Advice regarding tele-extender

[-MO]

I'm a complete newbie at this, so much so that I'm not sure if there is a difference between tele-extender and tele-converter (is there a difference?).

I want to get a 1.4x extender for my 20D. I have the EF 75-300mm IS USM f/4-5.6 lens. From what I've read on the internet and searching for posts on various forums (including this one), it looks like Canon doesn't even make one for this lens. I've also read that not all tele-extenders will work with all lenses.

So far I've come across the Tamron 1.4X AF Teleconverter for Canon EOS cameras and Tamron SP AF1.4X PRO Teleconverter for Canon EOS. It seems that the SP is a better one, but from its decription it indicates that "When used with lenses with smaller maximum apertures (F/4 and F/5.6, for example), there will be little difference in image quality as compared with the standard Tamron teleconverters."

Another problem with the SP is that it's backordered on both B&H PHoto and Adorama, which are the only 2 places I trust so far.

Does anyone know if either of these would work with my lens, or if there would be any difference between the two? I realize that these may degrade the image quality a little, but I just can't afford a larger lens right now. But then again, I've read that IS won't work with some of these past a certain point, so I'm wondering if maybe I'm even better off just getting a larger lens without IS?

Any advice you can give would be most appreciated.

Thanks!
Mo

[gcogger]

Both will lose you 1 stop of light (making your lens an f/8 ), but only the SP (Pro) teleconverter will report this fact to the camera. So, on the cheaper TC you will have to dial in +1 EV exposure compensation.

The problem with the more expensive TC is that your camera will refuse to auto-focus, as it requires f/5.6 or better. With the cheaper one it will at least try to auto-focus (since the camera sees f/5.6), although it may not always succeed.

[tommykjensen]

This thread will tell You amost everything You need and want to know about extenders:

http://photography-on-the.net/forum/showthread.php?t=41922

[robertwgross]

Years ago, when I had the old 75-300 lens on my Canon film camera, I got a simple non-Canon 1.4 teleconverter to "boost" that focal length. It worked, but it really requires bright daylight with that combination. The problem is that you don't get something for nothing. If you start with a mushy consumer-type lens, stretch it out to its longest, and then put a 1.4 teleconverter on it, you are likely to get a lot of mush in the image. That is OK in some cases, since a mushy image might be better than no image at all. Autofocus can get seriously impaired or halted.

If you have a very sharp long lens, then the Canon teleconverter is very sharp also, so you are likely to get far better results. My recent experience would attest to that.

If you try to put a Canon 1.4 on an ordinary lens, it probably will not fit. If you put an ordinary 1.4 on a very sharp L lens, it will fit, but you'll probably be wasting some of the sharpness of the lens.

---Bob Gross---

[-MO]

Thanks so much for all the feedback everyone, I appreciate it! I had seen that compatibility chart once before, but couldn't find it again. Thanks so much for posting it!

I think I'll go for the SP Pro for now, if I can find one around. Eventually I would like to be able to afford the 100-400 IS lens, but that won't happen for quite a while yet. I'm hoping this will do the trick until then. If anything, perhaps I'll get the hang of better manual focus! LOL