Focus Stacking in the field – becomes a reality with the Panasonic GH4

Focus Stacking in the field has become a practical reality for me thanks to what Panasonic calls 4K post focus, avaiilable in the GH4 and several other models…..

The very first time I saw the remarkable images that a scanning electron microscope could generate I was completely hooked. The Sunday Times colour supplement, a journal of quality in those pre-Murdoch days published a series of images by the remarkable Lennart Nilsson. Every detail was revealed in sharp focus by taking layers within the target and building up an image created via reflected electron beams from these. I dreamed of one day being able to do something similar with natural light and with living material, not the dead specimens coated with a thin layer of gold deposited in a vacuum chamber…now I can.

Grasshopper 5 (B, 3, 5)(LR) copy

Head of an Egyptian grasshopper (Anacridium aegyptiacum): this is a section of the 4K frame (original 1153 x 1730 pixels) that reveals the level of detail the stacking process picks up. Note the softness of the background..this is determined by the aperture used in creating the stack. Here Exposure per frame was f /5,6 at 1/500th sec.

The Revolution: 4K post focus in the Panasonic GH4 (and various other Panasonic cameras that boast a 4K video capability)

For the past few weeks I have been like a kid in the proverbial candy store using a feature of the Panasonic GH4 called 4K Post Focus. The result has been some superb stacked image results.What this camera does differently is to use its high resolution video capability (something for which many pros have bought it) rather than a burst involving the shutter. The 4K video mode employed allows super detailed video for the 4K refers to the approximate value of the long edge of each frame captured.

a. The frame rate is 30 fps and the exposure of individual frames is set beforehand. I use f/4-f/5.6 as the marked lens aperture for this tends to cover the proverbial ‘sweet spot’ where the lens has its optimal performance.

b. You also get the Bokeh associated with the wide aperture and this gives soft backgrounds that accentuate the detail of the final stacked image

c. I then adjust the ISO between 200 and 400 (say) to get a shutter speed that will freeze movement. The stacking software can cope with tiny movements between frames when it aligns images but the more you can cut down movement of subject and camera the better. To this end I always use a tripod and a flexible arm when possible to steady plant stems during the scanning of the subject and focus shift by the camera.

Untitled 2

These three frames are taken from the focus stack…nos 3, 50 and 70. You can see how the focus shifts as the camera goes through the stacking process…just over 2 secs – I cut a few frames from the beginning and 20* from the end where the camera tries to image up to the background.

d. The aspect ratio of the frames can be selected beforehand: 1:1, 4:3, 3:2 and 16:9, for example and the pixel counts along the edges adjusted to give more or less the same final overall file size (about 5.5 MB).

frame dimensions

The table shows the frame dimensions for various common picture proportions. The total pixel count is very much the same and the file size is approx. 5.5MB as a RAW file.

By current standards, obsessive pixel counters (and those seduced by the bigger is best myth with sensors)  might think these are low. However, my first published Digital images with a Nikon D100 and then Sigma SD10 produced very sharp A4 magazine cover shots with smaller files… Large prints are easily possible with these file sizes – eg.  28 x 21cm at 300dpi before any recourse is made to On-Ones fractal software in the case of the 4:3 ratio.

e. When set up in 4K photo mode the camera works with virtually all available exposure modes and some effects.

f. First one must focus with a macro lens (I have the exquisitely sharp Olympus 60mm f/2.8) with a first long press of the shutter release cable (better than touching the camera) allows the camera to ‘assess the scene. With a full press things begin as focus shifts during a video burst…much faster than a series of shutter actions and you can see the focus points jump over the screen as the burst advances.

g. Typically this takes less than 2 secs giving a series of some 60-70 images, each with slightly different focus. If the background is far away then times are around 5-6 seconds but these will be frames you discard in all likelihood. The sequence you work with will be about 1 – 1.5 secs long.

Focus Result 5 (B, 3, 5)blog

The first animal subject for the stacking experiment with 4K Post Focus had made its web just outside my study. I used a Baby Benbo tripod (20 old pattern–built like a tank and with a flexible arm from tripod to plant stem to create greater stability during the exposure sequence. There must be as little relevant movement as possible for a second or so whilst the crucial elements in the stack are produced as the camera scans front to back focus.

Panasonic advertise this as feature enabling you to select frames and get the best shot in a burstexcellent for insects in flight using natural light

For me, however, the exciting thing is that 4K Post Focus mode provides a large image stack quickly and painlessly.

