Canon 400mm F5.6 lens v 300mm F4 + TC
 

I am looking to buy a Canon lens for wildlife capture & wondered
which of the above would be the best option. (with 5D )

If you are going to leave the tc on the 300mm most of the time then I reckon you would be better off getting the 400mm f5.6. From the many threads I have read on this subject the bare 400mm f5.6 is better than the 300 with a tc. You can also use a tc with the 400mm which will bring it up to 560mm (AF only with the pins taped).
If, on the other hand you think you would use the bare 300mm a fair bit then that would be the way to go as you are gaining a stop. Either way they are both very good lenses.

Valid points from Roy

300mm has a closer minimum focus distance ( assuming your talking about the IS version).
If you talking about the non-IS version beware some parts such as AF unit are no longer available for repair.

I use the 300mm f4 IS with and without TC. I find it very flexible as I shoot stuff at 5 or 6 feet.

The 400mm is said to be faster focusing which is better for birds in flight.

Thanks for your replies Roy & robski! Both lens sound very good! The 300mm seems very flexible with the shorter focusing distance, also IS & greater f stop! Decisions, decisions!!!

LOL - I know some on birdforum who have both :D

If you could stretch to the 300mm f2.8 there would be no contest;)

Can I just throw a spanner in the works!!! and suggest maybe the 100-400 IS.If you are only shooting wildlife eg birds or distant animals,deer etc,then yes the 400F5.6,but if your subjects are varied inc distance of focus,then the 100-400 is so very much more versatile.
Just a thought!!!.

In terms of resolution www.PhotoZone.de will give you some idea, but do not take the results too literally as sample variation does exist, especially with zooms i.e. you might get a good one, or maybe not.

Another point is to consider is max object magnification at minimum focus distance.

300mm f4 IS ~1:4 with x1.4TC ~1:3 ( makes a good butterfly lens)
400mm f5.6 ~1:9 (the minimum focal distance could be reduced with extension tubes - I think Saphire tried this but I can't remember the results)
100-400mm ~1:5


We have not talked about the lower sensor pixel density of the 5D compared to 30D or 400D for a given sensor area.

The 5D favours wide angle work whereas the 30D & 400D favour telephoto work.

Of course a lot depends on the size of your wildlife and the shooting distance - any clues in this department Earthtones ?

Thanks to all for your great replies! Robski, I would like to be able to capture
anything from robins in the back garden to lions in a safari park! Looking at the minimum focal distance, perhaps the 300mm would be the better choice!