Shutter speed - for real?

[sparktography]

On old film cameras it was impossible to get a true shutter speed over 125th of a second. On faster exposures the first and second plane would travel nearer together creating a narrower band of light that would pass over the film, but the entire transit of the two curtains would take at least 125th of a second. How do digital cameras work around this? Do DSLR’s truly have a shutter with curtains, or do they use an electronic cutoff? How would this electronic cutoff work?

Thanks for the info asks the new to digital guy!

[robertwgross]

Modern DSLR cameras, like Canon EOS xxx, operate with two curtains, rather like the old ones. With this system, you can get very fast shutter speeds much faster than 1/125. This is not an electronic sensor cut-off like you find in cheaper digital cameras.

The only place that this gets tricky is when you are trying to synchronize the external flash. There is typically one shutter speed (e.g. 1/125 or 1/200) that is the fastest that an ordinary strobe will sync. To shoot faster (e.g. 1/1000), then you have to have a flash capable of High Speed Flash Sync.

---Bob Gross---

[sparktography]

Modern DSLR cameras, like Canon EOS xxx, operate with two curtains, rather like the old ones. With this system, you can get very fast shutter speeds much faster than 1/125. This is not an electronic sensor cut-off like you find in cheaper digital cameras.

The only place that this gets tricky is when you are trying to synchronize the external flash. There is typically one shutter speed (e.g. 1/125 or 1/200) that is the fastest that an ordinary strobe will sync. To shoot faster (e.g. 1/1000), then you have to have a flash capable of High Speed Flash Sync.

---Bob Gross---

Ok, lets assume that the dslr cameras, at least the upper end ones have a shutter. If it is a leaf shutter "two curtains" one following the other at what speed do those curtains travel? 1/60th of a second like the early Pentax Slrs, 1/125th of a second like the later Konicas or perhaps as fast as 1/250th of asecond that some of the Nikons were capable of. I guess where I'm going here is if it is a curtain type shutter is the shutter ever capable of a true shutter speed faster than 1/250 of a second?

On those high end cameras (if I understand it correctly) for exposures faster than the shutter is capable of moving, then they have the curtains fall closer together. The reason this question is coming up is due to some slight image stabilization problems at extreme telephoto and I'm wondering how a shutter speed of 1/800 of a second is really being rendered to the CMOS.

Have shutter speeds really gotten that much faster since the film days, or are they just using the same technique to "scan" the cmos with a strip of light that slides down it, thus exposing the top slightly before the bottom.

[robertwgross]

I'm not sure where you are going with this. Do you have a specific question?

Further, these still are the film days.

Even my old Konica Autoreflex camera has a shutter speed of 1/1000.

Your Canon EOS is not necessarily a "high-end" camera, depending on your perspective, but it has many high-end features such as a focal plane shutter that goes up to 1/4000 second.

---Bob Gross---

[PacAce]

Ok, lets assume that the dslr cameras, at least the upper end ones have a shutter. If it is a leaf shutter "two curtains" one following the other at what speed do those curtains travel? 1/60th of a second like the early Pentax Slrs, 1/125th of a second like the later Konicas or perhaps as fast as 1/250th of asecond that some of the Nikons were capable of. I guess where I'm going here is if it is a curtain type shutter is the shutter ever capable of a true shutter speed faster than 1/250 of a second?

On those high end cameras (if I understand it correctly) for exposures faster than the shutter is capable of moving, then they have the curtains fall closer together. The reason this question is coming up is due to some slight image stabilization problems at extreme telephoto and I'm wondering how a shutter speed of 1/800 of a second is really being rendered to the CMOS.

Have shutter speeds really gotten that much faster since the film days, or are they just using the same technique to "scan" the cmos with a strip of light that slides down it, thus exposing the top slightly before the bottom.

As far as the shutter is concerned, there's no difference between a film slr and the digital slr. They are both electro-mechanically operated and both work the same way. The same goes for the rest of the slr except for the parts that involve the fim transport mechanism and the CMOS/CCD sensor and related electronics.

[CyberDyneSystems]

Film SLRs have 1/8000 and higher shutter speeds these days as well.

Some can synch with the flash up to 1/500th of a second...

[DaveG]

On old film cameras it was impossible to get a true shutter speed over 125th of a second. On faster exposures the first and second plane would travel nearer together creating a narrower band of light that would pass over the film, but the entire transit of the two curtains would take at least 125th of a second. How do digital cameras work around this? Do DSLR’s truly have a shutter with curtains, or do they use an electronic cutoff? How would this electronic cutoff work?

Thanks for the info asks the new to digital guy!

