Chinese optics : divide by 3.141592.....

[Slocumotion]

... am I the last to realize that they are talking area not diameter?
http://e.tmartemail.com/a/hBb5YTWB88sEAB9uWYhABDPuXSw/dfhd6
30x60 binoculars - £6 ??!!

Filed for future reference alongside the response to my query about the very poor performance of my new "nightvision" Dashcam - "For Nightvision function always use in well-lit area"

 

[LadyInBed]

"For Nightvision function always use in well-lit area"

 

[davidej]

Don't understand this at all!

23mm objective lens = about 72 sq mm area

And where does the 30 came from? It says you see things 10 times nearer

 

[Slocumotion]

Don't understand this at all!

23mm objective lens = about 72 sq mm area

And where does the 30 came from? It says you see things 10 times nearer

I'm guessing they are what we would call 8x20. Then having decided to big up the objectives by giving their area (something less than 20 X 3 and a bit), instead of diameter - they applied the same factor to the magnification. Missed a trick there though - could by the same reasoning have claimed 64x for area magnification!
I 've seen the same thing with very cheap microscopes. In fact I bought one such . Magnification described as 600x max. I measured about 38x , times another 4 of digital zoom - again, around 1/3 to 1/4 of the claim.
I should add that "proper" microscope optics from China can be excellent and are described using the same conventions that we know.

 

[Aeolus]

I think there is a clue in the price. If something is too good to be true....