help with choosing a telephoto...

[neuroanatomist]

Welcome!

So I’ve been reading up on the Canon EF 70-300mm f/4-5.6 L IS USM Lens which seems to have a fairly mixed review conclusion here.

First time I've heard that - it's an excellent lens by all accounts. It may be there's some confusion because are two Canon EF 70-300mm f/4-5.6 IS USM lens (one older non-L version, one L version), and also a 70-300mm f/4.5-5.6 DO IS USM lens and the cheap 75-300mm f/4-5.6 lenses (several flavors). The 70-300 f/4-5.6 non-L ($550) is not that great a lens - IQ is pretty bad at the long end, so that's 'mixed'. The DO lens is overpriced for what it is, IMO. But the 70-300 L is a truly excellent lens, assuming your budget reaches to $1500.

I was shocked that the Canon EF 70-300mm f/4-5.6 L IS USM Lens doesn’t seem to be compatible with canons extenders… is this normal? I would have thought making it compatible would be a big selling point for a lens like this?.

It's a bit unusual, in that the other 70-xxx L-series zooms are compatible with extenders. But the 70-300mm lens goes to f/5.6, which means you'd lose autofocus with an extender anyway (unless using with a 1-series body except the 1D X). The design of the lens places the rear element right at the lens mount with the lens retracted to 70mm, which is why the Canon extenders won't fit.

I know it’s a bit of a wish list but I generally want a lens that I can use for those close up shots from afar whether it be sports, wildlife or scenery so any help/advice would be most appreciated.

What's your budget? If you've got $1500-1600, it really comes down to a choice between the 70-300mm f/4-5.6L and the 100-400mm f/4.5-5.6L. Both are excellent lenses. If you need 400mm and are willing to use a large, heavy lens then the 100-400mm is the way to go. Otherwise, I think the 70-300mm L is generally the better bet - it's smaller, lighter, has a better IS system, and delivers better IQ (assuming you don't need to severely crop your images). Personally, I have the 100-400mm and it's an excellent lens, although I generally use it with my 7D because if I need 400mm, the crop factor also helps put more pixels on target.

The 70-200mm f/2.8L IS II is also excellent and sees a lot of use on my 5DII, works very well with the 1.4x extender and decently even with the 2x extender (unusualy for a zoom lens to deliver high IQ with the 2x) but I'd not recommend that as a routine use - extenders are best reserved for occasional use. If you need 400mm, get a lens that reaches 400mm natively.

If your budget is more in line with the 70-300 non-L version, you might consider the Tamron 70-300 VC (cheaper than the Canon, IQ at 300mm is slightly better than the Canon lens, but nowhere near the 70-300 L).

Hope that helps...