What damage with 40D/50D with 100-400 L IS and Kenko 300 DG 1.4X

I am contemplating buying a 100-400 f/4.5-5.6 L IS to go with my 40D, 50D, and my Kenko 1.4X DG300 TC. I successfully use the TC on a 70-200 f/4 L IS and a 85mm f/1.8, however, I realize these lenses are within the autofocus maximum aperture limits of the 40D and 50D, while my projected purchase is not.

I am aware that unless I tape the pins of the TC, this lens will not autofocus using the TC. I am also aware that the autofocus will not function as well as when used to Canon requirements if I tape the pins.

My question is, if I do tape the pins, and attempt to force the lens to try to autofocus, what PHYSICAL damage can result to the lens or camera bodies, and how likely is that damage? Will there be obvious signs that damage will occur if the combination is continued to be allowed to either attempt to, or achieve autofocus? Will I get time to stop, and revert to manual focus before damge occurs?

Maxdave

No risk of physical damage at all.

Even taping the pins either body will not work....maybe occasionally, my 50d doesnt despite the 5D working fine. Would not consider it on 40 or 50d if you want AF.

Neilyb wrote in post #8898026
Even taping the pins either body will not work....maybe occasionally, my 50d doesnt despite the 5D working fine. Would not consider it on 40 or 50d if you want AF.

I've had it work on the 40D so long as conditions are optimal. Full daylight, decent contrast between subject and background, and plenty of time to wait for focus before taking the shot.

At least daytime, it works well with my 40D and either 1.4x or 2x TC. Because of the loss of IQ, I haven't really tested how my 40D likes the two TC stacked. I seem to remember that I probably had to use MF even in good light but it was a couple of years since I made very cursory tests.

The Kenko when taped works reasonably well with regard to AF, provided it isn't too dark or contrast isn't too low. It actually works quite a bit better than the Canon extenders, which make AF hunt significantly more when taped than does the Kenko. AF is slower however than it si without the converter.

You could also try a non-reporting converter, like the Tamron-F AF Tele-converter 1.4X C-AF1 MC4, but you need to be aware that IQ-loss is a little higher than with the Kenko.

Kind regards, Wim

Virtually all my intended use for the 100-400 & 1.4X TC on my 40D/50D will be in "good" light.

So, since no one has mentioned differently, I would have to assume there is no question of physical damage due to focussing issues. Is that correct?

Maxdave

Maxdave wrote in post #8902850
So, since no one has mentioned differently, I would have to assume there is no question of physical damage due to focussing issues. Is that correct?

My answer to this question is the very first response in the thread.

No. You will not damage the lens if using it in an environment where light and contrast is enough for the AF to work.

It isn't directly dangerous, but you will increase the wear on the lens if you use it in an environment where it will constantly hunt for focus. But this is normally a self-solving problem. If the lens is hunting for focus, you will either get too frustrated and remove the TC or switch to MF - possibly with live view zoomed to max.

krb wrote in post #8898461
I've had it work on the 40D so long as conditions are optimal. Full daylight, decent contrast between subject and background, and plenty of time to wait for focus before taking the shot.

I have had the 300 2.8 plus 2x and 1.4x stacked work in damn good light on the 50D....but never the 100-400

I never heard of anyone wearing out a USM focus motor...

Neilyb wrote in post #8905053
I have had the 300 2.8 plus 2x and 1.4x stacked work in damn good light on the 50D....but never the 100-400

I never heard of anyone wearing out a USM focus motor...

The motor itself is probably quite hard to wear out unless you overheat something. But the motor is moving mechanical parts and having the lens constantly hunt will result in a very significant increase in amount of mechanical movements per taken photo in relation to "normal" use.

Thanks for the information guys!

Maxdave

I just got the Canon 1.4x TC myself. It will arrive tomorrow in fact. Read up on it extensively lately and sounds like what is said before me, on my 40D in good light and high contrast scenes, it will achieve AF with the pins taped on the 1.4x TC. I have heard it will be slow at times, hunting. So in low light or low contrast, MF will likely be the best bet. Just in case you would benefit from a pic, below is one I found of the pins being taped on the Kenko 1.4x TC.

Use tape that don't leave glue on the contacts to make it easy to use the TC with or without the tape. Document tape works well.

It is easy to remember what pins to tape, since it is the three extra pins that are not available on the camera body.

pwm2 wrote in post #8905081
The motor itself is probably quite hard to wear out unless you overheat something.

When I tried this my patience wore out long before the USM would.