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12-14-2012, 11:42 PM   #31
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The registration distance from the mount to sensor is the same as the mount to the focus screen thru the mirror, 45.46mm.

On a full frame Pentax, the hinge on the mirror, the sensor/film plane, and the focus screen all intersect 45.46mm back from the mount. Therefore the mirror hinge would still be 45.46mm back from the mount. I don't see how an orthorhombic (brick) shaped body could be any thinner for a full frame camera.

On an aps camera (with same registration) the sensor is 8 mm shorter in the height dimension. If the back wall was moved in 4mm, the hinge of the mirror could be moved down 4mm on the back wall. You can only move the back wall 4mm (1/2 of the ff aps difference) to maintain the registration distance as reflected thru the mirror to the new sensor location.

Is it worth the effort and cost for 4mm? On the positive side of this possibility, you would gain a small triangle of space between the mirror and the back wall for more electronics or other stuff.

01-28-2013, 10:54 PM   #32
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QuoteOriginally posted by lmd91343 Quote
The registration distance from the mount to sensor is the same as the mount to the focus screen thru the mirror, 45.46mm.

On a full frame Pentax, the hinge on the mirror, the sensor/film plane, and the focus screen all intersect 45.46mm back from the mount. Therefore the mirror hinge would still be 45.46mm back from the mount. I don't see how an orthorhombic (brick) shaped body could be any thinner for a full frame camera.

On an aps camera (with same registration) the sensor is 8 mm shorter in the height dimension. If the back wall was moved in 4mm, the hinge of the mirror could be moved down 4mm on the back wall. You can only move the back wall 4mm (1/2 of the ff aps difference) to maintain the registration distance as reflected thru the mirror to the new sensor location.

Is it worth the effort and cost for 4mm? On the positive side of this possibility, you would gain a small triangle of space between the mirror and the back wall for more electronics or other stuff.
At first I thought this mirror-to-the-sensor idea was crazy, but now that you bring up the 4mm APS "gain" it is starting to sound better. If you ditch IS you will still probably only be able to actually gain 2 of those 4mm, due to the border bits around the sensor. However, if you then move the LCD on top of the camera, over the sensor, there are a few more mm to slim down. Make the battery fit in the space under the mirror. Now we are talking about some real change possibilities regarding form factor, and you would finally have a K-mount digital camera that is as thin as it's film counterpart. that is a big deal.
01-29-2013, 07:55 AM   #33
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KL Matt, I missed your thread till now
+1 for the idea.
The Hubble uses a secondary mirror (Cassegrainian) to the focal plane sensors, so your idea surely has merit.
01-29-2013, 08:17 AM   #34
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QuoteOriginally posted by KL Matt Quote
Hi,

Why don't pentax put the sensor up where the prism is on a dslr and fix the mirror at 45 degrees in place?

You could take up to 20 mm of thickness off the body with just this one move.

Matt
I doubt it will work ... if anything you will probably add to the width of the camera ...
Why you ask? Have you seen how bulky the sensor and SR system are together? If you put that on horizontal you will end up with a thicker body than you have now.

The only way to reduce the width is to reduce the distance between the lens and sensor ... that will mean a new mount.

01-29-2013, 11:08 AM   #35
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I think the answer--why not do this--will always come down to cost and value: these aren't small systems, even if we make the camera body as small as possible, so the cost of making one component smaller isn't compelling enough to consumers to produce such a product. There is an argument to be made that following Sony's lead with absurdly small bodies has merit, though, especially considering how good Pentax is at designing small lenses.

While pondering this, I decided to give my new tablet a spin and try to diagram how this would work, and what the benefits would be. I apologize for my kindergarten-level drafting.


Attachment 157518

From left to right, a standard SLR, the relocated-sensor idea proposed, and a slightly more radical version with a curved mirror and small sensor.

The key to the last design is that, while the mirrorbox is full height, it only needs to be about half-depth; when the light reflects back to the front of the mirrorbox, it has traveled the full 45.46mm. The idea is that if you're going to be messing with the optical path, why not do something fun with it? Putting a curved mirror in there wouldn't require changing the sensor size, but because 135-frame sensors are so expensive, it makes sense for it to basically act like a "speed booster," and probably at a lower cost. Note that "small sensor" could mean APS-C, MFT, or whatever; the lens mount and image circle becomes independent from sensor size. This will greatly increase the incident angle, though, so this would need very good microlenses on the sensor.

Either way, I see more size gain from removing the prism and adding space under the mirror than I do from actually relocating the sensor, and the ideal implementation would have the sensor assembly in the hand grip area, not the eye-level viewfinder area. But until electronic viewfinders take a few more steps forward, I personally am quite happy with my flipping mirror and prism.
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