How the Panasonic Post Focus function works

Sample images above supplied by Panasonic. Photo Review tests below.

Panasonic’s new Post Focus function, which was officially announced on 20 November, is designed to allow photographers to select a point of focus after a shot is taken and provide the ability to select different points of focus within the same image. While this might appear to represent new technology, it’s actually an innovative approach to focus stacking, achieved by integrating two existing functions in the company’s latest cameras.

The new firmware is available for the DMC-GX8, DMC-G7 and DMC-FZ300 at the LUMIX Global Customer Support Site: http://av.jpn.support.panasonic.com/support/global/cs/dsc/index.html.(The firmware that enables the DMC-GH4 to comply with Post Focus will be released in early 2016.)  

When the firmware is installed, it adds a Post Focus mode setting to the camera’s shooting menu (shown above). If Post Focus is switched on, every shot will be recorded using this mode.

The new Post Focus mode is added to page 3 of the GX8’s shooting menu.

Panasonic’s system is much simpler and cleverer than the pan-focusing systems developed by Lytro back in 2011  and more recently by Light (which put 16 micro-cameras with different focal lengths in a single body). It also utilises functions already available in the latest cameras ““ without compromising any of the camera’s capabilities or performance.

How it works
 Instead of adding extra components, the Post Focus system works with the camera’s existing Depth from Defocus  autofocusing and movie capabilities. The 4K movie recording function is used to record roughly one second of MP4 video at 30 frames/second. During this recording, the camera’s autofocusing system scans the lens around the subject, moving from the foreground to the background to cover the entire scene.

It’s like a sophisticated form of focus bracketing and produces a movie clip containing about 30 frames. You can see the AF system searching while the shot is captured and follow the focus points as they are identified by rectangles around areas that are selected.

 The indicator showing the image is being recorded and processed.

During the one-second exposure and continuing roughly a second after, a whirling indicator on the screen lets you know the camera is ‘busy’, as shown in the screen grab above. This is important because if you move the camera while the shot is being captured ““ or if the subject moves substantially ““ the end result probably won’t be totally sharp.
 

 Selecting a frame to save.

After that image has been captured, you can review it on the camera’s screen and select the frames containing the desired sharp area. When a frame is selected, the camera will ask you if you wish to save the frame. If you tap on ‘Yes’, it will be saved at 3328 x 2496 pixels (8.3 megapixels).

This is smaller than the highest still-capture frame of 5184 x 3888 pixels (20.1 megapixels) but large enough to print at A3 size. Interestingly, the frame is also cropped slightly, although its aspect ratio is unchanged.

Press the play button to move on to subsequent frames and repeat the selection and saving process. Each time you save a frame it is given the next number in the JPEG sequence that is selected after the source image (which has the first number in the sequence), as shown in the grab from a computer screen below.

You can save as many frames as yuo like from the sequence. All Post Focus shots are numbered in the same way as JPEGs so they appear in order when you download the contents of a memory card to your computer. (Post Focus doesn’t work with raw file capture.)

The camera’s touch screen controls can be used to select the Post Focus mode (which is on page 3 of the camera’s shooting menu) and also for triggering the exposure and selecting frames during playback. Touching the point where you want the focus to be during playback will cause the camera to find and save that frame as a separate JPEG file. Normal playback functions like magnification and peaking are available in playback mode to make it easier to select the frames with the best sharpness.

One of the really clever features of this function is that, because the image is actually a normal 4K video recording, there’s no real need to select the frames via the Camera’s playback mode. It’s easy to grab individual frames later when you’ve downloaded all your images to your computer, although the file names won’t be in the regular JPEG format, as shown in the screen grab below.

 

Any frame-grabbing program that supports MP4 movies can be used to capture individual JPEGs. We used MPC-HC, a freeware player for Windows, which is available for downloading at  https://mpc-hc.org/. Lightroom is another alternative.

While Panasonic sees the main use of Post Focus is to help photographers who find it difficult to decide where the camera’s lens should be focused, we can see a few other reasons to use it. The 30-frame sequences provide plenty of scope for focus stacking to increase depth of field in situations where it’s difficult to stop down. Focus stacking can also help you to avoid the diffraction-related loss of sharpness at small apertures caused by diffraction.

The main downsides we can identify with the Post Focus function is the time taken to record the video footage and the brevity of the clip. Although it’s relatively easy to hold the camera still enough during the one second recording with stabilisation engaged, it’s not so easy to control subject movements. You may encounter some problems when recording fast-moving subjects, particularly if they’re large and move suddenly in front of the camera. Smaller moving objects can often be imaged sharply by the 1/30 second shutter speeds the camera uses, as shown in the sequence below.

Note that the bee remains in focus while the flower is sharp but becomes defocused as the focus shifts towards more distant parts of the scene.

It would be nice to extend the length of clips a bit if you had some way of steadying the camera, such as mounting it on a tripod or resting it on a wall or benchtop. Having a slightly longer ‘exposure’ time would give the AF system longer to scan the scene and allow the camera to record more frames, thereby giving users a wider choice of focus options.

Post Focus works best with wide lens apertures so if you set the camera to the P mode, the fastest lens aperture will usually be selected. You can also use Post Focus in other shooting modes, but may not get the results you want if the lens is stopped well down.

Panasonic is marketing the Post Focus function as a way to assist people who can’t get the focus right while they are shooting and those who aren’t certain where the plane of sharp focus should be in different scenes. We think it’s also useful for providing different perspectives on focus and making novice photographers more aware of depth of field and selective focus controls.

In theory, you should be able to record 4K video using the MP4 codec and achieve a similar result to Post Focus. However, the camera’s AF system would need to be programmed to scan the scene and record a rapid sequence of frames, varying the focus continuously. We’re not sure how many cameras would be capable of this but we suspect very few at present. In the future, we think there might be more. Panasonic plans to introduce the Post Function in subsequent cameras introduced from next year.  

The main advantage of the Panasonic system over competitors like Lytro (which created the first excitement about post-capture focusing) and Light is that it’s included in regular cameras. The Panasonic camera images are also larger, easier to view and generally more readily usable. Light field cameras provide a better facility for depth-of-field-related image editing and are better able to record fast-moving subjects.

Whether these factors are deal-breakers is anyone’s guess, as is the value of Post Focus as a reason to buy or upgrade a camera. It will be interesting to watch both technologies through future developments.