Originally posted by OregonJim The "magnification" doesn't happen until you enlarge the image 1.5x to match the image size of the FF image. That is done post capture.
I see it as being dependent on the field of view at capture time, whether you enlarge it afterward or not. You would normally compare the resulting images at the same size to decide which one is magnified more, yes, but the smaller field of view was always more "magnified" to begin with. At least, that's how our brains see it. Looking at 4x6 images, the one with the smaller captured field of view looks more magnified, even if it was captured with a P&S and you "shrunk" all of the images in resolution terms. If they all had the same output dimensions to begin with, where is the post-capture "magnification"?
DAZ has a very good point about resolution though. That would help explain the physics, since the distance of motion projected for a given field of view should be proportionately larger (so faster) in a physically larger image circle. If a physically larger sensor has the same resolution (and therefore more total pixels and greater physical magnification, in terms of detail), then it would be more sensitive to the motion.
That makes a lot of sense to me: sensor resolution combined with field of view, with both accounting for physical magnification. An FF-sized lens on a APS-C sized sensor doesn't change this relationship, because the smaller sensor sees a smaller field of view as well.
Then the guideline works because of the typical viewing resolution of images at that time. Hmm.
Originally posted by Damn Brit If you have a 40mm lens what makes you believe that the lowest shutter speed you can use is 1/40sec? What are you going to do if there isn't enough light, wait until it gets brighter or send someone for a flashlight.
OregonJim, I think someone was pulling your leg or you are trying to pull others legs.
This sub-discussion is in reference to the guideline for avoiding visible camera shake in your images when taking handheld shots. We were trying to figure out how it makes sense physically.
It was originally relevant to the OP because the camera seems to follow it, or something similar, when auto-adjusting shutter speed. We kinda got sidetracked though