Monday, August 8, 2016

Couch-based Practice makes Perfect

As readers of my blog are aware, I believe in practice, especially when in comes to knowing the limitations of your equipment: and where better to practice, than in your own armchair!

My current 'focus' is my Canon EOSM APS-C mirrorless, which I love using with my Sigma 10-20mm crop lens; especially at the 10mm end.

The downside of the EOSM is that the lens can't currently be controlled by Magic Lantern. With a normal length lens, his would create problems if I wanted to auto focus stack using one of my Lua scripts. However at 10mm things get simple, even on an APS-C camera.

Assuming I'm 'just' publishing on the web, ie via a PC monitor, and not creating a print for a competition, I can afford to use a total blur spot (a combination of the sensor limit and diffraction in quadrature) of, say, 19 microns. This gives a maximum depth of field sweet spot at between F/8 and F/11.

Using F/8 and focusing at 1m, gives a near depth of field limit of just under 0.5m. which leads to a second focus point at just under 0.4m. On the Sigma 10-20mm the 1m and 0.4m marks are clearly identified and thus convenient to use, although with ML I could use the on-screen focus feedback as well, as the Sigma reports this as it has AF.

Thus, using these two manual focus marks, gives me a two image focus stack that goes from just under 0.3m to infinity. A pretty impressive coverage. 

The following couch-shot, taken with room lights on, used the above settings, at ISO100. I also used Magic Lantern's auto exposure bracketing at each focus point, resulting in a 2 x 4 image set: with the 4 exposure brackets 2Ev apart. The second focus bracket was set manually.

Post processing followed my normal workflow: ingest into Lightroom, use LR's HDR feature to create two 32-bit DNG images, undertaken basic exposure correction in LR on one of the images, sync to the other image, do a round trip to Zerene Stacker and finish off in Photoshop and LR.

As usual, a boring image. But what it does show is the power of using a wide angle lens and Magic Lantern to achieve full exposure and focus control, ie over a high dynamic range and from less than 300mm to infinity. It clearly shows the sharpness of the image, ie the newspaper was placed at just over 300mm from the sensor's plane and is clearly readable, as are the books, and the outdoor background is tack sharp (ignoring the wind movement in some of the tree branches).

Although I understand that not everyone likes the WA-look. For me, 10mm on my ASP-C and 12mm on my FF cameras, is great, if you want a dramatic look, with a strong near field feature, and the entire scene to infinity, tack sharp.

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