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Normans In Action: Another Art Shoot

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

DFAC-10-BTS-001

 

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.

DFAC-10-BTS-002

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.

DFAC-10-BTS-003

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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Moving Vintage Norman 200Bs into the Modern Era…

**** UPDATE *****

UPDATE:  NEW DESIGN COMING SOON THAT REDUCES CURRENT IN THE CAMERA/TRIGGER SWITCH AS ~20mA MAY BE TOO HIGH FOR CAMERA INTERNALS.

*****************

This post needs to be prefaced with a major disclaimer: Open your Norman 200B at your own risk. The 500V inside is potentially lethal. The author was careless once and accidentally discharged the cap with a meter probe which caused a big char streak in the connector and took a hunk out of the meter probe and one of the head plug pins. Proceed/attempt at your own risk. If you die, break your 200B, or both, I am not responsible.

Now that that’s out of the way, on the to the good stuff.

The Norman 200B trigger voltage is on the order of 100V. It was fine for old film cameras with mechanical sync switches. Modern digital cameras don’t care for such high voltages, so some sort of conversion or adaptation needs to be made. Optical slave triggers are one way to go, but the author smoked one accidentally by just letting the 200B sit waiting to flash. Apparently, some modern optical slave triggers do not care for such a high trigger voltage either. They are also going to end up dangling and exposed where they can become disconnected or in the extreme, get broken off.

Slave triggers and the like are not inexpensive, either. Sure, they come encased in a nice little plastic package and all, but at $8-10 or more apiece, they add up quickly, especially after having acquired four complete pack and head sets. Sometimes, it’d be useful and nice to use all that fire power at the same time and not have to carry all those little slave triggers and wires and stuff…

So, what to do? Reverse engineer the trigger circuit and make and a low voltage adapter for it using piece parts… Here’s the photo of the board alongside a mirrored and colorized photo of the traces on the bottom side that was used:

Norman 200B controller board

Here is the partial trigger circuit (please ignore all the extraneous numbers and notations) of the stock 200B blue circuit board:

Norman 200B LowVmod-5

Observant readers of Harold Edgerton’s book, Electronic Flash, Strobe, will notice that this circuit is pretty much the opposite of one within his book. The difference is that the Norman 200B is uses a positive ground, so everything is upside-down in comparison to Edgerton’s circuit. Another thing that should be noted is that when the SYNC connection is grounded, the charged 0.02uF capacitor discharges, turning on the gate of the SCR. Only a small amount of current will flow if the SYNC connection is held grounded, probably as an added safety benefit.

One would think that adding an optoisolator across the SYNC connection and the chassis would be sufficient to adapt the 200B for low voltage operation. That was tried but it did not work because the current that flows is too small to latch the triac within the optoisolator ON, so the capacitor does not discharge quickly enough, and the 200B never triggers. An early attempt to correct this consisted of shorting the diode. When the two resistors dividers are shorted together at their center points, the 200B could be fired with an optoisolator between SYNC and the case. But then additional current flows unnecessarily from the high voltage supply.

The first incarnation of the low voltage adapter was built into a plastic Tic-Tac and hung off a house hold plug that was plugged into the head. A sync cord then plugged into the Tic-Tac trigger. It was too many connections, something extra to carry and/or break. So when the opportunity to use two of the Normans for a photo shoot presented itself, it was time to move the adapter inside the pack and make the outside connections simpler…

In order to hook this into the 200B, three parts on the blue controller board need to be removed: a diode and two resistors. The colored circles indicate where the tap points are for the adapter board. The three parts need to be removed to completely isolate the SYNC connection to the head so that only optoisolated low voltage goes to the head socket. Note that two of the removed devices have a colored circle on one of their leads. The third one is unmarked in this photo but it is to the right of the orange filter capacitor and +12V connection (it can be seen in a later photo).

Norman 200B LowVmod

Here is the schematic for the low voltage adapter:

Norman 200B LowVmod-4

And here is the parts list with Digikey part numbers:


Digikey part number
Description
Note
497-2960-5-ND
IC REG LDO -5V .1A TO-92
negative 5V regulator
160-1378-5-ND
OPTOISO 400VDRM TRIAC OUT 6-DIP
optoisolator, MOC3023
CF18JT180RCT-ND
RES 180 OHM 1/8W 5% CF AXIAL
I limit resistor
399-1249-1-ND
CAP CER 0.1UF 50V 10% X7R 1206
output cap
399-1285-1-ND
CAP CER 0.33UF 25V 10% X7R 1206
input cap

The negative 5V regulator is probably not absolutely necessary, but the most often quoted number for DSLR maximum sync voltage I’ve seen is on the order of 7-9V; 12V would then be too high. A negative regulator is required because of the positive ground design of the 200B. The two capacitors are required by the regulator; surface mount chip caps were used because they take up a whole lot less room. The 180 Ohm resistor limits the current for LED inside the MOC3023 to about 20mA.

The circuit was wired onto a small perforated prototype board as can be seen below on the left. The board is positioned in this photo so the devices can be seen. The bottom of the board is normally up when assembled into the pack.

Norman 200B LowVmod-3

The pack assembled with the “protective” plexiglass cover can be seen in the photo below. The protective plexiglass is often broken on these old units… The cover also does not afford a whole lot of protection anyway since fingers can still get at the high voltage. I typically keep my fingers well clear when the power is applied and for a long while after the power is turned off as a precaution.

Norman 200B LowVmod-2

 

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