Each burst is recorded as an MP4 video and these files are then imported into Lightroom 6. Frames are examined individually… especially those at the beginning and end of the focus that I tend to reject as the camera gets in and out of its stride when, with the first frames, it has not quite found the nearest sharp point. It then shifts focus front to back (even vide versa) … even to ‘infinity’ if you have any of anything of a distant background in the viewfinder. Usefully there is a jump when the camera tries to record background as well as subject and these frames can be rejected.

Currently, I have to capture each frame from the video burst and then export these frames individually into Helicon Focus and then press the button to render. It is just repetitive with a series of on-screen clicks where the image sequence is displayed…you advance frame by frame and click each time.

An excellent on-line video  by Photo Joseph…..shows how the burst can be exported in its entirety into Photoshop CS and worked more easily there with stacking performed in Adobe fashion. Sadly I do not have Photoshop CS but with a mix of Lightroom 6 and Quick Time things are not much slower.

These are early days… I shall post more as things progress. I am just very excited by this – It gives me the best of two worlds…amazing depth of field for the subject with the soft, out of focus background associated with wider apertures (which accentuates the subject sharpness).

For a sharpness freak this is approaching Nirvana… So many ideas of shots to take and so little time. But then, ‘twas ever thus.

Focus Result 3 (B, 3, 5)cropblog

Another small section of a 4K spider image (that posted above). It reveals the detail that stacking reveals – something that cannot be reproduced so crisply in any other way because of the limits of diffraction as aperture size decreases..

Musings on sharpness…a personal take.

I confess, I love sharp focus, as readers of my blog posts, articles and books might have guessed. I want to be able to see images in biting sharpness and marvel at detail revealed for therein lies the value to me, both personally and scientifically…Here are the stories that abound in nature – how, why, what, where and when, all added value to images.

Photographs made in the name of ‘art’ (and the jury is still out on what that is and whether photography can actually be described as such…) that rely upon on using out-of-focus imagery strip this extra visual information out completely and I, for one, often feel a sense of deprivation. Sometimes, however, my senses are stimulated and I enjoy the aesthetic appeal and readily admit I love the work of Sandra Bartocha, Sue Bishop and Leo Battista, all of whom I am fortunate to know and count as friends…they really are artists and bring something to their work that I could not. The approach works beautifully with plants, in particular, but far less so in my opinion with insects and other creatures.

Focus Result 4 (B, 5, 5)low

This time of year I collect the tiny flowers of fennel and dry them to make a ‘spice’ that is one of the undiscovered delights of my part of Italy…it can be used to flavour roast potatoes, fish, aubergines. Here the flowers are a subject for stacking with the background the blue sky

A question…what exactly does one get from a ‘blur’ when the subject is unidentifiable as far as many people are concerned? It can work wonderfully well with stampeding animals, flocks of birds and so on with things that confound the senses. However, more often than not, when you strip out the pretension and ‘copy cat’ adherence to a current ‘fashion’ (all done with protestations of originality…) then there is often not a lot left. I have seen a few butterfly shots and one or two beetles that have grabbed me but those usually have the insects in focus (the eyes at least) and the emotional manipulation /creation of mood occurs via  background and lighting via highlights and so on. But those I can count on the fingers of one hand.

My quest for sharpness, a veritable Holy Grail, has spread over more than four decades and has resulted in using a veritable plethora of macro lenses and many other optics not specifically designed for that purpose. To that you can add  an in depth study of the factors that affect and limit what is obtainable from the mathematics outwards. The problem is that you get better depth of field with ever smaller apertures but then an irrefutable property of light begins to act against you and soften the image. This is diffraction – a phenomenon inherent in the properties of light waves where the edges of a wavefront are affected by an aperture through which it passes. The wavefronts are curved slightly at their edges and this becomes more pronounced with small apertures – the smaller the aperture the proportionally more this curvature affects the whole wavefront. I have studied this during and from university days as well as considering the pyschological factors that contribute to a perception of sharpness….lighting to generate relief (those small surface shadows that delineated detail), contrast, background choice and so on…

Focus Result 4 (B, 5, 5)-2

I have included this section to show the level of detail recorded where the stem branches.

