Lumix GH3 Review Part 4, Single Shot Focus

LUMIX GH3 REVIEW  PART 4,  SINGLE SHOT FOCUS

It really is very good

Author AndrewS  April 2013

Note about AFC: I will explore the GH3's performance in AF Continuous  with sport/action style subjects in a separate blog post. My investigation is ongoing but at this stage I can say that the GH3's  AFC  performance is better than many reviewers appear to realise and quite adequate for many sport/action situations.  Optimum setup, preparation and technique are essential for best results.

Lumix GH3 with Lumix 35-100mm f2.8 lens

Introduction    Way back in the good old days of mechanical cameras and manual focus lenses  [there were no consumer zooms in the 60's and 70's]  every lens had a focus distance scale and usually a depth of focus scale.  You could, and I often did, set the focus distance directly on the scale and set the lens aperture to give the required depth of focus. Many modern autofocus lenses lack a focus distance scale. Some new manual focus lenses with M43 mount, such as those from Cosina/Voigtlander,  do have such scales. But they lack electronic communication with the camera body so there is a downside to these lenses.   Many zooms, and as far as I am aware, all M43 zooms are of varifocal type which are not compatible with such scales as they change focus with zoom.  To date, no M43 cameras have implemented an effective electronic alternative to the old mechanical focus distance scale. I wish they had such a feature as the ability to pre set focus distance by scale would be very useful. It seems to me that it should be possible as the focus distance set by the lens is presumably known by the camera.  One consequence of this lack of focus scale is that modern camera/lens combinations are highly reliant on the effectiveness of their autofocus systems.

SLR and DSLR autofocus systems For many years I used Canon EOS film SLR's then Digital SLR's. The main reason I abandoned this camera system several years ago was it's unreliable single shot autofocus. If my memory serves me correctly I owned about ten of these cameras over the years and every one had an AF problem, some worse than others.

Micro Four Thirds System autofocus   Lumix M43 cameras had very good single shot AF [AFS] right from the first model, the G1. The early Olympus Pens were not so good but Olympus caught up with successive models and now the Pens have very good AFS.  Lumix M43 AFS has steadily improved with each model since the G1 to the point I would now say the GH3 has the best AFS of any camera I have ever used.  Other reviewers have expressed the same view. For instance Jordan Steele reviewing the GH3 on his Admiring Light blog wrote  "...in my opinion it's the best single shot autofocus available in ANY camera on the market today".

Qualities and Characteristics of GH3  SAF 

* It is Sensitive. I mean this in two senses  The first is that  it will focus on anything with texture, for instance brush marks in paint, the weave in cloth and similar. The second is that it continues to operate accurately in low light although in very low light the AF process slows a little.  As a result I have the AF assist lamp switched off  in the [Custom Menu, Page 2/8].

* It is Precise.  The word "precise" refers to the ability of a measurement to be consistently reproduced.  If you AFS  on a subject the camera will select the same focus distance time after time.

* It is Accurate  The focus distance precisely selected by the camera is the correct one. You could have an  AFS  system which is precise in the sense that it regularly selects the same focus distance, but that could put the subject out of focus every time. This is a problem for many DSLR camera/lens combinations using Phase Detect AF.

* It is Fast  So fast in fact that with most current model lenses and most subjects I hardly notice the AF process occurring.

* It uses Vertical lines [with the camera in landscape orientation] in the subject to acquire focus. The camera will not focus on a subject containing only horizontal lines with no texture between the lines. It will focus on diagonal lines presumably because of their vertical component. I do not know whether focussing on texture is a product of the camera identifying the multiple small vertical line components of texture or whether another process is operating in this case.

* AFS works Everywhere in the frame. However my tests show that with the particular camera body in my posession AF in the extreme top left corner of the frame is inaccurate in about 50% of test shots. I can't imagine why one would want to focus in one of the extreme corners but for safety I would exclude the corners. AF appears to be reliably accurate to the edges, top, bottom and sides.

Conditions favouring accurate AF

Lens:  Medium wide, standard, short telephoto. Wide aperture.

Subject: Bright light, definite shapes and structures, sun or other light behind the camera or from the side. Clear conditions with high subject brightness range. Subject close to the camera.

