Focus Stacking In The Forest

Something a little bit different today, and no mention of Lugnaquilla in sight ;).
I’m also going to only talk about one image this time, so something very new for readers of my blog!
This is going to be quite a technical post I am afraid guys, so if you are not terribly interested in the pursuit of absolute image quality then this might not be for you.

One of the age old problems in photography, especially with landscape photography is getting sufficient depth of field in a photograph. The traditional method is to stop down your lens. Most photographers understand that if you stop a lens down to f/11, you will get a larger depth of field, or zone of focus than if you shot the same image at say f/4.
So why don’t we just stop the lens down to f/22?
Well, because of diffraction – on my full frame Nikon D810 – diffraction is evident at f/11 but at f/16 its really quite noticeable and the sharpness loss and contrast reduction is easily perceptible, especially when viewing on a large monitor.
This is why I don’t tend to shoot at a smaller aperture than f/16 (most of the time).
Basically, diffraction is an optical effect which will limit the resolution of a photograph – why buy a high resolution camera and then limit it by stopping down too far?
Diffraction occurs when light begins to disperse or “diffract” when passing through a small opening (i.e. a lens set to a small aperture).

Life is all about compromise, and so is photography. If you have a near subject that you want sharp and a far subject that you also want sharp – the usual advice is to stop the lens down. However, high resolution photography magnifies the negative effects of diffraction.
So, a compromise must be made (unless using a tilt shift lens – but they have their own issues). You have a choice to make:

A) Stop down and accept some diffraction that will limit the resolution of your photograph. Sometimes though, especially with a very close foreground and distant background, no amount of stopping down will achieve critical sharpness throughout the frame.

B) Accept a blurred background but a sharp foreground (or vice versa) – sometimes this is desirable for artistic effect. Usually though, in landscape photographs we really do want ‘everything sharp’ and in focus. For some scenes, that is simply impossible – without focus stacking.

What is focus stacking? According to wikipedia:
“Focus stacking (also known as focal plane merging and z-stacking or focus blending) is a digital image processing technique which combines multiple images taken at different focus distances to give a resulting image with a greater depth of field (DOF) than any of the individual source images.”

Lenses I use for focus stacking include Zeiss Milvus 18mm f/2.8, Zeiss Milvus 34mm f/1.4 and the Zeiss Milvus 100mm f/2.

One of the many reasons I favour Zeiss glass is the power and control over exactly where the zone of focus can be placed. This, coupled with low aberrations (spherical, chromatic aberration and field curvature) means you have absolute control of where focus falls. There are no surprises.
The focus rings are extremely precise and have a long throw – most autofocus lenses have bad focus rings in my experience, with a short focus throw. It’s hard to describe but once you have used a Zeiss lens for landscape photography – there is simply no going back.
I’d like to add here, that all opinions posted on my blog (and my other content) are my own. Any conclusions I come to are after many hours testing various pieces of equipment. I am not affiliated with any camera/lens manufacturer and all of my gear is personally bought by myself (at my expense, great expense I might say!).

Zeiss Milvus 35mm f/1.4 at f/10, nikon D810 – 40 frame stack2019-04-01-10.56.44 ZS retouched.jpg

At this low resolution (I don’t think WordPress allows high resolution uploads) there is no difference between the above image (a stack of 40 images, shot at f/10 each) to the one below:

Zeiss Milvus 35mm f/1.4 at f/10, nikon D810 – focus was placed on the large tree at left
focus on tree copy.jpg

So, to demonstrate this I will have to show some crops.
The following are 100% (pixel level) crops from my 36 megapixel Nikon D810.

CENTRE :: 40 frame stack
stacked centre.jpg

CENTRE :: single shot at f/10 – focus on the tree trunkfocus on tree centre.jpg

What might be already apparent from the above two crops is that whilst the tree trunk is sharp in both crops, taking a cursory glance to the right shows the power of focus stacking. Strong blur (insufficient depth of field) on the non stacked crop but the stacked crop is very sharp. Remember this was shot at f/10! I did a test shot at f/16 (the minimum aperture of the Zeiss Milvus) with the same focus placement and still the background was blurred.

