I recently got my hands on one of the Cadillac DeVille/Raytheon/L3 cameras with the 320x240 BST sensor, and I found two things to be extremely inconvenient:
- The almost completely fixed-focus, and nearly telephoto lens was focused close to infinity, which made is almost useless in an indoors setting.
- The chopper wheel on my unit was slightly warped from previous use and replacements are both expensive and unavailable. (the former likely the result of the latter )
To solve these issues, I designed a set of three easily 3D-printable components that require almost no post-processing(more on that later) that I'd like to share with everyone here.
This is how the manual focus assembly looks like:
The replacement lid, transparent in this image, has a large thread cut into it, and allows you to focus anywhere from beyond macro to beyond infinity(
though not recommended as focusing beyond infinity also crushes the chopper wheel).
The lens holder, metallic, is designed to accommodate the lens block, which is what you get after you remove everything possible.
A quick guide on removing the lens block from the original front casing:First, you have to remove the ring that sits on the very top of the lens housing. It has a small notch on the side that is easy to place a prying tool in. Be careful when removing it.
Next, you have to remove the protective window and heater element, which is done by first shearing off the head of the soft black plastic rivet on the side - this is the only destructive operation in this mod. Once the pin is sheared off, the window holder and heater block can be removed by rotating it counterclockwise and gently pulling. Rotating it may be very difficult if the protective window was broken previously and has let dust inside the cavity, so don't be afraid to put a bit of force into the twist.
After the window is removed, turn the top casing around and remove the metal ring holding the focusing mechanism in place, this is done by unscrewing the three self-tapping screws.
Now, this next part is tricky. There is a small gap between the very top of the outer shell and the focusing mechanism, right next to the alignment slot(into which the case fits). You have to place a small flat-blade screwdriver into that slot and slowly pry around the gap, until it's about 5mm wide. This may require a lot of force, so be careful to not slip into the Ge front element.
At this point, you should be able to pull the whole focusing assembly out of the front case.
When the assembly is out, place a hex wrench or appropriately-sized screwdriver into the small brass gear on the back of the focusing assembly, and turn the gear until the back of the lens assembly(the bit with the plastic cover, which is also very fragile) is all the way in, if looking from the back. Once it's in, firmly grasp the lens assembly from the front, and unscrew it.
Note: There is a very tight and angry but short spring holding the lens assembly in place.
At this point you should have just the lens block itself, with all the unnecessary components removed, and it will fit into the lens holder as shown here:
The bottom of the lens assembly should be flush with the bottom of the lens holder.
It's also a good idea to stuff the original o-ring between the lens holder and the lens block.
The replacement lid was not designed to conform to the curve of the device, and therefore is not as rugged, however it does fit the original bolts, and it should sit flush with the casing. A bit of electrical tape around the metal edge of the case is a good idea.
This is how the final assembly looks:
This also shows that the print quality tolerances are very large - the print came out half-broken and it still functions.
The design incorporates a ~0.4mm gap between the case and lens holder, so it should thread in easily.
And here's a video of it in action, focusing on objects closer than infinity(hand, lighter, cracked window in autumn, space heater, cold metal):
Now, a bit about the chopper wheel:
The design may look a little odd, but this was done for a reason - it follows the original
Fibonacci-ish exponent-ish curve of the original almost perfectly, and it's balanced to (ideally) within tens of microns. The balance part depends on what you make the wheel out of and how good your printer is, but it's also possible to create it out of almost any sheet material on a CNC router/mill(though the pinch may be a bit difficult to mill out).
You will also have to wrap a bit of tinfoil around one of the legs to make a reflective surface for the closed loop speed sensor.
Although the wheel is identical to the original in terms of shape, when installed onto the motor it results in rather poor performance, with a very large non-uniformity, sometimes even image inversion, and awful dynamic range.
I'm not entirely sure what's causing this, and more research is needed, though my suspicion is that the sharp transition between solid plastic and air makes for a poor image, and the original approach of diffusion must be used instead of complete interruption.
The next step would be attempting to replicate the wheel's film print by printing the pattern on a regular transparency sheet using a laser printer and dithering.
This is the result of using the printed chopper wheel, same lens setting as the previous video:
As evident, it needs more work, but I've got other projects on hold that need work, so I'm publishing it as-is, in hopes that someone else may further improve the design.Update: The unacceptable image quality is caused by a phase shift in the readout of the sensor in relation to the chopper wheel position. This can be fixed by tweaking the position of the tinfoil reflector - try to get it to be as close as possible to the location of the reflector on the original wheel.Here is a video of the printed chopper in operation:
Note that the phase is still slightly off - this is my mistake, and if you place the reflector in the perfect position, you will get a very clear, crisp image with a
better dynamic range than the original chopper.
The files can be downloaded here:
https://spirit.re/projects/files/download.php?file=/raytheon/raytheon_stl.zipNote that the chopper wheel must be printed at 200% size in X and Y, 100% in Z.
If you'd like the original design files, made in Autodesk Inventor 2018, send me a PM.
Any ideas and suggestions welcome.