Monday, January 27, 2014

More on Focus Stacking!

First of all, let me apologize in advance because the weather in Tucson is spectacular.  I know that large portions of the country are in the deep freeze - no doubt if we were at our place in Chicago we would be bitching about how cold it was.  The local weather here in Tucson pointed out that today Tucson was 100F warmer than the current wind chill temperature  in Chicago!  And while the rest of the country is getting affected by the Arctic Vortex, or Alberta Clipper, or whatever the phrase of the week is, that same weather phenomenon is causing our temps to be about 10F to 15F warmer than average.  We've hit 80F recently while normal are in the mid 60s...

That being said, about the only thing blooming in our yard is the Rhus lancea tree, African Sumac.  Triggered by the warm weather, it has a subtle fragrance, and though it has an unremarkable flower, is thick with them this Winter.  The view at left shows a small branch full of the blossoms.  I say unremarkable because visually they look pretty blah, but in search of a blog post, I dug out the macro yesterday and wow - they are pretty cool close-up! 

In order to get a reasonable image of the microscopic flowers, I practiced the technique of "focus stacking" some more, something I've posted about twice now.   In brief, what you do is take multiple images from a tripod, and perform slight focus changes between the frames.  In macro imaging, depth of field is quite limited.  While stopping the lens down to small apertures you can increase the depth of field, it also increases diffraction noise in the image from small apertures, so while more of the image can appear to be in focus, sharp focus is more elusive.  With Focus Stacking, you stick to moderate apertures little affected by diffraction, and blend together only the sharp sections of each image with Photoshop.  At left is one of 8 frames I took of a sprig of the Rhus lancea flowers.  The central, yellow part of the flower is quite small, only about 1mm diameter, with the entire flower about 2mm diameter.   I took 7 others in quick succession with minimal focus shifts between with the focus knob.  Serious macro photographers have a geared stage for microscopic motions, but this is what I did.  There are several (free!) tutorials on the Internet, assuming you have a version of Photoshop less than 5 years old or so.  The tutorial I used is by Tony Northrup, who does a good job of explaining things and leading this neophyte through the simple Photoshop steps.  The image at right shows the result of focus stacking the 8 frames, all the little blossoms are now in focus, not just a few located in the shallow field of view of the left picture.

It isn't till you look at it at the highest camera resolution that you get a true appreciation of the power of this technique.  Since I'm limited to images 1600 pixels across, lets look at something like the full camera resolution.  At left again is a small part of one of the 8 images, showing one or two flowers in focus.  At right is the same section of the focus stacked frame.  Not only are nearly all the flowers and buds in sharp focus now, but a multitude of sap-sucking aphids, that I was actually looking for visually but not seeing, come into plain view!  I can certainly see using this technique pretty often in my future macro imaging!  The sharp-eyed among you might notice in these and the above pictures that some flowers seem to have 4 stamens per flower and some 5.  I went back with a magnifying glass to find out which it was supposed to be, but can confirm that the number is indeed, 4 OR 5...  Anyway, fun stuff - try the technique and I'll bet you like it!  More of this as Spring develops!

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