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Anonymous
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I know we, the CN binocular community, have already talked about the advertised FOV vs TFOV discrepancy in the past, but this is a huge blunder in my opinion. How (and more importantly why) does this happen? This could be considered false advertisement by some. What's your take on this EdZ?
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12565
Loc: Cumberland, R I , USA42N71.4W
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I think distributors should make every effort to show in their advertising the proper values. It's an easy number to put your fingers on. It is a significant number in the buying decision. It would appear some of the major distributors are already addressing the issue.
Personally, I haven't yet found a binocular with Afov that varies much from a standard 60° to 65°. The Pentax lines and many 8x42s and 10x50s can be much narrower.
I expect Tfov for any brand binocular to be no more than Afov64°/Magnification, regardless of advertising. The results I get are almost always in line with that expectation.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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KennyJ
Reged: 04/27/03
Posts: 10142
Loc: Lancashire UK
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Ed,
I think you're probably correct to expect most binoculars to fall within those parameters , but there are notable exceptions.
My Swift Audubon Kestrel 10 x 50 , for example , measures out at more or less a genuine 70 degrees AFOV.
I can only qualify this assertion by stating that my "square card tests" confirm a magnification very close to a genuine 10x magnification.
( i.e a 10 cm x 10 cm card viewed through one lens of the binocular from 30 feet appears equal in size to a 1m x 1m square viewed naked eye by the other eye at the same time )
AND I can certainly see beyond the parameters of the
1m x 1m square from 30 feet through the binoculars
( which computes to well over 65 degrees AFOV )
Of course , the QUALITY of image in these outer regions renders that "extra 0.4 or 0.5 degrees TFOV" practically useless in terms of "positive identification" , so going back to comments made by Barry and yourself , it is becoming more and more apparant ( no pun intended ! )
to me at least , that the "band" of 60 to 65 degrees AFOV probably represents the generally prefered , and most "user -friendly" "sweet spot" of binocular viewing.
This of course IF any given binocular in question actually provides such a TFOV.
As far as "moral" or previously well -intended suggestions for "legislative" issues go ,I might add that the
"more respectable" and / or "higher priced" manufacturers DO tend to be more accurate with their stated and stamped fields of view of binoculars than some, if not most, of the others.
Regards , Kenny.
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Two eyes and a preference to use both
Zeiss 7 x 42 BGAT
Captain's Helmsman 7 x 50
Nikon 10 x 42 Superior E
Swift Audubon Kestrel 10 x 50
Helios 15 x 70 Observation
Strathspey 20 x 90
Televue 76 APO
Zeiss 85 Diascope
Helios 102 f5 refractor
Various eyepieces barlows tripods mounts etc.
Panasonic Lumix DMC - TZ5 digital camera
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sftonkin
sage
Reged: 02/25/04
Posts: 395
Loc: Kent, UK
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An exception, Ed, is the Swift Newport. It claims 8.2deg AFoV and, whilst I have yet to measure it precisely using stellar separation, the claim is not grossly excessive. The eyepieces are socking great things -- I imagine some sort of implementaion of an Erfle. However, because of the severe vignetting (no part of the exit pupil is fully illuminated), you can't see the whole FoV at once so, whilst the claim may technically be approximately true, it is functionally useless.
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Stephen
Hindsight: The only truly diffraction-limited system
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12565
Loc: Cumberland, R I , USA42N71.4W
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Stephen,
What magnification is this Swift.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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sftonkin
sage
Reged: 02/25/04
Posts: 395
Loc: Kent, UK
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EdZ wrote:
>What magnification is this Swift.
x10 (it's a 10x50)
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Stephen
Hindsight: The only truly diffraction-limited system
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12565
Loc: Cumberland, R I , USA42N71.4W
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wow, that is a wide one then, isn't it. edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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sftonkin
sage
Reged: 02/25/04
Posts: 395
Loc: Kent, UK
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EdZ wrote:
>wow, that is a wide one then, isn't it.
Indeed! If this cloud ever clears, I'll measure it properly.
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Stephen
Hindsight: The only truly diffraction-limited system
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