The science of in-body image stabilization query

Sony and Pentax claim that their sensor-shift image stabilization allows for the implementation of such technology even with lenses older than the technology itself. However I have been thinking about it, and do not understand how it can work with every available lens fitted to a given body with stabilization.

A 0.05 degree camera shake will surely seem more significant on a 100mm lens than a 50mm one, so it calls for a larger sensor shift for compensation. However, what about lenses that do not transmit focal length data to the body? I am in search for a DSLR and I've been keeping an eye on the Pentax K-X. How will this body work with a Pentax-A SMC 50mm f/1.7 that "doesn't digitally transmit focal length data" ?

Thanks.

For what it's worth, Canon's stated position for avoiding in-camera stabilization is that (paraphrased) "you need different IS characteristics for different lenses" - so at least Canon agree with you :)

http://en.wikipedia.org/wiki/Image_s..._Stabilization

Quote:

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The sensor is moved to maintain the projection of the image onto the image plane, which is a function of the focal length of the lens being used; modern cameras can acquire focal length information from the lens.

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Well, there you have it. I'm right.

I remember reading somewhere that if you attach a Pentax-A lens onto a Pentax D-SLR, it will recognize that the lens is model A; at least it's a start :(

If the lens does not transmit focal length information to the body, as you mentioned in your first post, how does the body know what the focal length is?

BINGO!

Quote:

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To function properly the camera needs to know the focal length of the lens. If you are using a Pentax DA, D FA, FA J, FA or F lens this information is acquired automatically. For all other lens types you can enter it manually in the menu.

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You simply enter the information manually! I hope this is no different on the Pentax K-X. (k-x is newer than the k200d after all)