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Question: Will autofocus work if i put a 2x teleconverter on a 55-200 (tamron) with max aperture of 4-5!.6!?
i am looking at 2 2x teleconverters,
1 is jessops 2x and the other is sigma 2x

http://www!.jessops!.com/Store/s33050/0/Te!.!.!.

http://www!.dpreview!.com/news/0510/051005!.!.!.

i get confused about the numbers and i want to know which or if any would still retail autofocus!.
i have a budget of £100 and i can buy second hand (ie ebay) so if you have a suggestion of what to buy then let me knowWww@QuestionHome@Com


Best Answer - Chosen by Asker:
If the teleconverter is designed for your camera then it will work !.!.!. sort of!.

Remember, teleconverters "eat" light, so your f/4~5!.6 lens will transmit the same amount of light to your sensor/film as a f/8~11 lens!. You are also intermixing your Tamron lens with different third-party teleconverters, so you can expect further degradation on the edges of your images when shooting wide open!. As you read further, you will see that when you use lenses that are slower than f/2!.8 the autofocus feature is lost and you are back to shooting using manual focus!. Maintaining sharp focus a the equivalent of f/11 when wide open (at the 200 mm focal length) is problematic to say the least!. Stop down two stops to attain the sharpest aperture and you are shooting nearly in the dark!.

In a perfect world, you would be using a 55-200 mm Nikon or Canon lens and maybe using a 1!.4x (Nikon or Canon) teleconverter to extend your shooting range and avoiding ANY third party lenses!.

What to do!? Take your camera and lens into a store that sells such a teleconverter and attach it to your lens and see for yourself !.!.!. see if you can focus it well enough in the store and shooting out one of the stores windows!. Then when you get home, look at the images on your computer and see if you have good focus and if there is a lot of camera movement in the images!.Www@QuestionHome@Com

If you read the stats on the jessups site, you'll see that the converter maintains autofocus on lenses f/4 or faster - as set by the camera, and not the converter - and this usually with canon lenses, not third party manufactured!. You'll have to get the compatibility stats of the sigma from their site, they usually list which lenses are compatible with their converters!. Unless the lens has its own autofocus motor, you will likely not have autofocus with the converter because they don't have the linkages to drive the focus of the lens from the body!.Www@QuestionHome@Com

Assuming the teleconverters are compatible with your camera model then it should work!. Be careful as not all of them do

Good luck!Www@QuestionHome@Com

Yes, autofocus will still workWww@QuestionHome@Com

it'll work, sort of, probably not auto-focus!.Www@QuestionHome@Com