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5D projector.jpg
09-Nov-2013

5D projector.jpg

Canon EOS 5D
479s f/5.6 at 85.0mm iso400 full exif

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Guest 24-Nov-2013 04:59
Now THAT is geeky - nice observation, and good job bringing it out!
Lensrentals14-Nov-2013 15:01
What you're looking at here is the focus screen of a 5D mk 3, projected *out of the lens* onto a mat board, photographed by a 5D mk 1.

It all began when I noticed the focus points on the 5D3 light up very brightly; indeed they're so bright that when shooting portraits the subject can often see the points lighting up through the lens.

I pondered that for a while, and realized that meant the focus screen is actually being projected out of the lens onto the subject. And where the lens is in focus, the focus screen projection should be as well.

But a little testing in a dark room showed the projection is extraordinarily dim, and I left it at that, until this contest. When this contest arrived, I realized I'd finally found people who would actually appreciate a photo as geeky as this one.

The rig here is a macro lens, a Sigma 150mm f/2.8, focused on a mat board at nearly 1:1. The image of the focus screen projected out through this lens is so dim that even completely dark-adapted eyes can barely see it. However, an eight minute exposure with a 5D mk I, with an 85mm f/1.8, shot at f/5.6 to bring the other camera into something resembling focus, and ISO 400 to try to keep the noise under control, and with dark frame subtraction enabled (which I forgot I'd enabled - so that was a surprise), was able to bring it out.

To keep the 5D3 focus screen illuminated, I was constantly pumping the select-focus-point button for the whole exposure.

I flicked a flashlight on and off during the exposure to shed a little light on the camera and mat board. Other than that the light is supplied by the 5D3's focus screen projecting out the lens.

You can see not all of the focus points are available. The Sigma 150mm f/2.8 macro, like some other macro lenses (including the Canon 180L), does not allow the use of all the focus points. I believe what you're seeing there is the Group G focus points.

The most interesting feature is the six bright lights, three on each side, which mark the focus screen, resembling the whiskers of Hello Kitty. I wondered what their origin is. I've concluded there must be 6 LEDs providing the illumination, and there you're seeing is them. If you look carefully through the viewfinder in a dark room, the marks are visible when selecting focus points.
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