Andy’s hacked LED flashlight (the man stuck an 18650 Li-Ion cell inside a $2.99 keychain LED flash. God that thing is bright) worked pretty decently in the previous light painting exercise, so I figured I’d up the fire power. Ran to Harbor Freight during lunch and picked up a 1 million candlepower flashlight for $12.99.

First try was to set the camera’s white balance to tungsten (since that’s what flashlights are), camera on a tripod, f/8, ISO100, bulb mode, and lock the shutter open in a dark room. For the sake of learning, I painted one side of the car at a time:

Here’s the front of my car

And the sides:

And here’s the combined shot:

There is some spillage of the light cone. Basically the parabolic reflector throws a pretty tight beam spot, but there’s some secondary reflection / refraction off the front lens cover that’s lighting up stuff I don’t care to light up.

A quick trip to the mail room for an envelope or two, and a bit of packaging tape, solved that problem:

Results:

Next, I set up my Photek softlighter with the secondary diffuser, and hoisted it up high on my light stand. I really need a sturdier stand, or something with a counterweight to help hold this up. By lighting from up high, I am hoping to eliminate the hot spot on the bodywork. Something to do with family of angles and stuff. .

HEY! This is pretty good. Of course, a softbox is kinda like a shotgun approach to lighting, but at least there’s a choke in this shotgun barrel.

One thing to note (if you zoom in on the original) is that the light stand holding up the Photek Softlighter is visible in the shot. It’s being back-lit by the softlighter, and shows up as black lines in the reflections in the window.

I fixed this by installing the diffuser the “wrong” way. Normally I don’t do this, as it eliminates the ability to tilt the softlighter and blocks off the flash’s controls, but for what I’m doing here, it solved my problem nicely:

I moved the car to shoot the driver’s side. While there, I also popped just the hazard lights by themselves, to give an idea of their contribution independently in the final image:

With the “gimpy” configuration on the softlighter, I retry the overhead lighting:

Not bad, but the sides are a bit dark. By the way, the strobe is at M1/16 and I’m firing 2-3 shots per second while slowly walking down the side of the car. Essentially turning my 60″ photek into a virtual, 8ft x 60″ strip lighting softbox. That’s powered by 4x AAs

Another shot, this time using a 70-200 for a tighter crop and less background clutter:

Looking nice. Need to do something about lighting the front surfaces though.

Here, after lighting the top and across the hood, I walked sideways across the front and held the softbox out to the side, aiming straight at the car.

Ooops, ended up in the camera’s field of view. The edge of the photek lights up from secondary bounce; so I have to be extra careful. The next time around I’m going to try to find a proper softbox, and probably put a cardboard grid on it to control the spread more.

Now that I have a better understanding, I reshoot the sequence, being mindful to stay outside the camera’s field of view at all times with the side firing softbox:

Straight out of camera, vantage point 1

Straight out of camera, vantage point 2

To get the camera low enough for the second shot, I twisted the Manfrotto tripod around like a pretzel:

And with a bit of editing in Lightroom:

The only mistake? I got into the car to flick on the hazards, HID lights and fog lights. The suspension reacted accordingly, so there is a mismatch where the side turn indicator lit up, versus where the indicator lamp sat during nominal exposure. Nuts.

I think I’m at the point where I’ve outgrown this warehouse – the white walls really distract from the final image, but it offered me a nice, warm and dry place to practice my light painting. By the way, here’s a behind the scene shot of the “studio”:

Total time: About 3 hours, after work, for about 20 images. And a lot of head scratching.

Now, I need to location scout for an outdoor place that’s got low ambient light…

Tonight, the goal was to test the breadboarded prototype of the bullet flight sensor’s electronics. Remember – I am a mechanical engineer; this is a completely new foray into the world of electronics for me, aside from some simple “hook a solid state relay to a microprocessor and bit bang some code to turn on the rice cooker” projects. So even though this may seem like kindergarden EE stuff, it’s a fairly big leap for me, design wise; I’m no longer relying on the ability to clobber code and instead using discrete logic ICs and doing actual calculations and setting RC time constants, etc.

We begin with the breadboarded model:

And our setup in the lab:

On the bench is a trusty oscilloscope to look at the signals at different lines, a DC power supply set to 5V, 100mA current limit, and a signal generator. The signal generator won’t be used for this project here.

First, I verified that the *new* sensor is working – the last one had a round put through it by accident:

Next, I verified that the 555IC is getting the power that it needs. Turns out that the power rails aren’t fully connected all the way. A bit of poking with an ohm-meter fixed that. Now I am ready to insert my test points:

And trip the break-beam sensor, with my gimpy fingers:

Orange line, or Ch1, is my sensor’s output. It goes from High to Low when the beam is broken. The turquoise line, or Ch2, is my 555’s trigger output. It goes from low to high when the input pulse is received. That’s a VERY promising sign.

