A method for optimal landscape focussing 20 April 2021

Canon RF 35mm f1.8  lens on Canon EOS  full frame. I simply focussed at the center of the frame in the viewfinder at f11

Perusal of various “how-to-do-it” articles and books on landscape photography will reveal  a range of recommendations for optimal focussing and aperture selection.

Few if any of these recommendations acknowledge that lenses can differ markedly from each other with regard to their characteristic  three dimensional distribution of sharpness at any comparable focal length, focussed distance and aperture.

When I googled “optimal focus in landscape photography” I got a host of results, many containing potentially useful information and tips but none that I saw dealt with the differences between lenses which can in fact be considerable.

Some of the advice I found includes

* Focus at double the distance to the closest part of the scene.

* Use the hyperfocal distance.

* Focus one third of the way into the subject.

* Focus at infinity then back up a bit.

Advice like this is all very well and none of it altogether wrong as far as my own 60 year experience leads me to believe.

But several of the methods involve measuring distances into a scene which is rarely practical.

The hyperfocal distance method fails to take into account that distant elements of a scene (which are small) need to be rendered sharper than close elements (which are much larger).

In addition none of these suggested methods is really photographer-centric. They are rather more theory-based.

I want a quick, reliable method of focussing landscapes which  I can implement right in the viewfinder or on the monitor screen.

I found that such a method does exist and that with many subjects and lenses it is ridiculously easy to use.

The method simply consists of focussing at the center of the frame in the viewfinder. The lens aperture is adjusted by experience which is easier done than you might think.  For landscapes I generally use f8, f11 or f16, with f11 often giving the best balance between depth of field and sharpness.

But this method does not always give an optimal result. I never understood why until I started photographing grass then applying the Photoshop [find edges] filter.

I discovered that particularly with zoom lenses at wide angles of view there is great variation in the way sharpness is distributed as the lens aperture is closed down.

Look at the photo below. This is a type of landscape where the subject is fairly flat with the foreground quite close to the camera and the background effectively at infinity. Of course not all landscapes are flat but even when there are trees or other subject elements between the foreground and background the point of optimum focus will be found somewhere around the center of the frame provided that location is not occupied by a foreground subject element protruding upward.

RF 24-105mm f4L lens at 24mm at f11 focussed slightly above the center of the frame

The next picture is a diagram of my grass test photo setup which approximately reproduces the relationship between subject and camera seen in the landscape photo.

You can read more about the grass test procedure here.   And also here

Next we see the distribution of sharpness produced by the RF 24-105mm f4 L lens at 24mm f8.

RF 24-105mm f4L at 24mm f8. Focussed on the stick.

 And now the distribution of sharpness produced by the RF 24-105mm STM lens at f8. I used the same (EOS R5) camera, tripod, subject  and camera position for both test photos which were made within a few minutes of each other. Both test photos have Adobe camera raw lens profile applied.

RF 24-105mm f4-7.1 STM lens at f8. Focussed on the stick

 You can see the amount and distribution of sharpness, represented by the dark parts, differs greatly between the lenses. The L lens delivers more sharp areas, distributed more across the frame to the edges.

The f4 L lens distributes sharpness more towards the camera.  For best focus with this lens I put the focus box above the center of the frame.

The STM lens distributes sharpness more towards the background. For best focus with this lens I put the focus box below the center of the frame.

Note however that no matter what I do the final image from the budget price STM lens will never be as sharp at the edges and corners as can be achieved with the more expensive f4L lens.

Yes it is worth getting the higher priced optic.

I find with a full frame camera using a 24x36mm sensor and a focal length between about 24-35mm,  f11 will usually give me sufficient sharpness from foreground to background with this type of subject.  If the foreground is very close a smaller aperture will be required. If the foreground is further away a larger aperture can be used.

Summary

Every lens has a characteristic depth of field distribution.

When testing a lens these days I always evaluate the way in which the depth of field distribution varies with focal length and aperture.  

This gives me a much better sense of what to expect from the lens and how to achieve optimal focus.