Nikon BC-7

Discussion in 'Nikon' started by FPapp, Jul 25, 2020.

  1. While searching for a vintage flash gun to use with my recently acquired Agfa Record III, I stumbled across the Nikon BC-7 flash. It seems like a good option since I also own a Nikon F and F2. I also like the fact that this unit can use bayonet base (e.g. #5), Miniature base (M2, M3) and all glass (AG-1) bulbs. I happen to have a bunch of these various types of bulbs.

    I'm curious if there are any other vintage folding reflector type flashes that can take all three bulb types? The disadvantage of the BC-7 is that it requires a specific cord to attach it to a PC outlet, and I would also need the AS-2 adapter to attach it to a standard accessory shoe.

    Thanks BC7.jpg.JPG
  2. The beautiful Nikon F with the plain prism. Was there ever a more perfect design? OK, maybe Leica M4.
    FPapp likes this.
  3. Agfa, for one, made a fan-type folding flash. There are probably many more.

    I also seem to remember you could get bayonet to wire-ended flashbulb adapters back in the day. You'll probably look long and hard for such a thing today though.

    And the film ain't gonna care whether its photons came from a flashbulb, an electronic flash or a tray of magnesium powder.

    Does the F2 support M synch? I've never bothered to check, since flashbulbs went out with the Ark, and a fair few years before the F2 was introduced.
  4. Just curious, is Flash Powder still legal in this wonderful Nanny World?
  5. Apparently still in use for theater pyrotechnics and fireworks I am guessing you'll need a license to manufacture and use it.
    mike_halliwell likes this.
  6. It must have been common- I had a "Goldcrest Flash" bought at K-Mart that could take multiple type bulbs. It had a cold-shoe and used the PC cord.
    I also have many AG-1 type flashbulbs, bought when they were 50cents to 10 cents for a box on clearance.
    FPapp likes this.
  7. So after doing some searching on the web, many people recommended the Honeywell Tilt-A-Mite flashbulb holder. I found a new in box one for $20 and it works perfectly! I can use it on my Nikon F and on my Agfa Record (plus a few others).

    Another question I have, call me crazy but I wanted to experiment with the flashbulbs on my DSLR's. The flash holder doesn't have a hot shoe connection, only the PC connector. Will plugging it into the PC port on the camera have any potential to damage the camera due to incompatible voltage and current? Or is the PC sync just a simple trigger?



  8. That's critical. There are sources on-line for "old, new stock" flashbulbs, but they're not going to last forever. (see also LINK)

    This outfit claims to be the last manufacturer
    but they mostly don't sound like the flashbulbs I used on my old folding cameras back in the 50s.
  9. There are tons of various types of flashbulbs, flashcubes, flashbars, etc. available on eBay and other online sites for fairly reasonable prices. Even though most of these bulbs are no longer manufactured, I'd wager there are more of them out there than will ever be used up by vintage camera enthusiasts such as myself.

    I think Meggaflash only makes the large Mazda base bulbs.
  10. I guess it's a sort of race between the increasing mortality of the users and the vast (or half-vast) numbers of flashbulbs on eBay.:rolleyes:

    not commonly my own experience
    FPapp likes this.
  11. Nikon quote a voltage limit of 250 volts for both the P-C socket and hotshoe of their DSLRs - those that have a P-C socket. They say nothing about the current.

    IIRC, most old bulb flashes worked off either a 15v or 22.5v battery (good luck finding one of those in your local store!). So the voltage should be no problem. However the current to the flash bulb was boosted by a capacitor of a few tens of microFarads value, for reliable firing. This is going to put a few Amps through the firing circuit, and whether it'll cause damage or not, I wouldn't like to guess.

    Maybe the camera's circuit will limit the current and not fire the bulb. Maybe it won't fire it reliably. Maybe the current will fry the camera trigger circuit. Maybe it'll work just fine.
    Stick a pin in any of the above options.

    Personally, I wouldn't risk it without an interposing isolating circuit. Something like a meaty bipolar transistor.

    P.S. Modern DSLRs expect only a positive trigger voltage WRT 'earth'. There was no such convention in the days of flash bulbs, with polarity probably being equally divided between positive and negative according to the whim of the designer.
    Last edited: Aug 1, 2020
    FPapp likes this.
  12. The PC cord of these Flash Units put the full charge through the camera. The cameras had mechanical switches in them.
    These flashes often incorporated a capacitor to up the voltage. The camera also provided an M-Sync for flashbulbs rather than X-Sync. X-Sync fires when the focal plane shutter is fully open.Flashbulbs typically required 1/30th second or so to fully discharge, I used 1/30th for my leaf shutter rangefinders.

