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canon 50mm STM lens, manual focus

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Eric Mac
canon 50mm STM lens, manual focus
on Jun 3, 2016 at 2:57:30 am

Hey, I think I am posting in the correct spot for this.
Heres whats up, I recently got a EF 50mm STM as my first lens for my EOSM. Just kinda starting out and from my research both of these are viable options. Now I have been messing with the manual focus for pulling focus and what. If I put a piece of tape on the focus ring and barrel at focus point "A", manually shift to the next focus point, mark it similarly (point "B"). Then shift back to point A, my focus will be off.
My question is, is this normal to not be able to accurately pull focus with this lens? Or is this a problem?
I called canon support... they told me that they had never heard of anybody having this problem. And to buy a cine lens if I want to shoot movies!
Thanks.
Eric M


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Aaron Star
Re: canon 50mm STM lens, manual focus
on Jun 3, 2016 at 8:26:23 am

You need to determine if you can run old school still film lens on that camera. The old school film lens will have a physical focus gear and iris settings. You can feel the resistance in the focus ring when you have a manual ring. Film/Cine lens have a more accurate stop or light transmission, sharper optics, better optics coating, and better distance markings for pulling focus like you are trying to do.

The kit lens for your camera is likely automated or servo controlled, and not returning to the exact position you have marked. Most kit lenses are pretty loose in the accuracy of manufacture, and rely on the electronics to keep adjusting the lens until the camera see what it wants in focus.

There are a variety of focus pulling add-ons out there. Try and find one that has physical stops, because operating and pulling focus at the same time is hard, and almost impossible to hit your mark on the lens due the angle.


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Eric Mac
Re: canon 50mm STM lens, manual focus
on Jun 4, 2016 at 2:18:45 am

Ok, So short of it is, lens is fine for photography but lousy for video.
I can run the EF and the EF-S lenses with my adaptor, will look to see what I can find.
Do you know if the old lenses (late 80's to 90's) that have auto focus are mechanical with the manual focus portion?
Thanks for your help.
Eric M


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Aaron Star
Re: canon 50mm STM lens, manual focus
on Jun 5, 2016 at 4:36:19 pm

You will habe to just do some tests on your own, but my guess is lenses from that Era used a servo to turn the manual gears. Today they do it the opposite way, and the ring tells the servo how much to turn.


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