AFoV Calculations (1 Viewer)

[Tringa45]

There are two methods of calculating the apparent field of view.
The first is to multiply the true FoV in degrees by the magnification of the binocular.
The second ISO method is to calculate the angle as if the binocular were nearer by a factor of its magnification.

To take an example, the Swarovski 7x42 Habicht Porro has a rather narrow FoV of 114 M @ 1000 m. Its angular FoV is 2x arctan 114/2x1000, i.e. 6,52°.
According to the first method this would translate to an AFoV of 7x6,52° or 45,6°.
According to ISO the AFoV would be calculated as if the 114 m FoV were seen at 1/7th of 1000 m or 142,9 m, i.e. 2x arctan 114/2x142,9, which results in 43,5°.
So there's not a lot of difference at narrower AFoVs. The wider the AFov however, the greater the discrepancy.

On another thread I incorrectly stated that the discrepancy was lower for higher magnifications.
A scope at 60x magnification with a FoV of 22 m @ 1000 m would have an angular FoV of 1,26° with AFoVs of 75,6° according to the first method and 66,8° according to ISO.

The true value for AFoV usually lies between the two calculated numbers and can be measured as follows: A simple and precise method of measuring AFOV

John

 

[kimmik]

Another way to measure AFOV is to take a photo with your phone. Then work it out with trigonometry or eyeball estimate.

Iphone 13 cameras have been measured. The main camera has approximately:

54 degrees short side
72 degrees long side
90 degrees diagonal

What Is the Angular Field of View for an iPhone 13?

I don’t know about you, but my iPhone isn’t just for Snapchat and cat videos. Nope. Sometimes I also use it for physics — because I love…

rjallain.medium.com

 

[Canip]

The true value for AFoV usually lies between the two calculated numbers and can be measured as follows: A simple and precise method of measuring AFOV

That‘s the method I use mostly since it is both easy to use and quite precise.

Canip

 

[lucy411]

There are two methods of calculating the apparent field of view.
The first is to multiply the true FoV in degrees by the magnification of the binocular.
The second ISO method is to calculate the angle as if the binocular were nearer by a factor of its magnification.

To take an example, the Swarovski 7x42 Habicht Porro has a rather narrow FoV of 114 M @ 1000 m. Its angular FoV is 2x arctan 114/2x1000, i.e. 6,52°.
According to the first method this would translate to an AFoV of 7x6,52° or 45,6°.
According to ISO the AFoV would be calculated as if the 114 m FoV were seen at 1/7th of 1000 m or 142,9 m, i.e. 2x arctan 114/2x142,9, which results in 43,5°.
So there's not a lot of difference at narrower AFoVs. The wider the AFov however, the greater the discrepancy.

On another thread I incorrectly stated that the discrepancy was lower for higher magnifications.
A scope at 60x magnification with a FoV of 22 m @ 1000 m would have an angular FoV of 1,26° with AFoVs of 75,6° according to the first method and 66,8° according to ISO.

The true value for AFoV usually lies between the two calculated numbers and can be measured as follows: A simple and precise method of measuring AFOV

John

There are two methods of calculating the apparent field of view.
The first is to multiply the true FoV in degrees by the magnification of the binocular.
The second ISO method is to calculate the angle as if the binocular were nearer by a factor of its magnification. https://calculatorspro.com/

 

[Tringa45]

There are two methods of calculating the apparent field of view.
The first is to multiply the true FoV in degrees by the magnification of the binocular.
The second ISO method is to calculate the angle as if the binocular were nearer by a factor of its magnification. https://calculatorspro.com/

This is very strange. A first post merely quoting text from the original post and adding a dubious (?) link, where calculation examples were already given.

 

[GrampaTom]

Related question?
What're folks using to secure binos to tripod? Mostly wondering about Berelach's old wooden platform, that seems no longer available in the US at least, near as I can tell. Hopefully Im wrong about that... Is there anything else that replaced this system?
Tanks
T

 

[Tringa45]

Related question?
What're folks using to secure binos to tripod? Mostly wondering about Berelach's old wooden platform, that seems no longer available in the US at least, near as I can tell. Hopefully Im wrong about that... Is there anything else that replaced this system?
Tanks
T

My personal favourite is the Leica tripod adapter, which works best with 32-42 mm roof prism bins, although I once had a Zeiss Conquest 56 HD on it, which was a bit of a stretch. I have an Arca-Swiss compatible QR plate on mine.
There is also the Swarovski UTA, which I believe is directly Arca-Swiss compatible but rather expensive.
The wooden Berlebach platform was cheap but had a few shortcomings.
Although a big Berlebach fan, I don't know what they were thinking with their new "binoculars support deluxe". Do they expect you to swap tripod heads or even buy another tripod dedicated to binocular use?

John

 

[Binocollector]

Related question?
What're folks using to secure binos to tripod? Mostly wondering about Berelach's old wooden platform, that seems no longer available in the US at least, near as I can tell. Hopefully Im wrong about that... Is there anything else that replaced this system?
Tanks
T

I use the plastic version of the Berlebach. Actually pretty sturdy and large enough for even a Tento 20x60 porro.

https://www.amazon.com/dp/B07SDBG5BH/ref=mp_s_a_1_18?crid=1QSSMMFNZ8SPP&keywords=Gosky+adapter&qid=1680816077&sprefix=gosky+adapter+%2Caps%2C367&sr=8-18

 

[brocknroller]

I'm sure this all make sense to Jethro and others who know their ciphering and goes-in toos, but I got a "C+" in trig in H.S. (my worst subject and only other subject I ever got a "C" in other than gym--I'm tall and the chin-up bar was too low, so I had to bend my knees while doing chin-ups). So, I wouldn't know a tangent from an arctangent if it hit me between the eyes, and I don't own a laser, though I saw one making a red dot between my eyes, I'd hit the ground!

