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Archive 2005 · Canon autofocus information

  
 
Monito
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p.6 #1 · Canon autofocus information


In a thread today, a 20D user obtained excellent AF results for a sequence of frames in a burst, recording an owl in flight: https://www.fredmiranda.com/forum/topic/261295

The pictures are excellent and the sequence is stunning. The camera performed very well.



Aug 04, 2005 at 06:12 AM
RDKirk
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p.6 #2 · Canon autofocus information




1. 20D with latest firmware froze and had to take out the battery
2. My hotel room was confi at 75F and less than 10% humidty, so when I took the lens out of the room in the morning I saw some condensation on the lens (don't see how this can affect horizontal picture focus)
3. Did lots of lens changing to test all my new toys (all lens changes were done quickly in controlled environment to leave out the elements - but never turned off the camera to do so)


You have to do some more picturetaking under somewhat more controlled conditions (which initially means merely taking care to note what the actual conditions are) to see if you can recreate the problem. Then start removing variables to see when the problem stops.

Condensation on the lens from leaving a cool environ to a warm, humid one should evaporate within seconds (by the time the front surface of the front element reaches the ambient temperature). You can shorten that time by blowing it with an air syringe (the same one you use to blow off dust). But a picture taken with condensation would be soft but not actually out of focus--you should still be able to see that the plane of focus is where you intended it to be.

It's not normally necessary to turn off the camera to change lenses. From what users have been able to determine, the camera is never truly "off." The on/off switch appears merely to disable the shutter release.

It appears that the camera does an initial interrogation of the lens when it's mounted regardless of the position of the on/off switch (just as it does when the battery or CF doors are opened, although the "busy" light doesn't flash). I think I've found that older Tokina lenses do benefit by having the camera turned off, however, because one I have doesn't seem to like responding to the interrogation if the camera is "asleep."



Aug 04, 2005 at 08:05 AM
mcjeong
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p.6 #3 · Canon autofocus information


Thanks RDKirk.
I did take over 50 pictures of a flower at about 30 feet away, unfocusing manually and having the camera focus automatically. Put the 20D on a tripod and put the aperture at 2.8 to 11. None of the 50 pictures were sharp, they were very soft (shutter speed average at 1/500) when taken horizontally. When taken vertically, the pictures are perfectly in focus. On the horizontal pictures I manually tried all 9 autofocus points.

I was wondering if maybe there is any any way that the sensor array that you show has a vertical and horizontal setting. Perhaps the horizontal sensors got dirty from dirt in the condensation.

This is driving me crazy! I first thought that it may be lens, but I tried them on a Rebel 350 and most of the pictures were sharp. The tipical focus testing showed spot on focus.

If any one can help me here! Wondering if there is a hard reset function in the 20D



Aug 04, 2005 at 11:54 AM
Monito
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p.6 #4 · Canon autofocus information


Here is a full chart and explanation of the 20D Autofocus Custom Functions:

http://doug.kerr.home.att.net/pumpkin/20D_CF04_chart.pdf



Aug 08, 2005 at 08:56 AM
Lalfer
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p.6 #5 · Canon autofocus information


what about replacing this with a EOS 5D?


Aug 11, 2005 at 06:40 AM
astrolucida
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p.6 #6 · Canon autofocus information


mcjeong wrote:
Perhaps the horizontal sensors got dirty from dirt in the condensation.


Condensation is distilled water so there is no dirt in it. However, it is possible that it helps existing dust attach the sensor.



Aug 12, 2005 at 07:07 AM
astrolucida
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p.6 #7 · Canon autofocus information


RDKirk wrote:
2. Canon's latest application for a US patent on their autofocus system
Go to www.pat2pdf.org and enter patent # 6,603,929


Wow! That patent is a great source of information! The focusing mechanism described there is revolutionary!

However, I am left wondering which cameras actually use circuitry described here. I made a Google search on that patent number and Canon 20D - and I got exactly one match, which was this very thread!

Fortunately there is a simple method of finding out whether 20D uses the focusing mechanism described in the patent. If the autofocus sensors are visible beneath the main mirror (visible in the sensor cleaning position), then 20D does not use the new system. I don't have a 20D myself, so I cannot check it. 10D has clearly several holes there, for the AF sensors. Also, if the shutter does not move when focusing, 20D cannot use this method.

The autofocus system described in that patent is revolutionary. It uses the current Canon (D)SLR focusing first. That method is based on the phase difference and blind (from the camera point of view) movement of the focusing group to the proper position. However, after that, the second method is engaged.

