Notes on focus stacking
'Focus stacking’ (or focus bracketing) is the process of extending the depth of field by combining several images taken at different focal planes. For me, this only became practically useful for nature macro photography once suitable shooting functions were integrated into the camera body. This allows a sequence of photos to be taken automatically in succession by gradually shifting the lens focus backwards from a starting point.Nikon introduced this feature with the D850 in 2017. Unfortunately, the function has remained virtually unchanged since then. A burst of shots can only be initiated via the camera menu and there is a delay of around 2 seconds before it starts. The viewfinder and display remain dark during this time. A Nikon Z7 fitted with the Nikkor Z MC 105mm takes around 15 seconds to capture a series of 50 images – starting at the minimum focusing distance and thus a magnification of 1:1. The significantly more powerful Z9 takes around 13 seconds. Similar figures are seen with other lenses. The speed is clearly well below the cameras’ technical capabilities and is held back by the software. – An OM System OM-1 Mk II fitted with the M.ZUIKO 3.5/90mm macro lens takes approximately 2.5 seconds to complete the process described. –
Under these conditions, a focus stack only works when using a tripod or a similarly stable surface, and can be problematic with subjects that are likely to move. Nevertheless, I have managed to produce numerous stacks of small animals using this method.
However, Nikon’s macro lenses only offer a magnification ratio of up to 1:1. I was thoroughly impressed by the optical quality of the Nikkor Z MC 105. However, the sharpness drops dramatically – even in the retro position – if you extend the focus range using extension rings or a bellows to achieve a magnification greater than life-size. Teleconverters cannot be attached either.
The Nikkor Z 24–70 mm f/4 S achieves perfectly acceptable sharpness at magnifications of up to 2:1 when used with a Novoflex NIKZ-RETRO automatic reverse ring. As all functions are retained, stacking is also possible. However, its use is not very practical due to the very short working distance.For macro photography on Nikon Z cameras, I have used a Canon EF 180mm f/3.5 macro lens, mainly because of its relatively long working distance. A Fringer EF-NZ adapter ensures that all automatic functions work properly, and the autofocus speed is perfectly acceptable. For the reasons mentioned above, stacking is just as quick as it is with original Nikkor lenses.
Occasionally, I have screwed a PLAN X 4x microscope objective into the filter thread of this lens using an adapter, thereby achieving a magnification ratio of 5:1.
I also enjoy ‘stacking’ slightly larger subjects, such as large dragonflies and, above all, lizards, using the Nikkor Z 100–400 mm f/4.5–5.6 VR S, which has a minimum focusing distance of 98 cm (from the sensor plane at 400 mm). The image area is then 9 cm x 6 cm and the reproduction ratio is 1:2.6.
In my view, however, this is not a disadvantage when it comes to small objects. For example, a seven-spot ladybird is up to 8 mm long. With sufficient surrounding space, it could be photographed ‘filling the frame’ (in 3:2 format) on the MFT sensor at 1:1 magnification. The same field of view (17.3 x 11.5 mm, 18 megapixels) results in a resolution of just under 10.5 megapixels (3980 x 2648 px) on the Nikon chip – as the individual pixels are approximately 70% larger. The rest would have to be cropped away. A full-frame image of the ladybird (including its surroundings) requires a scale of 2:1. With such magnification ratios and the very shallow depth of field, focus stacking is essential; and when photographing a living subject in the wild, this is practically impossible to achieve without an autofocus lens. Unfortunately, Nikon doesn’t offer anything like that; it would be possible with the new Sony FE 100mm f/2.8 Macro GM OSS + teleconverter.
As stacking software, I use Helicon Focus Pro.
Here are a few tips on double-polarization flash technology and how to build your own flash diffuser for macro photography.