Is it worth getting a teleconverter?
Non-scientific test of the Canon EF 2X II extender (teleconverter) on a Canon 60D with Canon 70-200mm f2.8 L IS lens. This lens is a Canon classic so in this test I have a quick look at what kind of image degradation we might experience if we add a teleconverter and are we gaining more image detail than without the extender.
I have had a comment that the Crop factor on the Canon 60D (1.6) does NOT create longer (higher mm value) lenses -> technically true. The sensor is just smaller than a full frame sensor so it only receives a cropped portion of the lens view.
Practically, though, the crop factor creates a magnification value on the sensor that is equivalent to a certain focal length on a Full frame sensor. For example, a 100mm lens on a canon 60D becomes equivalent in magnification to a 160mm on a Full Frame sensor like in a Canon 5d Mark II. It does not actually change the Focal Length just the perceived magnification. Your field of view is actually narrower in the final image on a cropped sensor.
In my opinion, technical details are important but photography is an Art as well so technicalities should not get in the way of understanding basic points.
If you are interested in extenders or teleconverters, on Amazon the Canon new improved version III 2X extender is $474
For less image degradation but less magnification you could look at the Canon EF 1.4X III
Nikon users should check out the Nikon TC-14E II (1.4x) for the least image degradation, the Nikon TC-17E II (1.7x) for a balance between image degradation and magnification or the Nikon TC-20E II (2.0x) for the most magnification and most image degradation.
IMPORTANT NOTE: You need to check that your lenses are compatible with the Teleconverter you buy – the manufacturers have a list of compatible lenses. Because of the image degradation involved I would not buy third party Teleconverters but stick with Canon for canon lenses and Nikon for Nikon lenses.