    It depends on the rating of the camera for switching this kind of current. Modern electronic flashes no longer dump the capacitor through the camera, but are activated using a switching circuit.
    FPapp likes this.
  13. It sounds like I shouldn't risk trying flashbulbs on my DSLR's, at least not directly. I'd be really bummed if I fried the circuitry on my D850! At some point I might try a cheap remote flash trigger like the guy in this video did, so that there's no physical connection to the camera.

    Last edited: Aug 2, 2020
  14. Capacitors in parallel with a battery don't increase the voltage. They increase the current available in order to fire the flashbulb reliably.

    Small layered batteries can only supply a few milliamps of current, due to their internal resistance. This low current isn't sufficient to reliably fire a flashbulb. Therefore a parallel capacitor is needed to slowly store energy and then release it as a quick burst of high current through the low resistance of the bulb filament.

    The voltage stays at whatever the terminal voltage of the battery is.
  15. Not the place here for a discussion of how a capacitor discharges, and how current and voltage depend on load, etc., but I will say that it is without doubt that what you see if you measure across the terminals of a charged flash is a voltage potential, and the trigger voltage can far exceed the voltage of the battery source. I have a couple of electronic flashes using 3 or 6 volts as a source which have a measured trigger voltage over 200. So, by the way, do the very simple flashes used in disposable cameras.

    You can test the voltage by using a voltmeter across the terminals that are switched by the camera, either at the hot shoe (outer frame to center terminal), or the PC cord.

    Note also that, although Nikons are tolerant of surprisingly high voltages (usually 250), they are not, these days, tolerant of negative polarity, so if you're measuring the potential across the switched terminals of a flash, keep track of polarity. All the electronic flashes I've tested seem to be OK on this, but since polarity was no issue for a mechanical switch, you can't be sure unless you test it.

    I don't think I'd take the chance with a D850!
    FPapp likes this.
  16. That's an electronic flash circuit that has an inverter Matthew. A totally different case from the simple circuit of a flash-bulb gun, which is barely more complicated than a hand flashlight (torch).

    The facts and physics are indisputable and easily testable - if you simply place a capacitor across a battery there is no increase in voltage, at all.
    Then why continue the discussion and confuse the issue by introducing what happens in an electronic flash circuit? That's completely irrelevant!
    That's not quite the case either. Electronic flash trigger circuits often have a safety resistor of many megohms in series with them. Testing those with a common voltmeter will give a false and attenuated reading that can be a fraction of the true open-circuit voltage.
    Last edited: Aug 2, 2020
  17. As the light output of a flash-bulb takes quite some time to peak, any slight delay in a wireless connection is not significant, it may infact be the opposite, that's the problem.

    When the shutter is tripped with M sync, the flash fires 'slowly' and illumination grows and 20 ms latter the shutter fires.

    Unless you're trying to freeze motion and there's nothing moving quickly and the ambient is poor, you could almost trigger it manually....;)
    FPapp likes this.
  18. I gave up trying to get my BC-7(or perhaps a different "fan" type Nikon gun-not sure) to actually fire. New production 22.5V batteries(the rectangular ones about the size of a 9V, but with a terminal on each end) are available with some hunting and I have a few, but I suspect that the condenser in it is bad and I've never bothered to order a replacement.

    With a focal plane shutter and only X-sync, you will probably need to use a fairly slow shutter speed(I'd think 1/60 at a minimum, maybe 1/30-something well below the flash sync speed) to make sure your shutter is open when the bulb peaks and avoid uneven illumination. It might be a good idea to use a slower burning bulb also, although it won't stop action overly well. In my experience, the GE #6, which is the same size as the #5(the common medium-sized bayonet bulb), is probably the easiest and least expensive to find, although you can expect to pay more for them than a #5 or Sylvania P25.

    As Nikons go, I honestly wouldn't want to do bulbs on anything other than an F. It has by far and away the most versatile sync system for both strobes and bulbs, although it's not immediately obvious how it works. It's also a pain(read virtually impossible) to set with any metered prism fitted. You do get M sync on several of the Nikkormats, but the F is king in versatility with bulbs.

    One of my favorite photographers is O. Winston Link, who primarily used very, very large arrays of bulbs at night to light up trains(and other large spaces). I've thought about talking to a local tourist railroad and seeing if I could try my hand with a bunch of studio strobes.
    FPapp likes this.
  19. Do Flash-bulbs have a GN like electronic flash?

    Total output or output within a given shutter open time?
  20. Yes they do. But it changes slightly depending on the reflector efficiency.

    I suspect the fan-type folding reflectors aren't particularly efficient.
    Since the BC-7 must be at least 50 to 60 years old, the capacitor drying out and going bad is hardly surprising. Apart from the capacitor, there's hardly anything else to go wrong. Dry joints or corroded contacts maybe?

    A modern 100uF / 25v axial cappy will cost you maybe 50p (60 cents) and be about 1/4 the volume of the original.

    O. Winston Link with what looks like eBay's entire stock of PF5s.
    Last edited: Aug 2, 2020

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