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I just purchased the Canon 40mm pancake lens for my 40D. I noticed that the barrel of the lens extends when focused close. Do I need to be worried about making sure the barrel is retracted before turning off and storing the camera?

Because this lens is focus by wire, turning the focus ring when the camera is off / asleep does not do anything. The only way to retract the lens is to focus on something at infinity or set it to manual focus and turn the ring before it turns off or goes to sleep. This seems like a lot of work and something I am going to frequently forget.

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All AF lenses are "focus-by-wire"... Also, Canon should return the lens to the home position when it's turned off. Surprising that don't do that. – BBking Nov 28 '12 at 0:52
I've been shoving it into my camera bag fully extended for weeks now, still works :P – dpollitt Nov 28 '12 at 2:39
@BBking -- All? Even if that is true of all Canon EF/EF-S lenses, it's not exactly universal. There are an awful lot of Nikon, Pentax and Minolta/Sony lenses (as well as third-party lenses) in which the manual focus ring is directly connected to the helical focus mechanism (and sometimes there's a mechanical clutch). That is true of screw-drive lenses as well as some older micromotor designs. – user2719 Nov 28 '12 at 3:18
@BBking - again wrong. Nikon has just begun to replace their all-mechanical designs recently (the 50mm and 85mm f/1.4 & f/1.8 AF-S models are new in the last couple of years; the f/2.8 wide angles at 20, 24 and 28mm are still all-mechanical, as is the 35mm f/2). That's just in the Nikon line. Both Tamron and Tokina (along with the Tokina/Pentax DA* lenses) have current models that engage mechanical manual focus with a push-pull clutch, even if autofocus is signal-driven (rather than linkage-driven) from the body. AF doesn't imply no mechanical manual focus, even with USM-type lenses. – user2719 Nov 29 '12 at 14:42
Because even when focusing manually, with an FBW lens the focus collar is an electrical switch that causes the lens' focus motor to move the lens the specific amount indicated by the specific amount the focus collar is moved. There is no mechanical connection at all between the focus collar and the focus elements in an FBW lens. With other lenses, the focus elements move when the focus collar is twisted, even if the lens is not attached to the a camera. – Michael Clark Nov 27 at 5:09

2 Answers 2

up vote 3 down vote accepted


I imagine you'll be storing it in a bag or somewhere its not going to get bumped around, so there's no reason a lens needs to be in a special configuration for storage, other than to minimise space, but its not exactly taking up a lot of space either, even fully extended.

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Maybe. Retracted will almost always be safer than extended.

There is another lens, the EF 50mm f/1.4, that is well known to be more susceptible to damage from a relatively minor side impact to the front of the lens when the lens is focused to a closer distance and the front of the lens is extended out a little. When the lens is focused to infinity and the focus collar is fully retracted it is much less likely to be damaged because the tabs that engage the helical collar that effects the movement of the focus elements inside the lens are not parked at the weak point of the collar.

The original EF 24-70mm f/2.8 L is another lens known to suffer more from relatively minor bumps to the front of the lens when the barrel is extended. One of the key centering adjustments is located near the front element and can be moved out of adjustment. Since that particular lens is most extended at 24mm and most retracted at 70mm, it is much safer to keep the focal length set at 70mm when not in use so that the front tube is protected by being retracted into the main tube of the lens.

Pretty much any lens that extends for some settings and retracts for others will be more secure when retracted. How much that difference is will vary on a lens-to-lens basis depending on the individual design of each lens in question. Note that pretty much all compact cameras equipped with a permanently attached zoom lens retract the lens and park them in the shortest position during the shutdown process after you turn them off. This is deemed important enough that many of them also retract the lens after a period of inactivity or even if the battery power drops too low (so as to be sure the lens is retracted before there is not enough power left in the battery to retract the lens).

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