Velocity Reviews > Re: Angle of view instead of focal length

# Re: Angle of view instead of focal length

David Dyer-Bennet
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Posts: n/a

 10-03-2012
Alfred Molon <(E-Mail Removed)> writes:

> In article <(E-Mail Removed) >, bugbear
> says...
>> Of focal length, sensor size and field of view you need (any) two.
>> The third can be calculated. Since your viewing of EXIF
>> is always mediated by software, this is a non-issue.

>
> Of course everything can be calculated, but actually focal length and
> sensor size are irrelevant. What really matters is the angle of view.

Focal length is what's physically inherent in the lens (and many people
use the same lenses on DX and FX cameras; some also use lenses via
adapters on M43 bodies), so the angle of view can't really be marked on
the lens without creating confusion, while the focal length can.

Also the focal length is a required in put for things like depth of
field calculations, you have to know the *actual* physical focal length

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David Dyer-Bennet
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Posts: n/a

 10-03-2012
Alfred Molon <(E-Mail Removed)> writes:

> In article <(E-Mail Removed)>, David Dyer-Bennet says...
>> Focal length is what's physically inherent in the lens (and many people
>> use the same lenses on DX and FX cameras; some also use lenses via
>> adapters on M43 bodies), so the angle of view can't really be marked on
>> the lens without creating confusion, while the focal length can.

>
> The focal length is not something you can touch or measure with a ruler.
> A lens with a focal length of 300mm is not 300mm long and an 8mm lens is
> not 8mm long.

Well, a ruler isn't the *only* tool you need, no. But it's a physical
property of the lens system that *can* be measured (using the ruler) on
a proper optical bench, or by improvising a bit.

> You could place two angles of view on the lens, one for APS-C format and
> one for full-frame format.
>
> For a wide angle lens it is certainly interesting to know that it covers
> for instance an angle of 120° in the horizontal.

Is it? Most people can't draw you a 76 degree angle freehand
accurately.

> By the way, for my panoramic shots I'm providing FoV data. This panorama
> for instance has a FoV of 224° x 118° (data calculated by PTGUI):
> <http://www.molon.de/galleries/Malays...aches/img.php?
> pic=11>
>
>> Also the focal length is a required in put for things like depth of
>> field calculations, you have to know the *actual* physical focal length

>
> You could calculate that from the angle of view of the lens, using the
> size of the sensor and the size of the pixels (needed for circle of
> confusion calculations). The pixel pitch matters - a 6MP full-frame
> sensor has more DOF than a 60MP full-frame sensor.

Only as a secondary result -- degree of enlargement is what actually
matters. But of course people tend not to buy and use a 60MP sensor
unless they're doing something that uses that resolution, which almost
always means BIG prints.
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David Dyer-Bennet
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 10-03-2012
nospam <(E-Mail Removed)> writes:

> you really need *seven* values, for 1x (full frame), 1.3x, 1.5x, 1.6x,
> 1.7x, 2.0x and 2.7x crop factors.

Plus the Pentax Q, right?

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me
Guest
Posts: n/a

 10-03-2012
On Wed, 3 Oct 2012 21:23:41 +0200, Alfred Molon
<(E-Mail Removed)> wrote:

>In article <(E-Mail Removed)>, David Dyer-Bennet says...
>> Focal length is what's physically inherent in the lens (and many people
>> use the same lenses on DX and FX cameras; some also use lenses via
>> adapters on M43 bodies), so the angle of view can't really be marked on
>> the lens without creating confusion, while the focal length can.

>
>The focal length is not something you can touch or measure with a ruler.
>A lens with a focal length of 300mm is not 300mm long and an 8mm lens is
>not 8mm long.

Well actually with another piece of info it is close. The front
objective needs to be at least a smidgen larger in diameter than the
lens f/f#, no? ie an f/4 400 mm lens has an objective greater than
400/4 = 100mm.

nospam
Guest
Posts: n/a

 10-04-2012
In article <(E-Mail Removed)>, Alfred
Molon <(E-Mail Removed)> wrote:

> > Focal length is what's physically inherent in the lens (and many people
> > use the same lenses on DX and FX cameras; some also use lenses via
> > adapters on M43 bodies), so the angle of view can't really be marked on
> > the lens without creating confusion, while the focal length can.

>
> The focal length is not something you can touch or measure with a ruler.

of course you can measure it with a ruler. what do you think rulers are
for, if not to measure things?

> A lens with a focal length of 300mm is not 300mm long and an 8mm lens is
> not 8mm long.

so what? you don't measure the lens itself, you measure it's focal
length.

> You could place two angles of view on the lens, one for APS-C format and
> one for full-frame format.

you could, but that won't help much.

you really need *seven* values, for 1x (full frame), 1.3x, 1.5x, 1.6x,
1.7x, 2.0x and 2.7x crop factors.

it will become very confusing, very quickly.

nospam
Guest
Posts: n/a

 10-04-2012
In article <(E-Mail Removed)>, David Dyer-Bennet
<(E-Mail Removed)> wrote:

> > you really need *seven* values, for 1x (full frame), 1.3x, 1.5x, 1.6x,
> > 1.7x, 2.0x and 2.7x crop factors.

>
> Plus the Pentax Q, right?

forgot that one, so eight.