100-300 & convertor issue

Purchased a Sigma 100-300 F4 to use on my 40D and it works fine until i use my Kenko 1.4 convertor with it then is struggles to focus, the Kenko convertor has always worked perfectly with my 70-200 F4 so i presume there is no problems with it.

Should i look into buying a Sigma convertor or does anyone know if this lens has issues with convertors.

Any help would be much appreciated

Leigh

It should work A-OK. Never had any problems with the Kenko on my 100-300/4. AF is perhaps very slightly slower but should still hit target. I guess it may depend on the amouont of available light... if you are indoors, it will struggle.

Which version of the Kenko is it? (post a picture if it helps)

Its the newest version of the kenko....I dont have any pictures taken as it would not focus at all just kept hunting.

I could use my Kenro DG 300 2x TC with my Sigma 70-200mm f2.8 on a 5D but when I fitted the 2x TC on my Sigma 100-300mm f4, the AF just hunted violently. So I sold the 2X TC...it was pointless really.

I tried a kenko, but found it hunted to much. I've used the Sigma for awhile now, doesn't hunt unless I really push it on lighting . It seems to AF faster with the Sigma and doesn't seem to take as big as hit on IQ either. I use a 30D and sometimes a XT

Are you using a filter ?

I have 40D and 350D, Sigma 100-300 F4 and Sigma 1.4TC. I have not had any problems with focus. I do not have any other TCs to try though.

lnk wrote in post #6048824
Its the newest version of the kenko....I dont have any pictures taken as it would not focus at all just kept hunting.

Sorry, I meant a picture of the converter to identify it if you didn't know the model... What are you trying to photograph? Also, as someone else asked, do you have a UV filter on the lens?

The Sigma 1-3 f/4 should work fantastically with a converter. Could this be your problem?

http://forums.dpreview​.com …rum=1029&messag​e=28777679

Answers to the above posts:

I dont have a filter on the lens at all.

I am using the lens outside in good lighting.....i use it for motorsports but it even hunts on still subjects.

It hunts worst when the lens is at 300mm end

The convertor type is Kenko 1.4x Teleplus Pro 300 DG

Leigh

The Kenko PRO 300 C-AF DG 1.4x needs to have some of it's pins taped to work with some lenses. The cheaper Kenko version (model details unknown) will allow AF without this attention, at least with my 100-400L IS. This is also true of Canons own TC's.

Details of how to tape the pins should be stickied here somewhere. Before sending things for repair, try it and see what happens.