Now I’m going to keep this simple as is the nature of this site.
If you are looking for an in depth explanation I suggest typing ‘crop factor explained’ into Google and read away.
However, this is something that I will be making mention of throughout the site so you just need to understand what I’m talking about.
Whereas on film cameras the light was directed through the lens to the film in the back of the camera, on Digital SLRs (DSLRs) the information is stored on a sensor in the back of the camera. Now on a professional camera the whole of this sensor receives the information and is able to capture a wider shot. These are refered to as full frame sensors and cameras like the Canon 5D and Nikon D700 are ‘full frame’ cameras. The benefits include better image quality and better handling of high ISO levels but as I’m assuming you’re not particularly interested in spending thousands on your next camera I’ll go no further.
What you do need to know is that non full frame cameras crop the sensor and in effect zoom in on the image.
Nikon crop by 1.5x and Canon 1.6x as illustrated here.
This becomes important when you’re trying to determine what zoom you are shooting at. You see if your lens is a 70-200mm but you’re shooting with a Canon 500D for example, your lens is actually 112mm-320mm due to the 1.6x crop factor.
Now in some cases that can be a good thing. I remember changing up from my 30D to my 5D and I really missed the extra 120mm at the top end of my 200mm zoom. However on some studio work I’ve taken the same shot with the same lighting and been amazed how much better the 5D was than the 7D. I actually sent one back one assuming it was faulty and eventually upgraded to my 5D mkII.
The important bit…
Just know that if you’re setting your exposure manually and not wanting have your shutter speed lower than your zoom, you need to be thinking of the number on your lens x 1.6 (Canon) or 1.5 (Nikon). So if you’re shooting hand held make sure you keep your shutter speed well above this multiplied focal length (zoom).
If this doesn’t make sense please comment and let me know. It really isn’t something that you need to know WHY just know these new numbers.
NOTE: This doesn’t mean that the image you see through the viewfinder is being cropped like this, that view is already cropped.