Monday, March 14, 2016

Lessons in Aerial Photography

I've still not got it quite perfectly down.

I flew on Saturday in a 1950s Cessna tailwheel plane. It was a neat experience, almost akin to riding in an antique car, something I've never done. I can't say I've driven or rode in anything older than the early 90s. Ironically, I do my flight training in a 1979 Cessna, which looks and seems modern and common for me, not old at all, yet this '50s plane was still quite interesting. It reminded me somewhat of the old fishbowl '70s era OC Transpo buses used right up until around 2008.

I was flying with someone who wanted me to take some pictures for him, and afterwards, I tried doing some more vertical orthophoto-style images (orthophotos are images taken directly straight-down at the ground, and true orthophotos remove any geometric distortion, i.e., buildings do not 'lean' to the side due to perspective). Orthophotos are the primary kind of aerial photos I intend on producing/focusing on, because the idea is to eventually be able to stitch the entire city together using these as one huge image.
Valley Ridge Crescent, Feb. 18th, 1500 feet, 104mm

I'm still having problems, however. Images still come out blurry or with sharpness issues. It's a learning process, particularly with the lens I'm using, because of the circumstances: Wind, buffeting, the window, airspeed, etc.

Saturday gave me the easiest circumstances I've had yet, but a lot of my images - more than half probably - turned out soft or wholly blurry altogether. The window had an arm that held it open instead of my having to hold that and the camera, and it wasn't too cold out. Yet at least once, with gloveless hands, I still managed to switch at one point to 'bulb' instead of 'manual' on the camera.

Those that turned out sharp still had blurry edges.
Montreal Road at Olgilvie Drive. The gas station roof is perfectly sharp; the bottom corners are not.

Each flight gives new reasons for my continued difficulty. First it was exposure time. Then it was inadvertent zooming out in the wind. Now it's simply blurriness as a result of the lens and not due to camera shake (at 1/4000th a second I expect there should be no problems there).

That leaves autofocus and image stabilization.

The lens barrel can be locked to prevent any zooming. That was checked. The exposure was adjusted. But what I didn't do was aim the camera out at the distance, focus it as such, and then take both the autofocus and image stabilization off. The ground is far enough below for the lens to focus to infinity on it, and the exposure time is such that I do not need image stabilization.

Autofocus re-focuses the lens each time the shutter button is pressed, so the lens may focus on something else or fail to focus altogether, at which point no photo is taken. In the picture above the front wheel of the plane as well as the foot hold below the door, and the side of the door itself, show up to be focused on or at least to mess it up. A lot of my images were potentially messed up thanks to those obstacles, or entirely focused on them. The motor in the lens seems slow to me - it's soundless and relatively quick, but it will focus the wrong way before it goes the right way; I can't take pictures of planes in the sky above unless they are close enough for the lens to literally be right on them.

Image stabilization works in one circumstance only: When you're in low light and don't have super-steady tripod-like hands/arms, especially if you're zoomed out. On a tripod, with long exposures, and in the sky, it more or less ruins the quality of the image. It works by having the lens elements free to move slightly in a solution inside the barrel so they can counteract any movement by the barrel as a whole in one's hand. They hold the image steady by keeping steady within. When the lens is already steady on a tripod, however, they're still free to move, if slightly, and with a long exposure you end up with the same result you would had you been holding the lens. With high exposures like the aerial photos I've been practicing, it's sharp - but only where the lens elements happened to be in perfect alignment on a given point on the sensor. The edges and other random areas are blurry because the buffeting wind and vibration exacerbated the lens elements in their free movement, causing them no doubt to go everywhere, in and out of focus randomly on a small scale via bad alignment, causing the edges where it's the most obvious to go entirely out of focus.

Next time I'm using my 50mm lens. It doesn't have image stabilization, its focusing motor is fast and smart, it's smaller and there's no zoom issues or other problems. Focus out once, and then turn it off. The wind won't have a long barrel to buffet, and furthermore, the lens itself is fast - it can go up to f/1.8. The focal length is perhaps the best as well, because I won't likely get any plane parts in the image and it's also not too close.

When I really get into this kind of thing, I'll also ensure I don't get any closer than 7,500 feet. 2,000 and less gives great detail but I don't necessarily need a 1cm resolution and I'd rather not take thousands of image to capture one part of the city. It would take forever and altitude at least gives range - both in the image and in the plane's fuel tanks.


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