I saved some money, I´d like to buy an prime for nature photography (animals, birds,...). I will use it for day trips, no longer expeditions.
As they are not cheap, I´d like to ask which lens to buy?
300mm 2.8 with 2x converter?
400mm 2.8 with 2x converter?
500 or 600 mm 5.6 with an 1.4x converter?
Optically, all 4 lenses are now very good. (my old 400mm DO IS was not).
I will carry it around all day long - so low weighted will be an plus, but I want an good optical quality too. So the 2x converter is not the best solution....
But which one to decide? Can you give me an advice?
My cameras are: 5DII, 6D and 7D
I own/have owned 3 of those 4 lenses so may be able to throw a little light (or confusion) on your quandary.
The most important consideration is the subject matter. As the lenses get longer they become more specialised as well as much heavier!
Firstly any of your cameras will give their best on lenses like these and, if you are going to use the 2x extender make sure it's the Mk3 version - much better than the Mk2.
My current wildlife setup is the Canon 300 F2.8 L IS and the Canon 800 F5.6 L IS though I have owned both the 600 F4 L IS and 400 F2.8 previously. Firstly if your subjects are small then discount the 400 F2.8 - It doesn't have enough reach and is too big and heavy if you need to stalk your subjects.
As to the 600mm I would say that it depends on which version you are looking at. I had the IS Mk1 and whilst it is a great lens my current 800 F5.6 beats it in almost all respects except minimum focus distance. It is lighter, slimmer and significantly more manageable as well as being sharper and having much better IS (which I don't use?!?). Now if you are looking at the 600 Mk2 then things change around a bit due to it's better IQ and greatly reduced weight. This would be my choice for smaller subjects like songbirds etc.
The Canon 300 F2.8 (any version) is simply a stunning lens and they work very well with extenders. However if you are constantly using extenders - is this really the right lens?
This is just a personal view but I would suggest you look at having two lenses (if funds will allow). I normally carry my 800 and 300 F2.8 (V heavy!) but I do get shots that I would have missed otherwise. Perhaps a better alternative would be a 500/600/800 lens + a Canon 300 F4 L IS - I really regret selling mine!
Well that lot has probably left you even more confused! Perhaps if I/we knew a little more about what you are specifically after I could be a little more precise in my suggestions. Anyway feel free to PM me if you want to pick my brains any more.