Tuesday, February 16, 2021

A few thoughts for the landscape photographer

In this post I wish to say a few more words about focusing for landscape photography, with and without Magic Lantern; when we are trying to achieve 'deep focus' capture, ie everything from infinity to a point of interest in the near field.

As a 5D3 Canon (Magic Lantern) user, I wrote my Depth Of Field Information Script (DOFIS) to give me all the info I need for focusing, either on the LV screen or on the Quick Shooting screen. For example, the latest version of DOFIS’s QS screen display, on my 5D3, looks like this:

Here we see DOFIS providing us all the information we require:

  • Where we are focused (65cm from the sensor's plane);
  • What the diffraction aware defocus blur is (30um above, as diffraction aware is switched off), ie the one we will use as the focus bracketing overlap criterion;
  • The infinity blurs, ie defocus, diffraction, and total (49, 13 and 51 um);
  • How many brackets we will need to take to get to the hyperfocal, ie 2 above;
  • Plus, some helpful, additional information, eg: the focal length we are at (16mm), and, as a warning, whether Dual-ISO or Silent Picture is switch on (SP and/or DI showing, as above).

So, in the above example, I would switch off SP and DI, as I don’t need them to be on; and use DOFIS to guide my focus bracketing, until I had captured an appropriate infinity shot, ie at a low defocus blur, accepting that, even at infinity, I will still have around a 13um diffraction blur, ie from the f/10 aperture.

But what if you are not a Magic Lantern shooter?

The first guidance I would give is to focus on the nearest object of interest that you wish to see in focus, ie don't worry about depths of field at the moment. Choose your near field focus point, as you know what your far field focus is going to be: infinity!

Knowing/using the Rule of Ten (RoT) comes in handy now, and is especially suited for focal lengths around and less than the CoC of the camera format, eg 30um or 30mm on a full frame, or 20um or 20mm on a crop sensor: whether you shoot Sony, Nikon or whatever. Noting, that you can adjust the RoT hyperfocal to any CoC you wish to use.

If you need to be reminded of the RoT approach, then have a look here.

In the above scenario, ie at 16mm at f/10, we know, using the RoT, that the,16um CoC, hyperfocal is at 1.6m, ie focal-length/10, Plus, a 16um CoC is a pretty good quality to use, ie for printing, thus I won't need to adjust the RoT hyperfocal in this case.

Of course, knowing the hyperfocal is at 1.6m, tells me that the near depth of field, when focused at 1.6m, is 0.8m; which is not going to cover my current focus at 65cm (0.65m), using a CoC of 16um.

Of course, if I had used a CoC of nearer 30um, then the hyperfocal would be less than 1.6m. For example, if we double the RoT based hyperfocal CoC, from 16um to 32um, the hyperfocal distance is simply halved, ie to 0.8m. Plus we know that the near depth of field at 0.8m is simply h/2 or 0.4m. So, in this case, one shot at around 0.8m should cover my needs.

But let's assume we wish to work with a RoT CoC, ie of 16um.

Using the odds hyperfocal based bracketing rule, as we are starting at the hyperfocal, I know that my 'perfect' focus brackets are at h/3, h/5, h/7 etc; and that the near or far depth of field, either side of the point of focus, are the even values, eg focused at h/3, the depths of field are at h/2 and h/4. 

With h being 1.6m, h/3 is just over 0.5m, ie less than nearest point of interest at 65cm, thus, in my head, I've now worked out my optimum focusing strategy:

  • Take a focus bracket where I am, ie at 65cm;
  • Take another around the hyperfocal, ie 1.6m.

By using the point of focus for the nearest feature of interest, rather than attempt to work out whether the near depth of field is covering it, we guarantee our closest near field feature is tack sharp. Noting that we will also have a little focus insurance as well, ie out to the near depth of field at our point of focus.

As usual, pragmatism should guide you, especially if you are poor at judging distances. So an alternative to the 'perfect' two image example capture above is to:

  • Take a focus bracket at my nearest point of interest, ie 65cm
  • Take another focus bracket at my RoT estimate of h, but biased towards the camera, ie get to know/visualise your height ;-)
  • Take a final image at 2-3 times h, ie for infinity.

So, even if you are not a Magic Lantern shooter, by knowing/using the Rule of Ten and the Odds/Evens rule, you can always pre-plan focus brackets in your head.

As usual I welcome any feedback on this post or on any of my posts. 


1 comment:

  1. For those of us not quite so sophisticated in our photographic skills, this treatment of the Rule of Ten and the Odds/Evens rule is a clever and effective guide for selecting focus brackets. Nicely done.