Stacking has been an evolution in progress for our main work of imaging semiconductor chips at Mike's Labs. Many of these images are displayed or printed in very large formats (some over 6'), so composition, lighting, detail and sharpness are all important.
The Lab's have been involved with focus stacking since ~2010 when we realized we couldn't get the images of the chips we've designed with enough resolution using a single image. Many of these images were not flat chip images, but a more "composed" ascetically pleasing angled view to create a "3D" perspective which has significant depth. However, even stacking became a limitation when wanting very high image resolution and sharpness of detail, which required higher magnification but suffered reducing the field of view. This evolved to Stacking and Stitching, where multiple XY positions are stacking in Z, then "stitched" together like a panorama for a much larger field.
Lighting for stacking can be extremely challenging with certain subjects, more so than for a single image, and especially so when doing Stack & Stitch images.
As things progressed we soon required extreme performance beyond the normal excellent commercially available equipment and began designing our own custom focus rails utilizing surplus industrial gear, mostly around the superb THK equipment. However, the excellent commercial controllers were also limiting performance at the extremes and this lead to the development of custom controllers based around the Trinamic devices and custom developed controlling software.
S&S requires 3 axis of control. After doing X and Y manually, a development for an automated controller began at the Lab's. This lead to the development of many 3 axis controllers (even 4 axis for rotation) based upon various Pololu and Trinamic devices, eventually yielding a fully Automated "Hands Off" S&S system capable of operating for many hours (even days) without intervention producing 10,000, 20,000 or more images.
S&S brings even more difficulty to the table, as each XY position must be precisely aligned and illuminated with respect to the other positions and throughout the Z axis stacks. Also, the image perspective comes into play, as each XY perspective must be exactly alike, which imposes a very difficult requirement on the lens characteristics. This leads to lenses that are "telecentric", meaning the apparent subject magnification and perspective doesn't change with subject position. Semiconductor chips are more difficult in some ways as the features are known and can't be distorted to get things lined up, and some areas have a very specific and uniform color or gradient which can't be blended easily during stitching. These are also very susceptible to JPEG artifacts, so mostly are done with lossless TIFF.
Along this development evolution, hardware, control algorithms and techniques were developed, and continue, to improve the time between image captures without suffering image degradation due to vibration blur. Vibration induced blur comes for many sources, including camera mirror, front & rear curtains, motor and rail movement, motor current waveforms, motor, rail & setup resonances, setup mechanical characteristics and many external sources, all of which must be addressed! Consider a 10,000 image S&S session with 15 second intervals requires almost 2 days to complete, at 2 seconds this is a more reasonable ~6 hours. The Lab's have succeeded in reducing the time to under 2 seconds and now approaching 1 second per image.
Lately we've been developing techniques at the Lab's to get very precise levels of movement in nanometers utilizing piezoelectric devices. This effort is leading towards doing pixel level shifting outside the camera body, and also used for extremely high magnification stacking. Also developed is a Voice Coil Motor control system that utilizes a quality small "speaker" as a replacement for a focus stacking rail and stepper motor. The Lab's produced an experimental custom VCM "Current Mode" controller that works very well and allows smooth and precise subject movement for stacking.
Details on all these developments at Mike's Labs can be reviewed at PM.
http://www.photomacrography.net
Here's a couple old stacked examples I can show.
Old low-res image I can show of a patented circuit in IBM 9HP SiGe BiCMOS 90nm process. This was with the $18 AmScope 4X finite objective! More on this lenses if folks want.
Direct Digital to Antenna 5 Bit
Another old image of patented circuit in same process.
Direct Digital to Antenna 8 Bit
My bad! Not always good at Mike's Labs!!
BTW I don't just focus stack images, although most of my efforts at Mike's Labs is devoted to such for chip images, I've captured the Clearwater Offshore Racing World Championship (2010~2016), Opening 2 page image The Huntington Library, Art Collections, and Botanical Gardens in Pasadena CA (ISBN 978-0-87328-263-5), Sebring and a few more.
2016 World Offshore Racing Championships, 150~200MPH!
Hunington Gardens and Museum Desert Gardens
Sebring 2014
Best,
BTW please view Andreas Kay's work on field stacking over at PM.
http://www.photomacrography.net/forum/viewtopic.php?t=40393&highlight=
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Research is like a treasure hunt, you don't know where to look or what you'll find!
~Mike