My inderstanding was that the first Canon D1 had an "electronic" shutter that functioned by turning the CCD on and off. A Canon rep specifically refered to this during a lecture on the new Mark II last week. The original D1 would x-synch at 1/500 while the Mark II, with a CMOS and a conventional shutter, synchs at 1/250.

With digital cameras I think that the issue of flash synch speeds is much less important than with film cameras. First I can instantly change the ISO if I get into a very bright situation, say the bride in a white dress getting out of a white limo in bright sunlight. I'd just lower the ISO until the shutterspeed and aperture were what I wanted (or could get). With every stop of ISO lower I increase my camera's x-synch speed by "one stop" as well.

The other advantage that a DSLR has is a failsafe. I would routinely use my Nikon FM2 - which synchs at 1/250 of a second - at 1/60. Then if I inadvertantly changed my shutterspeed I still would have two clicks before I shot off-synch. You could go for a fair bit of time without noticing this if you weren't careful, and could ruin a whole bunch of a shoot. With digital and the review screen, you'd have to be a complete moron to shoot more than one frame off-synch.

[PacAce]

I'd just lower the ISO until the shutterspeed and aperture were what I wanted (or could get). With every stop of ISO lower I increase my camera's x-synch speed by "one stop" as well.


??? You lost me here. The camera's x-synch speed is fixed. How does changing the ISO have any bearing on the x-synch speed?

[DaveG]

I'd just lower the ISO until the shutterspeed and aperture were what I wanted (or could get). With every stop of ISO lower I increase my camera's x-synch speed by "one stop" as well.


??? You lost me here. The camera's x-synch speed is fixed. How does changing the ISO have any bearing on the x-synch speed?

If I'm outside and I want to use fill flash and my ISO is 400 then the exposure should be 1/400 @f16. So my shutterspeed for x-synching will be 1/250 at between f16 & f22. Now if my camera synch's at 1/60 I'll need two more stops of aperture to compensate, say between f32 and f45. Well almost no lenses have those apertures, never mind the diffraction if they did.

Now if I switch to ISO 100 film this is what happens. The light hasn't changed but my exposure has. It's now 1/100 @ f16. In practial shooting terms that would be 1/60 @ f16/f22 and I do (probably) have those apertures on my lenses.

That's what I meant by "increasing the synch speed". I know that you really haven't increased it but the main reason that you DO have higher synch speeds is so that you can fill flash outside. Lowering the ISO give you the same effect.

The other purpose of high synch speeds is that it gives you some choice of aperture as well. If the light was bit lower say 1/125 @ f8 with ISO 400 film, you could choose to fill flash at 1/250 @ f5.6. 1/60 @ f11 and so forth. But at least when you play with the ISO of the film or capture you GET to use fill flash even if the synch speed is too slow for ISO 400.

[PacAce]

I'd just lower the ISO until the shutterspeed and aperture were what I wanted (or could get). With every stop of ISO lower I increase my camera's x-synch speed by "one stop" as well.


??? You lost me here. The camera's x-synch speed is fixed. How does changing the ISO have any bearing on the x-synch speed?

If I'm outside and I want to use fill flash and my ISO is 400 then the exposure should be 1/400 @f16. So my shutterspeed for x-synching will be 1/250 at between f16 & f22. Now if my camera synch's at 1/60 I'll need two more stops of aperture to compensate, say between f32 and f45. Well almost no lenses have those apertures, never mind the diffraction if they did.

Now if I switch to ISO 100 film this is what happens. The light hasn't changed but my exposure has. It's now 1/100 @ f16. In practial shooting terms that would be 1/60 @ f16/f22 and I do (probably) have those apertures on my lenses.

That's what I meant by "increasing the synch speed". I know that you really haven't increased it but the main reason that you DO have higher synch speeds is so that you can fill flash outside. Lowering the ISO give you the same effect.

The other purpose of high synch speeds is that it gives you some choice of aperture as well. If the light was bit lower say 1/125 @ f8 with ISO 400 film, you could choose to fill flash at 1/250 @ f5.6. 1/60 @ f11 and so forth. But at least when you play with the ISO of the film or capture you GET to use fill flash even if the synch speed is too slow for ISO 400.

OK, now I see where you're coming from.

But, if you don't mind my saying so, I think trying to use a flash for fill flash in bright sun is a little more complicated than what you described, trying to fit the flash to the "Sunny 16" rule. The way I used to manually used the flash for fill was to determine what aperture I needed for the flash based on the subject to flash distance to get the right amount of flash lighting on the subject. Then, using this aperture, I had to determine the actually shutter speed required to get the proper exposure for the background.

