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7D brightness shift even when in fully manual

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joel jackson
7D brightness shift even when in fully manual
on Apr 6, 2010 at 11:08:18 pm

Hey cows,

I just got my 7D yesterday and have been shooting video all night and day trying to work out the controls. I have figured out how to get everything fully manual but I am still getting brightness shifting when zooming in and out. The camera is set on M, AWB is off, I use the "*" key to lock the f-stop and everything seems hunky dory until I zoom in or out. At that point the Expo. Comp/AEB decides to adjust itself. Even if my wheel is set to lock it still changes when I zoom in and out.

I'm using a 28-135 ultrasonic EF canon lens with the image stabbilizer and auto focus turned off. I can't find the answer in the instruction book. If I listen closely to the camera when in full manual mode I actually hear something changing inside the camera when I zoom in and out when everything is supposedly in manual.

I'm sure this is a really easy fix but super newbie boy can't seem to figure it out. Any ideas?

Joel



Joel Jackson
http://www.creativebloc.com/port.html


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DV Dude
Re: 7D brightness shift even when in fully manual
on Apr 6, 2010 at 11:27:29 pm

It's a "bug." Any lens (Canon, Sigma, Tamron, etc) with a variable aperture will produce this when zooming, even if you stop down to f/8.

The only solution is to either not zoom when in movie mode, or to buy lenses with a constant aperture (i.e f/2.8, f/4).

This happens on the 5D as well.

Terry Steyn
The DV Shop
Toronto, Canada
http://www.dvshop.ca



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joel jackson
Re: 7D brightness shift even when in fully manual
on Apr 6, 2010 at 11:34:24 pm

Wow, that's great. I'll tell my client next shoot that we can't zoom (lol) they will get a kick out of that one.

What lens do you recommend at a medium price point with fixed aperture? I'd think to get the most out of the lens it would be a fairly open aperture but 2.8 seems like it may be to open.

Your thoughts?

Any firmware updates on the horizon?

Thanks,
Joel

Joel Jackson
http://www.creativebloc.com/port.html


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DV Dude
Re: 7D brightness shift even when in fully manual
on Apr 7, 2010 at 1:51:11 pm

Lens to recommend - for the cropped sensor cameras, that's tricky because they all have variable apertures except for a few, like the Tamron 17-50 f/2.8 and Canon 17-55 f/2.8 IS. Both are good lenses. But you're not going to get any range and a fixed aperture unless you go up to the Canon 24-105 f/4 L IS lens (over $1000), which is the kit lens for a 5D.

As for firmware updates, I doubt it, since it hasn't happened yet.

DV Dude
The DV Shop
Toronto, Canada
http://www.dvshop.ca


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Jonathan Ziegler
Re: 7D brightness shift even when in fully manual
on Apr 6, 2010 at 11:37:08 pm

If it's the lens I'm thinking of it has an fstop range of something like f3.5-5.6, right? What's happening is during a zoom, it's stopping the lens as you zoom. You need a lens with a fixed f-stop during zoom or it will stop down during zoom. It's because the lens is for photography where that feature won't be noticed, but will be during video. The lens is working as designed, but not as expected. If you need to zoom during a shot, you may be able to get away with a steady f-stop above f5.6, but I haven't tried that.

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


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joel jackson
Re: 7D brightness shift even when in fully manual
on Apr 6, 2010 at 11:45:19 pm

The funny thing is that the display says that the f and shutter speed are locked. But it is obvious that this is not the case. I just tried at f13 hoping that your high f-stop solution would work but it does not.

I love when things work like they are supposed to with undesireable results!

Joel Jackson
http://www.creativebloc.com/port.html


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joel jackson
Re: 7D brightness shift even when in fully manual
on Apr 7, 2010 at 12:27:35 am

Isn't the AE lock supposed to stop this effect from happening?


Joel Jackson
http://www.creativebloc.com/port.html


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John Davidson
Re: 7D brightness shift even when in fully manual
on Apr 7, 2010 at 8:13:11 am

Think of the lens as a gear. If you shrink one side (zoom in), the aperture is forced to get smaller. You're most likely rocking a 28-135mm lens, which is a manual lens that forces the f-stop change, no matter what, when you zoom. If you're at 13, locked down and pulled out, then slowly zoom, the internal gears will force the fstop to go to 14 and then likely 15 when you're zoomed in full.

I was mystified too - thinking of it like a gear helped me understand it. More expensive lenses have better gears and don't require this. Although, I rarely zoom - it's more about sliders and cranes these days.


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