Hi

I have had this lens for the last two months or so. My intention was to couple it with a Sigma 2X converter on my 20D to photograph jets to try and get some better angles at shooting.

I have not used the lens very much on its own or with the converter. I have found it to be rather heavy when hand held. Also, if you are doing ground to air photography on any aircraft that is quite close and and you are using the max aperture of F2.8 at max zoom, I think there is a high risk that only part of the aircraft will be in focus due to the limited zone of sharpness.

You may be tempted to use a 1.4X converter or a 2X converter and your 350D should still outo focus but to be honest I have found the image quality with the 2X converter to be rather disappointing. This may be in part to me not getting to grips with the combo yet. I need more practice.

I do not know if your camera has better auto focus sensitivity at F2.8 but I question whether it is necessary due to my earlier point about zone of sharpness. I do get the impression that the lens is very quick to auto focus
without a 2X conveter but can hunt a lot with it.

Personally, if you have not already got one, I would go for the Cannon 100-400IS lens. It costs about £600.00 less than the Sigma lens but with £600.00 spare you could splash out £670.00 or less and get a 30D as well.

I hope this helps.

Martin