My next buy will the Canon 400mm f5.6 Prime.

Well I'm getting a Kenko 1.4x tc for Christmas... it arrived today but I don't get to play with it until Christmas...

Next purchase will probably be a Sigma 100-300 f4, as I want a good quality mid length lens to use along side my Sigma 500.

That's really not fair... come xmas day it will dark and cloudy ;)

I'd have to disagree with the first bit. Now, I've not much experience of safaris (only been once - Botswana and Zambia two months ago) but what I did notice was that I spent more time wishing I had more width than yearning for more length (I was using a 70-300 mm on a 20D).

It was amazing just how close we got to the animals. Often so close that I couldn't fit the whole beast in the frame at 70mm. If I'd been restricted to 200mm then I'd have missed a lot more, I'm sure.

But I would have liked the 400mm for many of the birds.

After much deliberation (prime over zoom) I've decided to save my loonies (that's Canadian dollars) for the Sigmonster, the 300-800mm zoom. I think the clincher was some shots I saw on another forum by a Filipino member who has posted some amazing images with his Sigmonster, full out at 800mm, with a 2x, etc. Just spent two weeks in Florida, mostly hanging about Ding Darling, with my Bigma (50-500mm) and a 2x always on, but felt the extra reach would have come in handy with some of the warblers and other songbirds. Also, I really enjoy shooting the smaller birds, so the Sigmonster would be a nice fit.
Why not a prime? Well, I feel the Bigma is an excellent lens at 500mm, and pretty workable at 1000 with the 2x. The next step would be a 600mm (Canon) plus TCs, but that still would only get me to 1200mm. The Sigmonster's reach with a 2x is 1600mm.
And cost is also a factor. In Canada, the 600mm Canon goes for about $11,000 (before taxes), while the Sigmonster cashes out at about $6,200 (before taxes).
And it also has the zoom, which I find more practical for the type of bird photography I do. So many times, I see fellow photogs with primes having to back up or close in on a particular bird (because of the fixed focal length), while I stand and rotate the zoom ring.
cheers,
jim

For me it's more like next purchases,
im currently using a Canon EOS 650 35mm SLR and a Cosina 100-400mm f4.5-6.7 Af lens, and a Canon 35-70mm f3.5-4.5. I inhereted this kit of my dad, and it still works well.

The upgrade, A dslr, planning on going for canon, with the lens thats usually supplied, and a sigma zoom, possibly the 175-500mm.

Think that's not fair? Pete postie sold me a monopod, and I'm not allowed to use it until xmas!

Yes, Romy is a great advert for the Sigmonster. I had the decision to make as well, but a 600/4 won when the AF aspect comes in to play... it's a longer lens where AF is concerned, with a 1.4x tc it will AF as fast as without and at 850mm f5.6 (with a 1.7x tc, AF is still rapid)... the ability ability to shoot at f4 is pretty important in the U.K. as well as the amazing bokeh of an f4 (i hate that 'word' but it's general parlance these days).
Value wise, the Sigmonster has it, the zoom offers great flexibility as well.

Building websites is beyond my capabilities, unfortunately, so shelf-stacking in ASDA is looking quite atractive...:o

300 f4 is lens
 

I can think of a number of reasons why the 300 lens would be a good buy. Would be the perfect lens for butterflies and dragonflies with a 1,4 converter with a close range of just 1,5m. Also for taking shots of wildflowers with a nice blurred background, flight shots of small birds at close range and mammals,not too small in size.I think we better start saving,Tom. :)

Digi