So which lenses do you have?

[adder]

@BF1983

No way dude ! a 2x teleconvertor on a 75-300mm type zoom no matter how good should be a strict NO NO ! The image quality will be useless and focusing will be very difficult with such a dark viewfinder.

The 2x telecon is for the Sigma 70-210mm f2.8 lens for an effective 140-420mm f5.6 lens

BTW i thought you still had the A200,when did you upgrade to A700.