Here are some behind the scenes photos from the latest art shoot.
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.
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.
And here is a final image of the other sculpture piece out in the hall way:
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:
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:
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.
Ok, so the blank boards show up. As it turns out, the footprint I chose for the optoisolator was too small for the parts I ordered, which I only discover when I place them next to the board. Doh! That’s what happens when you don’t have parts in hand and check them against a full scale print on paper of the board design…
Oh, well, it’s easily fixed. A search through Digikey turns up different optoisolators that should drop in place without bending anything and just shorting over one pin. Here is the finished first board with a mangled MOC3023 soldered down. It’s the biggest part on the little green board with 6 legs.
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:
**** UPDATE *****
UPDATE: THIS IS AN OLD DESIGN. SEE THE NEWEST AND SIMPLEST LOW-V MOD HERE.
A recent previous post detailed the first and second passes at converting Norman 200B strobe packs to low voltage so as to be compatible with modern cameras. Those were not quite up to snuff because the first pass stole too much voltage to be usable and the second allowed 20mA of current to flow through the camera or trigger it was connected to.
After doing some reading about the subject, it would appear that at least for some older cameras, the trigger circuitry used an SCR, in which case the 2nd implementation above would fail because the constant 20mA would keep the SCR latched on. It might also be way too much current for the trigger circuitry to handle. The numbers I recall were 1.5mA max trigger current that decayed to something under 750uA.
So, back to the drawing board… Here’s what I came up with: