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Re: [OM] X-synch M-synch question

Subject: Re: [OM] X-synch M-synch question
From: "John A. Lind" <jlind@xxxxxxxxxxxx>
Date: Wed, 19 Dec 2001 01:19:25 +0000
At 00:27 12/17/01, you wrote:
Howdy,
I guess I'll try to make this question a little more generic. If my electronic flash fires with M-synch, but not X-synch. Is it possible that I am _in fact_ getting X synch? I just don't know how these actually work. Camera is Pen FT.
Thanks,
MEBachofen

Not certain if you're asking about what the generic difference is between M-sync, F-sync, FP-sync and X-sync, or exactly what the triggering mechanism is in your Pen FT.

Short answer:  NO

M-sync is for flash bulbs and pre-fires the flash about 20 milliseconds prior to the shutter being fully open. Typical sync speed is 1/25th or 1/30th second because burn duration of a flash bulb is much longer than for a strobe.

X-sync is for electronic flash with zero pre-fire. It triggers in the middle of the time the shutter is fully open. Typical sync speed was 1/60th for a very long time. However, "F" type flashbulbs could often be used with X-sync *if* a 1/25th or 1/30th shutter speed was also used.

If you try to use M-sync and its 20 millisecond prefire with an electronic strobe, expect problems! Your strobe will go off *before* the shutter is open (leaf shutter) or the first curtain has fully traveled (focal plane shutter).

For those with older cameras having various sync positions, the following are the gory details about flash syncs . . .

=== Flash Powder, "B" shutter speed, and Invention of Flash Bulbs ===
The oldest "sync" is the "B" shutter speed. Prior to the invention of flash bulbs in 1929 (by Westinghouse, Sylvania or G.E., cannot remember which) flash powder was used in a small trough. Open shutter and hold it open, ignite the flash powder, then close the shutter. This stuff was similar to the finely ground metal powder used in the "Daisy Cutter" high explosive, but in *much* smaller quantities. However, it was a small explosion, very dangerous if not handled carefully, and hazardous even if it was handled properly. When flash bulbs were introduced, there was no shutter sync. Indeed, there was nothing on the camera to fire a flash. The "B" (bulb) shutter speed was introduced and used prior to sync mechanisms and necessary connections being built into cameras to fire a flash. In short, bulbs were fired much like the flash powder, except it was safer, but still not without hazards. Early flash bulbs occasionally exploded and the nifty plastic coatings to contain the shards of glass were not added until later (after enough exploding bulbs occurred to demonstrate a problem truly existed).

=== "M" and "F" syncs, and flash bulb pre-fire ===
As flash bulbs caught on as a safer alternative to flash powder, flash syncs were added to camera designs during the 1930's. Some camera companies would retrofit models with a flash sync that were originally made without them (Leitz offered this for its Leica). Because flash bulbs require time for the burning filament inside to reach full intensity, they need to be fired *before* the shutter is fully open. Older flash bulbs are "M" type (M = medium speed). These require about 20 milliseconds of pre-fire. As newer bulb types were developed the ramp time to full light output decreased, creating the "F" type bulb (F = fast speed). These only required about 5 milliseconds pre-fire. AFIK, older bulb types (by bulb number) were not updated. This kept them compatible with older camera sync speeds and their flash attachments. There are numerous older cameras around that have "M" and "F" sync settings (some even have an "X" setting also).

=== FP sync ===
There has always been a desire to use faster shutter speeds with flash. The FP sync survived longest of all flash bulb syncs in camera designs using focal plane shutters (FP = focal plane). It is found on the OM-1[n]. This also has about a 20 millisecond flash pre-fire. It is intended for use with long-duration "focal plane" flash bulbs. These special flash bulbs allowed using shutter speeds faster than the normal flash sync; speeds at which the shutter would never be fully open, but a slit traveling across the film gate. Their long duration of constant output allowed the shutter slit to travel across the entire film gate. The Olympus F280 "FP" mode does approximately the same thing through extremely rapid firing of the flash tube starting before the first curtain begins travel, and continuing until the second curtain has finished travel.

=== Electronic Strobe and "X" sync ===
With the advent of electronic strobes, the "X" sync was added. This has zero pre-fire as a strobe has near instantaneous output for a very short duration compared to flash bulbs. Some older cameras only have an "M" and "X" sync selection. These are the models that often allow using "X" sync with an "F" bulb, provided a slow enough shutter speed is also used (1/30th second is 33 milliseconds; 1/25th is 40 milliseconds).

-- John


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