A Question For The "Birders" On Lens Choice.

[Bandit4000]

I thought the same thing! I've very recently converted to Canon with a 7D and that lens. You will need at least the 400 for bird photography, and the zoom focal length should suit your motorsport photography. Win win.

Thanks for this post, i have been wanting to know the same thing
Mark

[DNA]

Tony, would you mind posting full frame image of the Red-kneed Dotterel at 275mm? I am curious as to how you were able to get so close to shoot with such short FL. Or is that a big crop? Thanks mate.

[Tannin]

Cheers DNA. It's a pretty big crop, but yes, it came very close. I just sat in the car beside the water and tried to keep reasonably still for an hour or two and let the birds do as they pleased. I was really after Black-tailed Native Hens but you never say no to whatever comes along, do you.

[DNA]

Thanks Tony. I thought you were trying to make me look stupid with your smartie posts earlier and it appears that I was right and it worked. In my opinion, a 400mm or longer lens would have given you a far better quality image than cropping this above image to some 1/5th of its original size. My point was meant to be and is proven now that people tend to crop images to bits, whereas I personally like to get as close to a full frame image in camera as possible. Hence why I would NEVER consider using a lens shorter than 400mm unless in a zoo or at a duck pond and I will always stick to that advice. If people look at the image you have posted earlier they would think that gee, I can do that at 275mm? Would you think they would be amazed? I think so, but experienced photographers would know better. The inexperienced ones will not. I think presenting actual facts when advising about equipment is useful for less experienced photographers when it comes from experienced photographers like you or others. I think I will refrain from advising in future because I feel that I really have little value to add to any discussion, because I have little or no idea about equipment or photographic technique when it comes to photographing wildlife; therefore, I would hate to mislead people who might be genuinely interested in learning something useful.

[Tannin]

^ With respect, that is nonsense, DNA.

1. I had, and still have, no intention of trying to make you "look stupid". You are perfectly entitled to use a prime lens if that is what you prefer. I use one myself for bird work about 80% of the time.
2. It is not sensibly possible to fill the frame with a moving bird reliably, and most certainly impossible to do that and achieve sharp focus. You need space around the bird to work with. This is one of the great advantages of zooms for bird work. Ideally I'd have preferred a bit less space and a bit more bird in this particular example, but far, far better to leave too much and crop a bit than leave too little and throw away the shot. It's the result that counts, and I submit that the final version is worth keeping. In the case of this particular shot, I probably overcooked the zooming out as the bird came closer - easy done with the push-pull 100-400 - (or perhaps I was half-wondering whether to go for a bird plus reflection composition - give me a break here, this was winter 2008 and I don't recall every detail now) but I most certainly could not have got this shot with a 400mm or 500mm prime. They don't focus anywhere near close enough, and there would not have been time to fit an extension tube. (Indeed, the fact that, as is my habit, I had a 500mm Canon prime and a 1D III on the front seat beside me but chose not to use them speaks to this point.)
3. You are perfectly entitled and indeed welcome to advise others, DNA. You have demonstrated in other threads that you can make quality bird photographs and that seems to me to be a pretty good qualification for having an opinion. (Not that most people need qualifications!) Similarly, I am also entitled to offer advice. The reader is free to make his own assessment as to the worth of that various advice. I imagine that some readers will follow yours, and others will follow mine., That is as it should be - diversity is good!

[I @ M]

If people look at the image you have posted earlier they would think that gee, I can do that at 275mm?

And so they can do that at 275 mm just as that one was taken. Many many photographers crop, either to bring the subject into more prominence or for compositional reasons or both.
The fact that that image was taken at 275mm and stands as a good clear image is testament to several things, the photographer knew what they were doing with their gear both pre capture and post and also that the gear is up to scratch to record the image well.
Simply put, it is a fact that it was taken at 275mm and yes, others with the gear and the knowledge can reproduce that image at 275mm.