MikeMcGowan wrote in post #8505021
I'm going to be picking up a Canon 70-200mm f/4 L(non IS)this week, and I have a 50D. I was planning on getting either a 1.4x or 2x teleconverter later on for extra reach. Since I already have 1.6x crop factor, that makes the lens 112-320 already right?
Now if I add either one of the teleconverters does it add onto the already stretched focal length? And what brand of teleconverters do you suggest? I would just go Canon, but I'm sure there's one that's just as good for a smaller amount of money.
Also, if I used the 1.4x converter on this lens, it would make me one stop down to f/6.3. Now does that mean I can't shoot at f/4, or that I can but the amount of light coming in will be equivalent to what it is at f/6.3?
Mike, the part I put in bold in the quote above is NOT correct. A 70-200mm lens is, and always will be, a 70-200mm lens. Nothing can change that.
If you add a 1.4x extender to the 70-200 f/4 lens, then the combination becomes a 98-280mm lens. The maximum aperture becomes one stop smaller (higher f-stop number) with the 1.4x extender. Thus, the maximum aperture of the 70-200 f/4 with a 1.4x extender mounted would be f/5.6.
To the "crop factor" issue... Please read this "sticky" covering the "crop factor". The one thing to understand is that the focal length of a lens DOES NOT CHANGE when putting it on different format camera bodies. Note that "Format" refers to the size of the film frame or digital sensor in a camera. The "crop factor" essentially has one purpose in life. That is to compare the field (angle) of view provided by a particular focal length on two different format cameras, one of which is considered the reference format for the comparison.
The camera manufacturers have decided to use the 35mm film format as the reference format for DSLRs. However, the 35mm film format is not, never has been, and never will be the "master" format against which all other formats are measured. Thus, the current Canon marketing lingo for a 50D reads thusly: "35mm-equivalent focal length is approx. 1.6x the lens focal length". This language is far better than the old "magnification factor" that Canon used to use or even the very common "crop factor" term that you see/hear a lot today.