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Meostar Binoculars Afov? (1 Viewer)
- Thread starter Northman
- Start date
eitanaltman
Well-known member
It will be interesting to see the measurements, but the Meostars in general are a classic “curved field” design with considerable pincushion and field curvature. As such they should tend more towards the “angle x mag” side vs the “tangent condition” end with flatter field bins like the Swaro SV.
My old Meostar 8x32 had a very relaxing “walk in” feel, an 8 degree field in an 8x with curved field makes for a very “deep” view. And the fall-off towards the edge is gentle, gradual softening that is largely curvature, so it feels like a huge sweet spot unless you intentionally start peering towards the edges. I find this profile more pleasing since there isn’t any weird stuff to distract you in the viewing zone. This is unlike the Kowa 8x33 (otherwise superior to the Meopta in nearly every way) which has a weird blurry zone with odd distortion around 60-70% out, so the edge is sharper than half way to the edge :/
If the eyecups work for you I wouldn’t have any hesitation about the little 8x32 Meostar, it is very strong optically in nearly every way including AFOV.
My old Meostar 8x32 had a very relaxing “walk in” feel, an 8 degree field in an 8x with curved field makes for a very “deep” view. And the fall-off towards the edge is gentle, gradual softening that is largely curvature, so it feels like a huge sweet spot unless you intentionally start peering towards the edges. I find this profile more pleasing since there isn’t any weird stuff to distract you in the viewing zone. This is unlike the Kowa 8x33 (otherwise superior to the Meopta in nearly every way) which has a weird blurry zone with odd distortion around 60-70% out, so the edge is sharper than half way to the edge :/
If the eyecups work for you I wouldn’t have any hesitation about the little 8x32 Meostar, it is very strong optically in nearly every way including AFOV.
The method used to measure AFOV has been described some years ago on CloudyNights. This is the formula that goes with it:
AFOV = 2 * ARCTAN ( (illum. circle diam / 2) / (distance to eyelens – eye relief) )
Glenn LeDrew, who has been using this method much longer than I, estimates that the precision is likely within about +/- 0.5 degrees. Of course, everything depends on how careful the measurements are made.
Here are my tentative values for the binos indicated by Northman (in bracket: "simple" calculation of real angle of view x magnification)
8x32: 60.8 +/- 0.5 deg. (angle x mag = 63.2)
8x42: 62.3 +/- 0.5 deg. (angle x mag. = 62.4)
12x50: 61.5 +/- 0.5 deg. (angle x mag. = 62.4)
15x56: 61.1 +/- 0.5 deg. (angle x mag. = 63.0)
So for the 8x42 and the 12x50, this would confirm what Eitan suspected, i.e. the AFOVs are quite close to the angle x mag values; only for the 8x32 and the 15x56, the difference is more than one degree.
Northman, my favorite is the 10x42 HD.
fwiw.
Canip
Canip,
Not sure how that is done but this is a direct measurement https://www.birdforum.net/threads/a-simple-and-precise-method-of-measuring-afov.359127/ and also works rather well.
I adapted it from a method demonstrated by Walter E. Schön, which I described back in 2009 (as my alter ego, John Russell) and which Henry linked in the above thread.
John
John,
thank you for the link (I had seen this before).
The formula at the end of your 2018 post is in it's essence the same as mine, so we use the same approach; you just measure "the other way around", i.e. by looking into the eyepiece, whereas I look into the objective and measure the circle produced by the field stop. I find my method easier, but that is just my personal preference.
Canip
thank you for the link (I had seen this before).
The formula at the end of your 2018 post is in it's essence the same as mine, so we use the same approach; you just measure "the other way around", i.e. by looking into the eyepiece, whereas I look into the objective and measure the circle produced by the field stop. I find my method easier, but that is just my personal preference.
Canip
Got a reply from Meopta.. they linked to the Nikon page for how top calculate AFOV.
Which gives much smaller AFOV then "the normal way".
tan ω' = Γ x tan ω
Apparent field of view:2ω'
Real field of view:2ω
Magnification:Γ
For example, the apparent field of view of 8x binoculars with a 7.0° real field of view is as follows:
.
Which gives much smaller AFOV then "the normal way".
tan ω' = Γ x tan ω
Apparent field of view:2ω'
Real field of view:2ω
Magnification:Γ
For example, the apparent field of view of 8x binoculars with a 7.0° real field of view is as follows:
- 2ω’= 2 x tan-1 (Γ x tan ω)
= 2 x tan-1 (8 x tan 3.5°)
= 52.1°
.
Last edited:
Hi Canip,
I think I see what you are doing now, projecting the image of the field stop on to a wall with a torch and them measuring the diameter of the image to calculate the AFoV. This is very similar to Walter E. Schön's method. He, however, set up the binocular at 4-5 m from a wall and needed an assistant to mark the extremities of a green laser projection through the objective.
I also view through the objective but don't need any calculations apart from a subtraction of values on the panorama scale of the tripod head. One cannot achieve coincidence of the panorama axis with the eyepiece, but if viewing a building edge left and right at 50-60 m, the parallax error is negligible.
With a scope set up at 45° tilt one can even achieve consistant results for the AFoV at the 60x setting although the "magnification as seen is 1/60th.
John
