Re: 70-200f4L, is IS worth an additional $ 500.00?
StarNut wrote: Ascribing any such thing to \"crop factor,\" without taking into account pixel density, makes about as much sense to me as people talking about \"crop reach,\" as if the cropped sensor magically gives a 1.6x on focal length; it doesn\'t (it just crops the image being projected). But, for instance, the higher pixel density of the 7D overy the 5D2 gives the 7D some very usable \"digital zoom\" over the 5D2.
That only applies if you enlarge everything to \"100 % crop\", so that the pixels are the same size. The result will be a variety of print sizes.
The degree of enlargement, the viewing distance, and the visual acuity of the observer is what you have to take into account, just like for depth of field. However, for the sake of discussion, let\'s ignore the latter and assume a \'good eyesight standard observer\'. It is also important to note that when discussing camera shake and handheld photography one has to take a statistical view (to avoid the trap of binary thinking). But more on that later.
Consider a 50 mm lens on a full-frame sensor. To make an 8x12 inch print that you view at a comfortable viewing distance (seated at a table), you need to enlarge the image 8 times (8x) because the image is the 1 x 1.5 inch image that forms on the sensor (24 x 36 mm).
If the camera moves 0.04 mm during the shot, you might be able to just see it in the print if you look carefully. If it moves 0.03 mm, you probably won\'t see it. Enlarged 8x, the 0.04 becomes 0.32 mm.
Now put the same lens on the crop sensor camera, which captures an image 15 x 22.5 mm (about 2/3 x 1 inch). That has to be enlarged 13 times (13x) to make the same print. So if the camera moves 0.03 mm during the shot, the enlarged blur becomes 0.39 mm and you will be able to see it.
Note that it is taking less camera movement to become visible.
In fact, if you divide the 0.04 mm full-frame camera movement by the 1.6 crop factor, you will find that a 0.025 mm crop-factor camera movement will make the same 0.32 blur in the print.
Thus you have to increase the shutter speed 1.6x to cut the blur to match the blur from the full-frame camera with the same focal length.
This is what Jim Colwell means by \"do the math\".
Jan 20, 2013 at 03:33 PM
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