Wednesday, May 30, 2018

Solving My Blur Problem With A Bit Of A Tilt

Photography test setup in my modeling room.
Hello everyone!

I'm still working on the next Pre-Alpha release, it's just been delayed a bit by my son's birthday, the end of the school year, and some more extensive editing than I'd anticipated. 

But... I did discover a solution to a problem that had been bugging me, so I thought I'd do a quick post on that. At some point relatively soon, I'm going to need to produce sets of introductory gameplay videos. But how would I do that? It's not enough to simply aim a camera at a table and hit record, because some things on that table would be in focus, and others wouldn't. The solution, as it turns out, is rather interesting, and uses some tech that was originally developed for spy planes.

What's The Problem Again?

When you're taking a photograph, or shooting video, you have to balance three things:
  1. Aperture
  2. Exposure
  3. ISO
Put in very simple terms, the Aperture controls the size of the "hole" in the lens through which light enters the camera, the Exposure controls how long the shutter is held open to let light in, and the ISO (pronounced "Eye-So") controls how sensitive the camera's sensor is to the incoming light.

Each of these settings has a trade-off.

Close-up of a high-ISO (12,800) photograph. It's far too noisy to show any detail.
In general, you want your ISO (sensor sensitivity) set as low as possible, otherwise you'll get a bunch of noise that will make your picture too grainy to use. Especially when photographing small objects on a large table. 

It gets worse with video. Since this noise is random, it will be different in every frame, making the video look like it was shot on VHS tape instead of a high-end digital camera at 4K.

So that leaves Aperture and Exposure to play with.

This shot shows how, if your Aperture is too wide open, you'll only get part of a scene in-focus.
Wider (more open) Apertures let in more light, but they lower the camera's Depth of Field. Meaning that whatever you focus on will be sharp, but anything closer or further away from the camera will be blurry. Make the Aperture more narrow, and the depth of field range increases, putting more things in focus. But this also lets in less light, and you'll either have to compensate by adding tons of lights, increasing your exposure time, and/or cranking up the ISO.

The camera's Aperture has been narrowed to put everything in focus, but the higher ISO required
(12800) has added so much noise that the image is unusable. Especially for video.
If you're shooting stills, this is no big deal. You just put the camera on a tripod, leave the ISO low, and adjust the exposure so that the shutter is open longer. 1/4th of a second? 2 seconds? No problem.

But... I'm planning on shooting video. Which has to be shot at 1/30th of a second, minimum. There's no getting around that. I've also got about as much lighting as I can manage to practically fit in my studio space. It's FAR brighter than this test scene, a good 6000-8000 lumens, but it's still not enough to shoot the game table with the Aperture stopped down to F22 without having to raise the ISO above its ideal of 64.

Enter The Freaky Tilt-Shift Lens

Last week, while watching photography videos on YouTube, I ran across one on Tilt/Shift lenses. Which were originally invented to allow spy-planes to take clear photos of enemy positions out to the horizon.

These lenses get used a lot in architectural photography. By using the shift function (the ability to move the lens up and down in its mount) you can take pictures of tall buildings and wide landscapes without any perspective distortion.

That's cool and all, but I was more interested in the tilt feature. It allows the lens to rotate in the middle, which lets you control the angle of the focal plane. So instead of objects being clear or blurry based on their distance to the camera, you can adjust it so that they're blurry based on some other angle. Such as... Oh... Their distance from a tabletop.

So by tilting the lens down a bit on the camera...

...Objects are now clearly in focus if they're in the plane of the table, and only get blurry if they go above or below that level. Notice that the troops behind the pillars are sharp, while the pillar between them and the camera is blurred at the top. Weird, no?

Thus, I now only need to close down the Aperture enough to make sure that models 1-2 inches high will be in focus. Meaning that a LOT more light will get though to the camera's sensor. Which in turn means that I can use a lower, less noisy ISO. In the modeling room, with just the overhead LEDs and the table lamp, the tilt allowed the camera to keep the models in-focus while gathering 8x more light. This allowed me to lower the ISO to 1600, which resulted in a MUCH cleaner photo.

There's still a bit of noise at ISO 1600 though, so I adjusted the exposure from the 1/30th of a second required for video, to 1/1.5th of a second. Just to see how much cleaner an ISO 64 picture shot under proper lighting will be.

Now... What happens if instead of tilting the lens down, you tilt it up? Well, that makes the focal plane more perpendicular/vertical. Which is often used to make really big things look like tiny miniatures. Because the resulting pics mimic the look of macro photography.

If you've seen the movie "Game Night", you might have wondered how they made certain shots of real life look like pieces on a game board. Well, this is how. The blurring effect can be faked on a computer, but doing it-lens almost always looks better.


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