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Tuesday, June 28, 2011

Brief survey of focus stacking technique and software

I made a presentation at the Hasselblad User Group meeting in Singapore recently. The seminar was attended by about 100 photographers, and I am pleased that there is so much interest in macro watch photography.

Denis of Shriro, the agents for Hasselblad and Profoto asked me to share with those not present the photographs. And touch a bit on the technique

Many of you present also wanted to know the equipment used:

Hasselblad H3D-39 with HC 4/120 Macro with or without one or both H28 and H52 extension tubes. With both tubes, at maximum magnification (min distance) I can get approx 1.93X magnification.

I also use the Manfrotto 454 Macro Focussing Rail, as the technique I use is to put the lens in min distance for max magnification, and stack the images by moving the camera by turning the micrometer screw on the rail. This results in about 8 to 12 photographs, each with a slightly different plane of focus, though overlapping approximately 20% from frame to frame. As most of you would know depth of field even at f/11 or f/16 is very small at these focussing distances, so having 8-12 photographs, each with a slightly different focus plane will help greatly.

I shoot mainly at f/11 or f/16, near the optimum apertures for the lens. For lighting, I use one or two ProFoto Compact 600 strobes.

I show an example here, using the De Bethune DB28. A stack of 9 images are used. These are Quick Previews from Hasselblad's Phocus software. Shown below are frames 1, 5, you get the picture of what is required.

These frames are then combined digitally by software. I have looked as some software that do this job, and below is a short survey of those I have tried.

CombineZF is a free software. But I find slow. But it is free.

Here is the result from CombineZF. Quick Align, Do Weighted Average stack.

Note artifacts around the crown, and case. Note the double reflected image on the sides of the case. These can be touched up and cleaned either in CombineZF or Photoshop.

Photoshop CS4 and CS5 also have a facility to do this stacking. Load all the files as layers. Then a two step process...Align, and then Stack.

I don't have CS5, but on CS4, I find the resultant stacked photograph to be ok for web, but for print, too many artifacts remain. PS creates a mask for each layer, and does not do a good job with the masks, resulting in the said artifacts. You can clean up by touching up the masks, but this is tedious, and difficult.

I did produce and sold several A0 prints done this way. Tedious and slow, but possible. Even for the 39MP Hasselblad files, an A0 image is still a 4X linear magnification of the original file. And you have to work carefully. The resultant print image can be about 30X to 100X the original size, so everything is magnified.

But the superior method to stack is via a software known as Helicon Focus. The software is not free...but license is a very reasonable fee. See this link for licensing. The software is excellent. On my laptop (Dell Studio XPS15, i5, 4GB, 1GB dedicated video), it is lightning quick on medium jpegs. Quite fast on full sized jpegs (The H3D produces files 7212x5412), and reasonable for full sized tiffs.

But the results are superb. The result shown above is without any touchup. And what little touchups, are done quite easily with the touchup tools available within Helicon. Much easier than painting white and black masks on CS4. I highly recommend Helicon Focus for those who are serious about focus stacking.
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