Excuse me, I know this may sound silly, but can a Graflite damage Copal shutter synch contacts? Reason I ask is, in its shutter sync cable description the Graflite Instruction Manual (circa 1960) says, "Do not attach to contact posts of an (x) type shutter." Also, this site's Graflite brief (in Flashbulb Equipment Recommendations) mentions M synch only. Neither of these items actually came out and said "because M provides correct timing for flashbulbs." If that's not the only reason, maybe someone on this forum can say.

The Copal No. 0 shutter in my Nikkor-W lens has no M terminal, just one labeled X. I figure my 3-cell Graflite will for a very brief time push maybe 7 amps through a GE #5 bulb. Are the X contacts on newer Copal shutters built to handle this amount of current (as were the M terminals on older shutters) or should I use electronic flash only?

Thank you in advance for your insights.

I believe this answers the question: Post-1964 GE #5 flash bulbs pull a half-amp or less, posing no risk to any synch terminal on a mechanical shutter.

After more digging I located some related details concerning flash bulbs. What I found strongly indicates the use of ordinary flash bulbs is harmless to Copal mechanical shutter synch contacts, regardless of X or M markings.

To begin with, the 7-amp current estimate I started with is way too high. Despite what we find on page 10 of the Graphlite Instruction Manual -- "your batteries should test at least 7 amps" -- that current would be imposed on a synch terminal only if the cold inrush current behavior of flash bulbs matched that of ordinary tungsten lamps, which is certainly not true.

In his 1953 patent application for Ignition Devices in Photo Flash Bulbs, Stanley D. Eilenberger of Honeywell wrote, "the load resistance of the ordinary flash bulb will be on the order of 4 ohms." That load resistance in combination with the internal resistance of three brand-new, fresh D cells in series results in a current of 1.0 amps. Older, heavily-worn batteries with higher internal resistance could easily reduce that current to less than 0.4 amps. (A convenient calculator for this purpose is available at: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/dcex6.html)

Later technical advances reduced flash bulb ignition current to even lower levels. In a 1964 patent application, George W. Cressman and Louis A. Demchock, Jr. of General Electric described the reliability advantages gained by adding rhenium to the tungsten alloy used in flash bulb filaments, which increases that conductor's electrical resistance. They wrote, "by making the filament wire of tungsten-rhenium alloy, it is possible to provide a flash bulb filament having a greatly increased initial electrical resistance such that it more closely matches the impedance of an aging battery." The patent application does not specify an optimal resistance value for flash bulb production but did provide examples showing test results with batteries of up to 14 ohms impedence.

Selecting a value midway between that high of 14 ohms and a conventional bulb's 4 ohms, 9 ohms would better represent the impedence of rhenium-equipped flashbulbs. For a flash bulb with a resistance of 9 ohms the expected current from a 3-cell Graflite with fresh batteries is 0.48 amps, or 0.26 amps for weak batteries having 3-ohm internal resistance.

Given such small currents, it is unreasonable to expect any harm to a mechanical shutter's synch contacts from the use of GE #5 flashbulbs. And it is far-fetched to imagine Copal, after shipping so many quality shutters with both M-synch and X-synch, then re-designing and re-tooling to produce any later variant unsuited for flash bulbs.

Conclusion: Copal shutters equipped with an X-synch terminal and no M-synch terminal need not be limited to electronic flash due to concerns over excessive flash bulb current.

Thanks for reading, and please indicate any needed corrections.

Electronic flashes reach peak intensity as soon as they're fired. Flash bulbs take some time to ignite, burn and reach peak intensity. They can be used with X sync only at low shutter speeds. If used on X at high shutter speeds the shutter will be closed before the bulb has produced much light. That's why flash bulbs should not be used on X.

Type M flash bulbs take 15 to 17 milliseconds to reach 2/3 of their peak output, burn for 20 milliseconds before doping below 2/3 of peak output.
M flash sync on shutters fire the bulb instantly but hold the shutter closed until he bulb has reached 2/3 of peak. Leaf shutters reach peak opening .1 to .3 milliseconds after being released and close jut as fast once the delay timing has released the shutter or close faster at high speeds with the aid of booster springs.
FP flash bulbs take the same time to reach 2/3 of peak as type M flash bulbs but burn for 45 milliseconds.

Some early electronic flash such as the Strobe 250, stroboflash, Strobmatic put 455V to the flash contacts when fired. Other brands of the period are similar. Use a flash adapter with these flash.