« on: Today at 11:56:33 AM »
Hi Jock, PBD.
Not trying to be contrary, but I have seen it worked that way more often than not here, also just to add some more to the discussion, the 1/ focal length calculation for hand held minimum shutter speed, given no IS to complicate things, and not withstanding some people saying we should be using 1/ twice focal length.
(for joe average, not some of you guys that hand hold better than a cheap tripod!)
300mm lens on full frame 1/300s. Correct?
300mm + 2x converter i.e. 600mm on FF 1/600s
As above 600mm on 1.6 crop? Equivalent FOV of 960mm are we ok to shoot at 1/600s or are we more likely to have camera shake?
Edit Also the crop from the camera is a fixed physical fact, and surely exif really does mention the crop, not specifically in any lens calculation but it clearly lists camera make and model which determines crop!
Also many program's give us crop shooters the option to display lenses in crop or 35mm format, just saying.
Have a good day chaps.
Not contrary at all, this is how useful discussions are had!
Ok, a lens has a focal length. A lens has an aperture. Both of those intrinsic values are independent of sensor size, indeed they are true even if the lens is not mounted to a camera, like binoculars or a spotting scope.
If we are going to start throwing 'equivalents' out there then one, why, and two, shouldn't we be all inclusive, why just arbitrarily pick focal length?
It is true that on a 1D MkIV a 300mm + 2xTC lens gives you the field of view of a 780mm lens on a ff camera, but it doesn't give you the subject magnification of a 780mm lens on a ff camera, nor the dof. It gives you the subject magnification of a 300mm + 2xTC on a FF camera. Few people ever point out the 300mm f2.8 + 2xTC on a 1.3 crop is equivalent to a 780mm f8, why not? Because it isn't relevant, who cares what the equivalent is unless you want to take the same shot from the same place with a different sized sensor. A 300mm f2.8 on a FF camera is exactly the same as a 300mm f2.8 on a crop camera, it is a 300mm f2.8.
Now you ask about shutter speed, and that is a good point. Why, if a 300mm lens is just a 300mm lens on ff or crop would I need to use a faster shutter speed on the crop camera? Because of enlargement, the CoC for a crop camera is smaller because the output size is taken as a constant, if the CoC is smaller then any movement will be enlarged more, hence the need to use a faster shutterspeed. To be sure, if you take two pictures of a scene one with a ff and 300mm and the other with a crop and 300mm and made two prints such that the subjects were the same size on paper in both prints the shutter speeds could be the same, but what we do in real life is make two prints the same size, this means the subjects are bigger in the crop image print so any movement is enlarged more. Nothing to do with focal length, it is all to do with post capture enlargement.