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

[Binastro]

The size of the objectives does not affect the FOV.

The eyepieces, possibly prisms and any baffles determine FOV.

Regards,
B.

 

[WJC]

The size of the objectives does not affect the FOV.

The eyepieces, possibly prisms and any baffles determine FOV.

Regards,
B.

An important part was left out and the two words have since been added.

 

[Yellow hammer]

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.

Than you Canip! It seems like ONE tube is answer I am looking for.

 

[Yellow hammer]

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.

Thank you very much! One barrel measurement it seems to bee. Such a great knowledge in this group!

 

[Yellow hammer]

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

Mr WJC! Thanks alot. You have answer my question I have been thinking of for a whole year or so. FOV is measured from oblygt One barrel. Sincerely/Yellowhammer

 

[Yellow hammer]

The size of the objectives does not affect the FOV.

The eyepieces, possibly prisms and any baffles determine FOV.

Regards,
B.

But if not the size of the objectives affect the FOV - why is almost every 32 mm bino wider than the 42 mm? (Except for the NL Pure 8x42 that has a wider FOV than the 8x32). Does the focal lenght affect the FOV in this case?

 

[Binastro]

If a 42mm binocular is stopped down by a front mask of 20mm, the FOV is the same, but the view may be dimmer.

An 8x42 may have objectives with a focal length of 160mm.
The eyepieces have a focal length of 20mm.

An 8x32 may have objectives with a focal length of 120mm.
The eyepieces have a focal length of 15mm.

15mm eyepieces can have a wider FOV than 20mm eyepieces for the same field stop in front of the eyepiece.
However the prism sizes and field stop sizes depends on the dimensions of the binocular.
The 15mm eyepiece may well have one more element than the 20mm giving a wider AFOV.

As to the actual spacing of the two binocular tubes.
If these are 70mm apart, at a distance of 40 metres, the sideways field using the two barrels is 0.1 degree bigger than each barrel.

40 metres is quite a long distance and one that birdwatchers may use. So part of the say 0.2 or 0.3 degrees wider field with two barrels is because of tube spacing.

At 20 metres the difference is 0.2 degrees just from barrel spacing.

Regards,
B.

 

[Yellow hammer]

If a 42mm binocular is stopped down by a front mask of 20mm, the FOV is the same, but the view may be dimmer.

An 8x42 may have objectives with a focal length of 160mm.
The eyepieces have a focal length of 20mm.

An 8x32 may have objectives with a focal length of 120mm.
The eyepieces have a focal length of 15mm.

15mm eyepieces can have a wider FOV than 20mm eyepieces for the same field stop in front of the eyepiece.
However the prism sizes and field stop sizes depends on the dimensions of the binocular.
The 15mm eyepiece may well have one more element than the 20mm giving a wider AFOV.

As to the actual spacing of the two binocular tubes.
If these are 70mm apart, at a distance of 40 metres, the sideways field using the two barrels is 0.1 degree bigger than each barrel.

40 metres is quite a long distance and one that birdwatchers may use. So part of the say 0.2 or 0.3 degrees wider field with two barrels is because of tube spacing.

At 20 metres the difference is 0.2 degrees just from barrel spacing.

Regards,
B.

Now it is getting really complicated for me… But I am very happy otherwise 😊
Off topic/By the way - Wich one would you buy if you wanted a compact; Sw Curio 7x21 or Leica UV 8x20?
Wonderer
Yellowhammer

 

[Binastro]

Unfortunately I have neither binocular, so cannot comment.

Orebro is a nice town, I visited several times but a long time ago.

Regards,
B.