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Details Of The Photo Booth

As promised in a posting about the pseudo-neon sign, here are some details about the physical construction of the photo booth…

Here is the booth in action at a recent luncheon with the neon sign at the top:

photobooth at luncheon

The booth frame is constructed from 1″ electrical conduit. 3/4″ conduit would probably have worked just as well and would have been cheaper, but after buying the 1″ fittings, I was rather committed…

Here are two early photos taken during construction when I was still hanging the monitor on the back wall. (I’ve since moved it because it causes people to be looking up and off into space.) I’m also not using battery powered strobes any more.

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The conduit is joined with car port/canopy fittings I bought from Yuma’s Bargain Warehouse. (I recently discovered there is a relatively local supplier of the same fittings, Shade King, located just north of Austin, TX, so I could have bought these locally and saved the shipping cost.) Below is a diagram of the rough dimensions of the booth. I won’t bother with the specifics of the fittings and lengths because I would construct it slightly differently had I to do it all over again…

photobooth drawing

The shelf was constructed from 1×8 poplar painted black (it was on clearance at Home depot, so I bought it instead of white pine). It’s held to the frame by 1″ single-sided conduit clamps. The camera mounts to the center of the board with a Manfrotto 234RC tilting quick release mount, allowing the camera to tilt up and down for adjustment. It can’t be seen well in the image below because it’s behind the frame that holds the TV with HDMI input.

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The photo booth is skinned with tablecloths I bought from Amazon. These were the cheapest source of good weight material with which to skin the booth AND the edges were already hemmed. All the “real” fabric stores wanted more money for lighter weight material. Along with the tablecloths, I bought a 20 yard roll of hook and loop tape from Amazon for attaching the tablecloth curtains to the booth. More tablecloth was used to fashion a cap to cover the top of the booth. Again, I won’t bore with the details, since I don’t expect anyone to copy me exactly… The tablecloth skin can be seen in the photo at the top of this post.

Inside the booth, white tablecloth hangs as a background (unless the event organizer orders a custom printed background). Behind the camera and monitor, white tablecloth hangs as a bounce diffusion surface. Two 45 Watt-second AC slave strobes are optically triggered by the camera’s flash. The strobes and confined space of the booth allows using an aperture of F11 and pre-focusing the lens so that everything from about 2 feet out to 5 feet are in focus. (The camera I’m using is a Nikon D90 with a 24mm/2.8 prime lens, which has the focus distance markings on it.)

Constant illumination in the booth is provided by a home-made LED stick consisting of 3 meters of 3528 warm white strip LEDs stuck on an aluminum meter stick in a T8 protective tube.

The photo booth software itself is still a work in progress. It’s basically a Python script I wrote. Linux runs on a fanless quad core ARM computer (see below) with a Freescale i.MX6Q, 2GB of RAM, and a 32GB SSD inside. Everything I used is open source, mainly libgphoto2 and piggyphoto, python-pygame, and graphicsmagick. I’m reluctant to release the source code because it is not turn-key software.

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There are two USB flash disks plugged in. For redundancy, I copy each set of image files to multiple drives in case anything goes wrong. The additional advantage of extra flash drives is that at the end of an event, it is fully stocked with all the photos so I can deliver a purchased drive immediately. The USB hub has the wireless keyboard, the camera, and a custom “keyboard” plugged into it.

The custom “keyboard” is a microcontroller board programmed as a USB keyboard. The 50mm lighted arcade buttons (see below) provide the user input.

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The bottom board is a Freescale FRDM-KL25Z with a custom shield board I made on top. There is currently no differentiation in the script between the buttons, but they each generate a different letter. The buttons came from Amazon.

In operation, the Python script waits for a button push to start the sequence. Four photos are taken and displayed in succession, then two versions of composites are generated: one is intended for displaying on screens at the event and the other is a vertical strip much like what the old fashioned photo booths used to spit out. Two of these latter images side by side can be printed on 4×6 paper. All the raw source images are saved along with the composites.

All of the images are shared on the local network via SAMBA. This allows setting up several Android devices around a venue to display the photo booth images in a slide show. Although it’s hard to make out in the photo at the top of this post, there is a TV hanging from the top of the photo booth just to the right of the opening. Having this SAMBA share also allows me to look at the photos with my Android phone to check on things.

The booth is very functional at the moment but not quite ready to hire out. I plan to add near real-time uploading of the images to our SmugMug.com account (where examples of the booth photos can be seen in addition to on Facebook). I am also thinking of adding an option to print the double print strip images.

There are improvements I need to make to the booth physically as well – I need to be able to set it up and break it down in 30-45 minutes. One of the things that can help with this is to build a box to house the camera, computer, monitor and button(s) allowing all the connections to be left intact. All that would need to be done is fasten the box down and plug in the power.

One interesting side note is that the Nikon D90 will drain a battery dead if left plugged into an active USB host. To avoid the hassle of having to use, charge, and switch out batteries, I purchased an AC power supply for the D90.

 

 

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Normans In Action: Another Art Shoot

Here are some behind the scenes photos from the latest art shoot.