Let’s look at another couple of crops.
This sequence is taken from the far right.

FAR RIGHT :: 40 frame stack
stacked FR.jpg

FAR RIGHT :: single shot at f/10 – focus on the tree trunk
focus on tree FR.jpg

As you can see, absolutely nothing is in focus in the single shot crop. The focus stacked crop shows a very high level of detail. I think the benefits of focus stacking largely speaks for itself in this particular scene but let’s see some more crops.

This sequence is taken from the far left.

FAR LEFT :: 40 frame stack
stacked FL.jpg

FAR LEFT :: single shot at f/10 – focus on the tree trunk
focus on tree FL.jpg

Again, a similar pattern occurs. The area where focus was placed is sharp in the single shot but the background is blurred. Compare with the focus stack crop above. It’s not really a competition if absolute sharpness is required all over the frame is it?

I want to show another crop here, this time taken from the bottom left – this was very close to the camera (a couple of feet at most).

BOTTOM LEFT :: 40 frame stack
stacked BL.jpg

BOTTOM LEFT :: single shot at f/10 – focus on the tree trunk
focus on tree BL.jpg

No way was this area going to be sharp in a single frame. No amount of stopping down would give sufficient depth of field for an area of the image this close (when focus was placed on the tree). This area is simply too close to the camera.
However, focus stacking as seen in the above crop proves its worth.

One final crop, this time of the bottom right of the image.

BOTTOM RIGHT :: 40 frame stack
stacked BR.jpg

BOTTOM RIGHT :: single shot at f/10 – focus on the tree trunk
focus on tree BR.jpg

This area is too far away from the focus point for f/10 to cover it in the single shot (f/16 didn’t either). The advantages of stacking are pretty obvious I think.

So, what are the disadvantages?

Like everything in photography, focus stacking comes with compromises. Some limitations of focus stacking that I have discovered are listed below:

  • Wind and moving subjects pose a challenge for stacking. Any subject movement means extra time on the computer retouching ‘double images’ where the stacking software gets confused. For example, you may have two tree branches instead of one!
  • Time and effort both in the field and at the computer. Stacking in the field requires time and patience. I usually focus on the nearest object in the image and the slowly rotate the focus ring as required to ensure that the furthest objects will also be in focus. In fairness, it only really takes about five minutes but if you do that for 10 shots that’s nearly an hour! I use Zerene stacker (Zerene Systems) to automate the focus stack frames on the PC but usually it needs ‘touching up’ to varying degrees. It’s great software but not free, I bought the ‘prosumer edition’ ($189 USD at time of writing) I believe. It’s really worth it. For the image in this post, I think I spent an hour over several evenings (at a leisurely pace, I was unfamiliar with the software) retouching. It’s really not that bad when you consider how striking the image is when viewed on a large screen at full size. It all depends on how much you care about image quality at the end of the day. If you really care about quality then it’s a ‘no brainer’ investment in both time and money. 40 frames are a lot, but this scene required it because I had very close elements in the foreground – most scenes probably only require a handful of frames. This was quite an extreme example.
  • Storage – 40 images were used to stack the above. So that’s 40 images to obtain one! Of course, you can delete the ‘stack frames’ once you’ve finished building the stack to free up storage.
  • Blur can be beautiful – ‘bokeh’ is very popular these days! Smartphone software engineers are working overtime around the world to emulate background blur in smartphone cameras (software blur) – they are getting good (they are not great to a keen eye) but optical blur is, and will be for some time – king. You don’t always want ‘everything sharp’, it really comes down to intent in the photograph and what it is you are capturing.

I am sure there are other limitations I have not yet discovered but if you are serious about landscape photography (or still life/macro photography) then focus stacking is a skill that you really need to add to your arsenal, especially as camera sensor size and resolution is ever increasing (and depth of field decreasing with it).

Thank you for reading!

If you like what you see here please feel free to take a look at my portfolio site where you can see lots more of my work, or follow me on Twitter or Facebook here! I am also on Instagram now, as phillipjwells.

The images presented here are my intellectual property and must not be distributed without my consent.

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