The Big Box o’ Optics disgorged an ancient new-in-box Computar 4.8 mm lens, originally intended for a TV camera, with a C mount perfectly suited for the Raspberry Pi HQ camera:
Because it’s a video lens, it includes an aperture driver expecting a video signal from the camera through a standard connector:
The datasheet tucked into the box (!) says it expects 8 to 16 V DC on the red wire (with black common) and video on white:
Fortunately, applying 5 V to red and leaving white unconnected opens the aperture all the way. Presumably, the circuitry thinks it’s looking at a really dark scene and isn’t fussy about the missing sync pulses.
Rather than attempt to find / harvest a matching camera connector, the cord now terminates in a JST plug, with the matching socket hot-melt glued to the Raspberry Pi case:
The Pi has +5 V and ground on the rightmost end of its connector, so the Computar lens will be jammed fully open.
I gave it something to look at:
With the orange back plate about 150 mm from the RPi, the 4.8 mm lens delivers this scene:
The focus is on the shutdown / startup button just to the right of the heatsink, so the depth of field is maybe 25 mm front-to-back.
Pondering the sample code shows the camera focus setting involves writing two bytes to an I²C address through the video controller’s I²C bus. Enable that bus with a line in /boot/config.txt:
If you’re planning to capture 1280×720 or larger still images, reserve enough memory in the GPU:
I don’t know how to determine the correct value.
And, if user pi isn’t in group i2c, make it so, then reboot.
The camera must be running before you can focus it, so run raspivid and watch the picture. I think you must do that in order to focus a (higher-res) still picture, perhaps starting a video preroll (not that kind) in a different thread while you fire off a (predetermined?) focus value, allow time for the lens to settle, then acquire a still picture with the video still running.
The focus value is number between 0 and 1023, in two bytes divided, written in big-endian order to address 0x0c on bus 0:
i2cset -y 0 0x0c 0x3f 0xff
You can, of course, use decimal numbers:
i2cset -y 0 0x0c 63 255
I think hex values are easier to tweak by hand.
Some tinkering gives this rough correlation:
Focus value (hex)
Focus distance (mm)
Arducam Motorized Focus Camera – numeric value vs mm
Beyond a meter, the somewhat gritty camera resolution gets in the way of precise focusing, particularly in low indoor lighting.
A successful write produces a return code of 0. Sometimes the write will inexplicably fail with an Error: Write failed message, a return code of 1, and no focus change, so it’s Good Practice to retry until it works.
This obviously calls for a knob and a persistent value!
Rummaging through the Big Box o’ Optics in search of something else produced this doodad:
It carries no brand name or identifier, suggesting it was shop-made for a very specific and completely unknown purpose. The 5× objective also came from the BBo’O, but wasn’t related in any way other than fitting the threads, so the original purpose probably didn’t include it.
The little bulb fit into a cute and obviously heat-stressed socket:
The filament was, of course, broken, so I dismantled the socket and conjured a quick-n-dirty white LED that appears blue under the warm-white bench lighting:
The socket fits into the housing on the left, which screws onto a fitting I would have sworn was glued / frozen in place. Eventually, I found a slotted grub screw hidden under a glob of dirt:
Releasing the screw let the fitting slide right out:
The glass reflector sits at 45° to direct the light coaxially down into the objective (or whatever optics it was originally intended for), with the other end of the widget having a clear view straight through. I cleaned the usual collection of fuzz & dirt off the glass, then centered and aligned the reflection with the objective.
Unfortunately, the objective lens lacks antireflection coatings:
The LED tube is off to the right at 2 o’clock, with the bar across the reflector coming from stray light bouncing back from the far wall of the interior. The brilliant dot in the middle comes from light reflected off the various surfaces inside the objective.
An unimpeachable source tells me microscope objectives are designed to form a real image 180 mm up inside the ‘scope tube with the lens at the design height above the object. I have the luxury of being able to ignore all that, so I perched a lensless Raspberry Pi V1 camera on a short brass tube and affixed it to a three-axis positioner:
A closer look at the lashup reveals the utter crudity:
It’s better than I expected:
What you’re seeing is the real image formed by the objective lens directly on the RPi V1 camera’s sensor: in effect, the objective replaces the itsy-bitsy camera lens. It’s a screen capture from VLC using V4L2 loopback trickery.
Those are 0.1 inch squares printed on the paper, so the view is about 150×110 mil. Positioning the camera further from the objective would reduce both the view (increase the magnification) and the amount of light, so this may be about as good as it get.
The image started out with low contrast from all the stray light, but can be coerced into usability:
The weird violet-to-greenish color shading apparently comes from the lens shading correction matrix baked into the RPi image capture pipeline and can, with some difficulty, be fixed if you have a mind to do so.
As far as I can tell, Raspberry Pi cases are a solved problem, so 3D printing an intricate widget to stick a Pi on the back of an HQ camera seems unnecessary unless you really, really like solid modeling, which, admittedly, can be a thing. All you really need is a simple adapter between the camera PCB and the case of your choice:
The plate has recesses to put the screw heads below the surface. I used nylon screws, but it doesn’t really matter.
The case has all the right openings, slots in the bottom for a pair of screws, and costs six bucks. A pair of M3 brass inserts epoxied into the plate capture the screws:
Thick washers punched from an old credit card go under the screws to compensate for the case’s silicone bump feet. I suppose Doing the Right Thing would involve 3D printed spacers matching the cross-shaped case cutouts.
Not everyone agrees with my choice of retina-burn orange PETG:
Yes, that’s a C-mount TV lens lurking in the background, about which more later.
The toothbrush head has a convenient pair of neodymium magnets affixing the RPi’s power cable to the beam, thereby preventing the whole lashup from falling off. The Pi, being an old Model B V 1.1, lacks onboard WiFi and requires a USB WiFi dongle. The white button at the lower right of the heatsink properly shuts the OS down and starts it up again.
Zoom can show video only from video devices / cameras attached to the laptop, so the trick is to make video from the RPi look like it’s coming from a local laptop device.
Start by exporting video from the Raspberry Pi:
raspivid --nopreview -t 0 -rot 180 -awb sun --sharpness -50 --flicker 60hz -w 1920 -h 1080 -ae 48 -a 1032 -a 'RPi Cam1 %Y-%m-%d %X' -b 1000000 -l -o tcp://0.0.0.0:5000
The -rot 180 -awb sun --sharpness -50 --flicker 60hz parameters make the picture look better. The bottom of the video image There is no way to predict which side of the video will be on the same side as the cable, if that’s any help figuring out which end is up, and the 6500 K LED tubes apparently fill the shop with “sun”.
The -l parameter causes raspivid to wait until it gets an incoming tcp connection on port 5000 from any other IP address, whereupon it begins capturing video and sending it out.
That’s the edge of the workbench over there on the left, looking distinctly like a cliff.
The RPi will happily stream video all day long to ffmpeg while you start / stop the display program pulling the bits from the video device. However, killing ffmpeg also kills raspivid, requiring a manual restart of both programs. This isn’t a dealbreaker for my simple needs, but it makes unattended streaming from, say, a yard camera somewhat tricky.
There appear to be an infinite number of variations on this theme, not all of which work, and some of which rest upon an unsteady ziggurat of sketchy / unmaintained software.
Addendum: If you have a couple of RPi cameras, it’s handy to run the matching ssh and ffmpeg sessions in screen / tmux / whatever terminal multiplexer you prefer. I find it easier to flip through those sessions with Ctrl-A N, rather than manage half a dozen tabs in a single terminal window. Your mileage may differ.