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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 17 May 2010 (Monday) 10:37
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Non-reporting TC with fast lens

 
phigment
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230 posts
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Joined Jan 2009
Location: Waterloo, Ontario, Canada
     
May 17, 2010 10:37 |  #1

I have a question that I couldn't find an answer to on this forum.

If I have a fast lens (say 135L f/2) and add a 2X non-reporting TC, how would the auto focus compare to adding a reporting 2X?

The reason I ask is because with the non-reporting, the high precision sensor (activated at f/2.8 or wider) would be used by the camera because it thinks there is an f/2 lens attached.

With the reporting TC, the camera knows the aperture is f/4 and knows not to even try with the high precision.

So, from an AF point of view, would I be better off with a reporting TC, or will that not make a difference?

Thanks!


A7R, Firin 20mm, CV 21/4, CV 40/1.4, 100ZE, 300 4LIS, Tamron 150-600, Jupiter 8, RX100 IV

  
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avan
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Location: Montreal,quebec
     
May 17, 2010 10:44 |  #2

With a fast lens,I don't think you gonna see a real difference in AF speed. The light mesurement gonna be out a bit, if you let it at f2. When I use a non reporting tc, I alway close the aperture at the right place: with a f2.8 lens = f4. I better like the reporting TC, because I want to know in the exif when I use it. So if something are wrong, I have all the data in hand.


1DMK4, T6s, 100-400mmL IS II, 16-35mm f4, 100mm macro
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phigment
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Location: Waterloo, Ontario, Canada
     
May 17, 2010 11:00 as a reply to  @ avan's post |  #3

My concern isn't necessarily the speed, but accuracy.

Stopping down the lens doesn't really matter either, because all focusing is done with the lens wide open.

By adding a non-reporting TC it is straddling the camera's decision on whether to use the high-precision AF sensors.

What I really want to know is will forcing the camera to use the high precision focus points make things worse than using the other points?

I ask this because I already have a non-reporting TC and don't want to spend $250 just to get the correct EXIF data if it's not necessary.


A7R, Firin 20mm, CV 21/4, CV 40/1.4, 100ZE, 300 4LIS, Tamron 150-600, Jupiter 8, RX100 IV

  
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phigment
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Location: Waterloo, Ontario, Canada
     
May 17, 2010 11:18 as a reply to  @ phigment's post |  #4

Well, I think I found the answer in the whitepaper:

Section IV:
"Focusing is started using the f/5.6, horizontal line-sensitive central sensors with individual pixels arranged in a zigzag pattern for improved extreme defocus detection.When focusing is nearly achieved (and when using an f/2.8 or brighter lens) focusing is handed off to the f/2.8 sensitive vertical line sensors."

So I guess you get the benefit of both AF systems when using a fast lens.

The only part that I question in the above is:
"When focusing is nearly achieved..."
What if you don't have a 2.8 lens, does it hand off the rest of the AF to the 5.6 sensors?

Oh well, at least I now know that the 5.6 sensors are involved in the initial focus lock.

Cheers.


A7R, Firin 20mm, CV 21/4, CV 40/1.4, 100ZE, 300 4LIS, Tamron 150-600, Jupiter 8, RX100 IV

  
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Steve-R
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May 17, 2010 20:54 |  #5

If you don't have a f/2.8 lens, then there is no hand-off - only the 5.6 sensors are utilized.

In addition, if you are using a f/2 lens with non-reporting TC, the camera will try to use the f/2.8 sensors, but they will likely fail since the actual aperture is not sufficient for the AF sensor baseline.


Steve

Canon 70D,
10-22, 28-105, 70-300 f/4-5.6, 100 f/2.8
Tamron 17-50 f/2.8, Tokina 10-17 Fisheye, Tokina 35 f/2.8

  
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Non-reporting TC with fast lens
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