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Is FoV measured from one tube or both tubes? (1 Viewer)

Yellow hammer

Active member
Sweden
Hi!
I am pretty sure that if I look with my both eyes through both tubes it gives me a little wider FoV than if only using one eye. But how do the bino companies measure and report FoV in the specs?
Sincerely
Mr Yellowhammer
 
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Hi!
I am pretty sure that if I look with my both eyes through both tubes it gives me a little wider FoV than if only using one eye. But how do the bino companies measure and report FoV in the specs?
Sincerely
Mr Yellowhammer

I guess quality bino companies will make sure both tubes have, within narrow limits, the same FOV (in my experience, there are frequently small variations).
When I measure FOV (in case I suspect the specs might not be precise), I measure in both tubes and then take the smaller value as the one I use for that bino.
This goes for both measuring RFOV (Real Field of View) and AFOV (Apparent Field of View).

Canip

P.S. for the difference etc. between RFOV and AFOV, see numerous never ending threads here In Birdforum (e.g. IN PRAISE OF THE SWAROVSKI 12X42 NL PURE) or on other websites
 
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If you do not see a single, circular field when using both eyes, something isn’t set right.

Try adjusting the inter-pupillary distance.
 
FOV can be expressed in metres @1000 m or as an angle. In general, the higher the magnification, the smaller the FOV, but there are exceptions influenced by the design, e.g Swarovski Habicht 7x42 (114 m @ 1000 m) and Swarovski NL 10x42 (133m @ 1000 m).
A FOV of 120 m @ 1000 m would be 360 ft @1000 yds or 6,9°.
What you see is the apparent field of view (AFOV) and can be influenced by eye placement.
AFOV is often calculated by multiplying the true FOV by the magnification or according to the ISO formula.
The actual AFOV usually lies somewhere in between the two calculated values and can be measured quite easily: A simple and precise method of measuring AFOV

John
 
If you do not see a single, circular field when using both eyes, something isn’t set right.

Try adjusting the inter-pupillary distance.
Hi Maljunulo. I have no problem with the IPD or anything like that. My question was about the measure of the FoV. If it says 8 degrees on my bino. Is that measurement done from one barrel or both. Do you understand my question better now?
 
FOV can be expressed in metres @1000 m or as an angle. In general, the higher the magnification, the smaller the FOV, but there are exceptions influenced by the design, e.g Swarovski Habicht 7x42 (114 m @ 1000 m) and Swarovski NL 10x42 (133m @ 1000 m).
A FOV of 120 m @ 1000 m would be 360 ft @1000 yds or 6,9°.
What you see is the apparent field of view (AFOV) and can be influenced by eye placement.
AFOV is often calculated by multiplying the true FOV by the magnification or according to the ISO formula.
The actual AFOV usually lies somewhere in between the two calculated values and can be measured quite easily: A simple and precise method of measuring AFOV

John
Thank you John. But do you think the companies measure the FoV from one barrel or by both?
If I look with one eye in my binos, I am pretty sure I see a narrower FOV. If I look with both eyes the FoV seems to stretch out a bit, especially sideways (left to right). Not sure up and down.
 
But do you think the companies measure the FoV from one barrel or by both?

As I said in an earlier post, quality manufacturers will design binos with equal FOV in both tubes and then quality test in random samples (not in each and every sample) in both tubes.
Which bino do you have?
 
Thank you John. But do you think the companies measure the FoV from one barrel or by both?
If I look with one eye in my binos, I am pretty sure I see a narrower FOV. If I look with both eyes the FoV seems to stretch out a bit, especially sideways (left to right). Not sure up and down.

Yellow hammer,

I'm no expert but if I understand your question, IME the answer is "yes looking thru both barrels will show a larger FoV than looking through just one barrell at a time." At least that was my experience in experimenting with my UV 8x20.

P.S. I don't know how manufacturers measure FoV nor specify it, but would presume they measure and list/spec the FoV using both barrels.

