why do Canon TC's slow AF ?

The Big Bad · Nov 8, 2003

at first i didnt belive this but now i know it to be true. Canon makes their TC's slow down the speed of AF and other brand TC's do not do this.

Many people have suggested using other than Canon TC's to get the faster focus. Seems to make sense, However ...

Why would Canon choose to do this if its not for some benifit such as more accurate AF. Canon obviosuly knows a thing or two about AF technology with the 1 series bodies and USM etc etc

It is my belief that if they say the AF needs to be slowed to remain accurate there is a need for it. Whats everyone elses take on this ?

I want the fastest AF speed of course but dont want to deal with consistancy issues either.

--
http://www.pbase.com/bigbad

Adam-T · Nov 8, 2003

At a guess To make sure they get it RIGHT, slower AF = more time for the AF to lock accurately low light I'd think

--
Please ignore the Typos, I'm the world's worst Typist

-- Canon EF35-80 F4-5.6 Owners Club Member #3580 -- ;-)

Jim Trunck · Nov 8, 2003

AF requires light, and the darker the light is hitting the focusing sensors in the camera, the slower the focus. A 1.4x converter darkens 1 f-stop and the 2x converter 2 f-stops, and after f/8 the AF won't work on most Canon bodies...

JT

Jim V. · Nov 8, 2003

The Big Bad said:
at first i didnt belive this but now i know it to be true. Canon
makes their TC's slow down the speed of AF and other brand TC's do
not do this.

Many people have suggested using other than Canon TC's to get the
faster focus. Seems to make sense, However ...

Why would Canon choose to do this if its not for some benifit such
as more accurate AF. Canon obviosuly knows a thing or two about AF
technology with the 1 series bodies and USM etc etc

It is my belief that if they say the AF needs to be slowed to
remain accurate there is a need for it. Whats everyone elses take
on this ?

I want the fastest AF speed of course but dont want to deal with
consistancy issues either.

--
http://www.pbase.com/bigbad

--

The explanation I read from Chuck Westfall, of Canon, is that it allows for the AF to lock more definatively. This is based on the electronic communication of the TC with the body. The Canon TC's are recognized by the body and AF is adjusted accordingly.

A non-Canon TC doesn't communicate to the body and it is not recognized that a TC is on the body so the AF speed does not change from that of the lens alone.

I personally haven't seen any problem locking AF with my Sigma APO TC and no change in AF speed with or without it.

Jim V.

http://f2.pg.photos.yahoo.com/ph/[email protected]/lst?.dir=/Victory+Sports&.src=ph&.order=&.view=t&.done=http%3a//f2.pg.photos.yahoo.com/

Rusty1 · Nov 8, 2003

I am sure the above explanations are valid, but I sure see a lot of sharp photos here from 10D owners who seem to have no complaints about thier Sigma 1.4 TC's.

Rusty

jonlg · Nov 8, 2003

yap,yap,yap,yap.............................................

The Big Bad said:
at first i didnt belive this but now i know it to be true. Canon
makes their TC's slow down the speed of AF and other brand TC's do
not do this.

Many people have suggested using other than Canon TC's to get the
faster focus. Seems to make sense, However ...

Why would Canon choose to do this if its not for some benifit such
as more accurate AF. Canon obviosuly knows a thing or two about AF
technology with the 1 series bodies and USM etc etc

It is my belief that if they say the AF needs to be slowed to
remain accurate there is a need for it. Whats everyone elses take
on this ?

I want the fastest AF speed of course but dont want to deal with
consistancy issues either.

--
http://www.pbase.com/bigbad

anthony kohn · Nov 8, 2003

I disagree, I can definitely notice a difference with the 70-200 2.8 with either the EF1.4 of EF2.0. The difference is very small, and really not an issue, except where my subject tracking skills are woeful!!!!

My thoughts (from playing around with the lens in MF) are that it takes less focus movement to focus with a converter on than without (assuming similar subject size, so different subject ranges). Thus a slowing of the speed, results in similar focus time. Is this just my mind playing tricks, or is it accurate?

jonlg said:
The Big Bad said:

at first i didnt belive this but now i know it to be true. Canon
makes their TC's slow down the speed of AF and other brand TC's do
not do this.

Many people have suggested using other than Canon TC's to get the
faster focus. Seems to make sense, However ...

Why would Canon choose to do this if its not for some benifit such
as more accurate AF. Canon obviosuly knows a thing or two about AF
technology with the 1 series bodies and USM etc etc

It is my belief that if they say the AF needs to be slowed to
remain accurate there is a need for it. Whats everyone elses take
on this ?

I want the fastest AF speed of course but dont want to deal with
consistancy issues either.

--
http://www.pbase.com/bigbad

Click to expand...

The Big Bad · Nov 9, 2003

Weve established that the TC's slow down AF so the camera body can focus more accurately. Why would anyone want to risk their images to a TC that doenst then ?

I see so many people recommend buying something other than Canon to get around this issue. It just doesnt make sense to me. Canon obviously condisers AF speed important and wants their bodies and lens to be the fastest on the market to focus. Knowing that fact and seeing as they still slow it down, it has to be nessacary.

http://www.pbase.com/bigbad

Adam-T · Nov 9, 2003

The Big Bad said:
focus more accurately. Why would anyone want to risk their images
to a TC that doenst then ?

