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I don't understand this:

http://www.nikonusa.com/template.php?cat=1&grp=5

Why is it the 14mm lense has a 114 degree FOV, while the 16mm has a
full 180? Is there something special about fisheye lenses (the 16mm in
this case) vs. non-fisheye?

Thanks for any insight!

Dean

On Jun 21, 8:24 am, DeanB <deanbrow...@yahoo.com> wrote:
> I don't understand this:
>
> http://www.nikonusa.com/template.php?cat=1&grp=5
>
> Why is it the 14mm lense has a 114 degree FOV, while the 16mm has a
> full 180? Is there something special about fisheye lenses (the 16mm in
> this case) vs. non-fisheye?
>
> Thanks for any insight!
>
> Dean

Indeed, when we get to extreme fisheyes, the idea of focal length
controlling field of view breaks down. In order to truly get 180
degree FOV with conventional optics, it would take zero focal length,
which is of course impossible. So extreme fisheye lenses MUST have
distortion. Effectively, the focal length is not constant with field
angle. That "distortion" gives the field of view at the more extreme
field angles.

Don Stauffer in Minnesota wrote:
> On Jun 21, 8:24 am, DeanB <deanbrow...@yahoo.com> wrote:
>
>>I don't understand this:
>>
>>http://www.nikonusa.com/template.php?cat=1&grp=5
>>
>>Why is it the 14mm lense has a 114 degree FOV, while the 16mm has a
>>full 180? Is there something special about fisheye lenses (the 16mm in
>>this case) vs. non-fisheye?
>>
>>Thanks for any insight!
>>
>>Dean
>
>
> Indeed, when we get to extreme fisheyes, the idea of focal length
> controlling field of view breaks down. In order to truly get 180
> degree FOV with conventional optics, it would take zero focal length,
> which is of course impossible. So extreme fisheye lenses MUST have
> distortion. Effectively, the focal length is not constant with field
> angle. That "distortion" gives the field of view at the more extreme
> field angles.

One other possibility is that the 14mm f/2.8D ED AF isn't a full frame
lens, as this isn't specifically mentioned in the description for this lens.
The 16mm f/2.8D AF Fisheye-Nikkor is specifically described as having
"Full frame 180 degree fisheye coverage...", so I can only guess from
this that it will definitely cover the whole 24x36mm 135 film frame.
Another possible reason for the 14mm f/2.8D ED AF not being as "wide" as
the 16mm lens is that it might be a rectilinear (distortion corrected) lens.
This tends to "stretch out" the edges of the image to make objects
appear the same size at the same distance regardless of how off-axis it
is and make the angular coverage less than a non-rectilinear lens.

I don't have either lens and can't do anything other than speculate.

Perhaps looking through pbase.com for images tagged as being made with
these lenses will answer this aspect of the question?

"dj_nme" <> wrote in message news:467a91bb$0$22433$...
> Don Stauffer in Minnesota wrote:
>> On Jun 21, 8:24 am, DeanB <deanbrow...@yahoo.com> wrote:

>>>I don't understand this:
>>> http://www.nikonusa.com/template.php?cat=1&grp=5
>>>
>>>Why is it the 14mm lense has a 114 degree FOV, while the 16mm has a
>>>full 180? Is there something special about fisheye lenses (the 16mm in
>>>this case) vs. non-fisheye?

There are various types of perspectives (rectangular, spherical,
orthographic, one best approximated with very long telephotos
[as in old Chinese/Japanese paintings and drawings of buildings
made without perspective effects], etc.). In all, made by all lenses,
the focal lengths are rated similarly (by the distance of the lens
optical center from the sensor at infinity focus) - but the perspective
types (and distortions within the perspective types caused by lens
design shortcomings) may cause straight lines of subjects running
off axis of the image center (of an unshifted lens relative to the
sensor) to be curved, which causes a shift in image magnification
away from the center of the image, sometimes permitting a greater
angle of view to be photographed using some lens perspective
types. Or, a truly "distortion-free" rectangular-perspective type
of lens will show the same magnification in the center as a truly
"distortion-free" spherical-perspective type of lens of the same
FL, but as you look away from the image center, the fisheye will
show increasingly less subject magnification, and therefore more
included subject area (a greater angle of view).

>> Indeed, when we get to extreme fisheyes, the idea of focal length
>> controlling field of view breaks down.

Not really - see above...

>> In order to truly get 180
>> degree FOV with conventional optics, it would take zero focal length,
>> which is of course impossible. So extreme fisheye lenses MUST have
>> distortion.

Not "distortion", but a different set of perspective rules - see above...

>> Effectively, the focal length is not constant with field
>> angle. That "distortion" gives the field of view at the more extreme
>> field angles.

> One other possibility is that the 14mm f/2.8D ED AF isn't a full frame lens, as this isn't specifically mentioned in the
> description for this lens.

It is full-frame...

> The 16mm f/2.8D AF Fisheye-Nikkor is specifically described as having "Full frame 180 degree fisheye coverage...", so I can only
> guess from this that it will definitely cover the whole 24x36mm 135 film frame.

It will...

> Another possible reason for the 14mm f/2.8D ED AF not being as "wide" as the 16mm lens is that it might be a rectilinear
> (distortion corrected) lens.
> This tends to "stretch out" the edges of the image to make objects appear the same size at the same distance regardless of how
> off-axis it is and make the angular coverage less than a non-rectilinear lens.

Ah, close - but it doesn't really "stretch-out" the image edges. Try
a pinhole camera - it renders perfect rectangular perspective, but has
no optics to "stretch" things...

> I don't have either lens and can't do anything other than speculate.
>
> Perhaps looking through pbase.com for images tagged as being made with these lenses will answer this aspect of the question?

