Chris S. wrote:
On the subject of obtaining the small focus increments needed by high NA objectives, let me repeat Rik’s recommendation to use a microscope focus block, perhaps one cut off the microscope and motorized with a stepper motor. This is the current gold-standard solution, and such a motor can be driven with the Cognisys StackShot
Chris,
These Piezo Stages may be the new Platinum Standard
As noteworthy as piezoelectric stages are--I've read and re-read Mike's posts about them with real interest--they don't strike me as a widely-recommendable fit for most macro photographers, at least not at present. One issue I see is that, despite Mike's generous documentation of his work, I doubt anybody reading his posts could build a piezoelectric stage without a lot of additional input from Mike. I take it this is because integrating a piezoelectric stage requires a much higher degree of technical prowess than the rest of us possess. Perhaps Mike will find a way to boil his work down to a recipe that mere mortals can follow. But for now, piezoelectric stages are a black box for the rest of us. Hard to recommend black box technology, even if Mike continues to be very generous in helping out with it.
--Chris S.
Chris,
You are correct, these are more complicated devices than nice commercial stepper motor based focus rails like the Stackshot & WeMacro. I hope I haven't made them sound that simple, if I have my sincere apologies
However, certainly within the capability of those technically inclined and with some DIY skill to create their own system.
The level we've been able to achieve with a dedicated piezo stage is now almost Plug-In-Play, it's been distilled to this level of simplicity since all the difficult behind the scenes stuff is handled by the Controller/Driver/Amp. The computer simply issues a integer command (16 bit range) and the stage goes to that position, and as you've seen it's really linear and perfectly repeatable for any direction, even over time and with some temperature change (see hair dryer test). You can read that position with the built-in 16 bit ADC which reads the feedback voltage with a simple read command. You can vary the input supply voltage, stage temperature, even stage loading (pushing it with your finger) and the position won't change. It's neat to watch the feedback voltage and the use a DVM to monitor the piezo high voltage output, you can see the hysteresis and non-linearity of the piezo ceramic elements as the output voltage wanders to keep the stage in exact location with even these drastic "external" influences. This is the benefit of high gain precision negative feedback, nothing effects the result except the true input!
All the routines, drivers and such have been developed in Python and easily adapted for one's preference. I'm not a programmer, so wanted something easy to edit and paste without a lot of hassle. We've developed simple test, calibration and stacking routines (also trigger the camera and strobe utilizing the Trinamic Controllers). The design works with the latest Trinamic Stepper controllers (a baseline requirement) so complete S&S systems can be utilized with a single RPi, even ones that use both a Trinamic and Piezo Stage for Z axis positioning, and support X and Y plus rotary position.
The Controllers have a bunch of color LEDS that tell you what's going on (+12V , +130V, -25V, RPi Pwr, HV Out, -HV Out, Hi + Current and Hi - Current) and even if you've plugged in the RPi connector wrong (or the RPI is not powered), don't ask why we included that feature
You can watch the voltage output levels and currents on the LEDs, even see the piezo stage capacitance charge and discharge during large steps, I like diagnostics
We'll try and help those interested if they decide to develop their own controllers like we've done with the Trinamic controllers, and also help those that are inclined to give these Custom Controller/Driver/Amps a try. Would be great if more folks got involved since my abilities are limited and only one!!
So yes they are a Black Box somewhat, but the box has been opened and some nice jewels inside
Best,
Research is like a treasure hunt, you don't know where to look or what you'll find!
~Mike