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Manual Aperture Control Issue While Shooting Video

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Steve Pender
Manual Aperture Control Issue While Shooting Video
on May 27, 2013 at 6:51:36 pm

I have a 60D with an 18-135 mm 3.5 lens. I've set the camera for manual exposure. When I have the lens full wide, the aperture reads 3.5, when I zoom in tighter, the aperture decreases. Seems like there's something automatic going on that I don't understand. If I'm on manual exposure, shouldn' the aperture remain at 3.5 until I change it? Many thanks for any ideas.

Steve Pender
Family Legacy Video, Inc.
http://www.familylegacyvideo.com


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Ryan Holmes
Re: Manual Aperture Control Issue While Shooting Video
on May 28, 2013 at 1:37:01 pm

If you have the kit lens that came with the 60D then this is a property of the lens, not the camera. Your camera is fine and functioning normally.

I'm guessing that your lens is 18-135mm f/3.5-5.6. That means that at 18mm (very wide) your aperture will be at 3.5. As you zoom in towards 135mm your aperture will close up. If you reach 135mm your aperture will be 5.6. In the simplest terms it's very costly to build a lens that stays at a given aperture as you zoom in because it's hard to transmit light as efficiently as you zoom. So typically concessions are made to keep the cost of the lens down. Now if you want a lens that stays at f/2.8 throughout the zoom range then you're going to pay for it (cf - http://www.amazon.com/Canon-70-200mm-2-8L-Telephoto-Cameras/dp/B0033PRWSW/ ).

From Wikipedia:
Zoom lenses typically have a maximum relative aperture (minimum f-number) of f/2.8 to f/6.3 through their range. High-end lenses will have a constant aperture, such as f/2.8 or f/4, which means that the relative aperture will stay the same throughout the zoom range. A more typical consumer zoom will have a variable maximum relative aperture, since it is harder and more expensive to keep the maximum relative aperture proportional to focal length at long focal lengths; f/3.5 to f/5.6 is an example of a common variable aperture range in a consumer zoom lens.

Here's some additional info for you to read up on:
http://www.bhphotovideo.com/indepth/photography/tips-solutions/variable-ape...

http://en.wikipedia.org/wiki/Aperture

http://en.wikipedia.org/wiki/Lens_speed

Ryan Holmes
http://www.ryanholmes.me
@CutColorPost


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Steve Pender
Re: Manual Aperture Control Issue While Shooting Video
on May 29, 2013 at 10:45:07 pm

Ryan,
Many thanks!

Steve Pender
Family Legacy Video, Inc.
http://www.familylegacyvideo.com


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