Focusing in Landscapes

[AndrewMaz]

Stephen,

After years taking photographs in the mountains, my handholding is not bad but I accept it is a far cry from a compact, even a good one, to the weight of a DSLR. In the mountains, I find that f/8 and the consequential shutter speeds with a decent amount of light allows me to handhold.

Having read a number of articles, and a number of posts on this forum, it seems to me that I am going to being vary my photography between landscape (where foreground interest is just as relevant if not more so than the background interest) and mountains where focusing on infinity is more likely to suit me as I don't need the depth of field/focal plane sharpness to be as significant. With landscape, I think I'll need to stop down to f/13 or f/16 in order to balance the depth of field and focal plane sharpness against diffraction.

I am however very attracted to infinity focusing especially given everything I have read seems to suggest that focusing beyond the hyper focal distance is essential for sharpness in the background and that, with my 17-40mm lens ends up to being infinity or thereabouts in any event.

There's a lot of experimentation to be done, but those are the issues I am thinking about right now.

[StephenBatey]

DOF is based on a set of assumptions. Only one single distance (with a perfect lens and light behaving differently to the way it in fact does) will reproduce a point as a point; every other distance will give a circle, getting bigger as the subject moves further away from the point you're focused on. DOF depends on the eye accepting a circle as a point; which it will, until the circle reaches a certain size.

Hence DOF tables assume viewing distance, how good your eyes are, and how much you're going to enlarge. Once you step outside these assumptions, the tables lose their value.

If you're looking to produce a print larger than the DOF tables assume, or if your criterion for what is really sharp is more rigorous, if your near vision is more acute in viewing the image, or even if the viewing conditions are better than those assumed, the results at infinity will appear unsharp if you focus on the hyperfocal distance. And that's assuming that the focusing is accurate to start with.

[AndrewMaz]

Stephen, if I may say, that's a very clear, concise and comprehensible definition of, among other things, the Circle of Confusion, or rather the issues involved in where you set the CoC. I know many photographers deliberately set the CoC at a level which is lower than the manufacturer's guidance for the camera in order to compensate for the less rigorous approach the manufacturer takes to who might be viewing and image and at what print size (and from what distance) - both Cambridge in Colour and the Outdoor Photography article take this view and it is one that I find sensible.

When looking at DOF/HFD charts/tables/calculators, the best I have seen, on Cambridge in Colour's website, takes into account the larger print size and viewing distance which effectively results in a longer HFD. An HFD on a 'normal' calculator, if values are changed to reflect a larger print size and (as the Pete Bridgwood puts it in his OP article) the 'pixel peeping elite' scrutinising the image closely, then the HFD changes - it goes from perhaps 2m to around 10m. This change is also reflected in DOF calculators if you change the CoC from say 0.019 (Canon EOS 60D - my camera) to say 0.010 - it does not go to 10m, instead to around 4m but the point remains the same and accords with the advice given in a lot of articles I have read - "focus beyond the HFD to be sure".

Having read a great deal on this now - which is useful for more than just depth of field, sharpness and optical law, but also to see how aperture reacts and to entrench some of the basic principles involved in photography - I think my approach will be as follows:

For landscapes with great foreground interest, focusing at or, more likely just beyond, the HFD when set with a CoC of no higher than 0.010 or, indeed, using the values in the Cambridge Calculator which imply a larger print size, will be what I do. This may well mean a focus point of between 6 and 10m depending on where the foreground interest is.

For landscapes, particularly in the mountains, where foreground interest is a little further away or not quite so important, I will focus on infinity. This is largely because, on my 17-40 f/4L USM, focusing at 10m+ is pretty much dead on the Infinity bar anyway.

The sweet-spot for sharpness on both my lenses, 17-40 f/4L USM, and 24-105 f/4L IS USM, is f/8. I imagine f/11 will not be much worse (if at all) but as I may well be handholding a lot, especially in the mountains, f/8 is preferably.

Thanks for the responses.

[StephenBatey]

If you do want an approximate rule of thumb, the maximum possible resolution of a perfect lens in lppm is roughly 1500/f number; so at f/8 you're limited to about 180 lppm, and at f/11 137 lppm.

Although if the lens is correctly centred it should be approaching the theoretical limit at these apertures, you will be fighting your low pass filter which won't allow you to reach these figures anyway. (Assumption; I haven't done the maths on your camera, but I know that the limits are normally under 100 lppm.)