Panasonic GH4 User Review Part 3.3 Single Shot Autofocus

GH4, 100-300mm lens

 

The GH4 is reallytwo cameras in one body, a high performance stills camera and a highly capable 4K video camera.

This post is about  autofocus for still photos. There is extensive information about AF for video elsewhere.

Panasonic M43 cameras  have delivered very good single shot AF right from the G1 of 2008. Successive models have improved AF speed and added features and capability. The GH4 has the best AF Single of any camera I have ever used.

Newcomers to  the Panasonic AF user interface might be a bit overwhelmed at first by the number and variety of AF options and features available. Careful perusal of the owners manual is definitely recommended.  Fortunately the GH4 manual is well designed and easy to use but with 420 pages it's no light read.  I hope this and other posts in the current series will be useful for new GH4 owners.

Recommended Setup  In the Custom Menu, set Direct Focus Area On, AF+MF On, MF Assist On (Focus ring on lens), MF Guide On, Peaking On, AF/AE Lock button to AF On, Shutter AF On, Half Press Release Off, Quick AF Off,  Eye Sensor AF Off, AF assist lamp Off (not required:  the AF works just fine in very low light without the assist lamp), Focus/Release Priority FOCUS, .  In the Rec Menu set AFS/AFF to AFS. (page 1/7)

Allocate Autofocus Mode to the Fn3 button (this is the default setting so you can just leave it there).

General caveats about AF  All AF systems will fail in certain situations. Some of these are due to the inherent nature of AF technology, others are due to the inability of the camera to read your mind. Examples:

* A smooth subject with no lines or exclusively horizontal lines or no  texture provides nothing for the AF system to read.

* A dark/small foreground subject which you want in focus in front of a bright/contrasty background. The AF system will be attracted to the bright lights and focus there. You need to set an AF area smaller than the subject and make sure the AF area does not stray outside the edge of the subject.

* Lights on Xmas tree or any other subject with multiple bright light sources in frame will tend to confuse AF systems. The lights produce multiple small flare sources making it difficult for the AF system to figure out which are in focus and which are not quite in focus.

* A forest of little branches is another type of subject which the AF system can't resolve. No matter where the lens is focussed, some branches are in focus and some are out of focus. I switch to manual focus in this situation.

Hints about technique  Achieving accurate AF is not a passive process which you leave to the camera's automatic functions. It needs active guidance from the user.

* If time is not of the essence, half press the shutter button or press the AF/AE Lock button, wait for the AF square to go green and hear the double beep, check that the part of the subject which you want to be in focus actually is, then fully depress the shutter button.

* Adjust the size and position of the active AF area so it lies exactly over and is smaller than the part of the subject you want to be in focus. With the GH4 you can be very precise about this.

Settings  Set the Drive Mode dial to Single Shot. (single rectangle icon).  Set the Focus Mode Lever to AFS/AFF.

Activating AF  As usual with a high end Panasonic camera you get several options. You can activate AF with a half press of the shutter button or by pressing the AF/AE Lock button (back button AF start). However if you set Quick AF in the Custom Menu to On, the camera will continuously try to focus. If you set Eye Sensor AF in the Custom Menu On, the camera will focus when you bring the viewfinder to the eye. I find these last two options distracting so I switch them off. Some users might like them on although they do drain the battery somewhat.

But wait, there's more. The GH4 has a capacitive touch screen. This can be used to select and activate AF, change AF area position and size and fire the shutter. I mostly use the EVF for viewing so I find the touch screen functions not useful for me. Even with monitor viewing I find operating the touch screen awkward. Some reviewers and users report they like the touch screen. Anyway it's there if you want it.

There is also a function called Touch Pad AF which enables the user to move AF area with the touch screen while eye level viewing. Some users have reported they like this function but I found it very awkward as you have to push a finger between the screen and your face. I find moving AF area with the Control Dial much more satisfactory.

Autofocus Mode  The GH4 has a very comprehensive Autofocus Mode which enables the user to manage virtually every conceivable contingency. The price for this is a learning curve to manage the complexity. The AF Mode options are:

Face detect, Tracking, 49 Area, Custom Multi, 1-Area, Pinpoint.

Face Detect does what it says and I find it works well most of the time. The face detect system is quite sophisticated. It will identify a face then locate the eyes and indicate which eye will be selected, usually the closest.   If the system cannot identify a face it defaults to 49 area with auto selection. You may or may not like this as auto selection assigns selection of AF area(s) to the camera.

