Steven M. Anthony wrote:
The 1.6 crop factor associated with many digital cameras does NOT change the effective focal length of a lens. It does NOT make a 200mm lens a 320mm lens. If it did, any time you wanted a 1,000mm lens, all you would have to do is put duct tape over most of your sensor and a thrifty-50 would be magically converted into a 1,000 mm prime!
The 1.6 crop factor is not magic. It is simply a crop factor--a crop factor relative to the content that would be contained on a full frame of 35mm film.
Here's an example: Close one eye and look at something across the room. Go ahead, I'll wait... Okay, now roll the fingers of one hand up so your finger tips touch the palm of your hand. Now hold your hand up to your opened eye and look through the little tunnel in your hand at the same object across the room. Did the effective focal length of your eye change? No. Did the object across the room look closer the second time you looked at it? No. All that happened by looking through the tunnel in your hand was that you reduced (i.e., cropped) your field of view.
That's how the 1.6 crop factor works. If you put the same lens on a film camera, everything will look as far away as it did through the digital camera--but on the film camera, there would be more content in the viewfinder (above, below, to the left and to the right of what shows up in the viewfinder of the digital camera).
You have to ask yourself under what conditions does this rule work? Part of it must be the size of reproduction you are planning, and I'd say that an 8x10 print should be the minimal acceptable print size.
If you took an image with a 100 mm lens (on full frame 35mm) then the suggested "lowest" shutterspeed would be 1/125 or thereabouts, and most of the time will make an acceptable 8X10 print. If you cropped this image to give you the equivilent crop as a 1000 mm lens and made an 8x10 print, then you would find that it was very unsharp (excluding any grain implications), and now unacceptable.
If you leave the grain/noise out of the equation then the softness with a lens cropped to give you a 1000 mm "look" will be EXACTLY the same as if you used a 1000 mm lens.
It's not only the lens that's at issue here, it's the end use as well.
If you used a 300 mm lens and only made contact sheet sized prints then you could hand hold it down to 1/15 second mostly because you couldn't see the softness. With digital, and the 1.6 conversion you have to take the converted focal length into account because you are basically enlarging the image while maintaining the same size print.
After all this is said an done just remember that: a) the 1/focal length is a minimal not optimal standard; b) it is part of some guy's manhood to brag about how low they can handhold a camera, c) it's not true, their stuff sucks but they don't see it, & d) there are no contests for how slow you can handhold a camera, only for good images; so get over it.
"There's never time to do it right. But there's always time to do it over."
Canon 5D, 50D; 16-35 f2.8L, 24-105 f4L IS, 50 f1.4, 100 f2.8 Macro, 70-200 f2.8L, 300mm f2.8L IS.