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In the foreground, there are two PVC panels, each clamped directly to a light stand. Each panel is illuminated by two Norman LH-2 heads connected through a Y cable by a Norman 200B power pack. All the flat artwork was photographed leaning against the podium.

The sculptures were photographed in a light tent assembled from PVC panel pieces (four straight lengths and four lengths with elbows at each end). A piece of black velvety material hangs from the back so as to appear as an infinite black background. This was illuminated by AC powered slave strobes, but not all three were used for every photo – sometimes fewer were used, depending on the piece. They were alo moved around to change where they were aimed.

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There were two very heavy sculptures that had to be photographed in place out in the hall, so one panel was used as a reflector (the one on the left) and the other was used as the diffuse light source.

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And here is a final image of the other sculpture piece out in the hall way:

DFAC-10-BTS-004

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Norman 200B Low Voltage Sync Mod – details…

Finally, the details of the modification of the Norman 200B for low voltage sync…

DISCLAIMER: The high voltage inside a Norman 200B can be lethal. Never measure with bare meter probes; use something like these Pamona test clips. Always allow the capacitors inside the 200B to discharge by turning the power switch to the off position for a long time. Perform this modification at your own and your equipment’s risk.

Here is a partial schematic of the controller board:

200B LowV Mod schematic

The SYNC connection goes out to the head and test switch. With the components shown, the SYNC voltage is somewhere around 100V. I have seen several controller boards with two 33k Ohm resistors in place of R1 and R2. These boards have a SYNC voltage of around 30V. Note that the case of t he 200B is positive (+BATT) and that the SYNC connection is negative relative to the case.

The TRIG connection also goes to the head. It sits at around -400V. The voltage charges the trigger capacitor in the head. When the SCR fires, it shorts the capacitor across the trigger coil which then fires the flash tube.

As drawn, the SYNC side of the diode is slightly more negative than the R2 side, which is around -80V. In the steady state, capacitor C1 (0.02uF) has about 320V across it. When the SYNC terminal is shorted to +BATT, C1 temporarily acts as a short circuit, pulling the gate of the SCR positive and causing it to fire, triggering the flash tube.

In order to convert the SYNC connection to a lower voltage, the values of R1 and R2 need to be lowered to reduce the voltage. To get about 12V at the SYNC connection, the resistances should be changed so that R1 is 120k and R2 is slightly lower, say 100k. The resistors can be replaced altogether or appropriately sized resistors can be piggy-backed onto the existing ones to yield the equivalent parallel resistance.

When the divided voltage is lowered, though, the flash will no longer reliably fire. This happens because when SYNC is shorted to +BATT, the positive spike on the SCR gate is smaller because the voltage across C1 increases when SYNC is made smaller. To correct this, the capacitance of C1 and the resistance of R3 both need to be increased. I found that adding a 0.1uF @ 500V capacitor in parallel with C1 and replacing R3 with a 330 Ohm resistor worked well to keep the current in the SYNC line when first shorted and then held about the same as with all the original component values.

Now, here’s a photo with the components labeled:

200B LowV Mod board

If a SYNC voltage lower than about 12V is desired, then the resistors dividers will need to be changed accordingly. Then R3 and C1 may also need to be adjusted for reliably triggering the flash.

Please forgive me for not actually inserting photos of the modification itself – if I wait until I get a chance to take them, this will never get posted… Please also forgive me for not giving real explicit details; the reason is twofold: 1) If you know what you’re doing, you can figure it out and 2) I’ve seen component value variations in the 8-10 boards I’ve touched which makes providing explicit details somewhat pointless.

The next project is to replace the analog logic performed by the op amps (which really should been comparators instead of op amps, but I digress…) with a microcontroller board that monitors the SYNC connection, triggers the flash, and controls the capacitor recharging. Using the microcontroller allows watching for pre-flash pulses used by Nikon CLS/AWL, which then allows the 200B to be remotely controlled.  If I get really ambitious,  I can kludge a way for the micro to control the power but that’s very much less trivial given the high voltages and currents in the capacitor/flash tube path.

Stay tuned…

 

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Oh Happy Surprise!

The PCBs for the low voltage adapter for the Norman 200Bs have finally arrived! (See this post for the schematic and layout.)

Surprise! Surprise! Surprise! I’ve never ordered before from BatchPCB.com, but it would seem that if your board is small enough, they’ll fill out extra panel space with your board and just send it to you when they’re done. I’d ordered 4 and got 14 in the mail. Wah hoo! I was expecting to have to order more but now I won’t have to. The per board cost comes down from over $5 each to about $1.65.

Here’s a photo the pile of finished boards that I can’t build up until tomorrow:

lowVpcbs-01

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Light Saber – DIY Saberstrip

Recently, I came across a nifty light modifier for small battery flashes called the Saberstrip. It’s a tube with a mount for the flash at one end, and a mirror at the other end, and a long window covered with diffusion fabric. The long linear light source makes a diffuse shadow in one direction. They can be doubled up and oriented as an “L” to give a look closer to an umbrella or soft. One big advantage of the Saberstrip is that it’s not a big sail that’ll catch the wind out on location. At US$135 plus another 15 for shipping, though, it’s rather expensive for the hobbyist.kat-01

Continue Reading…

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