50d + 1.4 kenko + 400mm f5.6

[Nikon Kid]

50d + 1.4 kenko + 400mm f5.6
I just wanted to know if others had a problem with this combo tapped pins for AF it will focus for a split second then it goes to infinity. When I had it on the 450d it would AF OK all but slowly.

[Roy C]

Terry, is this with just the centre focus point or with any focus point enabled? Also does this happen all the time or just in poor light or with a poor contrasting subject?

[Nikon Kid]

I have only tired it on the centre point, and only in the garden, all time I was trying for a few minutes, did not like to play around with it anymore in case the motor failed or played up. The light seemed OK, the contrast OK, just wondered if anyone else using the 50d kenko 400mm combo had same problem ?

[Roy C]

I doubt if your experience is different from anyone using a taped tc with the 40D or 50D. From what I understand the 50D is the same as the 40D when it comes to taped converters. You will probably find that one of the outer points will work better than the centre point. Also you can try disabling focus search, this will stop it going to infinity and hunting if it cannot find focus.
On the 30D the kenko pro worked better than the Canon tc with taped pins but with the 40D (and 50D I presume) the Canon works better.
I have been using a taped tc with my 400/5.6 for over three years now and must have taken over 20,000 shots with the combo but there is a technique to using it (I use AI servo all the time and focus via the AF-on button and not the shutter button - that way you can tap the button if the lens starts hunting or even go to manual without having to touch any switches).If the contrast is not good enough you can help by roughly manual focusing and then letting the AF finish the job.
Then lens takes a tc very well with very little drop in IQ if you get it right, this gives a handy lightweight 560mm f8 although when using a tc with this non IS lens I always use a Tripod or Monopod.

BTW I have read thousands of post on the subject of taped tc's with the 400/5.6 or 100-400 and have never heard of anyone actully damaging the lens because of the 'hunting'. My lens must have hunted back and forth tens of thousands of times over the years and it is still going strong. Having said that a lot of people are put off by the hunting and give up.

[Nikon Kid]

Thanks Roy, as usual very good advise, I will do some more test armed with the information you have supplied.

[macshark]

If you use one of the non-center AF points, you will see slightly better AF behavior...

[Nikon Kid]

Thanks Roy and Macshark tried it out in the Garden on another AF point and now works fine even in bad light........