Lanky wrote:.

Hi I know I am asking an old question but a search of the forum turneup no obvious answer..

If I buy a fast lens ie. f/2 or f/4 and use it with a teleconverterwill I still get good images?.

Depends on the lens and teleconverter. A cheap teleconverter and a good lens will give you bad images; a good teleconverter and a good lens will give you good images. A good lens with a teleconverter designed for that lens will give you better images, but these are rare..

Also what effect does a teleconverterhave on in lens VR/IS?.

That depends on the camera, lens, teleconverter, and anti-shake system..

I am looking at buying a 30d plus a 120-300mmf/2.8 lens with a 2times or 1.4 times teleconverter..

Nobody makes a good 2x teleconverter...

See CK Shene's excellent web page for quantitative comparison of teleconverters. It is possible to get a GOOD Olympus B-300 on eBay for about $60.http://www.cs.mtu.edu/~shene/DigiCam/.

If the front lens of the teleconverter is large, and the rear lens (actually exit aperture) is also larger than the entrance aperture of your primary lens there'll be little light loss..

I just experimented with my Panasonic FZ30 at 420mm. Without a teleconverter it chose f/5.6 @ 1/250 sec; with a TCON-17 (same as B-300) it also chose f/5.6@1/250 for the same scene & ISO..

I did the same with a Canon 300D at 55mm and got the same result - no exposure change due to adding the TCON-17..

Both these primary lenses were at around f/5 at max zoom so I can't promise what'll happen with a faster primary lens. However the lesson is that it won't change things much. Even if there's vignetting the open area may be ok..

Dave.

PS not to imply there's no light loss - of course there's a bit due to interface reflections but it is usually relatively small...

Dave Martin wrote:.

If the front lens of the teleconverter is large, and the rear lens(actually exit aperture) is also larger than the entrance aperture ofyour primary lens there'll be little light loss..

This is true for front teleconverters. Most DSLR teleconverters are rear teleconverters, which lose a very predictable amount of light, regardless of design: a 1.4x TC loses 1 stop of light, while a 2x TC loses 2 stops of light...

First, check whether Canon convertoers are compatible with that lens. They only work with some, not all, Canon lenses..

Generally, if a lens is stopped down two stops, high quality teleconvertersdeliver high quaility results. So a 1.4 teleconverter, on an f2.8 lens, acts like f4. Stop it down to f8 and it should be pretty good..

That said, really long lenses are usually a problem; lens shake, camera shake, too much distance so too much haze....

BAK..

BAK wrote:.

First, check whether Canon convertoers are compatible with that lens.They only work with some, not all, Canon lenses..

Generally, if a lens is stopped down two stops, high qualityteleconvertersdeliver high quaility results. So a 1.4 teleconverter,on an f2.8 lens, acts like f4. Stop it down to f8 and it should bepretty good..

That said, really long lenses are usually a problem; lens shake,camera shake, too much distance so too much haze....

In the right circumstances, really long lenses are extremely fun. You can take pictures that are completely impossible otherwise, like a head-and-shoulders portrait of an osprey 50 feet up a tree, or a macro of a flower ten feet down a cliff...