RB67 Flash setting.. X/M confusion

peter k. · Jan 10, 2019

Isn't the RB67 only suppose to flash when the setting is on X?
Background:
Years ago converted an my old 35mm Vivitar flash to be used with a MF speed. Now want to use it on my RB67 pro, but have never used a flash on this camera before. Testing the converted flash, it will fire on both the X or M setting. It really makes no difference to me, as we have to hand hold the flash when we use it, and will not have it permanently connected to the camera during 'normal' non flash shots. So no big deal, but was curious, as both my 90mm and180mm lens fire on both X or M, so it has to be the way we wired the flash up to be used on the speed that is causing this.
Whats important is that it works!

Rick A · Jan 10, 2019

Electronic strobe flashes require the X setting, flash bulbs the M setting. The M setting has a slight delay before firing the shutter in order for the bulb to come to full brightness for the shot. Either type of flash will fire on either setting, but synchronizing is the issue for the shutter.

mpirie · Jan 10, 2019

Both X and M will trigger the flash.

The only difference is "when" in the shutter opening cycle the flash is at it's peak.

M is normally used for flash bulbs which took a lot longer (relatively) to reach peak light output compared to the much quicker X and electronic flash units.

Mike

Dennis-B · Jan 10, 2019

The flash will fire no matter what, when the contacts close. It's how the timing occurs in the shutter. At "X", the flash fires while the shutter is wide open, i.e. there's a lag. At "M", the flash is expecting an "M" type bulb (approx 20msec); the flash fires, and the shutter opens when the flash is at maximum light output.

mark · Jan 10, 2019

Thanks for posting this. I was wondering the same thing.

AgX · Jan 10, 2019

Rick A said:
Electronic strobe flashes require the X setting, flash bulbs the M setting.

The M-setting is one setting for bulb flashes.
There are also S, F and FP. There were bulbs of different characteristics and thus different sync setting. The M-setting was the one that finally only was used.

narsuitus · Jan 10, 2019

peter k. said:
Years ago converted an my old 35mm Vivitar flash to be used with a MF speed.

Exactly how and why did you convert your Vivitar flash to be used at MF speed and what does MF speed mean?

The reason I ask is because I use an old Vivitar flash on my RB67 and I did not have to convert it.

Rick A · Jan 10, 2019

I suspect the mod for MF speed is the cable was cobbled to fit a Bi-pole or other non PC connection used on a Baby Speed Graphic.

peter k. · Jan 10, 2019

Thanks guys, that makes sense, and when we flashed it on the M setting, it did seem to hesitate.

narsuitus said:
Exactly how and why did you convert your Vivitar flash to be used at MF speed and what does MF speed mean?

Yep as Rick A stated we cobbled it to fit a Bi-pole on the Baby Speed, using the original flash chrome battery container for the wiring, so we can plug in the correct connector for the RB67. .

shutterfinger · Jan 10, 2019

Type M flash bulbs take 15 millisecond to 17 millisecond to reach 2/3 of peak light output and burn for about 20 milliseconds from 2/3 output on the up side to 2/3 of peak on the down side which is the usable light output. Recommended shutter speed is 1/30 second or slower.
Type F flash bulbs are gas filled and take 5 milliseconds to reach usable light output.
Type FP flash bulbs are like type M but they have a 50 ish millisecond burn time for focal plane shutters in Graflex SLR's, Speed Graphics, and similar cameras.

Theo Sulphate · Jan 10, 2019

peter k. said:
Thanks guys, that makes sense, and when we flashed it on the M setting, it did seem to hesitate.
...

What was hesitating?

On the RB67, the normal operational cycle is:

- press the shutter release
- leaf shutter in lens fully closes, aperture stops down
- mirror / light baffle raises
- leaf shutter opens and closes for the required exposure
- manual cocking lowers the mirror, opens the shutter & aperture

So, as people have noted, with X sync the flash will fire when the leaf shutter is fully open, because electronic flash is very fast. With M sync, the flash will be triggered sooner (when the shutter begins to open) because slower flash bulbs need to be triggered sooner so that they'll reach proper brightness when the shutter is fully open.

Now, since you were using an electronic flash with M sync, the flash would've fired about 20 msec sooner than it would've with X sync. Maybe that's what you perceived: the flash going off before the click of the shutter blades. The RB's mirror is usually loud enough that some people don't hear the shutter.

peter k. · Jan 10, 2019

Theo Sulphate said:
What was hesitating?

Well we just fired in both X & M.. and could not tell the difference.. thought at first we could.. WRONG!
But have it set to X, no matter what we think.!

AgX · Jan 10, 2019

The most easiest test for the difference would be to release the shutter with back door open whilst looking through the lens, all in darkened room.

Rick A · Jan 10, 2019

peter k. said:
Well we just fired in both X & M.. and could not tell the difference.. thought at first we could.. WRONG!
But have it set to X, no matter what we think.!

You'll see the difference on film. Trust me, set it to X and leave it alone.

RalphLambrecht · Jan 10, 2019

peter k. said:
Isn't the RB67 only suppose to flash when the setting is on X?
Background:
Years ago converted an my old 35mm Vivitar flash to be used with a MF speed. Now want to use it on my RB67 pro, but have never used a flash on this camera before. Testing the converted flash, it will fire on both the X or M setting. It really makes no difference to me, as we have to hand hold the flash when we use it, and will not have it permanently connected to the camera during 'normal' non flash shots. So no big deal, but was curious, as both my 90mm and180mm lens fire on both X or M, so it has to be the way we wired the flash up to be used on the speed that is causing this.
Whats important is that it works!

the 'X' setting would be my choice as it is designed foer electronic flashes and to fire without much of a delay. However, be warned that these Vivitar flashes have a relatively high trigger voltage and should only be used with radio triggers and receivers or you're putting your camera shutter in danger.

GarageBoy · Jan 12, 2019

Those shutters were designed for it, no? You only risk damaging newer modern cameras with electronics inside

BrianShaw · Jan 12, 2019

Ah, the internet... where worriers worry....

RB67 Flash setting.. X/M confusion

Privacy & Transparency

Privacy & Transparency