Panasonic GH4 User review Part 3.4 Continuous autofocus

GH4, 35-100mm f2.8 lens

 

In the previous post  I commented that GH4 single shot AF  is not much better than  the GH3 largely because the GH3 is already excellent and difficult to improve.

But continuous AF   is another story altogether. Since the first MILCs appeared in 2008 they have lagged behind the best DSLRs in follow focus performance, using AF Continuous and Burst Mode to photograph subjects moving towards or away from the camera or moving unpredictably. 

The GH4 changes all that.  The GH4 is both faster and more accurate than the GH3 in Burst Mode using  AF-C. Even better the GH4's EVF blackout time after each frame  is substantially less than that of the GH3. Together these improvements make for a much improved user experience and much better results.

Recommended Setup  In the Rec Menu, page 2/7 set the Burst Rate to M. This is the fastest rate which provides AF and live view on each frame and is therefore the optimum rate for sport/action.

In the Autofocus Menu set 1 Area, not tracking.  Set the active AF area  usually to center position and the second or third smallest (not the very smallest) size.  AFC works with the AF area anywhere in the frame. I recommend placing it in the center for most situations as keeping the subject in frame is usually easiest that way.

Preparing for Continuous AF   The GH4 allows very quick shifting from  single shot settings for general photography to follow focus settings for sport/action.

1. Move the Drive Mode Dial to Burst.

2. Flick the Focus Mode Lever to AFC.

3. Move the Main Mode Dial to S (shutter priority AE) having pre set the shutter to a speed suitable for the lens in use. I use about 1/500 with the 35-100mm lens at 100mm and about 1/650 second with the 14-140mm at 140mm.

4. Set ISO to Auto ISO if it was not there already.

5. Check that OIS is On.

6. You can use E-Shutter or the mechanical shutter. I prefer the mechanical shutter provided the shutter speed is faster than the upper limit of the observed shutter shock zone, which is about 1/400 sec. Distortion of subject elements moving within the frame is quite likely with the E-Shutter.

Lenses matter  With the GH4 Panasonic has introduced some new AF technology which means that optimum performance is achieved only with certain Panasonic M43 lenses and not with lenses from other brands even though they are dedicated M43 models.

I  have not yet used many lenses with the GH4 in Burst Mode but I have determined that the Panasonic 35-100mm f2.8 and the  Panasonic 14-140mm f3.5-5.6 allow the GH4 to produce it's full  performance. The Panasonic 100-300mm does not. This lens is good optically but delivers about half the frame rate of the other two lenses together with a much lower success rate expressed as percentage of frames in sharp focus. The operational deficiencies of this lens have become glaringly obvious now the GH4 has arrived. I would like Panasonic to upgrade this lens tout suite.

Memory cards matter  For the results reported here I used a San Disk Extreme Pro UHS 3, 280MB/s card. However I also noticed and others have reported there is little or no loss of performance using a San Disk Extreme Pro UHS 1, 95MB/s card.  Any slower card is not recommended.

Technique  There is nothing arcane here. Zoom to frame your subject, place the active AF area over the part of the subject you want to be in focus, press and hold the shutter button.  Follow the action by panning as required. I have found it is not good practice to zoom while capturing a burst of exposures. Zooming seems to unsettle the AF function. My practice is to zoom between capture bursts.

Results  It is early days yet and I have many more tests to run but my initial results are worth reporting.  Remember these results are all obtained using Burst M and 1Area AF Mode setting.

Frame rate  JPG capture gives 7 fps.  RAW capture starts at 7 fps then  after about 15 frames slows slightly to about 6 fps.

Frames to slowdown  When the buffer is full the frame rate slows suddenly. This point is reached after 48 RAW files in 8 seconds. With JPG capture the camera was still ripping along at 7fps after 100 frames in 14 seconds at which point I stopped recording. Presumably capture will continue at that rate until the card is full.

Recovery after burst  (time to clear the buffer)  This was 23 seconds after 48 RAW files and 7 seconds after 100 JPG files. The camera continues to operate while the buffer is clearing, allowing adjustments to be made and photos to be taken.

Percentage of sharp frames  This is the big test. There is not much point having a camera which runs fast unless it is also accurate. I found that the  GH4 is indeed remarkably accurate, on easy and difficult subjects alike.

Easy subjects:  Cars moving towards and away from the camera and people walking or running towards or away from the camera. Just two model generations ago this would have been a difficult test but now it is no problem for the GH4 at all. On  all my tests in bright light or dull, overcast conditions the GH4 with 35-100mm lens scored 95% or better of frames in sharp focus. The only frames not in sharp focus have been those produced by holding the shutter down until the subject came impossibly close such that I doubt any camera could hold focus.

A more difficult subject:  As it happens three days after picking up my new GH4 I had the opportunity to photograph one of my grandsons playing indoor basketball. The occasion was a grand final so the 11 year olds were running as fast as they could and made very good game of it.   Lighting was mediocre, consisting of a few small skylights and a few high banks of fluorescent tubes. I set the shutter speed to 1/500 sec and Auto ISO selected ISO 6400-12800.

To my surprise and delight 95% of  the 200 frames of boys running were in sharp focus at the active focus area position. This means I didn't always get the right boy in focus but that was a framing issue not a focus problem.  Sometimes I didn't get any of the players in the middle of the frame. The camera simply focussed on the background on that frame then jumped back to the player on the next frame. The remarkable thing is this all happened at 7 fps.

Summary The GH4 represents a big improvement over the GH3 in follow focus performance using AF-C on fast moving subjects. The frame rates are impressive and  the number of sharp frames even more so. The main former advantage of the DSLR over MILC type cameras is held  no longer.

Footnote about technology  Over the last few years most camera makers already had beneath the mirror box (DSLR) or incorporated onto the imaging sensor (some Canon models and several MILCs)  the capability for phase detect autofocus. Many in the camera commentariat opined this was necessary for good follow focus performance. The only holdout using contrast detect AF exclusively is Panasonic which with the GH4 appears to have produced the current champion for AF-C among MILCs, with a performance equal to or better than many DSLRs.    Go figure.  It appears the commentariat was wrong. No doubt other manufacturers will catch up soon, using a variety of technologies. Us camera users are the beneficiaries.

There is a curious irony afoot right now. Camera sales are falling steeply across all categories but the actual cameras being offered are better than ever and improving with each new model.  Happy days for those of us who still like to use a real camera to make photos.