Conditions in which AF may not always be accurate

Lens:  Occasionally my ultrawide Lumix 7-14mm misses focus for no reason that I can determine.  Long zooms at the long end appear to have a slightly higher rate of focus misses than normal focal length lenses or the short end of zooms. This may be related to the subject, see below.

Subject:  Low light, ill defined subject elements, sun or other light behind the subject, haze, mist, dust, subject far distant from the camera.

In general the contrast detect AF [CDAF] system works best in conditions where high subject contrast is presented to the camera and worst with low subject contrast. No surprises there.  Sometimes CDAF systems struggle with subjects containing multiple small light sources within the frame.

Setting position and size of the active AF area  One of the advantages of a good CDAF system such as that found in the GH3 is that the active AF area can be positioned anywhere in the frame, [except with Pinpoint AF Mode which limits focus to a reduced frame area]  with reservations about the extreme corners as noted above. This enables the photographer to set the AF area precisely where required, as for instance on the near eye of a portrait subject. This enables multiple pix to be taken of the same subject without having to focus and recompose for each shot. In [1-Area] AF Mode, the GH3 provides two ways to change position and size of the AF area. You can use either or both.  With the touch screen active, [Custom Menu] > [Touch Settings] Page 7/8,  you can easily move the AF area around with the capacitive touch screen. There is also a feature called [Touch Pad AF] which renders the monitor touch sensitive when the viewfinder is in use, the idea being that you move AF area by touching the monitor while looking through the viewfinder.  All this touch screen/touch pad technology works as advertised.  The problem is ergonomic. When viewing on the monitor it is, in practice quite difficult to devise a smooth workflow in the Capture Phase of operation if touch screen AF area movement is used.  You have to remove either the right or left hand completely from the camera to be able to place a finger or thumb onto all parts of the screen. This completely unbalances the camera and disrupts all the Capture Phase functions of both hands while the AF area is being repositioned. The Touch Pad AF process when eye level viewing is even more awkward as you have to poke a thumb or finger of the right hand [for right eye viewers] or left hand [for left eye viewers] between the face and monitor.  

The second way to move AF area is with the Control Dial on the back of the camera. In [Custom Menu] Page 3/8, set [Direct Focus Area] ON.  Press the knurled ring around the Control Dial anywhere on the circumference once to activate the process. Now you will see the AF area bounded by a yellow box with yellow arrows on each side. Press up/down/left/right on the Control Dial to move the AF area around the frame.  If you press and hold the Control Dial the AF area will move. Rotate the Control Dial, Front Dial or Rear Dial to change the size. To return to Capture Mode press the Set button in the center of the Control Dial or half press the Shutter Button. To return the AF area to frame center press the Disp Button with the AF area bounded by yellow. All this is much easier to do than describe. Using the Control Dial works with Monitor View or Eye Level View and in practice, with practice,  works well. The left hand can stay in place supporting the lens, the right index finger can stay on the shutter button and  the right fingers can stay on the handle, although not gripping it. Some reviewers have complained that the Control Dial is difficult to operate as it's right side  is below the level of the surface of the handle.  I have found that as with many things a little practice is very useful although I do agree that a small detail redesign here could improve usability without making it too easy to accidentally bump the right side of the Control  Dial. Others have complained that the Disp button is hard to find as it is recessed, however again I have found that with a little practice it is actually easy to locate  by feel without having to look at the camera. With some practicethe whole process of changing AF area position and size can be carried out by feel without removing one's eye from the EVF. 

The missing JOG Lever  The process of changing AF area position would be greatly facilitated if this camera had a JOG Lever, similar to that offered in high end DSLR's. The optimum location would be in a spot between the existing AE Lock and Motion Picture buttons.  This would enable very fast, precise, direct control of AF area position without having to shift grip with either hand. Of course the existing buttons/lever would have to be relocated, but that would  pose no great problem. I will discuss my ideas about this in a separate blog post in the coming weeks.

