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GH2 23 Point Focus Question

Discussion in 'Panasonic Cameras' started by Tom Swaman, Apr 11, 2011.

  1. Tom Swaman

    Tom Swaman Mu-43 Veteran

    I am a new GH2 camera user. I have read the Operating Manual carefully, but I do not understand the operation and proper usage of the 23 point focus setting. Would someone kindly explain this to me in simple vocabulary including, but not necessarily limited to:

    1) When are there 23 focus points and when are their 9 focus points/zones?
    2) When ought this focus mode be used? How does one know on what point in the subject the camera focuses?
    3) Is this functional in both single servo and continuous servo auto-focus and where does it work best?
    4) How ought one use the touch screen when using the 23 point autofocus modw?

    Thanks in advance for enlightening me. Frankly, I tend to believe that whoever responds m,ay be helping a few more folks than me. I found the Manual to be very confusing on this major issue.

    Best regards,
    Tom
     
  2. sprinke

    sprinke Mu-43 All-Pro

    Apr 5, 2011
    Pasadena, CA
    Debi
    I agree the manual is kind of confusing, but after playing around with it, this is what I think.

    I think there are 23 POSSIBLE focus points. When you have the camera set to 23AF and point it at something and press the shutter halfway, you can see that the camera has chosen one or more of those points to use as focus points for the shot. You can identify the focus point because it has a green-bordered box around it. I have no idea what algorithm the camera uses to determine them, as it seems to choose different ones each time, even if I'm looking at the same thing.

    Now, the 9 zones comes into play if you want to restrict the camera to looking for focus points in just a particular area of the frame. Say you are taking a picture of your family in front of a waterfall, but they are off in the bottom left corner. You can touch the screen in the lower left. Now the screen will display a group of yellow-bordered boxes. This is the zone that you have selected. Now if you press the shutter halfway, you can see that it only selects focus points (green-bordered) from within your selected zone. You can see what zone you have selected even after the yellow boxes go away because a plus sign remains on the screen. If you want to cancel your zone selection, press the Menu/Set button.

    I'm not sure I answered all of your questions but hopefully things make a little more sense.
     
  3. ~tc~

    ~tc~ Mu-43 Hall of Famer

    Oct 22, 2010
    Houston, TX
    With the Contrast Detect Auto Focus our cameras use, there are more like 3 million focus points, as it's using the actual sensor, not a separate Phase Detect AF sensor.

    As above, it can select up to 23 at one time, but that's kinda ridiculous.

    As mentioned above, it TRIES to detect what it thinks you think is the main subject, but is only successful some of the time.

    Personally, I don't use this focus mode any more in favor of Face Detect or Center/spot.
    Face Detection (not to be confused with Face Recognition) is an awesome tool, and a power that PDAF can not perform. I have found it VERY reliable in finding faces in scenes and focusing on them accurately.

    The other option is center/spot (which in your case would be further improved by the touchscreen) where it will focus on whatever is in the box. Note that there needs to be some contrast in there for it to focus. You are often better off focusing on the EDGE of a subject rather than in the middle, as there is more contrast.
     
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  4. John M Flores

    John M Flores Mu-43 All-Pro

    Jan 7, 2011
    Somerville, NJ
    My understanding is that it works like most P&S cameras do, guessing what should be in focus. When taking typical photos - a landscape, a portrait of one or more people at an event, etc... - it does ok. Anything beyond that and it's just guessing IMO.

    Heck, sometimes I don't even know what I want in focus - how is the camera supposed to know LOL!
     
    • Like Like x 1
  5. Tom Swaman

    Tom Swaman Mu-43 Veteran

    Sprinke, ~TC~ and John,

    Thank you all for sharing. I understand better now, but I still cpould use more information to fully understand. It sounds like the camera selects a small zone on which to focus, i.e. one of 23 points. Then the photographer generalizes an area of 9 points, one of which is the point selected by the camera. Then the photographer optimizes the shot composition with the nine selected points hopefully in the correct area. Finally, the camera reselects one of the nine final points that contains some significant contrast ratio and focuses on this. Maybe I have it and maybe I do not. I am almost certain that phase detection need not enter this discussion as the sensors of the GH2 are not detecting phases/phase differentials/phase shifts.

