That's exactly what I thought. If the results/framing were similar at 12ft and were noticeably different at 1.5ft the 24-105 is exhibiting focus breathing near it's mfd.
"Focus breathing" is how the framing changes as the focus moves in. It looks like a tiny bit of zoom.
I took my 100 f/2.8 non-IS and focused in and out to see for myself just how much the focus breathing is. It is hardly noticeable at the distances you and I were shooting at. The change in framing is something like 3 percent for wide focus swings. It is more noticeable at macro distances.
I've never heard of the term focus breathing either, but it is well known that the 100 mm macro at minimum focus has a field of view equivalent to a 70 mm lens. I think that is breathing, i.e. changing focal length at extreme close focus. However you were at the 24-105's minimum focus of about 1.5 ft which is beyond where the 100 would be affected. So the assumption folks are making is that the 100 macro is correct or "truth", i.e. giving you a 100 mm field of view. Therefore it must be the 24-105 that has reduced its effective focal length. This would explain why your macro's image looks magnified.
The problem is that this so called breathing effect just looks too extreme in your images. A factor of 1.8 on a lens that only close focuses to 1:4 as compared to 1:1 for the macro. The 24-105 is my most used lens and I've never noticed this effect, although I've never specifically tested for it. So, I too am curious as to whats going on.
M Vers wrote:
That's exactly what I thought. If the results/framing were similar at 12ft and were noticeably different at 1.5ft the 24-105 is exhibiting focus breathing near it's mfd.
Yes but MVers, a factor of 1.8 in field of view difference? That seems pretty extreme for a 1:4 lens. Perhaps I can try this tomorrow. I have both lenses and the 100L.
Jeff -- I'm interested in what you find. It seems like if the field of view changes from that corresponding to a 100mm FL to that corresponding to a 70mm FL, then it gets wider, and yet the effect I see in the images I posted is the opposite -- it gets narrower.
I am intrigued by the idea that it's the 24-105 showing too wide a field rather than the 100mm showing one that's too narrow. Maybe tomorrow I'll try something similar with the 24-105 at a different focal length and another lens. I don't have any other macro lenses, though. But it might still be worth trying. Maybe at 35mm compared to my 35/2 at MFD.
Oh, and if the older 100 macro does "breathe" (change angle of view) more than the L (which it seems to me was a comment made by some when they moved from the old to the new), the combination of that with the opposite effect in the 24-105 would easily explain the OP's observation.
M Vers wrote:
Thanks Jess, that pretty much confirms what I've been trying to explain from the beginning.
Yup.
I just played with the 24-105 at 24 and at mid-range FLs and found that it "breathes" in comparable fashion to the behavior at 105. Interesting. Also, although I did the test shots at close to MFD, it does get a bit closer still. If you don't worry about "gee, is my lens really giving me the marked FL?" and just use it, you find that it has a useful close focus reproduction ratio. Nothing like a true macro, but adds to the all around flexibility of this lens.
Focus breathing...something I don't notice as much when I'm relying on AF. Another reason it's good to MF once in a while. Which brings me to the TS-E lenses, but I won't go that far OT right now.
Most zooms seem to widen as you get down to the mfd.
A couple of notable examples are the 70-200 vr2 which is thought to be only about 135mm at its mfd . I think the 70-200/4 IS as much the same issue (maybe not quite so extreme)
One way to resolve ( ) the issue would be to photograph a pair of crossed rulers or measuring tapes at two distances: minimum focus of the zoom and something like five or ten times that distance. Also measure the distance from the wall to the focal plane at camera (look for the symbol with the circle with a line through it). Be sure the camera is aligned with the wall by measuring the triangular distances to the edge of the field of view.
Then put up reduced size images of the complete frames, preferrably with the EXIF intact.
That way we can determine the focal length from the field of view.
I tried it with the 35/2 and the 24-105 at 35, at just about the MFD of the 24-105. The images are identical, so I don't see how the 24-105 can be said to change FL(or whatever) near MFD unless the 35/2 isn't really a 35 which seems unlikely. At the long end, nearer 105, the 24-105 may breathe but I don't have any other lenses at 100mm that will focus as close as the 24-105 does (my 70-200 won't) so I can't try it.
