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 Author Topic: angle of view?  (Read 2961 times)
spphoto
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 « on: January 12, 2006, 02:06:37 PM » Reply

Hi,  it's strange that canon's 17-40mm at 17mm has the same diagonal angle of view as many of it's 28-105mm lenses at 28!?  how can this be?

sp
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jdemott
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Angle of view is dependent not only on focal length but also on sensor size.  Many DSLRs have a sensor that is smaller than 35mm film, so the angle of view on those camera is equivalent to that of a longer focal length lens on a full frame 35mm camera; this is sometimes called the multiplier factor.  Here is a link to an explanation.

http://www.dpreview.com/learn/?/Glossary/O...ltiplier_01.htm
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John DeMott
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Angle of view = 2 acrtan (dimension of image plane / 2 x effective focal length)

Or

W = 2 arctan (d/2f)
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spphoto
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Quote
Angle of view = 2 acrtan (dimension of image plane / 2 x effective focal length)

Or

W = 2 arctan (d/2f)
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Whats *effective* focal length?  The lenses I mentioned were both for full frame bodies, yet have the same fov... I'm still a bit lost here.  Certainly the 17-40 @17mm would "look" different than the 28-105 @ 28mm?

sp

see:http://www.usa.canon.com/eflenses/pdf/spec.pdf
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Eric Myrvaagnes
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Whats *effective* focal length?  The lenses I mentioned were both for full frame bodies, yet have the same fov... I'm still a bit lost here.  Certainly the 17-40 @17mm would "look" different than the 28-105 @ 28mm?

sp

see:http://www.usa.canon.com/eflenses/pdf/spec.pdf
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I got curious (I have the 17-40/4L) and checked the specs for a few lenses on the B&H website. Indeed, a 28/1.8 claims 75 degrees coverage, while the 17-40/4L claims 74 to 29 degrees. The 16-35/2.8L claims 108 to 63 degrees, and the 24-105/4L claims "84-23 degrees (with full frame cameras)."

The listed specs for the 17-40 must refer to a reduced sensor camera (like the 10D or 20D), which may be what they expected it to be used most for. On a full-frame camera the 17mm end of the 17-40 should give more than 100 degrees.

Yes, the 17mm does look much wider on an FF camera.

Eric
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DiaAzul
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Quote
I got curious (I have the 17-40/4L) and checked the specs for a few lenses on the B&H website. Indeed, a 28/1.8 claims 75 degrees coverage, while the 17-40/4L claims 74 to 29 degrees. The 16-35/2.8L claims 108 to 63 degrees, and the 24-105/4L claims "84-23 degrees (with full frame cameras)."

The listed specs for the 17-40 must refer to a reduced sensor camera (like the 10D or 20D), which may be what they expected it to be used most for. On a full-frame camera the 17mm end of the 17-40 should give more than 100 degrees.

Yes, the 17mm does look much wider on an FF camera.

Eric
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Someone is possibly mixing up their horizontal, vertical and diagonal angle of views.

The diagonal angle of view of the 17-40mm lens is 104° - 57°30' which is just shy of the 108-63 you quote for the 16-35mm. Where B&H get 74 to 29 degrees is anybodies guess as it is neither 1.6x or 1.3x smaller than the recognised figures.
 « Last Edit: January 13, 2006, 01:13:45 PM by DiaAzul » Logged

David Plummer    http://photo.tanzo.org/
jani
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Someone is possibly mixing up their horizontal, vertical and diagonal angle of views.

The diagonal angle of view of the 17-40mm lens is 104° - 57°30' which is just shy of the 108-63 you quote for the 16-35mm. Where B&H get 74 to 29 degrees is anybodies guess as it is neither 1.6x or 1.3x smaller than the recognised figures.
See the original link to the Canon-supplied PDF spec sheet. That's where the numbers come from.

The numbers are for the horizontal angle of view, IIRC.

And yes, the 17-40mm lens was marketed as Canon's "first digital lens", IIRC, at a time when Canon hadn't launched the 1Ds.
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Jan
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