wjk
Newbie
The Canon 7 manual says that when you mount or dismount a lens of 85 mm or greater, that you should be sure to have the lens set on the "nearest footage setting." What does this mean? Thanks.
back alley
IMAGES
closest focus/minimum focus distance
jlw
Rangefinder camera pedant
And the reason they tell you to do that is that while shorter Canon RF lenses have a focusing cam (the part at the back of the lens that contacts the roller on the coupling arm at the top of the lens mount) that goes all the way around the back of the lens, the 85mm and longer lenses have just a tab at the top.
When you set the lens to its closest focusing distance, the tab is pulled all the way forward into the lens barrel, so it doesn't contact the roller as you screw in the lens. If you have the lens set to infinity, the tab sticks out a significant distance (you can see this by looking at the back of the lens) and as you screw in the lens, the tab repeatedly presses the coupling arm in as the tab goes by it, and then lets it snap back out again.
I guess they felt this repeated "banging" could eventually impair rangefinder accuracy, although I admit that I'm not very conscientious about setting my lenses to closest distance while mounting them and have never had any problems.
When you set the lens to its closest focusing distance, the tab is pulled all the way forward into the lens barrel, so it doesn't contact the roller as you screw in the lens. If you have the lens set to infinity, the tab sticks out a significant distance (you can see this by looking at the back of the lens) and as you screw in the lens, the tab repeatedly presses the coupling arm in as the tab goes by it, and then lets it snap back out again.
I guess they felt this repeated "banging" could eventually impair rangefinder accuracy, although I admit that I'm not very conscientious about setting my lenses to closest distance while mounting them and have never had any problems.