Sunday, 21 May 2017

Getting DoF at a distance

one of my pet "disturbances" is people taking pictures of a tiny toy on their keyboard from 5cm away and going on about the DoF and Bokeh of their new lens, especially when its clearly going to be useless at "normal focal distances"

The only way to get DoF is by pupil diameter, not "f stop" ... the bigger the pupil the shallower the DoF

Of course to get that pupil bigger for the same angle of view one needs either a bigger f stop OR a larger format. For instance a 50mm lens on a FullFrame camera has a pupil diameter that's about 25mm at f2 ... while the pupil diameter of a 25mm lens on a 43rds camera (capturing the same view from the same spot)  will be 12mm. Meaning less DoF

So I thought that (not having a full frame or a good 50mm f1.4 lens handy) that using my 45mm f1.7 would do the job at imaging my favourte tree if I stitched together an array of 4 shots (as it would approximate a 50mm on a full frame single frame grab).

Here that is:

Seems that while its better than my earlier attempt with the 20f1.7 (single shot with m43) it looks like its not really doing what I want ... a pixel peep (or a big print) shows that it does indeed have better DoF popping it out of the background, but not as much as my 4x5 had (standing pretty much in the same spot).

Well its better and shows more "separation" from the background.

So, I was right but there was a lesson to be learned

On a larger (again) format (like what is called Large Format) a "normal lens" (like the 50mm) is a 180mm lens and (my f5.6) lens yeilds 32mm at "wide open".

Perhaps a Full Frame with a 50mm @ f1.8 (using a 1.4 lens so as to not get too much corner darkness) would do it. However when one is using even 100ISO full sunlight will require super short shutters (or a ND filter) if you're using f1.8 ... Then there is the highlight clipping to deal with...

I still keep my 4x5 camera and some chemistry around for just this sort of specalised thing (and its cheaper than a Sony A7).

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