It seems evident that the macro, and it looks like from Photon's post that the L version does the same thing, does more than just allow closer focusing to achieve a 1:1 magnification. It clearly plays with FL/magnification/something as focus distance decreases to achieve 1:1. And the effect doesn't start to happen until fairly close -- in other words, at distances of a few feet the 100mm lenses produce the same images as any other lens at that FL. Up close, though, the macro lenses play some games. I am going to have to research the relationship between magnification and FL. If the 24-105 changes its FL too and they do it oppositely (is that a word?) then it would certainly make for an exaggerated difference.
This is all very interesting. I wish I knew more about lens design and optics!
Tonight I may try the crossed rulers test -- if I can find two rulers!
Thanks to all of you for participating in this exploration of lens physics!
k
Actually I just had a look at the specs on TDP . if you start to compare similar lenses you can see some instances where some lenses must loose a fair bit of focal length at MFD
the 24-105 at MFD (17.7") has a mag of .23x
while
the 24-70L at MFD (15") has a Mag of .29x
now I cant believe the 2.7" closer focus is going to make .06x difference in mag if the 24-105 is still 105mm
Oh and for reference here is the difference between those 2 Nikon 70-200 VR lenses (The mk2 as I said is noted for being well short of 200mm at MFD)
VR1 - 60" mfd = .25x
VR2 - 55.1" mfd = .12x
so the VR2 focuses 4.9" closer but gives quite a bit less magnification at the same time.
Remember all these focal Lengths are at infinity (and even then some lenses dont even make the stated focal length)
beanpkk wrote:
I tried it with the 35/2 and the 24-105 at 35, at just about the MFD of the 24-105. The images are identical, so I don't see how the 24-105 can be said to change FL(or whatever) near MFD unless the 35/2 isn't really a 35 which seems unlikely. At the long end, nearer 105, the 24-105 may breathe but I don't have any other lenses at 100mm that will focus as close as the 24-105 does (my 70-200 won't) so I can't try it.
It seems evident that the macro, and it looks like from Photon's post that the L version does the same thing, does more than just allow closer focusing to achieve a 1:1 magnification. It clearly plays with FL/magnification/something as focus distance decreases to achieve 1:1. And the effect doesn't start to happen until fairly close -- in other words, at distances of a few feet the 100mm lenses produce the same images as any other lens at that FL. Up close, though, the macro lenses play some games. I am going to have to research the relationship between magnification and FL. If the 24-105 changes its FL too and they do it oppositely (is that a word?) then it would certainly make for an exaggerated difference.
This is all very interesting. I wish I knew more about lens design and optics!
Tonight I may try the crossed rulers test -- if I can find two rulers!
Thanks to all of you for participating in this exploration of lens physics!
k...Show more →
It would be less likely for the lens to breathe at 35mm--most zoom lenses do this towards the long end and it occurs at or near a lenses MFD, which would mean under 1ft for most macro lenses. So, in the end, what you're seeing in the above example from the macro is a true 100mm FOV at ~1.5ft and a wider (~70mm?) FOV with the 24-105 at ~100mm. Breathing can only effectively shorten a lenses FL, it can never extend it.
Ian.Dobinson wrote:
someone alot smarter than me should be able to work out from the subject distance and magnifcation what the true focal length is .
Can't do it without measurments, such as I suggested a few posts above yours. I have the macro, but not the zoom, so somebody else will have to do the test and post here.
OK here you go. I don't know how to preserve EXIF through Flickr,, and I don't have any good way to do this on a wall across the room. But here are the close-ups...
5D, approx 17" from the subject on a tripod pointing straight down over a table.
Which brings me to the TS-E lenses, but I won't go that far OT right now.
) the issue would be to photograph a pair of crossed rulers or measuring tapes at two distances: minimum focus of the zoom and something like five or ten times that distance. Also measure the distance from the wall to the focal plane at camera (look for the symbol with the circle with a line through it). Be sure the camera is aligned with the wall by measuring the triangular distances to the edge of the field of view.
