Ad
Ad
Ad
Pages: [1]   Bottom of Page
Print
Author Topic: angle of view?  (Read 2841 times)
spphoto
Jr. Member
**
Offline Offline

Posts: 56


« on: January 12, 2006, 02:06:37 PM »
ReplyReply

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
Logged
jdemott
Sr. Member
****
Offline Offline

Posts: 434


« Reply #1 on: January 12, 2006, 04:56:23 PM »
ReplyReply

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
Logged

John DeMott
Anon E. Mouse
Full Member
***
Offline Offline

Posts: 197


WWW
« Reply #2 on: January 12, 2006, 05:51:27 PM »
ReplyReply

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

Or

W = 2 arctan (d/2f)
Logged
spphoto
Jr. Member
**
Offline Offline

Posts: 56


« Reply #3 on: January 12, 2006, 06:08:55 PM »
ReplyReply

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

Or

W = 2 arctan (d/2f)
[a href=\"index.php?act=findpost&pid=55889\"][{POST_SNAPBACK}][/a]
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?Huh

sp

see:http://www.usa.canon.com/eflenses/pdf/spec.pdf
Logged
Eric Myrvaagnes
Sr. Member
****
Offline Offline

Posts: 7898



WWW
« Reply #4 on: January 13, 2006, 11:54:40 AM »
ReplyReply

Quote
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?Huh

sp

see:http://www.usa.canon.com/eflenses/pdf/spec.pdf
[a href=\"index.php?act=findpost&pid=55890\"][{POST_SNAPBACK}][/a]
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
Logged

-Eric Myrvaagnes

http://myrvaagnes.com  Visit my website. New images each season.
DiaAzul
Sr. Member
****
Offline Offline

Posts: 777



WWW
« Reply #5 on: January 13, 2006, 12:31:55 PM »
ReplyReply

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
[a href=\"index.php?act=findpost&pid=55928\"][{POST_SNAPBACK}][/a]

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 - 5730' 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
Sr. Member
****
Offline Offline

Posts: 1604



WWW
« Reply #6 on: January 13, 2006, 03:27:24 PM »
ReplyReply

Quote
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 - 5730' 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.
Logged

Jan
Pages: [1]   Top of Page
Print
Jump to:  

Ad
Ad
Ad