The second method is based on contrast, i.e. moving the focusing mechanism to the position where the best possible contrast is produced. The information for this focusing method is gotten from the image sensor itself, though the half mirror. The shutter, however, needs to be opened for the focusing operation, but the mirror stays in the position. There is, no longer, a smaller mirror beneath the main mirror, but the AF sensor is built inside the pentaprism housing.

Because the aufocus is based on the data that the sensor provides and because the lens is driven with a special "precision mode" (depending on the lens type), there will be no autofocus errors ever with this method. No back- or frontfocus, no matter how imprecisely the lens or the camera has been adjusted.

Provided, of course, that there is enough light and contrast for focusing in the first place and that the AF point is pointed to where the photographer wants it. But when the focusing succeeds, it is not possible to gain any better focusing by any means (=manual focusing is about dead after that). After all, the lens is stepped one step at a time and the best contrast (as seen in the final image itself) is found out.

One important corollary of this method may be that third party lenses either stop working altogether or at least they cannot be used in the precision mode. The patent describes a different lens focus mechanism movement which is used with the contrast focusing mode.

The patent describes three different lens mechanisms, each of which has a specific precision mode, depending on the implementation technology (two types of stepper motors and USM). Because that "new" mode is not used with the current focusing system, there is no way it can have been found out through any reverse engineering by Sigma, Tamron or Tokina. This might mean, in the worst case, that all third party lenses need to be rechipped.

My gut feeling is that none of the current Canon cameras use this new autofocus mechanism. In that case, maybe the 1D Mark II n is the first one? And it will be a big success, if that is the case!

Think about it - always perfect focus with AF!



Aug 12, 2005 at 11:38 AM
rutt
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p.6 #8 · Canon autofocus information


I scanned this thread for the answer to a related mystery. How do the 1-Series cameras choose among the AF points? I think I understand how the 20D does this: it just picks the closest one that acheives focus. At least that's what the manual says. But I think the 1-Series cameras do something more intelligent. What?


Aug 12, 2005 at 12:32 PM
Teppo
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p.6 #9 · Canon autofocus information


astrolucida, seems interesting, although several issues come to mind:

1) A pellicle mirror has the light loss and mirror dirt issues etc.

2) How fast will the contrast operation be? Given that for sports and other timing-critical stuff you can't have any delays between shutter press and image record, this method might not work, in which case it would have to be turned off. At least if the system doesn't allow simultaneous phase and contrast focusing.

One thing to keep in mind too, remember that consumer cameras don't give perfect focus with contrast detection either, so while the system on the SLRs would be more advanced, it doesn't mean it could ALWAYS correct the errors made by the phase focusing.

This thing again brings to my mind my wish that one could use the LCD for framing. Such a sensor contrast focus with a pellicle mirror would allow this. Why would I want this? Simple. Overhead shots, as well as tripod work. Compact cameras, especially with a swiveling LCD, are a marvel to use for still life, macro etc in this aspect. Often it is nearly impossible to keep checking the shot from the optical viewfinder, at least with any level of comfort. This is a feature I've always wanted in a DSLR. On a side note, the new gadget attached to the viewfinder would work too I guess.

One thing out of curiosity though, I've heard that a CMOS sensor can't be turned on and off when the camera is powered on? It was said to be the reason CMOS cameras only have 1/250s flash sync somewhere on this forum. If this is true, can the described system be used with CMOS, where the shutter would have to be open? I suppose the rest of the camera circuitry should be able to get input from the sensor only for a selected period, but wouldn't this make faster flash sync possible as well?

As an end note, it does seem like an interesting system, if it really works.



Aug 12, 2005 at 12:58 PM
RDKirk
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p.6 #10 · Canon autofocus information




The autofocus system described in that patent is revolutionary. It uses the current Canon (D)SLR focusing first. That method is based on the phase difference and blind (from the camera point of view) movement of the focusing group to the proper position. However, after that, the second method is engaged.

The second method is based on contrast, i.e. moving the focusing mechanism to the position where the best possible contrast is produced. The information for this focusing method is gotten from the image sensor itself, though the half mirror. The shutter, however, needs to be opened for the focusing operation, but the
...Show more

What Canon did in that patent was to gang several concepts into one application. They don't have any one camera that has it all.



Aug 12, 2005 at 01:29 PM
astrolucida
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p.6 #11 · Canon autofocus information


Teppo wrote:
1) A pellicle mirror has the light loss and mirror dirt issues etc.

2) How fast will the contrast operation be? Given that for sports and other timing-critical stuff you can't have any delays between shutter press and image record, this method might not work, in which case it would have to be turned off. At least if the system doesn't allow simultaneous phase and contrast focusing.


No, it's not a pellicle mirror. It is turned away for taking the image. All DSLR mirrors are already half-mirrors (or, rather 40/60 mirrors) due to autofocus, so there is no change to that.

