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Focus Stacking


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I recently uploaded a number of images that I had accumulated over recent years, and these raised a number of questions about focus stacking and creating stereo images. So I thought I'd post a couple of articles on techniques - this one on focus stacking, and a separate one talks about creating stereo images.

 

There are UVP members who have automated devices to take sophisticated focus stacks. However, I have only my own hands to do this manually, so that's what I'll talk about here. So this is a sort of Focus Stacking 101. And I'll concentrate on close-up and macro, although focus stacking can be used for anything, including landscapes.

 

What is focus stacking? The idea is to overcome limitations of depth of focus so you can get the whole of an object sharp, from front to back. It works by taking a series of exposures each focussed on a different part of the subject, and then combining these with focus stacking software which pick out the sharpest areas from each exposure.

 

Focus Stacking is better than simply stopping the lens down because this only helps to a degree, reduces image quality (diffraction at smaller apertures), and may cause issues with getting enough light onto the subject.

 

To get close up, you'll need your normal UV camera gear plus a focussing helicoid, extension tubes, and/or bellows. Your normal macro lens probably will not work well for UV, unless you have a specialised UV macro lens.

 

If you are doing true macro (i.e. the image on the sensor is larger than the live subject) you'll need a reversing ring which turns the lens back to front so that the rear of the lens is facing the subject.

Longer focal lengths are better for macro work because they give more working space between lens and subject – important to let you get your light sources near enough to the subject. I generally use an El Nikkor 105mm/f5.6, but have also used the Cassar S 50mm/f2.8 very successfully. I use these lenses at f/8 because that gives the best image quality in normal usage – although I haven't confirmed that this is still the best aperture for macro.

 

My approach is to set up the camera/lens assembly so it is focussed in front of the subject, and then make the sequence of exposures, with each successive exposure being focussed slightly further away until the point of focus has moved beyond the furthest point of the subject.

 

I shift the focus by moving the whole camera rig forward – using the focussing ring on the lens is too coarse or doesn't provide enough movement. My bellows unit (an old East German M42 unit, based on an even older design from Exakta) has a knob which allows the whole bellows assembly to be racked forwards and backwards. If I am not using bellows, I use a Velbon Super Mag Slider to move the camera forwards: there are other slider devices available, but build quality can be grim which makes fine movements difficult.

 

I have also tried using a focussing helicoid between bellows and camera to move the camera while keeping the lens static. This also works OK, but you are limited by the movement of the helicoid – and in the case of a long-extension helicoid you can see the camera beginning to sag as you extend the helicoid.

 

How many exposures do you need to make? You'll get a feel from experience. It depends on the distance, the depth of the subject, and the aperture you are using. 30-50 will probably be OK for a close-up of a whole flower, but you may need up to 100 in macro work.

 

I always use flash as my light source, so battery life is often the limiting factor as to how many shots I can take. Repeatedly firing the flashguns at full intensity causes overheating of the batteries, and the flashguns may cut out temporarily until they cool down. I have burnt out about half a dozen flashguns in the last few years because of this heavy usage, but I use cheap Wansen WS560 flashguns which cost only about $30, so they're effectively a consumable.

 

Then you need to stack (i.e. combine) the image sequence. You will need specialised software for this. There is some freeware available, like Picolay, but I ended up buying some software for this. It is the only photo processing software I have paid for – I generally use freeware, but for focus stacking I found that the paid-for software is definitely better. There are two products – Helicon and Zerene. I went for Zerene (30 day free trial, and then you can buy either annual or life-time licenses) because although it did not run as quickly as Helicon, it gave better results.

 

Focus stacking can obviously only be used with static subjects – it can take several minutes to complete a stack. And it's surprising how much flowers can move during this timescale – not just wilting, but waggling petals and stamens. So you will undoubtedly get some wasted shots, and may find that some types of flower are simply too mobile to work with.

 

Finally, one problem that may cause difficulties - dust on the sensor. You can get away with some dust on the sensor in general photography, but it becomes a major problem with macro and focus stacking. In macro, the dust spots appear a lot sharper than in general photography, because your effective aperture is a lot smaller and so the shadow of the dust spot is sharper. And this becomes a real problem with focus stacking because an insignificant dust spot becomes a highly visible trail. So keeping your camera clean is important, and you may have to resort to post-processing (e.g. spot healing/cloning or blurring) to get rid of these trails.

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I concur with what Bernard described. Focus stacking can be extremely helpful to make excellent and detailled photos, in particular for close-up and photomacrographic applications. The benefits do not come easily though, as there are much extra efforts to be invested in order to end up with a useful final image. Thus, one needs a lot of care in setting up for stacking, there are loads of images to process, and despite the stacking program being much better these days, often a lot of additional retouching in the last stage.

