Apature

[mark81]

So I've been reading a bunch of reviews for big binoculars with 45 and 90 degree eyepieces.  I keep coming across people mentioning whether the they were full apature or not?  

For example, the TS Optics 70mm 45degree, many people suggested the apature was actually 63mm.  So, whats the deal with this? Is it the way the light travels through to the prism...or is it just false advertising...or something else?  

Thanks

Mark

[Peter Drew]

It can be all of those reasons. Undersize prisms can affect the original aperture as can internal masks intended to offset other issues. As a rule of thumb, the more you pay, the nearer you get to the claimed specifications.  😀

[johninderby]

The objectives are proably the claimed size but the prisim can reduce the usable apeture. Informative thread on CN.

https://www.cloudynights.com/topic/532533-why-have-so-many-binos-a-smaller-real-aperture/

Edited September 23, 2019 by johninderby

[michael.h.f.wilkinson]

I am not sure about the angled ones, but the cheaper 15x70 BA-1 type binoculars, sold under a variety of brand names are effectively 15x63 due to undersized prisms and internal baffles. They are still good value for money in my book. My Omegon 15x70 pair (just 89 euro) lasted me many years and showed me the wonders of the southern hemisphere when I travelled to South Africa and Australia. Apart from limiting the effective aperture, undersized prisms can also cause a reduction of the maximum FOV of the EPs inserted. I have seen some 90 deg 100mm bins that clearly showed some vignetting when my MaxVision 24 mm 68 deg EPs were inserted.

[PeterW]

APM and Obserwerk big angles bins seem to not suffer from this compliant and deliver good views.

 

peter

[johninderby]

I should be a legal requirement to have to give the true or usable aperture. 

[Nigeyboy]

I own a pair of Celestron Skymaster 20x80's. I am pleased with them, but following a review I posted here on SGL, I found out they were nearer to 16x73. So I was a bit miffed really. If I buy a pair of 20x80's that is what I expect to get. Don't get me wrong, I am enjoying using them, but each time I pick them up, I do feel a little cheated! I only paid £100 for them though . . . . . .

[Merlin]

Note that the makers only say "aperture", not "clear aperture". That's why they can get away with it.

[johninderby]

1 minute ago, Merlin said:

Note that the makers only say "aperture", not "clear aperture". That's why they can get away with it.

The value of good legal advice.....at least from their perspective.🙄

Edited September 27, 2019 by johninderby