Mike
 
Thank you John. But do you think the companies measure the FoV from one barrel or by both?
If I look with one eye in my binos, I am pretty sure I see a narrower FOV. If I look with both eyes the FoV seems to stretch out a bit, especially sideways (left to right). Not sure up and down.
If the binocular is perfectly collimated (barrels parallel at all IPDs) then it doesn't matter whether you are viewing with one eye or two.
OK, at any specific distance the true FOV would be increased with two eyes by the objective spacing (typically 6-7 cm), but I think we can ignore that ;).

John
 
If you do not see a single, circular field when using both eyes, something isn’t set right.

Try adjusting the inter-pupillary distance.
What if, to fit a broader face, the binoculars are opened close to the limit, and the view is more oval, longer at the sides, than circular? That’s my experience with 8x32 as opposed to 8x42 glasses. Thanks for the advice n this.
 
Yellowhammer, you are correct, FOV is bigger sideways using two tubes/barrels.

This is because the two circles don't precisely cover each other.
This is partly due to the collimation process.
Also, slightly incorrect IPD.

In addition, the size of one's pupils changes the FOV.

Also, hand holding a binocular increases the FOV because the image moves slightly.
Persistence of vision means one sees the slightly wider field of view, without knowing it.

Also the exact position along the axis gives slightly different fields of view.

The actual value is measured by the maker with one barrel, fixed on the optical bench, supposedly for infinity.
However, some makers of lower priced binocular either cheat slightly or in many cases cheat a lot.

I measure the FOV using precise star measurements.
However, star charts are useless because of the map is flat and the measurements are spherical.

Computer programmes are better but still not highly accurate.

Spherical geometry is needed, although with Orion's belt stars a very good fit can be made using Pythagoras.
The outer stars are 2.736 degrees apart using spherical geometry or Pythagoras because the stars are so close the the celestial equator.

Alpha to beta Ursa Major is 5 degrees 22.4 minutes of arc separation.

However, the binocular must be held exactly square on to the stars.
If one's head is angled the FOV is completely wrong.

Nearly all specified fields of view are wrong.
Leica, Zeiss and presumably Swarovski get it closely right as do Nikon.
However, in their literature they often get mixed up converting metres to feet.

The Visionking 5x25 quotes 15.8 degrees.
I make it 14.8 to 15.0 degrees single barrel and up to 15.4 degrees both barrels.

The Minolta 7x35 Standard MK 11.05 degrees.
The Minolta 10x50 Standard MK 7.65 degrees but possibly 7.8 degrees as stated with both barrels.
Conquest HD 10x42 6.65 degrees.

The older extra wide angle specs are often over stated by about 7%.

Don't believe makers specs.
Measure the FOV yourself.

Regards,
B.
 
The top two stars of Orion are close to 7 degrees 33 minutes apart.
The bottom two stars are close to 8 degrees 21 minutes apart.

One can get 2% accuracy with care measuring binocular FOV, and occasionally better if the binocular FOV is just smaller than the star separation.
My 8.5x44 Swift HR/5 has a field of 8.26 degrees assuming the bottom two stars of Orion are 8.35 degrees apart.
However, I have not done a precise spherical geometry calculation of the two star's separation, so even here I may be slightly wrong.

In addition, the star images are often so distorted at the field edge that exact measurements cannot be taken.

B.
 
Hi!
I am pretty sure that if I look with my both eyes through both tubes it gives me a little wider FoV than if only using one eye.
Sincerely
Mr Yellowhammer

Hi Maljunulo. I have no problem with the IPD or anything like that. My question was about the measure of the FoV. If it says 8 degrees on my bino. Is that measurement done from one barrel or both. Do you understand my question better now?
I thought the first statement was part of what you said.

I‘ll stand on my statement that if you don’t see a circle when you use both eyes, something isn’t right.

