cm to 10cm in diameter.

 

Similarly on the second sheet, but with the larger circles ranging from 11cm to 20cm in diameter (due to their larger size, so as to fit onto the panel, arranged in two separate vertical rows, spaced apart from each other ).

 

Using a black sharpie pen to draw the circles, I then marked the inner circle in numbers from 1 to 10, and 11 to 20 respectively, so that at a glance I could easily see what size they all were ( and what magnification they very accurately represent )

 

It's just a case of placing the board a far enough distance away from the binoculars to enable perfect close focus, then looking through the magnified image of the 1cm circle through one eyepiece of the binoculars, whilst at the same time looking at the unmagnified image of the larger circles naked eye, slowly moving the binoculars in a downward direction until the two sizes match up.

 

As most of us may know, with the majority of binoculars, the magnification at closest focus is slightly larger than it is at infinity, and can even differ slightly from what is seen through the right hand eyepiece compared to through the left.

 

However, this is just a very simple, quick method that most people should be able to have fun with, in order to establish  a basic "ballpark" estimation of magnification, and would certainly very clearly show the difference between a binocular advertised as being 20x magnification, when in reality it is only 10x.

 

Related reports of a far more precise and technical nature, the likes of which I used to enjoy many hours reading back in my more enthusiastic days ( when I tended to contribute more posts of this nature to this forum ) can be found here:

 

https://www.birdforu...ad.php?t=118028

 

Kenny


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#6 Swedpat

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Posted 15 October 2020 - 07:48 AM

There are a lot of junk binoculars with very false stated magnification out there. And actually: in many cases the buyer of such a binocular have the reason to be glad the magnification is much lower than stated. This often means it's actually not totally useless which had been the case if the stated magnification was true!



#7 Binojunky

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Posted 15 October 2020 - 11:50 AM

To be fair even some binoculars with reputable names on them are victims of false claims by the seller /maker/ importer, Dave.



#8 SMark

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Posted 15 October 2020 - 12:15 PM

If you make a habit of even roughly calculating the Field of View claims on binoculars, you’ll find that many vintage, and even some modern binoculars come up well short.

 

Edit: I should qualify my statement a bit by saying that this comes as a result of my measuring fields of view from binoculars that were advertised as "Wide Angle," "Extra Wide Angle," or "Super Wide Angle."


Edited by SMark, 15 October 2020 - 01:31 PM.

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#9 Jon Isaacs

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Posted 19 October 2020 - 01:10 AM

If you make a habit of even roughly calculating the Field of View claims on binoculars, you’ll find that many vintage, and even some modern binoculars come up well short.

 

Edit: I should qualify my statement a bit by saying that this comes as a result of my measuring fields of view from binoculars that were advertised as "Wide Angle," "Extra Wide Angle," or "Super Wide Angle."

 

Mark:

 

I measure TFoV by finding two stars that just fit in the field of the binocular or maybe two stars that require just a bit of movement.  I then look up the two stars in Sky Safari Pro and measure their separation.  

 

The older 7x35's seem to come up short on a routine basis.

 

Jon


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#10 pat in los angeles basin

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Posted 27 October 2020 - 05:24 PM

Anyone care to venture a guess as to which bit of data screened on the rear prism covers is false?

 

https://www.shopgood.../Item/107004530

 

The last time I bid (and won the bid) on what I assumed was a fibbing binoc was an "8x50 wide angle" Turned out the angle was 7 degrees and change and the mag was 7 not 8.                                         Regards, Pat



#11 KennyJ

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Posted 27 October 2020 - 05:38 PM

The stated 5 degree TFOV is an immediate give away!

 

At 30x magnification, that would equate to AFOV of approximately 150 degrees!

 

On the other hand, the true magnification may only be 10x.

 

Kenny



#12 Grimnir

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Posted 28 October 2020 - 05:18 PM

Anyone care to venture a guess as to which bit of data screened on the rear prism covers is false?

 

 

The bit that says "Highest Quality".

 

Graham


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#13 pat in los angeles basin

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Posted 28 October 2020 - 05:41 PM

lol.gif lol.gif lol.gif lol.gif lol.gif

                      Thanks, I needed that!  Regards, Pat



#14 Chuck2

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Posted 29 October 2020 - 12:00 PM

Most binoculars under $250 typically do not meet stated spec. Due to undersized prisms and internal baffles to control lens aberations, the stated aperture is usually reduced by 10%, as well as corresponding magnification. Although each brand and style of construction will vary, typically these are the measured results...

 

  • 10x50mm as claimed is closer to  9x45mm
  • 15x70mm as claimed is closer to 13.5x63mm
  • 20x80mm as claimed is closer to 18x72mm

 

Use the measurement techniques described in the above posts tp derive the exact specs for your specific binos. Quality bino sources such as Oberwerk, actually share the true aperature % measurements with their customers. 

https://oberwerk.com...mparison-chart/



#15 Swedpat

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Posted 31 October 2020 - 05:57 PM

The stated 5 degree TFOV is an immediate give away!

 

At 30x magnification, that would equate to AFOV of approximately 150 degrees!

 

On the other hand, the true magnification may only be 10x.

 

Kenny

 

And it's clearly visible at the picture of the eyepiece that the exit pupil is AT LEAST 5mm, likely even larger. I actually wonder if the binocular may be a 7x50?



#16 PEterW

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Posted 01 November 2020 - 12:35 PM

Amazon in its infinite wisdom just recommended some $50 60x60 Night Vision binoculars, the description seems to be a “word salad”, at least the only 1star review points out one of the errors in the description. Kenny, interesting exit pupil tool!

Peter

#17 Phutatorius

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Posted 01 November 2020 - 01:51 PM


It was basically just a rectangular piece of plastic measuring approximately 5 inches x 3 inches, with 20 perfectly round holes drilled through it in every size from 0.5mm to 10.0mm. with the size indicators neatly printed below each one.

 

By simply holding binoculars up to a light source with one hand ( or mounted ) to see the exit - pupils, it was just a case of holding up the device and carefully moving it around until the small discs of light were matched in size.

 

I have a black plastic drill gauge that goes down to 1/16th inch (also marked in mm) that would probably serve this purpose.



#18 Foss

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Posted 04 November 2020 - 08:59 AM

So, what's your sign?

Attached Thumbnails

  • Astrology binoculars.JPG


#19 Jon Isaacs

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Posted 04 November 2020 - 09:16 AM

Most binoculars under $250 typically do not meet stated spec. Due to undersized prisms and internal baffles to control lens aberations, the stated aperture is usually reduced by 10%, as well as corresponding magnification. Although each brand and style of construction will vary, typically these are the measured results...

 

  • 10x50mm as claimed is closer to  9x45mm
  • 15x70mm as claimed is closer to 13.5x63mm
  • 20x80mm as claimed is closer to 18x72mm

 

Use the measurement techniques described in the above posts tp derive the exact specs for your specific binos. Quality bino sources such as Oberwerk, actually share the true aperature % measurements with their customers. 

https://oberwerk.com...mparison-chart/

I measure them using the flashlight method.. 

 

My Orion Ultraview 10x50s (made in Japan) measured the full 50mm.  Others not so much.

 

Jon


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