Lens "Magnification"

[Dave Leroy]

I recently bought a Canon 24-105mm zoom lens and decided to compare sharpness to my 100mm Canon macro. When I looked at the images on my laptop, the subject sizes were quite a bit different. The 24-105mm pictures at 105mm had smaller subject size than the 100mm macro.

So today I tried a canon 70-200 at 100, 24-105 at 100 (99 actually) and the 100mm macro. This time the 70-200 had the largest subject size and again 24-105 the smallest.

I would have thought all would be very close to same subject size and therefore same magnification. I tried checking online and got a bit lost in some of the technical details. I am wondering if there is a fairly straight forward explanation for this.

Dave

[arash_hazeghi]

The focal length advertised for a lens is measured at infinity focus, the focal length changes (shortens) for closer focus, especially for a 5X zoom lens like the 24-105. This is called focus breathing.

[Dave Leroy]

Ahh. Interesting. Thanks Arash. I'll google it.

Dave