Stupid question about Canon Lens in Manual Focus mode

[themos]

Hello, 

I  am using a non-LiveView Canon EOS 20D camera with a Canon 200mm f/2.8LII lens. To focus it, I need to take one exposure after another as there is no Live View feed, either on-camera or through USB cable. I put the lens in MF-mode and use the focusing ring of the lens. The actual focusing is done by an internal motor and the focusing ring is not mechanically driving the focusing mechanism but senses which direction the user wants instead. It is my impression that moving the focusing ring is only effective when the shutter button is half-pressed. This is because I tried to change the focus by turning the focusing ring between exposures without the shutter button being held  and it didn't seem like i was making any difference, judging by the appearance of stars in subsequent exposures.  Doing the shutter thing while adjusting the focusing ring is really cumbersome so I would like to know if anyone knows for ure what the correct procedure is. 

The manual manages to be slightly ambiguous, I can't copy and paste the text from it because Canon, in their infinite wisdom made the PDF protected (why, oh why...etc). But it's the PDF you can get from here

http://www.canon.co.uk/support/consumer_products/products/cameras/ef_lenses/fixed_focal_length/ef_200mm_f28l_ii_usm.aspx?type=manuals&language=

[happy-kat]

Does your Canon model support back button focus?

This if it does support it this separates focus from shutter which I find really useful.

[happy-kat]

page 142 of the manual for that camera, I use option 3

manual link

Have one EF USM lens here and don't notice what you are saying. The only that has to be on is the camera to use the lens as it's electronic fly by wire focus.

[StuartJPP]

The Canon 200mm f/2.8 L II lens should definitely allow focus in manual mode when not metering (half press of the shutter) as it is a USM motor.

Also since it is USM you can also adjust focus in auto mode at any time as well but you would have to switch it to manual before exposing otherwise it will try to auto focus...or do as above and set the camera to back button focus mode.

The only lens I have got that doesn't allow adjusting focus in manual mode without metering is the Canon 40mm f/2.8 STM pancake lens as it is focus by wire and the camera needs to be metering to control the motor.

[happy-kat]

Can't say I have noticed that with my 40mm pancake, will try it later. 

[StuartJPP]

17 minutes ago, happy-kat said:

Can't say I have noticed that with my 40mm pancake, will try it later. 

In live view it will allow focus all the tims because it is metering but if not in live view it will only allow focusing for about 3 seconds after half-pressing the shutter.

[themos]

Thanks to all, some interesting lacunae there!

 

[happy-kat]

Just tested my two lenses.

The USM lens will manual focus straight from turning the camera on. EF 85mm f1.8 USM.

The STM lens does need a brief shutter press to enable manual focus and back button focus means I won't actually fire the shutter by mistake. Thought I ought to test that as it hadn't caught me out yet but not the sort of thing you want to trip up at night, thanks for the heads up.

[StuartJPP]

The only real issue is if you ever want to use an STM (or other focus by wire) type lens on a CCD camera then you can't focus it, just something to be weary about. Coupled to a Canon camera there won't be a problem.

[happy-kat]

Update

Used the 40mm pancake last night. Camera is set to BBF and manual mode and manual focus, connected to DSLR Controller on my android tablet. I did not press the shutter button once and the focus ring stayed operational. Once happy with focus moved switch to auto focus and that was that focus was locked, job done.