# The Lytro, some simple math...

Started Oct 19, 2011 | Discussions thread
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The Lytro, some simple math...

f2.0!

That's a lot of DOF to control with the Lytro, right?

Not really.

The new dpReview article gives us some useful info...

http://www.dpreview.com/articles/7237351494/lytro-light-field-camera-first-look-with-ren-ng

The camera itself is a square prism in shape, around 11cm (4.4") long and around 4cm (1.6") square. Around two thirds of its length is bare anodized aluminum, which houses a 35-280mm equivalent, constant F2 lens.

A quick screen print and basic photogrametry says that the lens is about 26mm in diameter. At f2.0, that makes it, at most, 52mm at the long end, or a 6.5-52mm f2.0.

Since they call it a 35-280mm equivalent, that makes it a 5.4x crop factor. That means that the sensor diagonal is about 8mm, or it's a 1/2" sensor. At \$300, I'm betting more like a 1/2.7 inch, which would be 6.6mm, or a 6.5x. But we'll be nice and give Lytro the maximum size allowed by law (optical physics, that is), the 1/2", 5.4x crop.

That means, DOF wise, Lytro starts out with a 35-280mm f11 equivalent. Crop factors apply to both focal length and aperture, you know.

So, how big is the output image? The original Lytro used an f4 lens and a 13x13x decimation microlens array, so it could do DOF between f4 and f45, but that was on a MF camera, where f45 is practical. This "Camera 3.0" has a sensor that makes a postage stamp look huge. The 13x13 matrix also reduced the megapixel count by 13^2, or 170.

The output is "HD". That could mean many things.

• 1080p would be 1900x1080 or 2mp. From an 11mp sensor, that's only going down 5.5x in pixels, or 2.34x in resolution. You can have the DOF equivalents from f11 to f25. Not much range.

• 720p, 1280x720, is more sane. Of course, it's not a 16:9 aspect sensor, it's a 3:4, so, 960x720, or 0.69mp. Hey, it's a good size for the web, electronic picture frames, phones and pads. That's also an even 16x pixel count, or 4x resolution range. f11-f45, 2 full stops DOF adjustment range. You won't want to go down below the f45 equivalent, anyway, because even at such low resolution, diffraction will begin to show.

With just 16 "rays" per pixel to calculate, instead of 160, there's some possibility of near real-time results.

I guess that you're not going to use the "refocus" feature much at the short end. 35mm or 50mm f11 is already pretty shallow DOF. So, it's something you'd play with a few times at the telephoto end. Then, I'm guessing, forget about.

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Rahon Klavanian 1912-2008.

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Ciao! Joseph

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