Bulge in 60D Video

K

Kuhndog

Member
Hey guys, we are filming a large document using a 60D on a GlideTrack system. We are shooting straight down on the document. We are getting a really weird bulge in the video (See Pic). We're using an EF-s 18 - 135mm lens and we are at about 50mm in this shot. Just wondering if anybody might know why the video is bulging. Let us know if you have any fixes and/or workarounds.

Thanks!
KuhndogOriginal.jpg
 
its your lens. try it at 100 or at full tele if you still get that Barrel Distortion-thats what that "bulge" is called.
 
primes usually have less barrel distortion

if that's the only lens you have at hand, try different focal lengths; I think the distorsion from that lens is minimum at around 24mm
http://www.photozone.de/canon-eos/462-canon_18135_3556is?start=1

for stills, you could solve this in post with tools like those from DxO; for video, it's a big tradeoff, you can also try to minimize it in post but you'll probably loose quite a bit of sharpness
 
I thought that 75mm would be where the distortion stops? I get even just the slightest fish-eye curvatures with 55mm, not sure it's as much as the OP's picture though.
 
Wouldn't you possibly be better scanning/still photographing the document and doing any "Ken Burns"/scrolling in post?
 
This is one of the many reasons why most people don't like large zoom-range lenses. They compromise all sorts of things to be able to fit in a 8-10x zoom range. Every zoom lens will display barrel distortion and pincusioning (the opposite effect where straigh lines are compressed towards the centre of the frame) to some degree, and generally the severity will increase with a larger zoom range.

The results can be all over the place depending on the design of the elements/groups in the lens. On one lens tt might start perfect at the wide end, distort through the middle and pincusion at the long end - on another it might be severly distorded at wide and fairly straight at full zoom.

The simple answer is to use prime lenses or zooms with a smaller range (around 3x) to minimise these unwanted effect.
 
Hey guys, thanks for all of the info. I am still new to DSLRs but so far it has been a fun ride. I took some of your advice and actually applied it! My shots came out amazing. Have to give some props to the GlideTrack. Cool little tool!
 
I went through something similar last year before I switched from nikon to canon.

I would asume that the pinch and barrell effect is at the least amount right dead center of any zoom lens. I could be wrong.

In the nikon menu the pinch and barrel correction can be set to "on" and you won't see the effect no matter if the lens is tele or fully zoomed out.

I think the 60D may also have that feature but it's probably called something else.

if anyone needs more info in the future, it can be found here: http://en.wikipedia.org/wiki/Distortion_(optics)
 
Luis, did you use lens correction even in video mode? I have read than any sort of extra processing/correction in camera should be switched off when shooting video or you might get buffer issues.
 
I think that nikon I use to own said that the effect would be disabled in video mode (come to think about it) I can't remember though.

And I think I was shooting pictures when I was using it. I didn't own the nikon that long before switching to canon enough to run into the issue during video. And when I did record video with it I was using a straight 50mm lens, hmmm...

I just checked every index point in the 60D owner's manual and didn't see anything on it.
there's probably some info online if I search for info on the lens it's self.
I guess I'll find out sooner than later.:cool:

good info on overloading the buffer, it makes sense, thanks
 
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