by Ian Burley
Panasonic is rolling out its Post Focus feature to an increasing number of camera models, but what exactly is Post Focus and how does it differ to focus bracketing and focus stacking?
The DMC-GX8 is among the first Panasonic models to acquire Post Focus capability thanks to a firmware update
Basically, Post Focus is Panasonic's take on being able to shoot a still image and then being able to refocus that image afterwards. This is a feature that has been demonstrated in Lytro lightfield cameras and also some Nokia Lumia smartphones. Panasonic's cameras that are Post Focus enabled - a firmware update may be required - currently include the Micro Four Thirds DMC-GX8, G7 and the DMC-FZ330 bridge camera. The top of the range Lumix GH4 will also get Post Focus via a firmware update in the new year. None of these cameras works like a Lytro camera that uses lightfield optics and processing to record a still image that can be refocused, so how does Panasonic make it work?
How doest it work?
It's really very simple; the camera selects each of its 49 focus points (7x7 array) focuses on whatever it can at each of those points and records the resulting frame to build a movie clip comprising up to 49 frames. Sometime more than one point will be in focus at the same time so there may not be a need to record as many as 49 individual frames. Thanks to the fast focusing of most Micro Four Thirds lenses the process usually only takes a few seconds, although it's worthing noting that Post Focus is not really useful for scenes where the subject is changing during the process. After you have used Post Focus you can review the image and touch the camera's screen on the part of the frame that you want to refocus. The recorded movie frame that corresponds to the focus point you have tapped on the screen is then recalled and, hey presto, is focused as you requested. You can then export that frame as JPEG still.
It may have occurred to you that all the Panasonic camera models that have or will have this feature have a touch screen and are able to shoot ultra high resolution 4K video. The touch screen is needed for in-camera selection of the refocused point and to make the exercise worthwhile the still frames stored and recalled from the 4K clip are of course 8.3 megapixels in resolution. The one 4K-enabled Panasonic model that comes to mind which doesn't have a touch screen is the LX100. In theory, Panasonic could have added Post Focus to the LX100 but it would be less useful without the touch screen. On the other hand with all Post Focus enabled cameras a Post Focus 4K clip can be loaded in to a suitable application, for example Adobe Lightroom, and the desired frame extracted manually.
Comparing Post Focus with focus stacking and bracketing
Some Olympus Micro Four Thirds camera models now feature focus bracketing and focus stacking, so how does Post Focus compare? On Olympus models focus stacking is a process by which a series of frames are recorded with the focus shifted slightly for each frame. The focus of each frame is not determined by a focus point as is in Panasonic's Post Focus. Olympus focus stacking is aimed at macro photographers for artificially increasing the depth of field of a macro image and the donor frames are combined to form one new image within the camera. Focus stacking is not new and can be done manually and processed, for example, in Photoshop but automating it in the camera makes it much easier and more convenient. Only a small selection of Olympus lenses work with the focus stacking mode, incidentally. Like Post Focus, Olympus' other mult-focusing option, focus bracketing, works with any AF Micro Four Thirds lens, but like focus stacking and unlike Post Focus the process involves recording a series of frames with the focus shifted (in front of and behind the starting focus point) but each frame's focus is not determined by an actual focused point. If you are very unlucky, using an aperture and focal length that delivered a very shallow depth of focus, it's possible that a focus bracket might still result in the point you were interested in being slightly out of focus. As Post Focus actually focuses on each of the 49 focus points across the frame it is far less likely for a key point in the frame not to be focused sharply.
Is Post Focus actually useful?
Discussions with colleagues have resulted in the question mark over just what is Post Focus useful for. Apart from being a neat technology showcase for Panasonic, I do believe it has a useful purpose. You can concentrate on framing your image and not be distracted or held back by ensuring that the point you absolutely need focused is properly selected. There may also be situations where more than one part of the scene are of interest and so you would want to ensure they are all available as differently focused frames. But Post Focus does have notable limitations; it's not useful for scenes where there is any appreciable change in the subject while the set of focused frames is being recorded and for those who want to extract maximum image quality from the camera a 4K 8.3 megapixel JPEG still may not be good enough compared to a full resolution RAW file. Nevertheless, to have Post Focus available in camera mode armoury is certainly welcomed by me.
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