I need a little advice.

[Naytwan]

O.K., I have a 20D and a few lenses. I just bought a 17-85IS and I currently have a 50mm 1.8, Sigma 18-50, 28-135IS and a 75-300 III USM.

Here is what I am thinking. I want to sell the 28-135, 75-300 and 18-50 and buy a 70-200L, probably the F4 and a teleconverter. Probably a 2x. What do you guys think? After getting the 17-85 I never use the 28-135 0r the 18-50. There all fairly new as well.

[mikesd]

Sounds like a good move to me.

[Tom W]

The 2X teleconverter will cost you two stops of light, so your 70-200 f/4 will become a 140-400 f/8. The 20D will not autofocus on any lens or lens/converter combination that has a maximum aperture of f/5.6 (though there are some third-party teleconverters that will not report their existence to the camera). I would recommend a 1.4X with that lens instead.

the 17-85 is a very useful focal length range for the 20D, so I can see why you would not be using the 28-135 or the 18-50. Your plan looks pretty good to me.

[Scottes]

The 2x teleconverter will not autofocus on the 70-200 f/4 on the 20D.

Given that you might not get much for the 50mm f/1.8 you might want to keep it for low-light situations and the fact that it's a killer lens for the price.

[Naytwan]

I do plan on keeping the 50. Its a nice lens and was so cheap it wouldn't be worth selling. I'll look into the 1.4 as well. I see what you mean. It would be a pain to not be able to use the autofocus.

[cactusclay]

Sell everything but the 50/1.8 get a 17-40 or a 16-35 and the 70-200 and be done with it. 1 cent x2.

[Naytwan]

I thought about the 17-40, but it just didn't have the range I wanted for a "walk around" lens so I went with the 17-85 is. I also wanted the IS. I may get a 10-22 EF-S, but I haven't looked into it just yet.

[CyberDyneSystems]

As mentioned above,. look to the 1.4X T-con before getting a 2X. The results will be much better and you will retain full Autofocus.

[Medic1]

Definetly get the 70-200 f4L....I don't have any teleconverters, but you definetly won't be disappointed with the 70-200

[stckciv]

Will the 20d autofocus with the 2x converter 70-200 2.8? Does the 1.4x converter autofocus with all lenses on the 20d?

[Jon]

The 20D will autofocus with a 1.4x TC and any lens f/4 or faster. Some of Canon's super-teles are f/5.6 or slower; the 20D /1.4xTC combo won't allow AF with them. Also some of the variable-aperture zoom lenses are f/5.6 at the slow end. The 20D can't AF them with the 1.4x TC either (75-300 f/4-5.6, for instance). The Canon (and Sigma) TCs won't fit on all Canon lenses either. There's a thread here on TCs which spells out which lenses and TCs will work together.