teleconverters

[Firefox]

does anbody know of teleconverters that work with sigma 50-200 and the sigma 70-300

thanks in advance

[Geoff F]

The problem with teleconverters is that they only work well with the more expensive lenses. They can produce rather softer results and you need to increase ISO or other variations to cope with a reduction in light. This is particularly problematic with zooms.

Unless used on one of the really top quality lenses I wouldn't even try anything bigger than 1.4x.

[squishy]

Plus on cheap super zooms, with a slower max aperture than f/4, you'll lose the autofocus. (all but top of the range bodies can't focus with lenses slower than f/5.6 (except some sigma f/6.3 models, but they do something funny with the reporting aperture)).

Teleconverters reduce the max aperture, 1.4x tc's by one stop, 2x tc's by 2 stops (i.e, an f/5.6 lens with a 1.4x becomes an f/8, and with a 2x becomes an f/11).

[Firefox]

squishy, what do you mean by top of the range ie 40d upwards or ??

[squishy]

As far as I know, the only Canons that do it are the 1D series.

[bripriuk]

what do you mean by top of the range ie 40d upwards or ??

The f5.6 limit for focussing applies to the 50D and 7D. I've read that you can get round it by sticking tape over some of the some of the contacts on the lens, but I haven't tried it.

Brian