Focus breathing with the RF 100-500mm

AlanF

Hands. Face. Space.
CR Pro
Aug 16, 2012
7,345
7,146
The 100-400mm II has severe focus breathing, the effective focal length dropping from 400mm to 178mm at its minimum focal distance of 970mm.
Prompted by someone asking if there is focus breathing with the RF 100-500mm, I have calculated the focal length at the mfd from data reported in The-digital-photo site:
Specified Min Focus Distance 35.43” (900mm)
Tested Min Focus Distance (Wide / Long) 38.23” / 47.01” (971mm / 1194mm)
Maximum Magnification (MM) 0.33x

Combining them gives a maximum focal length of 224mm at the minimum focal distance of 1194mm.
 

AlanF

Hands. Face. Space.
CR Pro
Aug 16, 2012
7,345
7,146
I really like shooting the 100–400mm II at 400mm and closest focus distance. I didn't realize I was violating the laws of optics or anything. I just like the pictures.
Quite the reverse, you are faithfully following the laws of optics. If the focal length remained at 400mm as you focussed on an object less than a metre from the front of the lens, the image would be way behind the back of the camera for a lens of fixed length. So, the focal length has to shorten dramatically to allow focussing. Focus breathing is essential for these zooms to focus close up.