    If anyone else can add to this or straighten me out, admittedly a difficult task, please chime in.

    With appreciation,
    Tom
     
  6. zpierce

    zpierce Super Moderator

    661
    Sep 26, 2010
    Minneapolis, MN
    Zach
    Has anyone been successful using AFC? I'd like to get that to work better as I often photograph runners, but I haven't been very successful.
     
  7. sprinke

    sprinke Mu-43 All-Pro

    Apr 5, 2011
    Pasadena, CA
    Debi
    Can you describe the problems you've been having trying to use it? I was out today and it seemed to be working decently (I was trying it with walking birds and fast-crawling insects).
     
  8. Tom Swaman

    Tom Swaman Mu-43 Veteran

    Well, I am new to the GH2, but I tried AFC yesterday to photograph two hyperactive dogs on the loose. I can only tell you that this AFC is the best I have ever used. It is much faster than that on my Nikon D300s. I personally found the D300 to be the absolute best D-frame camera available for difficult photographic situations. I also found that I used manual focus or AFS and not AFC with those cameras regardless of what I shot. From what I have seen so far, I think that ADC on the GH2 offers some excellent possibile solutions to certain difficult focusing problems.

    To avoid problems, you may want to develop your AFC expertise by restricting yourself to good light/good contrast objects. Under these conditions, you will want to experiment with how your AFC responds to the angle of motion of your subject relative to your optical axis. Then, you can select those angles where your AFC works for you and expand your horizons from there.

    Best of success,
    Tom
     
    • Like Like x 1
  9. zpierce

    zpierce Super Moderator

    661
    Sep 26, 2010
    Minneapolis, MN
    Zach
    To be honest, I haven't played with it much. Your replies give me encouragement to give it some effort. I thought it only worked in the multi-point mode where you didn't have any influence over what it was focusing on. I just played around with it in my living room and looked at the manual again and noticed that it works in all the modes which is a lot more promising. I also may be projecting my trouble with it on the G1 to the GH2, which is clearly not fair. That's probably the last time I spent any real time with the function.
     
  10. ~tc~

    ~tc~ Mu-43 Hall of Famer

    Oct 22, 2010
    Houston, TX
    Tom, I get the idea you are used to an SLR, and that's why PDAF entered the discussion. Remember that the actual image sensor is what is determining your focus on these cameras. It is capable of evaluating focus ANYWHERE in the scene, not just at the 9/23/31/whatever points in the PDAF sensor.

    I think you're over thinking it too much. Wherever is in the green box, or wherever you touch on the screen will be in focus. Additionally, there are no front/back focus issues with CDAF, it is more accurate.
     
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  11. Tom Swaman

    Tom Swaman Mu-43 Veteran

    ~TC~,

    You gathered very correctly. I understand what you wrote and I shall follow the old adage and "learn by doing". I have sold all of my gear including a professional studio with very large lights and I am fully invested in and planning to learn MFT for generating quality still, high quality photographs. I am not interested in doing video.

    One question for you is which focus area mode is best for which kind of subject?

    Thank you ~TC~,
    Tom
     
  12. ~tc~

    ~tc~ Mu-43 Hall of Famer

    Oct 22, 2010
    Houston, TX
    If there's a person in it, definitely use face detection. Otherwise, it probably doesn't matter a whole lot, especially with the touch screen
     
  13. Tom Swaman

    Tom Swaman Mu-43 Veteran

    TY, ~TC~. Now that face detection is a whole new thing to learn. I am one of those old school fogies who still focuses on the nearest eye and optimizes for DOF. Oh, so much to learn, so little time!

    Much appreciation,
    Tom
     
  14. zpierce

    zpierce Super Moderator

    661
    Sep 26, 2010
    Minneapolis, MN
    Zach
    I don't like face detection, because if they're not straight on posing, it usually doesn't pick up the faces. That in and of itself wouldn't be a deal breaker except for it goes into the 23 point "camera's choice" focus mode. If the backup focus mode was the center point, I'd use it all the time, but when face detect only ends up working say 30% of the time, I can't live with the camera choosing random focus the other 70%.
     
