Why do lenses need a battery in the camera to manually focus?

[fugu82]

Just throwing this out as a query to the many sages out there. Why do lenses need a battery in the camera to manually focus?

Found this out when I was playing with a TS-E 24 on my [very new] 7D2, which had it's battery in the charger. I thought there was something wrong with the lens; found out that any of my lenses [whether manual or AF], on either of my Canon bodies would not appear to focus through the viewfinder unless a battery was physically in the camera, even though the camera wasn't turned on.

Not a problem or complaint - just curious as to why this is. ???

 

[Don Haines]

focus by wire.....

 

[pierlux]

Well, EF stands for Electro Focus, so any EF lens, even those without autofocus capability, need an electrical connection to the camera to drive the motor inside. TS lenses are no exception I suppose.

 

[privatebydesign]

Something amiss there, maybe the 7D MkII has something in the transmissive part of the focus system that makes the image look out of focus.

Certainly my 1Ds MkIII's, and every other EOS camera I have owned, don't behave like that, they manually focus just fine with no battery in the camera be that manual focus (17 TS-E) or AF (11-24).

Now the focus by wire lenses won't behave like that (STM lenses and a few exotics like the early superteles and the 85 f1.2 for example), but they don't focus even when there is a battery but the camera is turned off.

 

[privatebydesign]

Well, EF stands for Electro Focus, so any EF lens, even those without autofocus capability, need an electrical connection to the camera to drive the motor inside. TS lenses are no exception I suppose.

No, that is incorrect. Most of my AF EF lenses manually focus on a camera with no battery in it (11-24, 24-70, 70-200, 50 f1.4, 300 f2.8IS etc) but the 15mm f2.8 fisheye does not, it is not a USM lens, USM lenses allow full time manual focus control (the 50 is a Micro USM rather than a ring type but it still allows FTM focus. TS-E lenses are not 'EF' lenses, they are TS-E lenses, a small subdivision of the Canon lens stable, they have no focus motors at all and do not need power to focus, they do need power to operate the aperture though.

 

[Mt Spokane Photography]

Well, EF stands for Electro Focus, so any EF lens, even those without autofocus capability, need an electrical connection to the camera to drive the motor inside. TS lenses are no exception I suppose.

No, that is incorrect. Most of my AF EF lenses manually focus on a camera with no battery in it (11-24, 24-70, 70-200, 50 f1.4, 300 f2.8IS etc) but the 15mm f2.8 fisheye does not, it is not a USM lens, USM lenses allow full time manual focus control (the 50 is a Micro USM rather than a ring type but it still allows FTM focus. TS-E lenses are not 'EF' lenses, they are TS-E lenses, a small subdivision of the Canon lens stable, they have no focus motors at all and do not need power to focus, they do need power to operate the aperture though.

Yes, only STM or focus by wire lenses need a battery in the camera to focus. However, newer cameras with a transmissive lcd need power to see thru the viewfinder.

A TS-E lens does not need power to focus, its fully manual.

 

[neuroanatomist]

On cameras with a transmissive LCD, power is required for LCD to be 'clear' and removing the battery significantly dims the VF. But, except for the lenses mentioned (STM and other rare focus-by-wire lenses like the 85L), power isn't needed for focus. You can see the distance window move when turning the focus ring with the lens not mounted on a camera.

 

[neuroanatomist]

To close the aperture blades.

And despite there being no AF motor, the camera still needs to "talk" to the lens, find out what focal length it is, etc.

Huh?

Oh, never mind. Typical dilbert cluelessness.

 

[j-nord]

The 50 f1.8 STM not only needs a battery, the camera has to be on. This is annoying when the lens is extended and the camera is off. As some have mentioned, USM lenses can be focused with out baterries.

 

[pierlux]

Well, EF stands for Electro Focus, so any EF lens, even those without autofocus capability, need an electrical connection to the camera to drive the motor inside. TS lenses are no exception I suppose.

No, that is incorrect. Most of my AF EF lenses manually focus on a camera with no battery in it (11-24, 24-70, 70-200, 50 f1.4, 300 f2.8IS etc) but the 15mm f2.8 fisheye does not, it is not a USM lens, USM lenses allow full time manual focus control (the 50 is a Micro USM rather than a ring type but it still allows FTM focus. TS-E lenses are not 'EF' lenses, they are TS-E lenses, a small subdivision of the Canon lens stable, they have no focus motors at all and do not need power to focus, they do need power to operate the aperture though.

I've learned another thing today, I love this community! Waking up this morning I tried myself with TS-E 24 and both 7D2 and 5D2. Ironically, the transmissive LCD thing had already come out shortly before for a different reason in another thread - it seems I'm a bit obtuse - so I removed the battery twice in a few hours:
http://www.canonrumors.com/forum/index.php?topic=29668.msg592579#msg592579

 

[fugu82]

Thanks all for taking the time to clear this up for me. I didn't know diddly-squat about transmissive LCDs.