Of course, with the EOS cameras and EX flashes which support high speed synch, life is a little easier as far as fill flash in bright light is concerned.

[DaveG]

I'd just lower the ISO until the shutterspeed and aperture were what I wanted (or could get). With every stop of ISO lower I increase my camera's x-synch speed by "one stop" as well.


??? You lost me here. The camera's x-synch speed is fixed. How does changing the ISO have any bearing on the x-synch speed?

If I'm outside and I want to use fill flash and my ISO is 400 then the exposure should be 1/400 @f16. So my shutterspeed for x-synching will be 1/250 at between f16 & f22. Now if my camera synch's at 1/60 I'll need two more stops of aperture to compensate, say between f32 and f45. Well almost no lenses have those apertures, never mind the diffraction if they did.

Now if I switch to ISO 100 film this is what happens. The light hasn't changed but my exposure has. It's now 1/100 @ f16. In practial shooting terms that would be 1/60 @ f16/f22 and I do (probably) have those apertures on my lenses.

That's what I meant by "increasing the synch speed". I know that you really haven't increased it but the main reason that you DO have higher synch speeds is so that you can fill flash outside. Lowering the ISO give you the same effect.

The other purpose of high synch speeds is that it gives you some choice of aperture as well. If the light was bit lower say 1/125 @ f8 with ISO 400 film, you could choose to fill flash at 1/250 @ f5.6. 1/60 @ f11 and so forth. But at least when you play with the ISO of the film or capture you GET to use fill flash even if the synch speed is too slow for ISO 400.

OK, now I see where you're coming from.

But, if you don't mind my saying so, I think trying to use a flash for fill flash in bright sun is a little more complicated than what you described, trying to fit the flash to the "Sunny 16" rule. The way I used to manually used the flash for fill was to determine what aperture I needed for the flash based on the subject to flash distance to get the right amount of flash lighting on the subject. Then, using this aperture, I had to determine the actually shutter speed required to get the proper exposure for the background.

Of course, with the EOS cameras and EX flashes which support high speed synch, life is a little easier as far as fill flash in bright light is concerned.

Yes I think that you are right. With film I just use the metering information that the camera provides and then I match the flash output to that. Rarely is it as bright as 1/ISO at f16. But I just wanted to show a worst case scenario and how dropping a digital camera's ISO would get you out a pickle that would have required a faster synch speed or changing to a slower film.

[DAMphyne]

Perhaps the original poster isn't aware of how a focal plane shutter works, in relation to the flash-sync.
On a film camera, the sync-speed was controlled by the amount of time the shutters took to pass over the plane of the film.
Horizontal FP shutters were slower at sync speeds that vertical FP shutters, because of the distance the shutter traveled was longer.
These speeds were decreased by the use of new materials in the construction used in the shutter. Older shutters were cloth, newer were metal blades, similar to a leaf shutter, only in a horizontal or vertical configuration.
The leaf shutter was(is) constructed like an iris in the lens, so they would sync at every speed the shutter would produce(1/500-1/1000 sec)
It seems to me, that if the construction of the shutters are the same as in the film cameras, the dslr could have a faster sync-speed, simply because of the reduced physical size of the sensor.
In order to sync properly, the flash has to 'go off' at the moment the shutter is completly open.

[dtrayers]

It's important to differentiate between the speed the shutter curtains move and the time the film or imaging sensor is exposed.

At 1/4000 second, any given area of the sensor or film has 1/4000 second of light exposed to it. However, the shutter does this with a moving 'strip' of light, and that motion is fixed by the design of the shutter, and is related to the X-sync speed. If, for example, the camera's X-sync speed is 1/250, it takes 1/250 of a second for a curtain to go from the top to bottom of the sensor, so the first curtain is all the way down before the second one starts, implying that the 'strip' is exactly one sensor-height wide. Higher shutter speeds mean the second curtain starts before the first gets to the bottom, but the curtains aren't moving any faster; it's just a narrower strip, not a faster one.

You can clearly see this in the two examples below. The first shot is of a plug cutter at a shutter speed of 1/3200 second with the drill press off. The second is with the plug cutter and drill chuck spinning at 600 RPM. Note how the black lines on the chuck are slanted in the moving picture, even at 1/3200 second. That's because as the 'strip' moves from the top to bottom of the imaging sensor, the lines on the chuck move.

Stationary
http://home.comcast.net/~dtrayers/photos/stationary.jpg

600 RPM
http://home.comcast.net/~dtrayers/photos/600_rpm.jpg


You can see a similar experiment HERE (http://webs.lanset.com/rcochran/flash/hss.html) exploring the effects of high speed flash sync.