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Old Jan 18, 2005, 9:23 PM   #1
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I just got a canon 100-300 usm lens and I was under the impression that I could manually focus the lens while in the auto mode. The instructions sent to me are for this lens and they state that Do not touch the manual focusing ring on the lens during auto focus" Can someone explain?????? Im sure I read that I did not have to switch over to M from AU.
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Old Jan 18, 2005, 9:45 PM   #2
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If the instructions for it say don't, I wouldn't. :-).


There are seversal models/versions of that ef 100-300usm around.
Even though the ef 100-300 usmhas an early design of thefast USM motor, that sounds like it has a gear or two in thedrive somewhere. Forcing a gearwould be disaster.

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Old Jan 18, 2005, 10:11 PM   #3
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Thanks, I think I wont risk it
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Old Jan 19, 2005, 3:35 AM   #4
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How do you find the lens so far Alady?

Are you happy with it? Is it better then your older 90-300?!
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Old Jan 19, 2005, 6:58 AM   #5
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If it looks like this and the part number is 2565A003 Then it is equiped

with a USM ring style motor which will provide you with full time manual over ride

If the model number is different it may not have a ring style motor

which would mean you must switch to manual focus. Lets see some more

wonderful shots from " Down Under".


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Old Jan 19, 2005, 7:36 AM   #6
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redundo wrote:
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How do you find the lens so far Alady?

Are you happy with it? Is it better then your older 90-300?!

Much better than the 90-300mm, richer contrast and being so quiet has helped with bird shots. I only got it today but have taken 200 photos already in between housework, my job and child:-)
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Old Jan 19, 2005, 7:37 AM   #7
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Tomsch wrote:
Quote:
If it looks like this and the part number is 2565A003 Then it is equiped

with a USM ring style motor which will provide you with full time manual over ride

If the model number is different it may not have a ring style motor

which would mean you must switch to manual focus. Lets see some more

wonderful shots from " Down Under".


It looks pretty much the same but Im not willing to risk it, I dont mind changing it to manual anyway.:-)
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Old Jan 19, 2005, 8:19 AM   #8
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Actually, there is an interesting aspect to your quote. IT doesn't say "switch to manual focus before changing the focus manually." It says (to my reading) "don't change the focus while the camera is focusing." Those are different things entirely.

While full time manual override is the ultimate, being able to do it while it isn't focusing is still handy.

I didn't know there were USM lenses that didn't have full time manual override, so this is good to know.

I wouldn't be surprised if Cannon has a toll-free number for customer support. You might try giving them a call (with the lens and box handy) and see what they say.

Great avatar, btw. Very nice.

Eric
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Old Jan 19, 2005, 9:37 AM   #9
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Tomsch: where did you find that part number on the 100-300USM, I've looked all over mine and can't find one.

Eric S: There are 2 kinds of USM the fast ring USM (an old versionwas in the 100-300) and a stepperUSM which is on many of the new inexpensive lenses like the 75-300.

Withthe ring USM the lens body itself is part of the motor, no gearing.Very fast and very quiet).

The stepper USM is basically a separate USM motor and some gears transferring motion to the lens. Not so faston the focusing.

I just watched my old 100-300 lens focus, and while it is focusing the manual focus ring does not move. I tried to move it while the lens was focusing and while it moved it did not seem to be connected to the lens, as soon as the lens was focused turning the manual focus ring shifted the focus point again. (best on one_shot, I had the camera on ai_servo and every time I manually altered focus it got mad and refocused:lol: )

On the 75-300 the manual focus ring spins while the lens is focusing, and it is bad mojo to impede it. :-)

I'm trying to dig up the instructions for that lens to see what they say about manual focusing, but it must have been 15 years ago when I originally bought it not sure where they would be.
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Old Jan 19, 2005, 10:42 AM   #10
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Can't find my original docs but did find this EOSdoc info page for the original lens made in 1990:-)http://eosdoc.com/manuals/lens/EF100-300USM/

Thisinfo may not be valid for the newer models of the lens.



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