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Conquest 32 vs 42 FOV

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Old Thursday 19th July 2018, 04:24   #1
HeadWest
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Conquest 32 vs 42 FOV

I just noticed that the 8x32 Conquest model has a significantly larger FOV than the 8x42 model (140.0m @ 1000m VS 129.5m @ 1000m). Why would that be? I see 32s usually have a larger FOV than 42s. For some reason that is the opposite of what I expected. Just curious about the science behind this. Thanks!
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Old Thursday 19th July 2018, 05:37   #2
ceasar
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Quote:
Originally Posted by HeadWest View Post
I just noticed that the 8x32 Conquest model has a significantly larger FOV than the 8x42 model (140.0m @ 1000m VS 129.5m @ 1000m). Why would that be? I see 32s usually have a larger FOV than 42s. For some reason that is the opposite of what I expected. Just curious about the science behind this. Thanks!
That is often the case but there is also a trade off in eye relief. The eye relief will often be shorter in the 8x32 because the oculars are smaller. It is the design of the oculars and the numbers of elements in them that determines whether a FOV is narrow or wide and that will affect their eye relief.

Somebody with more knowledge than I have about this can give a more detailed answer.

Bob
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Old Thursday 19th July 2018, 09:46   #3
akltsang
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I think this is a matter of eyepiece design. Eyepieces in 8x42 are of longer focal length than those in 8x32 (because the objectives in 42mm models have longer focal length). It is more difficult to make wide FOV eyepiece with good peripheral image quality for long focal length. So a trade off is to restrict the FOV. Correct me if I am wrong.

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Old Thursday 19th July 2018, 09:51   #4
akltsang
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If you compare 8x32 and 10x42 of the same series of binoculars, their apparent FOV are usually the same. This is because they use the same eyepieces in the two models.
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Old Thursday 19th July 2018, 14:52   #5
Binastro
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Correct, akltsang.
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Old Tuesday 24th July 2018, 12:23   #6
Stephen Mark
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Don'y you mean 10X32 and 8X42 being about the same?
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Old Tuesday 24th July 2018, 13:14   #7
henry link
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Steve,

No, they have it right. An 8x32 and 10x42 binocular can use the same eyepiece with the same AFOV when the focal length of the 42mm objective lens is 25% longer than the focal length of the 32mm objective lens. The same objective lenses could be used in a 10x32 and 8x42, but in that case the eyepieces would need to have very different focal lengths and, if we assume similar sized eyepiece field stops, the AFOV would be much wider in the 10x32.

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Old Tuesday 24th July 2018, 23:44   #8
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This is an interesting question. I should not change the subject, but Henry could tell us more about how
Nikon does this with the SE porro models: 8x32, 10x42 and 12x50.

I assume the ocular part of the binocular is the same, and the only difference is the length of the barrels.
I wonder if this how they change the focal length ?

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Old Wednesday 25th July 2018, 13:35   #9
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Jerry,
This is common to many Porroprism and some roof prism ranges.

To keep it simple, say f/4 objectives although probably f/3.8?
32mm objective focal length 128mm
42mm objective fl 168mm
50mm objective fl 200mm

8x 16mm fl eyepiece
10x 16.8mm eyepiece
12x 16.7mm eyepiece.

What they would do is slightly alter objective fl to get the correct magnification using the same eyepieces.

Minolta Porros, Pentax etc.
Nikon Aculon and Action VII modern, probably a big range.
Russian 6x30, 8x40, 10x50.
They all have the same back end with different barrels.
However, the higher magnification ones need more accurate alignment to be within tolerances.
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