7D + 1.4x + 100-400L IS Focus problem

Hi All

Any comments/help appreciated.

I am using this set-up - 7D + 1.4x + 100-400L IS

V2.0.3 firmware.

This set up will not auto focus.

The 100-400 focuses ok without the adaptor. I have even used a Canon coupled extension tube with the 100-400 and it will not allow focus. Is there a particular contact on the 100-400 only used for the extenders?

I have tried the adaptor and extension tube combination with the 70-200 2.8MkII and its ok.

Can it be the V2.0.3 has a problem???

Thanks

You could be going over the AF's lowest aperture?

The 7D can't autofocus if the lens is slower than f/5.6. The 100-400mm has f/4.0-5.6. When you put on the 1.4x extender, the aperture decreases by a stop (the size of the opening doesn't change, but the focal length does), making it effectively f/5.6-8. So if you use a focal length that's too long for the maximal aperture for this lens, it's simply too dark for autofocusing. You should be able to autofocus near the wide end.

This is fine for the 70-200 f/2.8 because the extender only brings it down to f/4, well within tolerances.

Ray,

Your converter is probably telling the camera body that the aperture is over the "approved" f/no. and so the body is simply refusing to AF. The answer is to place a small piece of sticky tape over three of the converters pins (search here for the full details) and this stops the artificial refusal to AF.

Your lens and body will still struggle in low light/low contrast situations, but at least you know that it has tried to AF, not just refused because Canon has programmed the body to do so.

To the other posters: The 100-400 WILL AF at the lower end, its not that it cannot, its that Canon have instructed the body to refuse the attempt. I use a 100-400 and a 1.4X converter for my motorsports and it is fine now that I have the pins taped.

Maverique wrote in post #15082388
You could be going over the AF's lowest aperture?

Thanks Mav - You could be correct but how do I test it? I have used it before with the contacts taped over and it worked in an unreliable fashion.

Only 1-series bodies autofocus with the 1.4x/100-400 combination. There is a pin taping trick that can be used but I believe the resulting autofocus is very slow.

The 7D's autofocus system requires that the widest aperture be at least f5.6. The 1.4 converter loses you a stop of light. The 100-400 has a widest aperture of somewhere between f4.5 at the 100mm end of the zoom range and f5.6 at the 400mm end. Lose a stop by adding the teleconverter and you have an aperture range of f6.7-f8 - all outside the f5.6 required by your AF system.

If you look around, you can probably find some techniques for taping pins on the lens so it "doesn't notice" the widest aperture of the lens, allowing the AF system to at least "try" to function. I suspect the results may be, um, variable - but I've never tried so can't say for sure.

...Mike

i have heard that it is possible to use AF with some 3rd party extenders and the 100-400, can't remember which one, though.

Lowner wrote in post #15082409
Ray,

Your converter is probably telling the camera body that the aperture is over the "approved" f/no. and so the body is simply refusing to AF. The answer is to place a small piece of sticky tape over three of the converters pins (search here for the full details) and this stops the artificial refusal to AF.

Your lens and body will still struggle in low light/low contrast situations, but at least you know that it has tried to AF, not just refused because Canon has programmed the body to do so.

OK Lowner - Thanks - It probably looks like I have managed to ask a damn-fool question. As I said before I saw your reply I have previously taped the contacts and got unreliable results.
What made me query it was that I was trying to set a micro adjustment for this combination to see if it would recognise the adaptor/lens combination.

The camera does know the aperture and meters perfectly normally, the pin taping only stops this "tale telling" stupidity. Yes, it can get unreliable in low light, but thats an issue with any lens. Its certainly no slower as one post suggests.

Ray.Petri wrote in post #15082425
OK Lowner - Thanks - It probably looks like I have managed to ask a damn-fool question. As I said before I saw your reply I have previously taped the contacts and got unreliable results.
What made me query it was that I was trying to set a micro adjustment for this combination to see if it would recognise the adaptor/lens combination.

Ray,

Sorry, I don't know what you mean by "setting a micro adjustment". This daft behavior is hard programmed into the very soul of the processor. I know of no other way to "fool" it.

Lowner wrote in post #15082426
The camera does know the aperture and meters perfectly normally, the pin taping only stops this "tale telling" stupidity. Yes, it can get unreliable in low light, but thats an issue with any lens. Its certainly no slower as one post suggests.

Thanks for all your comments - Taping the contacts is not a very satisfactory solution as there is a lot of hunting when it attempts to focus.

I believe some adaptors operate ok in this combination.

I suppose I'll have to think about spending more money on a wider apperture 400mm. Could always borrow the wife's credit card - I suppose.

I am led to believe that there is an upgrade to the 100-400L rumoured - About time.

Lowner wrote in post #15082429
Ray,

Sorry, I don't know what you mean by "setting a micro adjustment". This daft behavior is hard programmed into the very soul of the processor. I know of no other way to "fool" it.

I only meant microadjusting the combination for best focus - It obviously cannot not apply if it will not focus by default.

Thanks

You could also pick up a Kenko Pro 300 which will AF with that combo. I use one with my 400 5.6L on my T3i and it works, and much better than I anticipated. You will need light though as you are gonna be at f8 constantly.

Ray.Petri wrote in post #15082435
I am led to believe that there is an upgrade to the 100-400L rumoured - About time.

Don't hold your breath waiting for that upgrade. It is probably the longest running rumor in Canon land -- at least 5 years.