I was experimenting comparing my 24-105 at 100mm with my 100mm macro non-L on a subject at minimum focus distance for the 24-105. Obviously the 100 macro can focus a lot closer, but then I couldn't compare the images. Anyway, it looks like the actual focal length of the 100 at that focus distance is ~way~ more than 100mm -- maybe 200? I've been looking for that spec for the 100mm and can't find it. What is, or where might I find, the spec for the actual focal length of the 100mm macro at minimum focus distance?
I took a couple of photos of a subject 15 feet away, and the two lenses (24-105 set at 100mm and the 100/2.8 macro) produce identical images. So something changes in the macro when it starts to focus close.
Is this a characteristic of all macro lenses?
One other question: the focus mechanism on the 100/2.8 is very twitchy (turning the focus ring a tiny bit changes the focus a lot), and there is some play in the mechanism. Does the L version (minus the play perhaps) have pretty much the same situation? I think I would have an easier time focusing at macro distances if the focus mechanism were a little less sensitive.
Yes. As the 100macro is internal focus it will lose some focal length as you get closer to mfd.
If you look at some of the other macro lenses at mfd the front element extends quite some way forward.
I'm sort of confused here...what do you mean by the lens being "way more than 100mm"? The lens may have some breathing when shooting at or just outside macro range, which many lenses do (The Sigma 150 has a lot of this, essentially becoming much shorter in FL as I focus closer). That said, while magnification will increase when shortening focus distance a lens will never become longer in FL. As for the focus ring, it isn't the best but it's manageable. Though I have limited experience with both lenses, the L felt better in this regard. Here is a quote from TDP:
"The focus ring is nicely placed and sized - and is very smooth with no play (even smoother with less play than the original EF 100mm macro). I find the flush-mounted focus ring to be especially useful when fine-tuning manual focus. I can let part of my fingers drag to the side of the ring (on the barrel) to add a variable amount of damping to the movement."
Thanks M Vers. I have talked with optics engineers (I work with a few) about focal length, magnification etc. and don't claim to understand the difference. Certainly the magnification seems much higher with the macro at that distance. The field of view has greatly decreased, call it effective FL increasing or magnification. Whatever the cause, the result seems surprisingly large.
Thanks too for the info about the L. It makes the L more enticing (as if it needed to be! :-) )
beanpkk wrote:
Thanks M Vers. I have talked with optics engineers (I work with a few) about focal length, magnification etc. and don't claim to understand the difference. Certainly the magnification seems much higher with the macro at that distance. The field of view has greatly decreased, call it effective FL increasing or magnification. Whatever the cause, the result seems surprisingly large.
Thanks too for the info about the L. It makes the L more enticing (as if it needed to be! :-) )
k
The 24-105 may have quite a bit of breathing as well, especially at shorter distances and MFD. Try shooting something further away with both lenses.
Bruce Sawle wrote:
I believe the issue is with the magnification of the two lenses. The macro is a 1/1 magnification while the 24-105 is not.
The macro is only 1:1 at its closest distance, not at the distance the OP was shooting at.
The 24-105 closest focusing distance is 0.45 metres (1.48 feet). At that distance, a 100 mm lens (whether zoom or prime or macro) will have a 1:3.5 magnification (or 'minification' if you prefer).
beanpkk wrote:
100mm macro ....., on Flickr
24-105 set to 96mm focal length: on Flickr
Thanks for posting. Unfortunately you stripped off the EXIF information (probably by mistakenly using "Save to Web" or not ticking the appropriate box when doing so).
Monito wrote:
The macro is only 1:1 at its closest distance, not at the distance the OP was shooting at.
The 24-105 closest focusing distance is 0.45 metres (1.48 feet). At that distance, a 100 mm lens (whether zoom or prime or macro) will have a 1:3.5 magnification (or 'minification' if you prefer).
At that distance the 24-105 is 1:4:5 magnification that along with focus breathing would cause the mismatch.
Lens manufacturer focal length labels are not 100% accurate, there being about +/- 5% leeway traditionally allowed. However that and focus breathing would not be enough to account for the difference observed by the OP.
Since you're getting closer to the subject with a macro lens, the image would certainly appear larger or closer. If taken from the same distance, both should produce similar images, as Monito's test showed.
Vatche wrote:
If taken from the same distance, both should produce similar images, as Monito's test showed.
Again, not necessarily. If the OP based his test off of the 24-105's MFD it could be skewed due to lens breathing, which would result in a wider AOV for the 24-105.
M Vers wrote:
Again, not necessarily. If the OP based his test off of the 24-105's MFD it could be skewed due to lens breathing, which would result in a wider AOV for the 24-105.
I can assure you that focus breathing is not sufficiently great with the 100 mm non-IS macro that would account for the difference observed by the OP.
I suspect that there is a much larger discrepancy in the OP's testing.
Monito wrote:
I can assure you that focus breathing is not sufficiently great with the 100 mm non-IS macro that would account for the difference observed by the OP.
I suspect that there is a much larger discrepancy in the OP's testing.
Read what I typed again. I'm not talking about focus breathing with the 100 macro, I'm talking about focus breathing with the 24-105. The macro would show breathing further towards it's MFD, which is considerably closer than the 24-105's.
M Vers wrote:
Read what I typed again. I'm not talking about focus breathing with the 100 macro, I'm talking about focus breathing with the 24-105.
I don't have that zoom, but it is not noted for focus breathing the way the 100 mm macro is, so I would expect less, not more, focus breathing.
Even if it were comparable it would still not account for the discrepancy, even if both lenses breathed in the opposite direction.
The first suspect is the OP's test.
I hope that someone else who owns both lenses will do a test themselves. Or other lenses in that format, such as the 100 mm f/2 to compare with the macro, since (for whatever reason) it is the macro that the OP suspects rather than the zoom.
OK, rather than arguing over unknowns lets propose this:
OP, set up your camera on a tripod and set an object as close as you can get it to the 24-105 at 100mm (should be around 1.5ft) then perform a comparison from there. Then, move the object to about 10ft or so and perform another.
Interesting discussion here. Perhaps one of you could explain "focus breathing". I don't think I've heard that term before.
M Vers: pretty much what you suggest is what I did. The tripod was set at very very close to the MFD of the 24-105 set at 100mm (I actually missed it, and EXIF reported 96). Without moving the camera I took photos of the same object with the 24-105 and the 100mm f/2.8 macro. I also set up the tripod about 12 feet from some objects across the room, and took photos with the same two lenses. Across the room, the images are identical.
If we take the 24-105 image as the "truth" for a 100mm image at that distance, then the 100mm macro image has been subjected to greater magnification. Since the magnification of the lenses is the same at 12 feet, then somewhere between 12 feet and 1.5 feet (MFD of the 24-105), the macro lens starts to add magnification. I don't know enough optics to know of that involves a change in effective FL, or just something to do with focusing or something else. I think Monito's example above shows that a given FL produces a given image size. I always thought that macro lenses produced their 1:1 magnification by getting close enough to allow that to happen, but apparently they (at least the 100/2.8) do some optical maneuvering too.