See above... I also have an article, "On Seeing and Perspective" on
my web page, at http://www.donferrario.com/ruether/a...ml#perspective
in which I try to explain how we see, and in which perspective type (it
may surprise you, but it is easy to prove....
--
David Ruether

http://www.donferrario.com/ruether

"DeanB" <> wrote in message news: ups.com...

>I don't understand this:
> http://www.nikonusa.com/template.php?cat=1&grp=5
>
> Why is it the 14mm lense has a 114 degree FOV, while the 16mm has a
> full 180? Is there something special about fisheye lenses (the 16mm in
> this case) vs. non-fisheye?

See my post below...
--
David Ruether

http://www.donferrario.com/ruether

"dj_nme" <> wrote in message
news:467a91bb$0$22433$...
> Don Stauffer in Minnesota wrote:
>> On Jun 21, 8:24 am, DeanB <deanbrow...@yahoo.com> wrote:
>>
>>>I don't understand this:
>>>
>>>http://www.nikonusa.com/template.php?cat=1&grp=5
>>>
>>>Why is it the 14mm lense has a 114 degree FOV, while the 16mm has a
>>>full 180? Is there something special about fisheye lenses (the 16mm in
>>>this case) vs. non-fisheye?
>>>
>>>Thanks for any insight!
>>>
>>>Dean
<SNIP>
> Another possible reason for the 14mm f/2.8D ED AF not being as "wide" as
> the 16mm lens is that it might be a rectilinear (distortion corrected)
> lens.

The 14mm is indeed rectilinear.

Cheers,
ink

"David Ruether" <> wrote in message news:f5e78m$9jm$...
>
>
> "DeanB" <> wrote in message news: ups.com...
>
>>I don't understand this:
>> http://www.nikonusa.com/template.php?cat=1&grp=5
>>
>> Why is it the 14mm lense has a 114 degree FOV, while the 16mm has a
>> full 180? Is there something special about fisheye lenses (the 16mm in
>> this case) vs. non-fisheye?
>
> See my post below...

Oooops! Shoulda been, "above"...
But it got me thinking - and I will probably add an article on my web
page next to "On Seeing and Perspective" called "On Lenses and
Perspective Types" (at www.donferrario.com/ruether/articles.html).
--
David Ruether

http://www.donferrario.com/ruether

In article <f5e78m$9jm$>,
David Ruether <> wrote:
>
>
>"DeanB" <> wrote in message news: ups.com...
>
>>I don't understand this:
>> http://www.nikonusa.com/template.php?cat=1&grp=5
>>
>> Why is it the 14mm lense has a 114 degree FOV, while the 16mm has a
>> full 180? Is there something special about fisheye lenses (the 16mm in
>> this case) vs. non-fisheye?
>
>See my post below...

Do you know if there is standard formula for fisheyes?

For rectilinear lenses it is easy: just imagine a pinhole at the focal
length distance of the sensor, and you can compute the projection.

For fisheyes, I never found an obvious way to translate focal length into
field of view.


--
That was it. Done. The faulty Monk was turned out into the desert where it
could believe what it liked, including the idea that it had been hard done
by. It was allowed to keep its horse, since horses were so cheap to make.
-- Douglas Adams in Dirk Gently's Holistic Detective Agency

"Philip Homburg" <> wrote in message
news:234vdj2s5fr9tgsp7idlgv4ip4@inews_id.stereo.hq .phicoh.net...
> In article <f5e78m$9jm$>,
> David Ruether <> wrote:
>>
>>
>>"DeanB" <> wrote in message
>>news: roups.com...
>>
>>>I don't understand this:
>>> http://www.nikonusa.com/template.php?cat=1&grp=5
>>>
>>> Why is it the 14mm lense has a 114 degree FOV, while the 16mm has a
>>> full 180? Is there something special about fisheye lenses (the 16mm in
>>> this case) vs. non-fisheye?
>>
>>See my post below...
>
> Do you know if there is standard formula for fisheyes?
>
> For rectilinear lenses it is easy: just imagine a pinhole at the focal
> length distance of the sensor, and you can compute the projection.
>
> For fisheyes, I never found an obvious way to translate focal length into
> field of view.
>
>
> --
> That was it. Done. The faulty Monk was turned out into the desert where it
> could believe what it liked, including the idea that it had been hard done
> by. It was allowed to keep its horse, since horses were so cheap to make.
> -- Douglas Adams in Dirk Gently's Holistic Detective Agency

Doesn't a fish-eye lens really have a very large amount of pincushion
distortion?
It looks to me like computing the angle of view is not such a simple task.
Jim

ink wrote:
> "dj_nme" <> wrote in message
> news:467a91bb$0$22433$...
>
>>Don Stauffer in Minnesota wrote:
>>
>>>On Jun 21, 8:24 am, DeanB <deanbrow...@yahoo.com> wrote:
>>>
>>>
>>>>I don't understand this:
>>>>
>>>>http://www.nikonusa.com/template.php?cat=1&grp=5
>>>>
>>>>Why is it the 14mm lense has a 114 degree FOV, while the 16mm has a
>>>>full 180? Is there something special about fisheye lenses (the 16mm in
>>>>this case) vs. non-fisheye?
>>>>
>>>>Thanks for any insight!
>>>>
>>>>Dean
>
> <SNIP>
>
>>Another possible reason for the 14mm f/2.8D ED AF not being as "wide" as
>>the 16mm lens is that it might be a rectilinear (distortion corrected)
>>lens.
>
>
> The 14mm is indeed rectilinear.
>
> Cheers,
> ink

I'm surprised that Nikon doesn't mention this on their website, it seems
like an oversight on their part.