Yes, I do understand the question better. I think the answer may depend on how many insignificant digits you want in the FOV measurement.
 
As I said in an earlier post, quality manufacturers will design binos with equal FOV in both tubes and then quality test in random samples (not in each and every sample) in both tubes.
Which bino do you have?
I have around ten binos 😊 mostly pockets and compacts with magnifikation from 6,5-8.

I was thinking if there was a world standard that all brands use the same kind of fov-measurement.
An example - If, for instanse Opticron, is doing their FoV-measurement from only one eye, it Will show a slightly narrower FoV in their specs. And another brand, for instance Leica, measure the FoV that you get with both eyes. Then Leica binos Will state a slightly larger FoV in their specs. Are you with me?

Maybee this differences is negligeable, I dont know. But for me it is clearly visible. I guess that I see around 0,2 - 0,3 degrees wider with both eyes looking, in 8x-binos. So if my Kowa bino says 8,0 degrees in the specs, it could teoretically be 8,3 degrees. Or 7,7 degrees. Depending on Kowas type of measurement. This is my question.
 
Ok, now I get you.
So forget everything I said in posts # 5 and 10, since these were not answering your question.
I am convinced FOV specs of manufacturers represent the value measured in ONE tube.
I haven’t encountered the phenomenon you describe.
 
The difference between one and two eyes is small, but as you say around 3%..

I would think that all good makers use a one barrel measure.

If a binocular is set up on a work bench and using very distant targets the measures will be the same with one barrel or two barrels

The only way a two barrel measure would be used is if the measure was done using actual eyes

The top makers are usually very accurate and a bit conservative by 1%.

The Canon 18x50 IS is listed as 3.7 degrees, but I make it 3.85 degrees.
Here this is about 4% more than stated.

Another problem with using eyes is that an eye in a fixed position, hopefully on axis, will give a smaller measure than if the eye is moved around the field.

This is also part of the reason two eyes give a wider measure as the IPD is never perfect.

But as I said before one cannot rely on makers specs.
One needs to measure it personally.

Another factor to consider is that the magnification is also often wrong.

Bushnell say the Xtrawide angle is 4x21.
It is actually 3.5x or 3.4x.
Their 5x25 is 4.4x.
This is done deliberately to enhance the specs.

A Celestron 8x30 was 6.7x27.

The 12x50 Optolyth is 12x42.

Etc. etc.

Regards,
B.
 
Hi!
I am pretty sure that if I look with my both eyes through both tubes it gives me a little wider FoV than if only using one eye. But how do the bino companies measure and report FoV in the specs?
Sincerely
Mr Yellowhammer

Field of view is measured in ONE telescope. Because the size of the objectives and magnification should be exactly the same. If the second telescope does not equal that,

1) The specs have been reported incorrectly,
2) The binocular is out of collimation (alignment),***
3) One or more elements is over or undersized compared to specs,
4) One or more baffles or field stops is over or under specs. These days that rarely happens and is nothing to worry about. Although a few observers seem to fixate on scientifically insignificant anomalies because it gives them something seemingly important to talk about.
5) The perceived problem is physiological and has NOTHING to do with the binocular.

Another example would be that LIGHT GRASP would equal the light grasp of BOTH objectives combined. That is totally REASONABLE. Also totally wrong! It may be right mathematically. However, the brain does not work on mathematics. A second objective allows for an increase in “perceived” light grasp that few people would even notice.

*** “perfectly collimated.” Of the several thousand I have collimated, none have been “perfectly” collimated. Any binocular can be collimated “perfectly collimated for all practical purposes.” However, that condition would be constantly changing due to changes in temperature and humidity. See attached.

Don’t worry; be happy.

Bill
Hi!
I am pretty sure that if I look with my both eyes through both tubes it gives me a little wider FoV than if only using one eye. But how do the bino companies measure and report FoV in the specs?
Sincerely
Mr Yellowhammer
 

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