Tracking  This has been a feature of Panasonic AF from the G1 but I never use it as I am not convinced it works for my requirements. The function identifies the part of the subject in the center of the frame when the shutter button is half pressed then endeavours to keep that part in focus if it moves laterally (left/right, up/down) within the frame. I think this could possibly be useful for video or some types of slow subject movement across the frame. Unfortunately many reviewers and users set tracking when they want the camera to follow focus on a subject moving towards or away from the camera as in sport/action. This is not a good idea, see 1 Area below. Unfortunately the owners manual does not clarify which situations are best served by tracking and which are best managed by another AF function.

49 Area  This covers a box about 3/4 linear size of the whole frame. You can let the camera decide which of the 49 areas to select using it's inscrutable electronic brain, or you can select any subgroup of  9 contiguous areas. I never use the 49 area option as it does not give me enough control over the position and size of the active AF area.

Custom Multi  This is a new AF mode for the GH4 designated by the [Free] icon in the AF Mode submenu. I have to confess this looks to me like the answer to a question nobody asked.  It is a variant of the 49 area Mode which allows you to create an AF area of any size or shape provided it is built up from any of  the 49 areas, which don't even need to be contiguous.  It also allows you to save three of these shapes as Custom AF areas.  

1 Area  I find this to be the most useful AF Mode for most types of photography. It gives the user full control of  AF area position and size. It also works best for AF-C, see the next post.

You can set the active AF area anywhere in the frame. The size can vary from a very small to a very large box.

Activate control of the AF area by pressing the Control Dial anywhere on it's rim (Pre select Direct Focus Area in Custom Mode)  and directly move AF area position by press and hold or repeated presses of the Control Dial. Change AF area size in big jumps with the rear dial or smaller intermediate steps with the front dial.  Return the AF area to center by pressing the Disp button while AF area is active (yellow with bounding arrows).  Half press shutter button to resume normal operation.

With practice this is much quicker to do than read about. I change AF area position and size very frequently as it is so easy to do.

The GH4 offers both smaller and larger options for AF area box size than the GH3. As a result I now find few situations where Pinpoint is required.

Pinpoint  This does what it says. Focus is confined to a very small pinpoint in the frame. Position of the point can be moved within a box smaller than that available for manual focus. Use the Control Dial as for 1 Area above. When the shutter button is pressed half way or the AF/AE Lock button is pressed focus is initiated and the monitor or EVF shows a magnified view of the in focus area as a box within a box. The time for  which this displays can be adjusted in the Custom Menu> Pinpoint AF time> Long/Mid/Short.  The Mid setting gives about one second which is usually plenty.

Pinpoint can be useful for situations like the bird in a tree subject where you want to focus precisely on the bird without catching  all the branches and leaves around it.  I don't use pinpoint very often but when I have used it focus appears to have been very accurate.

Results  You can see from the description above that the GH4 offers the user an astounding plethora of autofocus modes, functions and options. But does it all work ?

In a word, Yes. In a few more words, I have found the GH4 to have the most effective AF system of any camera which I have ever used.  In general use, with a variety of lenses in a range of conditions from very bright to so dark I can hardly see, the AF system nails correct focus almost every time. I have to put that "almost" in there because on my count about 0.5% of the 2000 or so photos I have made with the GH4 to date are not quite in sharp focus, for no apparent reason. The system is just ever so slightly less than perfect.

Panasonic claims that the camera will focus down to EV minus 4 which seems about right to me. In very low light levels the system shifts gears to Low Light mode in which the sensor is sampled at a slower than normal. This slows down AF acquisition but maintains accuracy.

In the early days of MILCs there was much discussion about the relative AF speeds of various camera types and models.  Recent model MILCs from many makers are now so fast at acquiring single AF that the process is almost instantaneous and too fast to measure effectively. The question "has camera A got the fastest AF" has become largely irrelevant as most of them are so fast it hardly matters. In the case of the GH3/4 the only exception to this is that some single focal length lenses, for instance the 20mm f1.7 are noticeably slower to AF than newer primes and zooms.

When comparing the GH4 with the GH3 it is hard to see much improvement in single shot AF as the GH3 was already so capable. Some reviewers have opined the GH4 is a bit faster, maybe that is so but the difference must be quite small. The big improvement in focus capability delivered by the GH4  lies in AF Continuous which is the subject of the next post.