 

I always run the camera from an A/C power source to avoid depleted batteries within a critical stacking process. Having an automated and programmable rail for performing the actual shooting sequence also is highly recommended. One can do the repeated movements in manual mode, but needless to say this induced a lot of stress to the operator and likely errors from not being able to do the increments properly.. When I do stacking in UV, I much prefer to repair to another room in my apartment to avoid being repetitively blasted by my high-output studio flash(es), despite my wearing protective goggles. I'm using the US-made Stackshot rails, which are pretty OK and their controllers have become better over time as well. At face value they don't come cheap, but depreciated over their long life time they are tolerably priced nonetheless.

 

The reasons why I prefer to use studio flashes are they run off the A/C mains, thus recycle very fast, plus they have all sorts of light modifiers to be attached to them. They are also versatile as the output can be fine-tuned in 1/10 EV steps, they can be fitted with uncoated xenon tubes, and light output is immense. In fact, due to the high output, one can put the flashes at a convenient distance say 0.5m or more away to avoid wilting the specimen. The light field further becomes wider and contrast declines as the shadows tend to fill in better (the light source is many times bigger than the specimen itself). I use radio triggers (Pocket Wizards) on camera and main flash.

 

A glimpse into the chaos typically surrounding a stacking set up (!). My kitchen serves as an impromptu studio. I made room for one of my Nikon Multiphot rigs on the dinner table. As the rig is very heavy, it dictates the future usage of the table. No more dinners here!! I eat with my girl friend in the next apartment instead ....(or used to do, now C-19 quarantine means we have to be on our own).

 

U202003301175_focus_stacking_UV-Nikkor_Tussilago_D3200.jpg

 

In this case, I experimented with an Autocrat 50mm f/3.5 lens stacked onto one of my UV-Nikkors to give 1.7 X magnification. I'll add the outcome later (if it is presentable, of course).

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OK, some results from the above. I had to shorten the stack as the flower head - not unexpectedly - moved over time. Thus only 41 out of the planned 71 frames could be used. That meant the stacking was not perfect and there are some glitches present. However enough detail remaining to ascertain whether the lens-on-lens technique works well to satisfaction. It does, well sort of.

 

The UV-Nikkor being such a sharp lens on its own does "survive" the reduction of image contrast and added chromatic aberrations introduced by the triplet (Autocrat lens) in front. An additional advantage is the setup becomes quite neat and tidy, in particular because the working distance shrinks to a few centimetres yet still suffices to allow good light to the subject. By contrast, getting to around the same magnification with extension only requires 2*PN-11 units being added plus the UV-Nikkor itself being extended all the way. The working distance now is around 12 cm overall. Thus the overall rig becomes much more comprehensive and bulky, and more awkward to handle in the studio. That has to be offset by better image quality. There is no free lunch.

 

Anyway, the overall frame of the little Tussilago farfara flower is here (Nikon D3200 built-in Baader U, UV-Nikkor + 50mm f/3.5 Autocrat, 2*800 Ws Broncolor studio flash with uncoated Xenon tube, f/8 ISO 100, 41 frames in Zerene).

 

I202003304213_UV-nikkor_Autocrat_f8_stack_Tussilago_D3200.jpg

 

Here is a 100% crop.

 

I202003304213_UV-nikkor_Autocrat_f8_stack_Tussilago_D3200_100pct.jpg

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Birna,

 

what's the reason for using the Autocrat as a close-up lens - wouldn't you get better results using the UV Nikkor with extension tubes?

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I just explained it was an experiment. Stacking lenses is an old technique well exploited back in the film era, still valid today.

 

The basic advantage is one gets a much shorter, compact and hence more easily handling package. The UV-Nikkor, being 105mm focal length and without any CRC mechanism, requires a lot of extension to get past 1:1 life-size. The working distance also gets much longer than with a close-up attachment in front. All of this adds up to a major inconvenience when one needs to shoot a subject directly from above.

 

Thus, as always: no free lunch. either more compact and easy setup, with less quality, or a long and awkward handling rig with potentially more instability, but better image quality.

 

I might experiment with my Coastal 60mm f/4 lens next, as it is much shorter focal length and thus needs less extension. However, this lens might have an issue with hot spots in UV unless a carefully crafted lens shade is present.

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Andy Perrin
The images look kind of foggy - is that the "reduction in contrast" you referred to, or some other effect?
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Lens flare of the "front" attachment, probably. The UV-Nikkor tends to yield very high contrast in UV.
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I have for many years followed the developments of the Stackshot without buying one.

My focus stacking interest stalled about 10 years ago.

Then my focus-stacking style sometimes needed high-resolution steps that I thought the Stackshot might have problems to achieve.

 

The Stackshot product is mature and I think the handling and operation of the software can be very good.

As the market seams un-sensitive to high prices the company appears to set very high prices even for the simplest of accessories.

 

I investigated if there were any alternative product an found the WeMacro rail.

An alternative to the overpriced Stackshot might be the Cinese WeMacro:

https://www.wemacro.com/?product=wemacro-rail

 

The reviews are positive and it has may interesting features, including wireless remote control of the stacking via an app on a phone.

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The Chinese rail apparently would be OK for studio work with a hooked-up laptop or similar. Outdoors, not so certain. As the price is less than half of the US product, perhaps worth a try albeit delivery time may be excessively long now during the C-19 pandemic.

