24 Jul 2010

Correcting optical aberration and geometric distortion on the Panasonic HVX200

Editing, Filming, Inside the Tomato, Latest Projects, Post Production No Comments

Optical aberration. Geometric distortion. “What?” you ask. I’ll explain. On the Project Hope Relay shoot, I wanted a really wide shot from across the lake with the runner in the distance. It’s a beautiful scene and I wanted the Furman bell tower on the right side of the frame and the lake as the lower third. So we journeyed across the lake to get our shot. To my surprise, the tower didn’t look quite right. After checking and re-balancing the tripod, the problem persisted.

That’s when I realized that when you are shooting at the widest angle (or at a very close angle) on the Panasonic HVX200, you really begin to notice some lens distortion when you have straight vertical lines. Have you ever taken video or a picture where you have a doorway in the foreground and it looks curved? If so, you’ve discovered optical aberration, or geometric lens distortion.

Well, since Furman is a beautiful campus and we have no reason to make the famous Bell Tower look it was designed by this architect, we decided to correct it in post production. In Final Cut Pro, if you open your clip in the viewer, there is a tab called “Motion”. One of the nifty little expandable sections under there is called “Distort”. Now, we were filming in DVCPROHD 720, which has a native frame size of 960×720. If you were to view the raw footage in it’s native size, everyone would look really skinny. On the camera’s viewfinder and in any program that can read the codec, the frame size gets stretched to 1280×720, but the program is still aware of the original frame size. That’s why you see 480 and 360 (multiply them by 2 and you get your original frame size of 960×720). What I did was make a slight adjustment to stretch the upper right corner slightly and correct the optical distortion of the camera. The key here is not to go too extreme. It’s always preferable to adjust your zoom on the shoot to compensate for lens distortion when you can, but in this case, we needed that wide frame to pull off the look we wanted. When you are going for that cinematic look and nothing else will do, a little work in post can go a long way. Here’s the final result:

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