What limits Shutter Sync?

The 1/500 sec shutters are for leaf shutter that are open and close like the aperture blades in the lens. They expose the entire frame at once but 1/500 is about their limit for speed, flash synced or not. View cameras and some MF still use them.

Modern dSLRs use focal plane shutters. In these shutters, there are two curtains that chase each other across the film plane. At faster speeds the two curtains form a slit that races across the sensor but never exposes the entire sensor at the exact same time. That's what limits flash sync. Flash can only be used if the shutter speed is slow enough to allow the entire frame to be exposed at the same time.

Focal plane shutters in film SLRs were usually about 1/60th for 35mm and slower for MF. My Pentax 67 synced at 1/30th which is the speed I use most even today.

These shutters were usually horizontal travel shutters with cloth curtains. About 30 years ago the first vertical travel metal curtained focal plane shutters appeared. This is the modern type. At first they synced at about 1/125 but that speed moved up to where we are today as technology improved.

Long winded explanation. I hope it helps.

I wish somebody could explain why can't have electronic shutters on CMOS. CCD can do it.

bobbyz wrote in post #15406611
I wish somebody could explain why can't have electronic shutters on CMOS. CCD can do it.

It's because these DSLRs are not point-n-shoot cameras. They have a mirror in the optical path to the sensor and it makes much more sense to design them the way they do instead of like a point-n-shoot camera. Of course, if you choose to use the "Live View" feature available in newer DSLRs the shutter operation could be made to be electronic and is to a degree according to what I've read.

SkipD wrote in post #15406992
It's because these DSLRs are not point-n-shoot cameras. They have a mirror in the optical path to the sensor and it makes much more sense to design them the way they do instead of like a point-n-shoot camera. Of course, if you choose to use the "Live View" feature available in newer DSLRs the shutter operation could be made to be electronic and is to a degree according to what I've read.

Actually Skip, the function of the mirror had nothing to do with whether or not the sensor needs a mechanical shutter in front of it or not. There have been CCD dSLRs without mechanical shutters. You just flip up the mirror, power on the sensor for the shutter duration and then turn it off.

I'm not a sensor engineer, but this seems to be less feasible for CMOS sensors.

Nikon D60 and Canon 1d did have elctronic shutters. Both were CCD based dSLRs. Now same can be done with CMOS and we get say 1/1000 max sync speed, that means huge for folks shooting with strobes.

bobbyz wrote in post #15406191
I am just looking forward to a day when we have electronic shutters for these CMOS sensors. Let me sync at any ss. Some day.

I use a shoe-mounted or Canon-master-contolled EX flash unit. I can use my flash at 1/8000 on all three of my bodies. Wait, I think the Elan only goes to 1/4000. I don't see sync speed being an issue. HSS is your friend. I know it cuts the range, but gradually, as you get further and further into the faster shutter speeds. I think at 1/8000 the range is limited to about 10 feet with f/1.8. HSS is a useful tool. The camera's sync speed is an artificial limit.

The camera's sync speed is very much a physical limit. High speed sync, on the other hand, is an aritficial way of getting past that limit.

With the introduction of the Canon EF in 1973, Canon did achieve a sync speed of 1/125 s. This was near the beginning of the FD lens range, and the EF model was the first to be faster than the then standard 1/60 s. At the other end of the FD era, the Canon T90, one of the most advanced cameras to take FD lenses, supported X-sync at 1/250 s.

TSchrief wrote in post #15408163
I use a shoe-mounted or Canon-master-contolled EX flash unit. I can use my flash at 1/8000 on all three of my bodies. Wait, I think the Elan only goes to 1/4000. I don't see sync speed being an issue. HSS is your friend. I know it cuts the range, but gradually, as you get further and further into the faster shutter speeds. I think at 1/8000 the range is limited to about 10 feet with f/1.8. HSS is a useful tool. The camera's sync speed is an artificial limit.

You need to read up on HSS and why higher max sync speed will be so nice. i know folks here say they did it in good old days with much lower max sync speed but then but i dont want to haul 2400ws packs where ever i go.

Before getting too concerned about flash sync speed, you might want to consider that during flash exposure the shutter speed might be irrelevant.

If the flash is the only or primary source of light (ambient light is not being recorded due to small aperture, low ISO and/or actual shutter speed), then the duration of the flash itself acts as a sort of shutter speed. With a lot of portable flash that's around 1/720. With studio strobes it's usually a bit slower. There are specialized flash where it's faster.

When shooting with flash as the main/only light source, you use the aperture size and ISO to control the exposure, distance or reach of the flash. The shutter speed can be the appropriate sync speed or any slower speed. It won't matter (until it's slow enough to start to record ambient light).

Previous responses are correct.... Leaf shutters give flash sync at all shutter speeds, but it is common for leaf shutter speeds to max out at 1/500 top speed.

