Binocular Apparent FOV - Does it help? (1 Viewer)

[SivaL]

Instead of starting a new thread I wanted to resuscitate this old thread http://www.birdforum.net/showthread.php?t=198292 that discussed AFOV, but BF rules didn't allow me to re-open it as it was a few years old. So I am starting a new thread for me to understand Apparent FOV.

Let me start with the back story. I was looking to purchase a nice 7x42 bin to complement the 10x42 I have. With only Leica continuing to make 7X42's I searched for alternate bins and found some Meopta Meostar B1 7x42's on sale. After reading through BF reviews I pm'd FrankD who had owned them and posted many times about the Meoptas. Frank was very generous in replying to me and commented that the 8X Meostar was a better option as it had a bigger AFOV compared to the 7X. I sent a few more pm's to him about AFOV which I couldn't understand.

Frank sent me a link to this picture trying to explain AFOV

He wrote in his pm - "What you see inside the image (true field of view) stays the same but the amount of black outside of it changes as you change magnification."

BTW, I am posting his pm after asking his permision. I am still confused about the concept and hence the new thread. Sorry FrankD! You tried hard to explain. I can't seem to get it. :-C



I own a Nikon EII 8x30 and a Leica UV 10x42.

The EII 8x30 specs from Nikon's site http://nikon.com/products/sportoptics/lineup/binoculars/nature/x32x35/spec.htm
Mag - 8x
FOV - 154m/1000m
RFOV - 8.8 deg
AFOV - 63.2 deg (Apparent FOV)

The UV 10x42 specs
Mag - 10x
FOV - 110m/1000m
RFOV - 6.3 deg
AFOV - 63 deg (Apparent FOV)

As I could not find a Leica page with AFOV I multiplied Mag by RFOV to get the AFOV. This may not be accurate as Frank pointed out in his pm.

That being said, how does this figure of 63 degrees for Apparent FOV that both bins have help me understand an optical quality. The circle I see through the Nikon 8x is bigger and encompasses more area than the one I see through the Leica 10x and they both have an AFOV number close to each other. If I am not wrong about this how does the AFOV number help me evaluate a bin.

 

[FrankD]

I have a little bit more time to expand on what we discussed previously so let me take another shot at it.

For one, you listed "UV 8x42" but then listed the 10x42 specs. I am guessing that is just a typo and you instead meant to write "UV 10x42".

Using the "simple method" they do have close to the same apparent field of view on paper. As I mentioned in my pm, the larger the apparent field of view then the less "black" you see outside of the circular image as represented in the image you posted above. In the case of that particular image the "outside" is gray and not black.

You can see from that image that the larger apparent field of view on the left has less "gray" outside the image. Both images have approximately the same "true field of view" in that you can see the same stars in both circles. The difference between these two, in particular, is obviously magnification. This could easily be the representation when comparing something like a Leupold Yosemite 6x30 (AFOV 48 degrees, TFOV 420 feet) with a binocular similar to the Bushnell Legend Ultra 8x42 (AFOV 64 degrees, TFOV 420 feet).

One other factor that I have found influences the perception of apparent field of view is the type and severity of edge distortion present in the image. AMD, pincushion, etc... can give the impression that the image actually has a larger, or smaller, apparent field of view than it actually does.

I didn't get to address one of your comments in the last message. You mentioned something along the lines of "How can the amount of 'black' outside the image be different if the eyecup is set correctly for proper eye relief?"

If the eyecup is set incorrectly, either too collapsed or too extended, then you loose the sharp edges of the field stop (the edge that separates the image from the "black". Blackouts or tunnel vision are usually the result.

The easiest way to illustrate what I am relating here would be to take something like the two bins I mentioned above that have vastly different apparent fields of view and compare them side by side. The difference in apparent field of view is instantly noticeable. One is more "tunnel-like" in appearance while the other is more "immersive".

Hope this helps.

 

[[email protected]]

Instead of starting a new thread I wanted to resuscitate this old thread http://www.birdforum.net/showthread.php?t=198292 that discussed AFOV, but BF rules didn't allow me to re-open it as it was a few years old. So I am starting a new thread for me to understand Apparent FOV.

Let me start with the back story. I was looking to purchase a nice 7x42 bin to complement the 10x42 I have. With only Leica continuing to make 7X42's I searched for alternate bins and found some Meopta Meostar B1 7x42's on sale. After reading through BF reviews I pm'd FrankD who had owned them and posted many times about the Meoptas. Frank was very generous in replying to me and commented that the 8X Meostar was a better option as it had a bigger AFOV compared to the 7X. I sent a few more pm's to him about AFOV which I couldn't understand.

Frank sent me a link to this picture trying to explain AFOV

He wrote in his pm - "What you see inside the image (true field of view) stays the same but the amount of black outside of it changes as you change magnification."

BTW, I am posting his pm after asking his permision. I am still confused about the concept and hence the new thread. Sorry FrankD! You tried hard to explain. I can't seem to get it. :-C



I own a Nikon EII 8x30 and a Leica UV 10x42.

The EII 8x30 specs from Nikon's site http://nikon.com/products/sportoptics/lineup/binoculars/nature/x32x35/spec.htm
Mag - 8x
FOV - 154m/1000m
RFOV - 8.8 deg
AFOV - 63.2 deg (Apparent FOV)

The UV 8x42 specs
Mag - 10x
FOV - 110m/1000m
RFOV - 6.3 deg
AFOV - 63 deg (Apparent FOV)

As I could not find a Leica page with AFOV I multiplied Mag by RFOV to get the AFOV. This may not be accurate as Frank pointed out in his pm.