  15. Tom Swaman

    Tom Swaman Mu-43 Veteran

    Zach,

    Thanks for your comments and perspective. I have not used face recognition and tend, albeit out of ignorance, to consider this to be an electronic toy. I also never used this on my last several Nikons.

    I still do not feel comfortable with my understanding of the 23 point focus mode and how it works/when to use this. I think I get 90% of what the GH2 does with still photography, but this 23 point mode finds me very uncomfortable.

    Best regards,
    Tom
     
  16. zpierce

    zpierce Super Moderator

    661
    Sep 26, 2010
    Minneapolis, MN
    Zach
    I don't use the 23 point mode at all, however this discussion prompted me to review the autofocus modes in the manual again and I think I may try and use it for some situations. 99% of the time I use spot focus and just choose to focus on however, when I'm shooting runners that are in motion, it's impossible to focus on their face then recompose while they're moving. What I discovered with the 23 point focus is that you can choose from 9 major areas of the 23 points. Therefore I want to try just choosing the upper middle section of my screen where their head should be and try that with rapid fire shooting. I'm hoping that it will hit on their high contrast face, even though the face will move around some, it should be in that general area if I'm doing my job. Other than specific cases like that, I suggest using spot focus and do the old half shutter focus and recompose method. That works wonderfully for me. The 23 point auto mode is just the camera guessing and more often than not it will not guess what you want it to focus on.
     
  17. Tom Swaman

    Tom Swaman Mu-43 Veteran

    Zach,

    Thank you for your comments. I agree with you, but I also do not consider myself to be an expert. I think a lot of what results from photographing moving/running subjects rests in the angle of motion relative to the optical axis. No, I have not forgotten shutter speed and rear curtain sync when making this comment. Its just that the smaller the angle between the optical axis and the axis of motion, the harder is it to maintain critical focus.

    Best regards,
    Tom
     
  18. Wasabi Bob

    Wasabi Bob Mu-43 Top Veteran

    This might help

    I was able to get the following explanation of how the 9 / 23 point focus system works:

    The latest VENUS engine is able to calculate up to 23 separate contrast points in a given photo. Using an internal database of scene conditions, these points are selected and used as focus points. The focus is calculated as if the lens was set at its widest aperture. The actual lens aperture, if smaller, will further reinforce the focus operation as the depth of field increases. Therefore, using a manual aperture selection or using Aperture priority will have no effect on the focusing performance. Both systems work with the AFC and AFS focusing modes.

    When using the Touch Focus, you are limited to ~ 5-6 points among the 23.

    Selecting between the 23 and 9-point systems is a user preference. While the 9-point system evaluates a slightly smaller area, the focus speed for both is virtually identical.

    If the user wants to focus on specific subject or point, it’s recommended that the 1-point focus be used.

    A good summation would be:
    23 points: Detects the contrast all area in the frame and is best suited for Landscape photos.

    9 points: Functions the same as 23 points, but in a slightly smaller area.

    1 point: Best suited in photos where a specific object needs to be in focus, such as a flower.

    Touch AF: Allows the user to select any given point.
     
  19. mick / Lumix

    mick / Lumix Guest

    169
    Oct 3, 2010
    RTM, lets miss out the other letter ! Just use centre point and recompose, easy. That said Face Detect is good as it will meter from the face and backlight problems will be avoided.
     
  20. Tom Swaman

    Tom Swaman Mu-43 Veteran

    Wasabi Bob,

    Thanks for the excellent explanation. If the camera is set to AFC and an object moves through the 23 point frame, and both the AE and AF lpcks are off and focus tracking is off, does the algorithm continually re-compute the focus? What about in AFS?
    I use single point focus, generally set to the smallest possible area, lock the focus, recompose and shoot. I simply would like to utilize the camera functions as optimum and understand these so they do not inhibit my picture taking.

    Much appreciated,
    Tom