Thursday, June 07, 2007

Extension tubes are fun

Photo concept blatantly stolen (without permission, but credit is being given now) from my brother.

Jupiter-9 80mm f/2.0 with extension tubes

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Jupiter-9 80mm f/2.0 with extension tubes

That's a portion of the back of a chair.
Hanimex 400mm f/6.3 with extension tubes

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Hanimex 400mm f/6.3 with extension tubes. Fuzzy optics was probably excarberated with shake from mirror slap

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Blogger plink said...

First metaphotography, now this.

Extension tube, mirror slap... all this very compricated.

Esplain, can? o.O

1:47 am, June 08, 2007  
Blogger Dr. Tan said...

Isn't the lens long enough to balance out mirror slap?

We assume the point where the mirror impacts the camera to be x, the hinge to be y; the centre of mass of the lens to be z.

z:y > x:y.

This is under the assumption that the lens is heavy enough so that the mirror slap is negligible.

Wouldn't it be more of you triggering the shutter, when your hand jerks the camera assembly.

8:34 pm, June 08, 2007  
Blogger Lao Chen said...

To be honest, this is just plain geek photography. Nothing of the higher order variety, unless geeks are transcendental :)

Extension tubes are simple tubes that attach between the lens and the camera so that it can focus on objects much closer than designed.

And this mirror slap is the delicious sensation one gets when one finds one's spouse in bed with another man/woman. Haha, no la, its the shake associated with the movement of the mirror in an SLR camera.

Dr. Tan:
Im not sure, i need to check. The tripod head is not very stiff, and its damping characteristics does not inspire confidence.

The displacements are small, but the system is absurdly sensitive. The extension tube adds 50 cm, making it a ~450 mm lens. The sensor size is 3152 pixels distributed over 22 mm. If we assume the treshold of blur to be a 5-pixel radius, then the projected image cannot displace more than 0.0352 mm.

The distance to lens centre is 450mm, the region of acceptable projection is 0.0352 mm. tan-1 (0.0352/450) gives 0.0045 degrees or a mere 16 arc-seconds.

Actually, a more appropriate consideration would be the angular momentum imparted by the slap and considering the moment of inertia of the camera and lens. This is simply F = ma applied for rotation.

10:50 pm, June 08, 2007  

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