Amazingly, I still have my all-metal Pickett slide rule in its original box and leather sheath and instruction manual, but now I need a magnifying glass to read the tiny numbers and lines.

I use a more subjective method to determine AFOV, which I call the "roaming eyeball method" that proves without a formal "proof" that the amount of pincushion or AMD can signficantly affect the AFOV, yielding very different results than the simple calculation method.

Case in point is the Nikon 8x42 EDG II vs. the Nikon 8x32 EDG II. Both have nearly the same TFOV (7.7* vs. 7.8*, respectively), which if one used the simple method would lead you to assume that the two binoculars would have an AFOV that was about the same. Not even close!

The 8x42 EDG II has a noticeably w-i-d-e-r AFOV than its smaller cousin. The feeling of openess while looking through the 8x42's EPs is similar to what I experience while looking through the EPs of the 8x30 E2 with its 8.8* FOV, despite the EDG having a degree less FOV. My eyes can easily roam about the field of view of both binoculars.

With the 8x32 EDG, the feeling I get while viewing through the EPs is similar to the 8x32 SE. The 8x32 EDG is sharp on axis and sharper to the edge than the 8x42 model, more like the SE, but the view feels more confined despite having 1/10* more TFOV than the 8x42 EDG. Because of this, when I want to see something at the edge of the field, I'm more apt to move the 8x32 EDG binoculars rather than my eyes despite the sharp edges. And despite the ER being nearly the same (18.5mm for the 32, 19.3mm for the 42), I'm more prone to image blackouts with the 32 than the 8x42 model, which may be another "roaming" limiting factor.

The only numbers I can offer to support the difference in AFOV I see through the two EDG binoculars are the pincushion percentages given by Allbinos for both binoculars.

For the 8x42 EDG, Allbinos measured the "Distortion" as "The distance of the first curved line from the field centre compared to the field of vision radius: 55% +\- 3%."

For the 8x32 EDG, Allbinos measure the "Distortion" as "The distance between the first curved line and the field centre compared to the field of view radius: 86% +\- 5%."

The 8x42 EDG doesn't have a lot of pincushion like most Leicas, but significantly more than the 8x32 model.

Now I've got to read the instruction manual "How to Use Trig Slide Rules" by Professor Maurice L. Hartung from the Univeristy of Chicago to find out how to compare them the objective way.

Brock

 

[quincy88]

It has never really made sense to me why the product of the magnification and the true field of view would yield the apparent field of view, so I've used the ISO method. A lot of manufacturers seem pretty dishonest about AFOV angles, and are probably also dishonest about their measured linear measurements. Nikon's math usually checks out when I look at it. Zeiss's math rarely makes any sense to me.
For example:
Nikon reports their field of view measurement for their Monarch HG 8x42s as 435 feet at 1000 yards. Doing the ISO calculation I got a AFOV of 60.2°. Nikon advertises a AFOV of 60.3°. Pretty dang close.
Zeiss reports their field of view measurement for their Victory SF 8x42s as 148 meters at 1000 meters. Doing the ISO calculation I got a AFOV 61.3°. Zeiss advertises a AFOV of 64°. Where did that additional 2.7° come from?
Swarovski and Leica stretch it a bit too, but it seems to me Zeiss is the most egregious about it. Purely anecdotal. Maybe they're doing some other calculation that isn't discussed here.

 

[Binastro]

Distortion comes into play.

Also magnification is not constant from edge to edge.

The four mentioned makers are in my opinion the most honest.

Are all measurements assumed to be at infinity?

I find it very difficult to achieve a 1% accuracy in measurement.
Usually 2% is more realistic, even using highly accurate star separations.

And these fields may assume a zero size for the eye pupil, which again is not realistic.

Also at the field stops some aberrations are inevitable.

Regards,
B.

 

[quincy88]

How does Zeiss calculate AFOV? I'd love to be able to double check their work.

 

[henry link]

Currently both Zeiss and Swarovski appear to actually measure AFOV. Typically that will result in a number somewhere between the ISO and the simple calculation, neither of which is likely to be accurate. High angular magnification distortion/low pincushion brings the true AFOV closer to the iSO calculation. High pincushion/low AMD brings the true AFOV closer to the simple calculation.

You can measure the AFOV yourself using one of two methods that have been discussed here and at Cloudy Nights before. Check out this thread.

Binoculars with near 70deg AFOV?

I was wondering if anybody has recommendations for a binocular pair, with emphasis on AFOV, Apparent FOV. 6-10 magnification AFOV above 65deg.. more is better. Sharp to 90% of field Center focus Waterproof Less then $2000 Intended use is with walking the dog, so should be easy to look through...

www.birdforum.net

The methods for measuring AFOV come up on page 2.

 

[Scott98]

The only numbers I can offer to support the difference in AFOV I see through the two EDG binoculars are the pincushion percentages given by Allbinos for both binoculars.

It could be a small difference in magnification. When I compare binos of the same magnification I can usually see that one is higher than the other.

 

[brocknroller]

It could be a small difference in magnification. When I compare binos of the same magnification I can usually see that one is higher than the other.

I've noticed that too. The image in the 8x42 EDG appears to be significantly larger than in the 8x32 EDG, but I thought that was just the "roof illusion" from the barrels being so close set. In the case of the 42mm EDG, the barrels are supposed to be 2mm closer than the competition.

According to Allbinos, the 8x42 EDG's magification is 7.94+/- 0.05x. So it's actually slightly lower than listed. The 8x32 EDG's magnification is just a hair higher at 7.96+/- 0.05x. But to my eyes, the image through the 8x42 looks like what I would see at 10x. Not higher resolution, just the image scale. Not sure why.

Brock