What limits Shutter Sync?

JohnB57 wrote in post #15409108
What's your explanation of how this worked other than tolerance built into the notional maximum sync speed?

The additional light of the flash was probably not needed or would not have been noticeable for that subject across that edge of the frame.

RDKirk wrote in post #15409119
The additional light of the flash was probably not needed or would not have been noticeable for that subject across that edge of the frame.

Possibly, or the YN flash had a longer than normal duration. The max sync speed has always been reduced to a safe limit for consistency I guess, even going back to mechanical days. A happy combination of all factors.

JohnB57 wrote in post #15409108
What's your explanation of how this worked other than tolerance built into the notional maximum sync speed?

do a search in the lighting section with the title "cheating maximum sync speed". It's probably not so much about tolerances as using the flash at less than maximum power either off the hot shoe or using a purely manual flash like the Yongnuo YN460 on the hot shoe. Interesting phenomenon - go ahead and try your flash on manual mode with manual triggers (e.g. RF-602) and set the shutter speed higher and see if you can cheat the sync speed!

watt100 wrote in post #15409495
do a search in the lighting section with the title "cheating maximum sync speed". It's probably not so much about tolerances as using the flash at less than maximum power either off the hot shoe or using a purely manual flash like the Yongnuo YN460 on the hot shoe. Interesting phenomenon - go ahead and try your flash on manual mode with manual triggers (e.g. RF-602) and set the shutter speed higher and see if you can cheat the sync speed!

I think it has everything to do with shutter tolerance and the reduced travel and inertia of a crop shutter - effectively, in comparison with FF, a crop shutter travels 66% of the distance, accelerating and stopping faster in the process.

Despite what I posted above (which wasn't accurate), normal sync only triggers the flash when the first/front curtain has completed its movement so I can't get my head round why using any flash unit in any mode other than HSS would make any difference, unless the shutter is fully open at speeds faster than normal sync speed, say 1/250th. Flash duration would make a difference, but only if it's triggered the instant the first curtain begins to move, as with HSS.

Edit... I do understand what you mean about manual triggers but I have no way to do this, although with a long flash duration I get it completely.

Pocket Wizard uses this technique with their "hypersync." The trigger unit detects in some way when the shutter is about to open--I suspect using the pre-flash signal--and triggers the actual flash slightly early so that it uses the longer toe of the flash duration for exposure rather than the initial peak.

The problem is that with studio flash, a long duration toe is considered a significant fault. Modern designs attempt to pack all of the flash power into the initial peak and reduce the amount in the toe.

RDKirk wrote in post #15409763
Pocket Wizard uses this technique with their "hypersync." The trigger unit detects in some way when the shutter is about to open--I suspect using the pre-flash signal--and triggers the actual flash slightly early so that it uses the longer toe of the flash duration for exposure rather than the initial peak.

Not something I have personal experience of, but that was my understanding.

JohnB57 wrote in post #15409648
Despite what I posted above (which wasn't accurate), normal sync only triggers the flash when the first/front curtain has completed its movement so I can't get my head round why using any flash unit in any mode other than HSS would make any difference, unless the shutter is fully open at speeds faster than normal sync speed, say 1/250th. Flash duration would make a difference, but only if it's triggered the instant the first curtain begins to move, as with HSS.

Edit... I do understand what you mean about manual triggers but I have no way to do this, although with a long flash duration I get it completely.

I don't know. But if you ever get any manual triggers try it, or if you ever get any manual flashes like the YN460 try setting your shutter speed above 1/250 - it could be surprising !

Mark II wrote in post #15406553
You'd thunk that if man could build a pacemaker to be reliable ....

The pacemaker is reliable because it has no moving parts, and it is designed to be very slow - as slow as a human heart.

A shutter needs to operate at high G loads to move fast. And it needs to be light, to keep the down the forces needed to accelerate it. And it needs to be thin because you don't want a significant difference in distance between sensor and the two blades that forms the slit. And they need to be close to each other.

It is way easier to play with high speeds when you have mechanical devices that are rotating. The shutter blades aren't rotating. They are going from stand-still to extremely quickly reaching their nominal travel speed. Then they travel with a constant speed over the sensor surface before they very quickly have to break to zero speed again. This results in huge loads on the materials.

Most materials suffers from increasing fatigue as the number of load cycles increases. At the same time, the mechanical precision needs to be high - but when the steering wears down, then the two blades aren't traveling perfectly anymore. They cut through air and gets affected by drag. The air wants to twist the two blades sideways, making them into air breaks. If they do twist enough, they can hit each other which is fatal since the drive mechanism is so strong to support the high acceleration needed.

The acceleration can be made less, by allowing the shutter blades to have a longer distance to accelerate before they reach their constant-speed travel over the sensor. But that would also mean extra shutter lag, which we as customers don't like.

At the same time, the total weight of the traveling parts will affect how noisy the shutter operation will be. So we don't want them to just step up the drive forces while making the steering parts more massive.

It is easy to complain about the performance of our shutters, but it really is not easy to design a better shutter that still fulfills all customer requirements and have a reasonable price and life expectancy. Progress in nano technology and new carbon constructs should probably give us way better shutters. But the question is when - and what the initial prices will be.

As already noted, lots of cameras for a very long time had a red "60" to mark the flash sync speed of 1/60. 1/250 is a significant improvement while better flashes can multi-flash to allow shorter exposure times - but at a weaker flash output. In the end, it's a question of what compromises to make.

Those early metal Copal Square shutters sounded like a man in a suit of armor taking a pratfall.