As for speed, let me quote the patent (last sentence of the abstract): "The autofocus process is thereby made high in speed and high in precision at the same time."



Aug 12, 2005 at 02:02 PM
astrolucida
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p.6 #12 · Canon autofocus information


RDKirk wrote:
What Canon did in that patent was to gang several concepts into one application. They don't have any one camera that has it all.


Let me quote the patent (column 2 in text part, "Summary of the Invention"):

"An object of this invention is to perform lens-drive control that is optimal for each focus detection in a camera system that employs a plurality of focus detection methods in combination to realize high speed and high precision of autofocusing at the same time."

Canon would not have been granted a patent on either the phase-driven focusing or the contrast-based focusing, because they are "prior art" (=already known), but their new invention is to have a camera with both of those methods at the same time. This means that they cannot appeal to the patent unless the camera has both systems at the same time - hence the value of the patent would be zero otherwise. Also, it specifies a camera with changeable lenses, so it is not for P&S cameras.

They have patented this because they have or have at least had plans of implementing such a camera. And I don't think they would have made the application unless it were actually implementable. It might have some technical limitations which would not make it attractive for all users, e.g. it might actually require a CCD sensor in order to succeed, and the CMOS development has driven over it.

The patent was granted 5th of August 2003, and it had been filed 14th of June, 2002, so at that time Canon did have CCD cameras, and they might have had such plans in mind for their cameras. It could be that the traditional method has been made to work so well that there is no longer need for the combined, and more necessarily complex method.

But I agree in that none of the current cameras uses the system that has been patented here. Whether such a camera will appear in the future, remains to be seen.



Aug 12, 2005 at 02:15 PM
Teppo
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p.6 #13 · Canon autofocus information


astrolucida wrote:
No, it's not a pellicle mirror. It is turned away for taking the image. All DSLR mirrors are already half-mirrors (or, rather 40/60 mirrors) due to autofocus, so there is no change to that.


Ah, crap. When I first read it I though it wasn't a pellicle mirror, but when rereading I somehow translated half-mirror into a pellicle mirror, oops.

Well that only escalates the problem though, since your viewfinder goes black while contrast focusing is going on. This seems to be very bad for sports and other action, and also will definitely increase shutter lag quite a bit. In more ordinary shooting it might of course still be useful. You could use this system for LCD framing as well, but for sports etc that's not much of a help



Aug 13, 2005 at 12:34 PM
astrolucida
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p.6 #14 · Canon autofocus information


Teppo wrote:
Well that only escalates the problem though, since your viewfinder goes black while contrast focusing is going on. This seems to be very bad for sports and other action, and also will definitely increase shutter lag quite a bit. In more ordinary shooting it might of course still be useful.


No, it does not go black when focusing. The contrast focusing gets the data through the half mirror. Only when the actual image is taken, is the mirror moved away. So, to all extents (from the user point of view), the camera works just like current cameras. And I understood from the patent description that even the speed would be quite the same. After all, a few steps with the stepping motor take almost no time at all (when compared to the larger initial movement).

So, in my opinion, this dual focusing mechanism would be as fast as the current system but more accurate. Contrast-focusing is slow, but it is used only for very small distances, as the initial focus is made through the phase-difference focusing.

Remember that not the complete image is transferred from the sensor when focusing but only the small part at the focus point. Hence, it is very fast, and the time spent on that cannot really be seen by the user.

So, this new accurate focusing could be used for sports as well as the current system can.



Aug 13, 2005 at 01:32 PM
Teppo
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p.6 #15 · Canon autofocus information


Ah, I see.. well, in that case, will just have to wait and see when such a camera comes out and see how it performs


Aug 14, 2005 at 10:50 AM
Rrexy
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p.6 #16 · Canon autofocus information


Great read - very Informative!


Aug 16, 2005 at 05:23 PM
wfr2
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p.6 #17 · Canon autofocus information


Thanks you!! I wish Canon made this stuff easy to find.


Aug 17, 2005 at 02:12 PM
helen
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p.6 #18 · Canon autofocus information


Just wanted to say thank you for a fantastic thread, the pointers on the orientation of the object to be photographed and the focus points really made some things click for me.
Thanks



Aug 18, 2005 at 08:45 AM
Thats Fresh
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p.6 #19 · Canon autofocus information


thanks for the info...i didnt know about 30% of that.


Aug 18, 2005 at 07:43 PM
oldsouth
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p.6 #20 · Canon autofocus information


Does anyone have a chart of the focusing points on the 1Ds Mark II and which sensors are doubles or +


Aug 25, 2005 at 07:03 AM
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