That being said, how does this figure of 63 degrees for Apparent FOV that both bins have help me understand an optical quality. The circle I see through the Nikon 8x is bigger and encompasses more area than the one I see through the Leica 10x and they both have an AFOV number close to each other. If I am not wrong about this how does the AFOV number help me evaluate a bin.

AFOV is huge because it allows you to compare binoculars of different magnifications. Think of it as TV screen.Here is a full explanation.

An eyepiece's apparent field of view is the angular diameter, expressed in degrees (°), of the circle of light that the eye sees. It is analogous to the screen of a television (not the picture seen through it). Eyepiece apparent fields range from narrow (25° - 30°) to extra-wide angle (80° or more). The true field (or real field) of view is the angle of sky seen through the eyepiece when it's attached to the telescope. The true field can be approximated using the formula:

True Field = Apparent Field ÷ Magnification

For example, suppose you have an 8" Schmidt-Cassegrain telescope with a 2000mm focal length, and a 20mm eyepiece with a 50° apparent field. The magnification would be 2000mm ÷ 20mm = 100x. The true field would be 50 ÷ 100, or 0.5° - about the same apparent diameter as the full Moon.

 

[FrankD]

This might help further. I took the pic above and changed it a bit. Ignore the gray outside of the black circles I inserted. Pay attention to the gray inside the circles but outside the image. That change in gray area inside the black circles but outside the image is the change in apparent field of view.

 

[SivaL]

For one, you listed "UV 8x42" but then listed the 10x42 specs. I am guessing that is just a typo and you instead meant to write "UV 10x42".

Corrected to 10x42. Thanks for pointing it out.

 

[henry link]

Some confusion is arising here from Nikon's use of the ISO method for calculating AFOV vs Leica's use of the simple method. If the simple calculation is used for both the Nikon 8x30 EII AFOV is 70º, not 63.2º. Neither is really correct because neither includes the influence of different distortion types and amounts in different binoculars.

The true AFOV of a particular binocular has to be measured, so that it includes the effect of the distortion profile. In general you can say the higher the pincushion distortion the closer the true AFOV will be to the simple calculation and the lower the pincushion the closer the true AFOV will be to the ISO calculation.

 

[WJC]

Some confusion is arising here from Nikon's use of the ISO method for calculating AFOV vs Leica's use of the simple method. If the simple calculation is used for both the Nikon 8x30 EII AFOV is 70º, not 63.2º. Neither is really correct because neither includes the influence of different distortion types and amounts in different binoculars.

The true AFOV of a particular binocular has to be measured, so that it includes the effect of the distortion profile. In general you can say the higher the pincushion distortion the closer the true AFOV will be to the simple calculation and the lower the pincushion the closer the true AFOV will be to the ISO calculation.

But then, on BF we often seek simple solutions to complex—often non-existent—problems. Sure, it's not really productive from a mathematical standpoint. BUT, if it causes one to turn his THINKOLOGY up a notch, it's worthwhile. :cat:

"The problems we face cannot be solved with the level of thinking we used to create them." —Albert Einstein

 

[SivaL]

I have a little bit more time to expand on what we discussed previously so let me take another shot at it.

For one, you listed "UV 8x42" but then listed the 10x42 specs. I am guessing that is just a typo and you instead meant to write "UV 10x42".

Using the "simple method" they do have close to the same apparent field of view on paper. As I mentioned in my pm, the larger the apparent field of view then the less "black" you see outside of the circular image as represented in the image you posted above. In the case of that particular image the "outside" is gray and not black.

You can see from that image that the larger apparent field of view on the left has less "gray" outside the image. Both images have approximately the same "true field of view" in that you can see the same stars in both circles. The difference between these two, in particular, is obviously magnification. This could easily be the representation when comparing something like a Leupold Yosemite 6x30 (AFOV 48 degrees, TFOV 420 feet) with a binocular similar to the Bushnell Legend Ultra 8x42 (AFOV 64 degrees, TFOV 420 feet).

One other factor that I have found influences the perception of apparent field of view is the type and severity of edge distortion present in the image. AMD, pincushion, etc... can give the impression that the image actually has a larger, or smaller, apparent field of view than it actually does.

I didn't get to address one of your comments in the last message. You mentioned something along the lines of "How can the amount of 'black' outside the image be different if the eyecup is set correctly for proper eye relief?"

If the eyecup is set incorrectly, either too collapsed or too extended, then you loose the sharp edges of the field stop (the edge that separates the image from the "black". Blackouts or tunnel vision are usually the result.

The easiest way to illustrate what I am relating here would be to take something like the two bins I mentioned above that have vastly different apparent fields of view and compare them side by side. The difference in apparent field of view is instantly noticeable. One is more "tunnel-like" in appearance while the other is more "immersive".

Hope this helps.

Thanks Frank. I get the "tunnel-like" view after finding picture online http://www.handprint.com/ASTRO/IMG/tfov.gif

If the angle of difference between the yellow line from the eye-piece and the green line through the objective lens is greater it will cause the tunnel image.

 

[WJC]

Thanks Frank. I get the "tunnel-like" view after finding picture online http://www.handprint.com/ASTRO/IMG/tfov.gif

If the angle of difference between the yellow line from the eye-piece and the green line through the objective lens is greater it will cause the tunnel image.

Hi Subzero:

Your eye must be positioned the right distance behind the rear eyelens or "blackout," your "tunnel vision," will occur. Being too close or too far from the correct point will cause problems—not mechanical, but biological.

Bill