Reasons for NOT buying a Canon TC are -->

A:- Canon TCs don't fit ALL canon L lenses - the Astoundingly good 80-200L and the superb 100-300 F5.6L are NOT canon TC compatible

B:- they cost the absolute EARTH (the 1.4 is $520 USD in the UK) and don't perform that much better than a Kenko Pro-300 for the price Difference

C:- they don't fit most 3rd party Telezooms, Kenko ones DO

D:- the 1D and 1DS don't need the AF slowdown to focus accurately (Sorry, Had to add that one ;-)

--
Please ignore the Typos, I'm the world's worst Typist

-- Canon EF35-80 F4-5.6 Owners Club Member #3580 -- ;-)

Karl Gnter Wnsch · Nov 9, 2003

Adam-T said:
B:- they cost the absolute EARTH (the 1.4 is $520 USD in the UK)
and don't perform that much better than a Kenko Pro-300 for the
price Difference

Similar situation in Germany. At current exchange rate the Canon is about $460 and the Kenco Pro 300 $200. Given your performance eval: Did you test them against each other yourself or do you know someone who did?

--
regards
Karl Günter Wünsch

Adam-T · Nov 9, 2003

Karl Gnter Wnsch said:
Did you test them against each other yourself or do you know
someone who did?

There is a webpage comparing the Tamron 1.4X (Inferior and cheaper than the Kenko Pro-300) on a 10D to the Canon 1.4X complete with examples in depth, the main difference seems to be the colour of the CA and soft corners with the Tamron

I've not compared them myself as I only have the cheapo tamron converters and geriatric L Zooms which won't take the canon (my 300F4L prime will but I'm not paying well over 500 euros for a converter for just one lens

--
Please ignore the Typos, I'm the world's worst Typist

-- Canon EF35-80 F4-5.6 Owners Club Member #3580 -- ;-)

Jim V. · Nov 9, 2003

The Big Bad said:
Weve established that the TC's slow down AF so the camera body can
focus more accurately. Why would anyone want to risk their images
to a TC that doenst then ?

There is no definitive proof that 3rd party TC's don't focus more accurately than the Canon. I don't think you are going to risk any image using a 3rd party TC vs. Canon

The Big Bad said:
I see so many people recommend buying something other than Canon to
get around this issue. It just doesnt make sense to me. Canon
obviously condisers AF speed important and wants their bodies and
lens to be the fastest on the market to focus. Knowing that fact
and seeing as they still slow it down, it has to be nessacary.

The only reason to buy a Canon over a 3rd party TC would be CA. I have noticed that a number of the 3rd party TC's are more prone to CA than Canon. I do not think focus or focus lock is an issue with their comparison.

Jim V.

http://f2.pg.photos.yahoo.com/ph/[email protected]/lst?.dir=/Victory+Sports&.src=ph&.order=&.view=t&.done=http%3a//f2.pg.photos.yahoo.com/

Adam-T · Nov 9, 2003

Jim V. said:
The only reason to buy a Canon over a 3rd party TC would be CA. I
have noticed that a number of the 3rd party TC's are more prone to
CA than Canon.

My cheap Tamrons are certainly, but when you consider that I paid £85 for BOTH the 1.4X AND 2X the pair and I don't use TCs a lot and when I do, it's on L lenses and mainly the 300F4L (which minimise CA anyway), they were a no brainer ..

--
Please ignore the Typos, I'm the world's worst Typist

-- Canon EF35-80 F4-5.6 Owners Club Member #3580 -- ;-)

The Big Bad · Nov 9, 2003

Canon made it so those cameras can AF at f8. Could it also be that canon chipped them so that they can AF at normal speed with a TC on even ?

I really dont like the idea of slowing down the AF, but still think that Canon had its reason in doing it.

Here in the states the canon tc's are only about $100 more than kenko pro. I felt it worth the money. Espcially since it would be going on a 300 2.8 Just wouldnt make sense to spend over $3k for a lens and then skimp $100 on the TC. Kinda like putting the $12 UV filter on a top quality lens

http://www.pbase.com/bigbad

Jim V. · Nov 9, 2003

The Big Bad said:
Canon made it so those cameras can AF at f8. Could it also be that
canon chipped them so that they can AF at normal speed with a TC on
even ?

I really dont like the idea of slowing down the AF, but still think
that Canon had its reason in doing it.

Here in the states the canon tc's are only about $100 more than
kenko pro. I felt it worth the money. Espcially since it would be
going on a 300 2.8 Just wouldnt make sense to spend over $3k for
a lens and then skimp $100 on the TC. Kinda like putting the $12
UV filter on a top quality lens

http://www.pbase.com/bigbad

--

Maybe Canon didn't plan on AF slowing down when the developed the TC's and there explanation that it is needed to lock focus is a cover up for its short comings in that area.

Jim V.

http://f2.pg.photos.yahoo.com/ph/[email protected]/lst?.dir=/Victory+Sports&.src=ph&.order=&.view=t&.done=http%3a//f2.pg.photos.yahoo.com/

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why do Canon TC's slow AF ?

The Big Bad

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Jim Trunck

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The Big Bad

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