 

Their camera platform design looks better than that of the Stackshot, though. Also liked the solution for using infinity corrected objectives.

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I have for many years followed the developments of the Stackshot without buying one.

My focus stacking interest stalled about 10 years ago.

Then my focus-stacking style sometimes needed high-resolution steps that I thought the Stackshot might have problems to achieve.

 

The Stackshot product is mature and I think the handling and operation of the software can be very good.

As the market seams un-sensitive to high prices the company appears to set very high prices even for the simplest of accessories.

 

I investigated if there were any alternative product an found the WeMacro rail.

An alternative to the overpriced Stackshot might be the Cinese WeMacro:

https://www.wemacro.com/?product=wemacro-rail

 

The reviews are positive and it has may interesting features, including wireless remote control of the stacking via an app on a phone.

 

Thank you for this link. Very interesting.

The rail lookds to have Bluetooth and can be controlled by android or apple phone. I will have to see if I can find the application to see in I can make sense of it.

What I liked about the stackshot would be to have very precise movement and link that between the rail on the camera and a rotating base on the subject.

Will have to see if this could do the same.

For the most part now I am just lazzy with single shot or in Olympus cameras stacking.

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Thank you for this link. Very interesting.

The rail lookds to have Bluetooth and can be controlled by android or apple phone. I will have to see if I can find the application to see in I can make sense of it.

What I liked about the stackshot would be to have very precise movement and link that between the rail on the camera and a rotating base on the subject.

Will have to see if this could do the same.

For the most part now I am just lazzy with single shot or in Olympus cameras stacking.

I bought a WeMacro-set from their UK-distributor.

 

I am very impressed with the mechanical quality of the rail and how easy it is to operate it bu the phone.

The controller app is running on the phone communicating wirelessly with the stepper-motor controller-box.

I have not needed to bother involving any computer.

I have no idea why a laptop would be needed if a shoot first and process later-operation is acceptable.

 

There are two things not en par with the quality of the rail.

 

The included battery box for field operation feels a bit tacky.

It has to be filled with suitable18650 LiPo-cells (not included).

If you need a better battery there are several 12V accumulator packages, not related to WeMacro that are good replacements.

I have not yet tried the rail in the field yet, only run it on the included adaptor.

 

They also include a very simple mini tripod with a clamp to hold the object to be stacked.

 

I did not like their fast release Acra-clamp design and replaced it with a more normal clamp.

 

Comparing the specifications of StackShot and WeMacro rails I think the step resolution is slightly better with the WeMacro.

The control software is not that advanced, but good enough for my needs.

 

What I like is

The excellent mechanical quality of the rail.

That the operation control can be done with my phone.

The reasonable price.

 

It is interesting to compare prices on similar accessories

https://www.wemacro....-cable-3c-canon

https://www.cognisys...e/sc-cd-01.html

 

 

Birna - you can upgrade your camera platforms on your Stackshot:

https://www.cognisys...pter-plate.html

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I don't use a smartphone -- hence the need for a laptop ... unless I use the Stackshot controller of course.

 

I do have upgraded the support platform for camera on my Stackshot. Still the Chinese version seems more robust. Also noted is your impression on the build quality of the WeMacro rail. Perhaps this will induce me into considering it later this year. At present, my Stackshot rails suffice.

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Lest we forget, focus stacking is sometimes very useful for applications outside the true "macro" range. Below is a contraption I built for that purpose, using an old Olympus OM 28mm f/3.5 lens and an even older bellows for parts. The basic idea is keeping the entrance pupil stationary hence the image perspective is unchanged as all focusing is by moving the camera back and forth. The lens stays put.

 

U201805164139.jpg

 

This was originally designed for use with my F-mount based Nikon cameras, and as one can observe, the sculpted outline of these modern cameras necessitate some judicious Dremel work to make all fit together. I did add a CPU to allow registering proper EXIF data with my D3200 and other Nikons. The D3200 having a built-in Baader U filter, is my normal candidate for this setup. It can also be used with my D5300 which is modified for IR only.

 

U202002214098.jpg

 

The Olympus can be used on my Z6 too and just allows a rear filter box to be added so UV (or IR) is feasible with the FX camera.

 

Contrary to my initial expectations, the Olympus lens dips sufficiently into the UV(A) to allow documenting the well-known UV patterns of for example a dandelion. One can get very extended depth of field using this setup, contingent upon the wind not being too severe. Just a struggle between the photographer's patience, and Nature. The stacking itself is by manual operation only. For images such as the one below of a dandelion meadow, I would perhaps use 10-20 frames at most. For deeper stacks when the front details are much closer, up to nearly 100, but then the motif must be perfectly stationary.

 

I2018051635132.jpg

 

If one can forego the "wide" aspect, an easily cobbled-together solution is a lens head such an EL-Nikkor 80mm or 105mm, and a bellows such as PB-4 where the rear standard can be moved. Deep-field landscapes in UV (or IR) is then within reach..

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