Using back button AF start  The GH3 offers back button AF start, a feature which has been commonplace on high end DSLR's for years and greatly appreciated by experienced photographers.  Previous G and GH cams can also enable back button AF start but the implementation is different, most noticably in AFC.   Go to  [Custom Menu, Page 1/8]  > [AF/AE Lock] > see Four options. Select the fourth,  [AF-ON]. In AFS, the AF-ON button starts, acquires then locks AF as long as the button is held down.  It also activates but does not lock AE.  This is very useful for acquiring and holding AF on a specific part of the subject while waiting for the subject to smile or whatever at which point the shutter button is pressed and the shot captured with minimal shutter lag.  In AFC the button activates and continues AF while it is held down.

AF + MF assist  As with previous Lumix models the GH3 offers AF+MF with MF assist if desired. Go to [Custom Menu, Page 3/8] Set AF+MF> ON. Scroll down to the next field, [MF Assist].    This allows you to allocate image enlargement to the Focus Ring on the lens, the AF Mode (Fn3) button, both or neither.  If [MF Assist] is allocated to the Focus Ring, the following sequence operates. First position the AF Area as desired. Next acquire AF with half press of the shutter button and hold the half press (right index finger). Second, start turning the Focus Ring (left hand). This will magnify the preview image in the EVF or Monitor. Rotate the Rear Dial (right thumb) to cycle magnification through 4x (with a central box), 5x or 10x (full screen). A certain amount of dexterity and practice is required to do this smoothly. With [1-Area] AF Mode this process alows you to fine tune focus very accurately on a specific part of a subject. Full press the shutter button to capture the shot. With practice all this is easier to do than read about.

Manual Focus  On the Focus Mode Lever around the AF Lock button, set MF. As described above you can set the MF Assist to the Focus Ring, Fn3 button or both or neither. If the Focus Ring has been selected, rotate it and the preview image enlarges, the degree of enlargement being controlled by the Rear Dial. The advantage of using MF is that focus will not be altered when you half press the shutter button. You just have to be careful not to bump the Focus Ring while making successive exposures at the same focus distance.

Using manual focus lenses without electronic contacts  Set [MF Assist] to the [AF Mode (Fn3)] button. This option is included for lenses without electronic contacts so you can control MF assist and preview enlargement from the camera body.

Riders Ready 1 Full Frame

Riders Ready 2 Full Frame

Riders Ready 1 Crop

Riders Ready 2 Crop

 

 

 

 

 

 

 

 

 

 

 

Explanation of the horse photographs:  The two photos were taken withing a few seconds of each other, with the GH3 and 35-100mm at 100mm and f2.8. The active AF Area was in the center of the frame for each photo. On the crops you can see that #1 is focussed sharply on the metal railing while #2 has the front horse's whiskers in sharp focus. I should have decided precisely which part of the subject I wanted in sharp focus and taken control of the process to achieve that.

Hints and tips for optimising AFS accuracy and reliability.

* You decide where to place the active AF area.  Use [1-Area] for most situations, or [Pinpoint] in specific circumstances. If you set AF Mode to [23 Area], [AF Tracking] or [Face Detect], the camera decides where to focus which may or may not produce the desired result.

* Dealing with backlight  When the light is coming from behind the subject and/or the background is brighter and/or more contrasty than the subject it is necessary to ensure the active AF area is smaller than the subject and is located within the visible boundaries of the subject.  All kinds of AF systems will home in on the brightest/most contrasty part of a scene unless specifically directed elsewhere.

* Explicit placement and size of AF area  I have found that on reviewing many photos that some have seemed a bit soft paticularly those taken with the Lumix 35-100mm f2.8 lens. On close scrutiny I realised the "problem", which is not really a problem, just a characteristic of the camera/lens combination,  is that:

1. Depth of focus at 100mm and f2.8 is quite shallow.

2. If I don't specify precisely which part of the subject I want to be in focus, the camera may select somewhere else, not to my liking. The camera cannot read minds, it requires explicit instructions about AF area placement and size.

Summary  I have found that in general photography using the GH3 in Single Shot Drive Mode and AF Single Focus Mode,  with thoughtful placement of the active AF area position and size, the camera delivers AF accuracy approaching 100% in a wide range of conditions. There are occasional slip ups which are usually due to operator error on my part. Most of my use and testing with the GH3 has been with the 12-35mm f2.8 and 35-100mm f2.8 zoom lenses.