Monday, January 12, 2015

From near to infinity

All landscape photographers, especially those using a wide angle lens, have one thing in common: they seek out ‘tack sharp’ images from near to far; and, for the sake of this post, let’s say near is a foot away.

Those who have read about hyperfocal distance will naturally first look at what this focusing approach can do; however, they will soon realise that a single image approach will simply not do. 

So, focus stacking to the rescue and the first step is the trusty FocusStacker App from George Douvos:

With a one foot to infinity objective, the App tells me at a focal length of 14mm, and using a combined blur spot diameter of 19 microns (for my Sony A6000), I need to shoot at 1.2 ft, 2 ft, and 5.9 ft at F/9. Using a single image, I could cover 2.5ft to infinity, if I shot at F/10. In other words, I would not cover my objective of a foot to infinity.

But then we begin to experience real-world practicalities. For instance, if I was to use any of my Canon auto focus lenses, I would find it virtually impossible to set those three distances, ie you will not be able to manually set an auto focus lens, as the focus ring floats; and who wants to be setting up distance targets in the field!

Thus, for landscape (as opposed to macro) focus stacking I have settled on another strategy, namely using a manual lens.

My manual lens of choice at the moment is the Rokinon 14mm F/2,8: At less than $300 a bargain that every wide angle shooter should have. I can use it on my 5DIII full frame and of course my A6000 APS-C.

The advantage with this lens is that it has a focusing scale that covers under a foot to 10 feet in about 180 degrees of the fixed focus ring rotation. It has markers all through the focus range. It also has a manual aperture, which means I have no image to image variability, ie for timelapses the aperture is locked in, thus minimising flicker.

Workflow is simple:

  • Dial in the aperture (F/9 on this occasion);
  • Compose;
  • Focus at 1.2 ft and take the first image;
  • Refocus at 2 ft and take the second image;
  • Refocus at just under 7 ft and take the third image;
  • Take a fourth image at infinity for insurance;
  • Ingest into Lightroom;
  • Export to Photoshop as layers;
  • Auto align the layers;
  • Auto blend the layers;
  • Merge the layers;
  • Bring the merged image back to LR and ‘finish off’.
The attached (indoor test) image is a four-stack, taken with the Rokinon on my Sony A6000, where each individual image had some ‘out of focusness’ somewhere in the scene. However, the focus stacked image is tack sharp from 1ft to infinity.

Bottom line: For focus stacking wide angle landscapes, where you will likely have a strong near field component to your image, I believe manual focusing, with a manual focus lens, is the way to go; and the Rokinon 14mm F/2.8 is a winner. Where as you would not wish to focus stack every image, for those occasions where you need a huge depth of field, I believe the ‘technology’ and workflow above can’t be beat: IMHO :-)

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