My fat butter fingers can only move so fast through a 10mm opening, so the event scrolls off the oscilloscope’s screen. I tried dropping a small machine screw through the opening, but that actually prove to be much harder than expected (don’t laugh!). Frustrated, I finally came up with the following idea:

By flexing the rubber ducky antenna on one of my pocket wizards and getting it to spring through the break-beam sensor gap, I can generate a quick enough blip from the sensor:

Each major division is 5 milli-second on this setting, so the rubber ducky antenna is only in the beam’s path for about 10mS. My fingers can’t move *that* fast, for sure

Repeating the test again a few times, got me the same result:

Note that irregardless of the pulse length from the sensor, the 555’s output always sits at about 35ms. This is a litte bit off from the design goal of 40ms (1/250 second shutter speed, or sync speed on a 1.6x crop camera), but close enough for government work. I attribute the difference in component value tolerances on setting the RC constant.

Now the final test – does the output from the 555 trip the SCR to fire the strobe and pocket wizard?
(I selected an SCR instead of a cheaper / more common transistor. The SCR is rated to 400V, so even an older, high voltage “digital camera killer” flash will work on this sensor. )

And…

*drum roll please*

Nothing happened.

Turns out the same bug that bit me on the 555 timer bit me again. The top and bottom half of the power bus on this breadboard is not connected, and the SCR wasn’t grounded properly because of that. Now, plugging in a pocket wizard, this is what I get (with Ch2 now monitoring the anode of the SCR):

Interesting, it seems to add a bit of noise to the sensor output line. But the characteristic beep of the PW firing can be heard as the beam is broken. (Note that the sync voltage of the pocket wizard is only 3V or so).

Plugging in the 580EXii:

Again, some electronic noise on the sensor line, but we got what we need out of it – the clean voltage drop that triggers the monostable multivibrator.

And here’s the happy camera dork with his new toy (click link for video:)

Now that the circuit is verified working, I am okay with releasing the resources to order the acrylic for laser cutting to form the chassis, as well as starting PCB layout. Stay tuned…

(Leave a comment, with contact information, if you really want to know ).

-=- Terence

Note the “unusual” arrangement with the pocket wizard. The “hot shoe adapter” is actually plugged into the sensor to simulate a camera’s hotshoe firing the pocket wizard.

Dad (a retired electrical engineer) had given it his blessing, so the next step up would be physically prototyping it. Looks like I’ll be placing an order with DigiKey or Jameco or some other online electronics component vendor.

While the circuit components are enroute – and they will be breadboarded up first – I’m going to try my hand at learning Eagle, a CAD design software. The circuit is simple enough that I can probably etch it myself using laser transfer paper, but I might also just job it out to someone like BatchPCB.com and deal with it that way. It’ll all depend on the mechanical fabrication lead time as well as other project loads.

Meanwhile, mechanical design needs to be refined a little bit. These are current CAD model screenshots:

Here the unit is partially disassembled to change batteries.

Here’s a top view looking straight down on the circuit card, with the detector barrel rendered transparent.

And finally an isometric view of the unit assembled.

Mechanical details for the battery contacts, as ewell as lead-in for the slots, needs to be integrated. Then it’s a matter of generating a file to drive Dave’s grandparent’s laser engraver to cut these acrylic parts!

W00t, can’t wait!

First, the setup. The sensor is securely mounted in my benchtop vise, with a phone book propped up behind the bullet path as a pellet trap. (Finally, a good use for those dead-tree edition phone books!). A regulated DC power supply is used to provide the power to the sensor module, and my oscilloscope is used to monitor the signal line. As before, we set the oscilloscope to trigger on a falling edge signal at a level close to DC Bus -.

(I need to get my garage sale O-Scope probes checked. They don’t seem to be reading the voltage right, but at least the signal generator test indicates a good test pattern. Probably something stupid I forgot to set in the software. I’m still learning how to use this thing).

Next, I set the oscilloscopes time scale to 100 nanoseconds per division. Yup, definitely picking something up! That’s a good sign. Rechecking at 1 microsecond per division shows a fairly clean signal.

To give Dad a good idea of what he’s engineering to, I need to take some measurements of the pulse width of the event. We’ve previously calculated about 18.3 microseconds for a round ball at 1000fps. (Note that we actually don’t know how fast the air rifle is shooting at, nor is the pellet perfectly round.)

Look at that! 20 microseconds. Love it when the calculations matches real life data.

The next shot clocked in at a mere 5 microsecond pulse. There could be 2 reasons: A) the angle of the flight path through the sensor might be changing, or I might be nicking the beam differently. Still, the oscilloscope clearly captures a 5ms pulse.

Another shot, this time generating a 10ms pulse.

Yet another 5ms pulse again – followed by a lot of electrical noise. That’s strange…

Looks like the round nicked the sensor housing. Yeah, that would explain the sensor noise.

Remarkably the sensor still works. Putting the gun aside, I grabbed the soldering iron sponge and started dripping water past the IR beam. It registers on the O-Scope! (translation – this can be used for those awesome water-drop shots!)

Finally, here’s a couple of pellets recovered from the phone book. Love how you can see the rifling marks on the pellets .