angle of view? Options

[spphoto]

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

[jdemott]

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

[Anon E. Mouse]

Angle of view = 2 acrtan (dimension of image plane / 2 x effective focal length)

Or

W = 2 arctan (d/2f)

[spphoto]

Angle of view = 2 acrtan (dimension of image plane / 2 x effective focal length)

Or

W = 2 arctan (d/2f)

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

[EricM]

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

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

[DiaAzul]

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

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.

[jani]

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.