Vertically running curtain shutters, like those in our DSLRs, are limited by the speed of the curtain movement. About the fastest synced speeds are 1/300, but most crop cameras have a max sync speed of 1/200 to 1/250 and many full frame are 1/200 or slower.

Modern DSLRs use electronically controlled curtain shutters that are very precise.

Mechancally controlled curtain shutters were common in the 1970s and earlier, often had a somewhat slower flash sync.

The vertically running Copal Square shutter introduced in 1960-62 was one of the first mechanical shutters capable of 1/125 sync (and a top speed of 1/2000, though most production was limited to 1/1000). It was later developed to offer as high as 1/250 sync (and a top sped of 1/4000)

Horizontally running curtain shutters, like those in a lot of FD-mount film Canon and many other SLRs up through the 1960s and 70s, plus many film rangefinders (these cloth shutters are largely based upon the Leica's, dating back to the 1930s) were very often limited to 1/90, 1/60 sync with electronic flash or as slow as 1/30 or 1/15 sync with flash bulbs (depended upon the type of bulb).

High Speed Sync works great... with some limitations. It limits the reach of flash, more-so with each higher shutter speed. You also can't use HSS in combination with rear curtain sync.

amfoto1 wrote in post #15408397
You also can't use HSS in combination with rear curtain sync.

Well, there is no specific time when the rear curtain closes when using faster speeds than the sync speed, so that's not any real surprise.
Actually, you can't use rear curtain sync at times of 1/30 s or shorter.

Alan, flash sync matters the most when shooting outside. in studio, who cares.

if instead of 1/160 of my 5d I could do 1/640, i can use cheaper and lighter strobes. if i could do 1/1200 or so then those little speedlites will be so much more useful outside without going Joe Mcnally route.

bobbyz wrote in post #15408272
You need to read up on HSS and why higher max sync speed will be so nice. i know folks here say they did it in good old days with much lower max sync speed but then but i dont want to haul 2400ws packs where ever i go.

I admit to not knowing much about flash photography. I do know that HSS can't possibly use any more than one full capacitor charge worth of juice. And I have to agree, using a full-charge with every shot would be extremely power consuming. I guess I should have said that "I" don't find the sync speed limiting. If I need to use fill at 1/800 or something, I just do it. But I am only taking a shot or two.

Speaking of the good old days.... I used to shoot manual film bodies and discovered that if you want to push things, you could get an extra stop of shutter speed out of the bodies when using manual flash. If you pushed it much further, you'd get the shutter blocking part of the frame. Today's cameras just push the shutter speed back to sync-speed automatically.

bobbyz wrote in post #15406611
I wish somebody could explain why can't have electronic shutters on CMOS. CCD can do it.

SkipD wrote in post #15406992
It's because these DSLRs are not point-n-shoot cameras. They have a mirror in the optical path to the sensor and it makes much more sense to design them the way they do instead of like a point-n-shoot camera. Of course, if you choose to use the "Live View" feature available in newer DSLRs the shutter operation could be made to be electronic and is to a degree according to what I've read.

JeffreyG wrote in post #15407098
Actually Skip, the function of the mirror had nothing to do with whether or not the sensor needs a mechanical shutter in front of it or not. There have been CCD dSLRs without mechanical shutters. You just flip up the mirror, power on the sensor for the shutter duration and then turn it off.

I'm not a sensor engineer, but this seems to be less feasible for CMOS sensors.

With a CMOS sensor each column is read independently, one after another going from left to right across the sensor. It is possible to perform three operations that roll across the sensor at the same speed - first each column is activated, then after a certain amount of time (the exposure time) the accumulated charge is read and the data sent to the A/D converter, and finally each column is flushed and reset, ready for the next exposure. This constitutes an electronic shutter. However, the speed of the A/D converter acts as a limiting factor, determining the maximum speed at which the "read curtain" can cross the sensor. It can work in a P&S with a tiny sensor but in high resolution/large sensor cameras the best speed obtainable would be too slow for hand-held. So in a DSLR the mechanical shutter opens and the sensor is activated simultaneously, then after the shutter closes the slower operations of reading and resetting each column are performed.

apersson850 wrote in post #15408254
The camera's sync speed is very much a physical limit. High speed sync, on the other hand, is an aritficial way of getting past that limit.

right, and there are other "artificial" ways to get around the sync speed, I can get 1/320 without seeing any black bar or darkened area using a yongnuo flash in manual mode on an XSi (450D). Outdoors for fill flash I get 1/400 shutter speed using a flash. I've cheated the physical limit !

watt100 wrote in post #15409032
right, and there are other "artificial" ways to get around the sync speed, I can get 1/320 without seeing any black bar or darkened area using a yongnuo flash in manual mode on an XSi (450D). Outdoors for fill flash I get 1/400 shutter speed using a flash. I've cheated the physical limit !

What's your explanation of how this worked other than tolerance built into the notional maximum sync speed?