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View Full Version : What's crop factor?


DHu
04-24-2005, 20:18
I've read the RD-1 has a crop factor of 1.5. Does that mean if I use a 50mm lens on the R-D1, it'll "fill" the frame as if I used a 75mm on a 35mm camera?

aizan
04-24-2005, 20:28
erm, i think of it as the sensor not covering the "full frame", so the lens's projection is clipped off at a 75mm's field of view.

jlw
04-24-2005, 21:56
The R-D 1 is built on a 35mm camera body, but its image sensor is smaller than the 35mm standard of 24x36mm -- in fact, it's the size of an APS film frame, or 15.6 x 23.7mm.

What that means is that for any given lens you put on it, it's as if you had shot that picture on film and then cropped and enlarged only the central 2/3 of the frame (which is why it's called a crop factor.)

That also means, as you suspect, that the lens would have the same angle of view as a lens with 1.5x longer focal length used to cover a 24x36mm frame. (Epson's exact figure is 1.53x, but that's a tiny difference.)

So yes, if you were shooting with both an R-D 1 and a 35mm film camera, and you wanted to equip both with lenses that would see roughly the same angle of view, you'd put a 50mm on the R-D 1 and a 75mm on the film camera... or a 28mm on the R-D 1 and a 40mm on the film camera... or a 35mm on the R-D 1 and a 50mm on the film camera... etc., etc.

This would let you frame up roughly the same shot with both cameras, without having to move back and forth. Kinda convenient, isn't it, that at least in the wide to normal lengths, focal lengths for 35mm cameras typically move up in roughly 1.5x jumps -- it means that if you want to carry both a film camera and an R-D and only one set of lenses, you'll usually be able to make up a pair that roughly match in coverage. Mind you, I don't know of anyone that actually does this, but it would be doable if you want...

DHu
04-24-2005, 22:28
Thanks guys.

That's exactly what I had in mind. I own a Bessa R2 with a CV 50mm/1.5. I've been looking for a 75/1.5 for low light portraiture but I've read the Bessa base length is too short for foucusing at wide open. A bit disappointed with my R2 for a while until I read about this crop factor thingy.

I was hoping not to have to go the Leica route ( money-wise) initially but then the difference is still the same now!