Image Stacking: some background and hints

Image stacking – is a truly ingenious process where you can use lenses at wide apertures (where they are sharpest and diffraction softening is at a minimum). In a flash (sometimes literally) the diffraction problem evaporates. In simplest terms, a series of images is taken and, between each exposure, the focus is shifted by a tiny, but controlled, amount. The knack is to ensure the size of the steps are such that the depths of field from one image to the next overlap. These separate images are then combined using Photoshop, Helicon Focus or Zerene Stacker – some of the best programs for taking these images. They all create a map of points of sharpest focus in each image, these layers are then aligned to compensate for slight movement between the shots. Finally,  the final image is built by merging these layers. The background shows the Bokeh associated with the wider apertures – a softness that accentuates subject sharpness, whereas stopping down can often produce a confused series of blurs unless you use a 150 or 200mmm macro lens.

Focus Result 3 (B, 3, 5)

The Egyptian grasshopper (Anacridium aegyptiacum) the next day after a skin shedding.

Usually, there is a small amount of cleaning up to do at subject edges where ‘artifacts’ occur. These originate for several reasons,

i. The stacking program used cannot quite get the alignment of layers right – worth trying both Zerene and Helicon focus on the same image or experiment with changing the stacking parameters (radius and smoothing)

ii. Focus breathing. changes in size of the subject in the field of vision as the lens focus alters. Most modern macro lenses focus internally. This is convenient because the physical length of the lens stays the same and you don’t have to change camera to subject distance each time you nudge the focus. The disadvantage of focusing by moving a lens group internally is that it changes the focal length and, in turn the magnification of the subject …something called focus breathing.

iii. You need to get larger stack than you might think for depths of field are tiny at wide apertures and get smaller as you increase image magnification. Steps in focusing between adjacent images in the stack need to be such that the depths of field overlap …no gaps in sharpness. To give an example at f/5.6 (which I tend to use for creating stacks)

d.o.f table

Focus Result 4 (B, 3, 5)detail

Again a section of an image – this time the Egyptian grasshopper (Anacridium aegyptiacum) –  to demonstrate the capture of fine structures here shown in all their detail: textures are particularly well revealed.

I have taken hundreds of images in this way though the process is time-consuming. My success has mostly been in the studio where the camera is fixed to an optical bench. My set up has evolved with time and currently the subject (often at the extreme macro and microscopic level) is placed on a Stackshot (computer controlled focus rail) and I can focus via the laptop screen thanks to Helicon Soft, a brilliant program that allows control of camera, focus rail and shows a ‘Live’ view. Zerene Stacker does the same job and many prefer it…if you can afford both they are worth using on  particular stacks for they give different results. My set up is coupled to a flash system with delays for recycling built in. I also have a set of LED lights – in particular a ring light (Chinese made with 144 LEDs). My background was in laboratories for a portion of my life and I love the precision…I have an unashamed inner nerd!

However, what I have always wanted is a system I could use in the field because the set up described above, whilst great at above life-size reproduction ratios (which I would never use in the field) is not portable. I have tried using a camera on a focus slide fitted to a tripod and advancing it whilst I kept the shutter firing…it has worked well with accommodating crab spiders and mantids, for example. Piotr Naskrecki has posted some superb examples of this kind of approach but I supect that he has led a more blameless life than I have and is that bit younger… Regretably, I just cannot handhold when doing this.

The other aspect I dislike, when looking at stacked imagery on line, is that the vast majority of insects subject have been killed for the purpose…I have always found something distasteful in the idea that an insect must die to satisfy the vanity of a photographer. So they are only insects, some will say, but then, like many naturalists who express their love of nature through photography I want to deal with the living animal and depriving it life does not come into the equation. I have managed several spider shots previously with obliging subjects… and even combined them with white backgrounds,  but never with the consistency I can achieve now.

Robber Fly 1 (B, 3, 5) copyblog

Recently, cameras such as the Olympus TG4 have incorporated a burst function that combines frames to get a stacked final image. Olympus then introduced a stacking feature in both the OMD-EM-5 and then the OMD-EM-1with a firmware upgrade that permitted a burst of exposures and shifted focus. The OM- EM -1  combines these in the camera.

In all these methods a reduced proportion of an already smaller sensor is used that some might see as a disadvantage. However, this begins to make field stacking a reality and, in truth, the results might not have the file size of a Nikon D810 but then for internet and illustration work in magazines and books (even covers) this is great.

©  Paul Harcourt Davies – neither images(s) nor text may be used in whole (or in part) without the express permission of the author.

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