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Visible exposure stepping when zooming on EOS7D

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Kenneth Scicluna
Visible exposure stepping when zooming on EOS7D
on Mar 5, 2010 at 6:58:16 pm

Hi

We've noticed that on an EOS 7D, with a Canon 18mm-200mm zoom, with the camera set on Manual, zooming in or out while shooting video causes the image to go increasingly brighter or darker.

Well, we would have expected that to happen, since the lens's max aperture ranges from f/3.5 to f/5.6. What we can't explain is that the exposure shift happens in distinct steps, which means that we cannot use this camera for any shoot that requires zooming in or out.

Has anyone else experienced this? Better still, has anyone managed to fix this?

thanks
k


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Lance Bachelder
Re: Visible exposure stepping when zooming on EOS7D
on Mar 5, 2010 at 7:15:12 pm

Is white balance on auto? Have you tried zooming with a pro lens like 70-200L? The 18-200 is a consumer lens so I would look there first. There may be another internal setting on. Haven't seen this with any lens but I don't do a lot of zooming during a take.

Lance Bachelder
Southern California



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Kenneth Scicluna
Re: Visible exposure stepping when zooming on EOS7D
on Mar 5, 2010 at 7:24:14 pm

White balance was set on daylight.

Unfortunately don't have access to L lenses...


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Lance Bachelder
Re: Visible exposure stepping when zooming on EOS7D
on Mar 5, 2010 at 7:39:04 pm

Do you live near a pro photo store like a Samy's? You could always bring your camera in and ask to try a lens out. Just curious if it's the lens or a defective 7D?

Lance Bachelder
Southern California



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Lance Bachelder
Re: Visible exposure stepping when zooming on EOS7D
on Mar 5, 2010 at 7:16:34 pm

Is white balance on auto? Have you tried zooming with a pro lens like 70-200L? The 18-200 is a consumer lens so I would look there first. There may be another internal setting on. Haven't seen this with any lens but I don't do a lot of zooming during a take.

Lance Bachelder
Southern California



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cowcowcowcowcow
Robbie Carman
Re: Visible exposure stepping when zooming on EOS7D
on Mar 5, 2010 at 7:51:31 pm

your most likely seeing the result of electronic aperture control employed by the camera. Unlike a lens with manual aperture control you'll often get stepping as you point out on a lens with a variable aperture. Not sure of what the mm points are for that lens but there are specific points along the focal range that the aperture has to be so again thats why you're seeing that snap to an aperture.

With photos this is no big deal cause you'll zoom take a photo and zoom again and take another photo and you'll never notice it. But if you're zooming while recording video you'll most certainly notice it.

Your best choice as Lance points out is to get a constant aperture lens. Even if you don't want to step up to the 70-200mm F/2.8 the 70-200mm f/4 and f/4 IS are also fantastic.

If thats not an option you could also find a an old nikor lens that has manual aperture control. Or don't zoom!

Robbie Carman
----------------
Colorist and Author
Check out my new Books:
Video Made on a Mac
Apple Pro Training Series DVDSP
From Still To Motion





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Jonathan Ziegler
Re: Visible exposure stepping when zooming on EOS7D
on Mar 5, 2010 at 9:45:36 pm

Do you have access to a full manual lens? Just to eliminate the sensor from the possible problems.

Jonathan Ziegler
http://www.electrictiger.com/
520-360-8293


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DV Dude
It's a bug with both 7D and 5D
on Mar 6, 2010 at 12:16:53 am

This exposure shift is a "bug". It happens on both the 5D and 7D with any lens that has a variable aperture.

We tested it with lenses from Canon, Sigma and Tamron and happened with all of them. It happens in both Auto and Manual mode. It happens even if you stop the lens down to f/8 or f/11.

Canon says the camera is functioning properly as they designed it :)

The only solution is to use a fixed aperture lens, or not to zoom.

Terry Steyn
The DV Shop
Toronto, Canada


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Kenneth Scicluna
Re: It's a bug with both 7D and 5D
on Mar 8, 2010 at 9:01:54 am

Cheers to all for the info.

In the meantime we tested the camera with a Sigma 10mm-22mm zoom with max aperture constant at f/3.5 and the problem did not manifest itself.

k


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