I have a feeling we went to the same air show ;-) I was happy with Beercan but because of the awful weather on Sunday lots of photos had a grain and were not sharp thanks to low viz and high ISO I had to use 800+ usually. Shame. If this is photo of Sigma then I am going for it. This is my album from Farnborough on a Webshots.
http://good-times.webshots.com/photo/2802934290061271690yeYkbh
Am I to understand that I will NOT gain anything by buying this lens? Is there no visual difference? So I have effectively 300+mm with Beercan on A200 and with Sigma I would have 450mm!? I think that would serve me nicely. I had to crop lots of photo because subject was distant on many occasion.
So, is that yes for Sigma or maybe in your opinion? I do need some more reach and if it gives me 450mm that sounds good but I have not seen it myself to measure the difference so I can only take your opinion guys.
Thank you.
Hiya mate.
Sorry for the late reply.....
The Typhoon shot was taken at Biggin. Couldn't get to Farnborough, had to take the Mrs on holiday

That shot was taken with the Sigma indeed.
I have a few more on my flickr account (see sig) if you wanna check them out.
You are correct about the focal lengths, in 35mm terms of course.
Like I said, I tend to ignore the 35mm stuff.
Just need to remember that on a Canon EOS, due to the crop factor you will get slightly longer zoom. But at the wide end (IE 18mm) lens won't be quite as wide as a 1.5 crop camera. Not really a problem, of course
It's difficult for me to give a definite answer, as I've never used a Beercan.
There's pro's and con's.
A few to mention:
Beercan is an F4 lens, so slightly 'faster'. (You can use faster shutter speeds). The Sigma is an F5.6 at the 300mm end.
The Sigma is slightly longer in focal length, and will double up as a macro lens too. It'll give you a decent 1:2 shot, which is almost a 'true' macro shot.
Don't expect to see a massive difference between 210mm and 300mm.
Oddly, there is not much difference at all.
Another post somewhere on a forum somewhere

there was a conversation about this.
The difference between the two is very minimal.
During the day at some point, I'll post 2 shots. One @ 200mm and one @ 300mm so you can see for yourself.
Bit of a long shot, but where do you live?