Canon 550D Exposure Question

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RicGrayMovies

Hey guys, just got my Canon 550D a few weeks ago and it is awesome, but i'm having a recurrent issue with it and I was wondering if any of you could help.

When on Movie Mode, zooming in or out of the frame causes the exposure to automatically correct itself and create a kind of "flicker" effect which looks really jarring and odd. I was wondering if there was any way to get rid of this, because it's ruining my zooms.

Thanks for any help.
 
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The short answer: this is a sacrifice made by the designers of the lens to keep it smaller, cheaper and lighter. The only way you can solve this is by buying another, more expensive lens, a "constant aperture" zoom.

The long answer: as you may be aware, you can open the aperture up more (a smaller f number) when the lens is fully zoomed out than when it is zoomed in. An f-stop is not a physical measurement, but an expression of the size of the aperture relative to the focal length of the lens. If the aperture stays exactly the same size as you go from wide to telephoto, the f-stop changes, because it is smaller relative to the focal length of the lens. What you are seeing in your camera is the aperture jumping from one position to another as you zoom in and out.

"Constant aperture" lenses solve this problem - the aperture smoothly opens up as you zoom in, and closes as you zoom out. The cheapest CA lens Canon make is the 17-40mm f/4, which can usually be had for under £600. The EF-S (won't work on the 5D or 1D) 17-55mm f/2.8 costs £7-800, and the 16-35mm f/2.8 is around £1200. Cheaper CA zooms are available from third-party manufacturers, but I don't have any experience of them. I have the kit lens and 17-40mm f/4 sitting next to me right now, so if a photographic/video example would help then let me know and I'll try and sort something out tomorrow.
 
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RicGrayMovies said:
Hey guys, just got my Canon 550D a few weeks ago and it is awesome, but i'm having a recurrent issue with it and I was wondering if any of you could help.

When on Movie Mode, zooming in or out of the frame causes the exposure to automatically correct itself and create a kind of "flicker" effect which looks really jarring and odd. I was wondering if there was any way to get rid of this, because it's ruining my zooms.

Thanks for any help.
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Yeah, chilipie gave you a great technical answer. My reaction is to tell you to just not do it. Zooms look like shit. I guess it's different if you're shooting nature documentaries, or something, but I can't think of many situations in which I think a zoom would be something I'd want to do.
 
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Thanks for the responses guys, I thought it may have been that issue.
I don't have any video evidence at he moment chilipie but I should soon and when I do i'll put it up here. Thanks for the great response though.

I was considering having to dolly in and out, I think it may look better anyway.
 
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This thread has made me feel kind of ridiculous. Some part of me must have thought zoom was a prevalent part in films, but now that I've actually thought about it - the only film I can think of that used it in a non-ironic fashion is Jaws.

I feel like a moron haha.

(for the record I've never used zoom in any of my films because it looked rubbish - I guess now I know why!)
 
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I would definitely not rule out using zoom, but I would try and be savvy about how you use it. As Columbus says there are several ways that you can use it alongside a dolly shot.
 
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Yeah, i've used it a few times but not particularly much. I usually find different ways of telling what I want to tell. The dolly tip is useful and i'm going to use it, but is there any cheap and useful recommendations for making one?
I considered weighting a camera w/ tripod to a computer chair and tracking in and out, has anyone tried this? The only issue i'll have is keeping everything in focus with the 550D while moving.

Cheers again for the useful responses guys.
 
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RicGrayMovies said:
Yeah, i've used it a few times but not particularly much. I usually find different ways of telling what I want to tell. The dolly tip is useful and i'm going to use it, but is there any cheap and useful recommendations for making one?
I considered weighting a camera w/ tripod to a computer chair and tracking in and out, has anyone tried this? The only issue i'll have is keeping everything in focus with the 550D while moving.

Cheers again for the useful responses guys.
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That's kind of a variation of the wheelchair dolly trick (operator sitting in a wheelchair).

You just have to pull focus as you dolly in. It takes practice, and is made easier with a follow focus.
 
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i question the flicker being CAUSED by the zoom... sure dont zoom and it doesn't happen.. but my zooms dont flicker, the do get darker and lighter, but its almost unnoticeable. Perhaps the camera is adjusting exposure AUTOMATICALLY on the fly which is causing the flicker..

and in defense of the pop zoom, I see them in action films.. here is my attempt.. (2nd one is most effective)


https://www.youtube.com/watch?v=nDUI6XR6zoY

In related news, I found an 80-200 F3 zoom for $15 at my goodwill (constant aperture) I used it for the burning tree footage in another post
 
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wheatgrinder said:
i question the flicker being CAUSED by the zoom... sure dont zoom and it doesn't happen.. but my zooms dont flicker, the do get darker and lighter, but its almost unnoticeable. Perhaps the camera is adjusting exposure AUTOMATICALLY on the fly which is causing the flicker..
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Yes and no - if you change the focal length on a non-CA EF zoom when it's not attached to the camera then the iris will change smoothly (albeit closing down as it gets longer) with the focal length. However, the electronics of the camera limit it to third-stop jumps (like the clicks on manual stills lenses), as it does with shutter speed. If you could find a way to use the lens without the electronic interface then you could zoom without the sudden change in exposure, but the shot would become progressively darker as you zoomed in, so it still wouldn't be that useful.
 
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