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High magnification wide field binoculars

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#1 astrocy

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Posted 29 December 2012 - 04:54 AM

Does true field of view of binoculars depend only on the apparent field of view of the eyepieces used? Why there are no binoculars that have both high magnifications (more than 12x) and wide fields?

#2 BillC

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Posted 29 December 2012 - 10:01 AM

The higher the power, the smaller the field. 'Just optics being optics.

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#3 Andresin150

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Posted 29 December 2012 - 10:35 AM

Depend on your definition of wide field. X degrees of TFOV may be narrow or wide depending on the magnification used. For example, 2.2 deg may seem narrow, but at 40x it is ultra wide....
Compared to unaided observation, everything is narrow.... When using UWA eyepieces, optically everything should be considered wide, since it is according to the magnification used....

#4 astrocy

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Posted 29 December 2012 - 10:38 AM

The higher the power, the smaller the field.


Not necessarily. An eyepiece with a wide apparent field can give even at a higher power a true field of view that is wider than an eyepiece with a narrow apparent field of view at a lower power.

#5 Andresin150

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Posted 29 December 2012 - 10:44 AM

I think Bill was assuming similar Afovs...
Of course a TFOV of 13 degrees may seem wide, but if it is in a 3x binocular it is another thing... Like looking trough a straw....

#6 GlennLeDrew

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Posted 29 December 2012 - 03:03 PM

To obtain a wide field at higher powers requires a large apparent field. To this end, my home-made bino uses Ethos eyepieces having 100 degree apparent fields. And so I can obtain a 12.8X50 with a 7.7, and a 20.8X60 with a 4.7 degree field.

But such eyepieces are expensive, my pair of 13mm focal length jobs having cost me $1700 at the time I purchased them.

There have been occasionally in past decades bino eyepieces having 80 degree apparent fields. But the simplicity of the designs, as demanded by cost considerations, provide poor edge-of-field performance, certainly by the more exacting standards set by persnickety amateur astronomers.

However, there is one standout instrument which comes to mind--at a pretty high cost. The Dokter 40X80, it uses 84 degree apparent field eyepieces of high quality.

#7 BillC

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Posted 29 December 2012 - 08:57 PM

The higher the power, the smaller the field.


Not necessarily. An eyepiece with a wide apparent field can give even at a higher power a true field of view that is wider than an eyepiece with a narrow apparent field of view at a lower power.


For his needs--at this time--I'll let the comment stand. Of course, we astro-twigits know there is SOME fudge room. But generally speaking . . .

Cheers,

BillC

#8 Tony Flanders

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Posted 29 December 2012 - 10:30 PM

The higher the power, the smaller the field.


Not necessarily. An eyepiece with a wide apparent field can give even at a higher power a true field of view that is wider than an eyepiece with a narrow apparent field of view at a lower power.


For his needs--at this time--I'll let the comment stand. Of course, we astro-twigits know there is SOME fudge room. But generally speaking . . .


Quite so. Almost all commercially available binoculars of decent quality have apparent fields of view within quite a narrow range, roughly 50 to 70 degrees. Maybe 40 to 80 in a pinch. So to a good first approximation, the higher the magnification the smaller the true field of view.

I wish the original poster would clarify what he meant. The fact that it's impossible to get a truly wide true field of view (say 10 degrees) together with a truly high magnification (say 20X) seems so obvious that it's barely worth explaining.

#9 BillC

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Posted 29 December 2012 - 11:16 PM

A quote from the other side of the counter:

" I doan see why a main kant gettim a good 7x50 attle fitinis shirt pocket." :pulpdnc:

My response:

"I don't see why I can't get an 18-wheeler in my garage; it's just they way things are." :jump:

BillC

#10 Jon Isaacs

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Posted 30 December 2012 - 01:38 AM

Does true field of view of binoculars depend only on the apparent field of view of the eyepieces used? Why there are no binoculars that have both high magnifications (more than 12x) and wide fields?


There is a direct relationship between the Apparent Field of View, the magnification and the True Field of view. It is not exact but as Bill said, the greater the magnification, the smaller piece of the sky one can see. The relationship looks like this:

TFOV = AFOV / MAG

Glenn's homemade binoculars can use 100 degree AFoV eyepieces so 8 degrees at 12.5 x would be possible but at the limit...

Jon






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