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Author Topic: Canon 24-105mm L IS f4 not a true 105mm  (Read 2579 times)

WXyz

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Canon 24-105mm L IS f4 not a true 105mm
« on: September 24, 2010, 05:35:42 PM »

Canon 24-105mm L IS f4 not a true 105mm. Comparing our new 24-105mm L IS f4 to the 100mm f2.8 macro we find the 105 focal length is not as long as the 100 macro and seems to be more around 90mm. Specs indicate this to be so as 24-105mm lists angle of view to be wider than the 100 macro. Anyone else have this experience? Is Canon lying or mistaken?
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Slobodan Blagojevic

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Re: Canon 24-105mm L IS f4 not a true 105mm
« Reply #1 on: September 24, 2010, 06:19:10 PM »

On a theoretical note, your comparison, of course, depends on the accuracy of 100 mm macro itself, i.e., is it really 100 mm. Some macro lenses, especially those with internal focusing, are notorious for changing focal length depending of where the focus is.

WXyz

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Re: Canon 24-105mm L IS f4 not a true 105mm
« Reply #2 on: September 24, 2010, 06:29:14 PM »

S~ Canon Specs say angle of view for the 24-105 is wider than the specs for angle of view for the 100 so Canon's own specs back us up. Also Macro is not IF.
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Slobodan Blagojevic

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Re: Canon 24-105mm L IS f4 not a true 105mm
« Reply #3 on: September 24, 2010, 06:36:48 PM »

It is not about what specs say. What if your macro actually has a 110-115 mm focal length at the focus distance you compared?

AFairley

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Re: Canon 24-105mm L IS f4 not a true 105mm
« Reply #4 on: September 24, 2010, 06:47:31 PM »

Should be easy enough to caclulate the true effective FL by calcuating AOV for a given distance?  Not hard to do with a little trig.
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JeanMichel

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Re: Canon 24-105mm L IS f4 not a true 105mm
« Reply #5 on: September 24, 2010, 07:35:08 PM »

Hi
I have the 24-105, a nice lens. The exact focal length, at whatever setting is not overly important, but if you must calculate and compare, remember that the focal length listed or stamped on the barrel of the lens is only valid when the lens is focused or set at infinity. As you focus on a closer object the focal length is no longer what it was at infinity, it is actually longer than the nominal focal length. Pick up a physics textbook or do an internet search to find out about this delightful subject. :D

Jean-Michel
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bradleygibson

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Re: Canon 24-105mm L IS f4 not a true 105mm
« Reply #6 on: September 24, 2010, 09:30:37 PM »

Marked figures of Canon's (and most small format) gear is +/- 5% (ie. a "100mm" lens can be designed anything from a 95mm to a 105mm and still be called a 100mm).  Posted focal length is only valid for infinity focus (subject to +/- 5%), particularly important with some focus designs (focusing closer can shorten effective focal length).  Nikon's most recent 70-200/2.8 has been singled out as a notable example of this, being reported as wide as 130mm when focused at minimum focus at the 200mm setting.
« Last Edit: September 24, 2010, 11:18:23 PM by bradleygibson »
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Bob Smith

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Re: Canon 24-105mm L IS f4 not a true 105mm
« Reply #7 on: September 24, 2010, 09:52:31 PM »

I have both the 24-105 and the older style (non L) 100mm Macro.  In a quick test (tripod mounted, looked through the viewfinder at a wall across the room) focused at about 25' the angle of view is virtually identical with possibly a tiny nod to the 100mm as having a very slightly wider field of view.

Bob Smith
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stever

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Re: Canon 24-105mm L IS f4 not a true 105mm
« Reply #8 on: September 24, 2010, 11:22:38 PM »

it's quite common for zooms to come up a bit short on focal length, and all lenses have a tolerance on focal length as well as everything else.

the more important issue with the 24-105 is the poor resolution from 90 to 105
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Re: Canon 24-105mm L IS f4 not a true 105mm
« Reply #9 on: September 25, 2010, 03:00:30 AM »

from a pop photo review:
Specifications: 24-105mm (24.60-106.10 tested), f/4 (f/4.12-4.27 tested), 18 elements in 13 groups. Focusing turns 130 degrees counterclockwise. Zoom ring turns 65 degrees clockwise. Focal lengths marked at 24-, 35-, 50-, 70-, and 105mm.
I must have an exceptional copy it's my favorite lens and is as sharp as any zeiss prime I have compared files with (comparison on the same camera)
Marc
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Marc McCalmont

Frodo

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Re: Canon 24-105mm L IS f4 not a true 105mm
« Reply #10 on: September 25, 2010, 04:54:02 PM »

the more important issue with the 24-105 is the poor resolution from 90 to 105

Just got a new 24-105 and tested it against my other lenses.  On a 5D it is as sharp or sharper than my other lenses at the same focal length and aperture.  In particular, it is sharper wide open than my 70-200 at 70 and 100mm and the same when stopped down.  And it is as sharp as my 50mm f1.8.  (And waayyy better than the 28-135 it replaced!).

It may be that 21MP sensors of the most recent cameras show up faults compared to primes, but I'm very happy with this lens.
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sojournerphoto

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Re: Canon 24-105mm L IS f4 not a true 105mm
« Reply #11 on: September 25, 2010, 06:07:19 PM »

Mine is not as sharp on my 1Ds3 as my Zeiss 28 or 35, or my canon 50/1.4 85/1.8 or 100 macro at similar apertures. It really neds f8 to give it's best on thatc amera, whereas 5.6 was fine on the 5D.

Overall, I find it a good and useful lens if I want to carry one lens that I don't mind getting rained on. OTOH, I'm equally likely to carry a 50 only or a Zeiss Ikon, so maybe I should be discounted:)

Mike
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