Shutter speed and strobe flash duration

[sdipirro]

I'm confused. I hadn't really played around with this before. The Elinchrom Dlite-4 supposedly has a flash duration of 1/800s, although I understand the reality is something less than that. I've been doing all of my shooting with these strobes using shutter speeds of 1/250 or slower. What I discovered tonight is that when using shutter speeds faster than 1/250...even 1/320, I see the shutter in the resulting image. I was expecting this when I got closer to speeds like the flash duration. I wasn't expecting it at anything over 1/250. Although that's the flash sync speed, I didn't think that would apply here (but could be wrong about that). I'm using PWII's, and I'm not sure at what point transmission delays become an issue. I figured that would be at much higher shutter speeds. I know I'm missing something basic, and it can't be the beers I was drinking during my experiments! I'm seeing the shutter on the right side of the image. So I'm not sure if this is the front end or back.

A secondary question would be that if my shutter speed limit is 1/250 and I want to freeze motion, do I simply do that by controlling ambient light and making sure the subject is only illuminated by the flash? Thanks.

[RGolfJ]

1/250 on 20D 1/300 on Mark III anything faster than that and you will start to catch the shutter.

Answer to second question>>>>> Yes

[vadim_c]

Currently the most cameras have the maximal physical shutter speed around 1/250 sec. Some 1/320 sec.
Everything faster than that is just half opening the shutter during actuation. If you could see it in slow motion you would see that the second curtain starts to close before the first one entirely opens the aperture. In effect you have a narrow slot traveling in behind the aperture with a speed of 1/250 sec.
That works somehow for normal shots but fails with strobes that have duration faster than the camera synch speed.
Surprisingly strobes with slower flash durations allow you to shoot with shutter speeds faster than the synch speed.

[brecklundin]

the way I have come to understand it, the shutter speed has little to do with freezing motion in a flash shot. It's the stobe effect of the flash that freezes the motion. I am guessing there is a point where the flash is not a factor, such as just a fill light, but I have found it is the flash which stops motion.

I know there is a LOT more to it than that but I am just getting the knack of flash use so.... ;)

[TMR Design]

The D-Lite's will safely sync at shutter speeds up to 1/160s. Beyond that and traces of the curtain begin to appear and by 1/250 the curtain is quite visible.

Flash duration and shutter sync speed are two completely different things. In the studio where ambient has no affect on the shot, the flash duration is the time in which the shot is captured. You can test this by setting your shutter speed to something like 1/20s (assuming there is no ambient light in the studio) and the shot will look the same as if you were using 1/125s because it's the flash duration that captures the image.

[sdipirro]

That makes sense in the studio, where all the light can be controlled. So how does this work in environments where you can't control the ambient light, such as a hockey game, where' you've positioned strobes strategically? Is it still the case that you try to underexpose the ambient to use light from the strobes to freeze motion, or do the strobes serve more as fill lights in that environment?

[bobbyz]

That makes sense in the studio, where all the light can be controlled. So how does this work in environments where you can't control the ambient light, such as a hockey game, where' you've positioned strobes strategically? Is it still the case that you try to underexpose the ambient to use light from the strobes to freeze motion, or do the strobes serve more as fill lights in that environment?


You just make sure you under-expose the ambient by 3-4 stops. That is where high sync speed come sin handy but for some reason CMOS dSLRs are still can't do what original 1d could do. That is why some folks still hang on to that 4MP camera.

[Curtis N]

Read about how focal plane shutters work, and you'll understand X-sync speed better.
http://en.wikipedia.org/wiki/Focal_plane_shutter

[PacAce]

I'm confused. I hadn't really played around with this before. The Elinchrom Dlite-4 supposedly has a flash duration of 1/800s, although I understand the reality is something less than that. I've been doing all of my shooting with these strobes using shutter speeds of 1/250 or slower. What I discovered tonight is that when using shutter speeds faster than 1/250...even 1/320, I see the shutter in the resulting image. I was expecting this when I got closer to speeds like the flash duration. I wasn't expecting it at anything over 1/250. Although that's the flash sync speed, I didn't think that would apply here (but could be wrong about that). I'm using PWII's, and I'm not sure at what point transmission delays become an issue. I figured that would be at much higher shutter speeds. I know I'm missing something basic, and it can't be the beers I was drinking during my experiments! I'm seeing the shutter on the right side of the image. So I'm not sure if this is the front end or back.

A secondary question would be that if my shutter speed limit is 1/250 and I want to freeze motion, do I simply do that by controlling ambient light and making sure the subject is only illuminated by the flash? Thanks.
In order to understand what's going on with your flash and the max sync speed, you first need to understand what that flash duration (1/800) is really telling you. Odds are (based of flash durations I've seen reported by Elinchrom for other strobes) that the flash duration of the D-Lite 4 of 1/800 is actually the T.5 duration, i.e. the duration when the light intensity is at or above 50% peak. A more meaningful flash duration is the T.1 duration which is the time when the flash intensity is at or above 10% of peak (this gives you about a 3 stop spread in light intensity). T.1 is about 3 times longer than the T.5 duration so the T.1 duration would be 1/267. And this duration is when the strobe is fired at full power. At lower power levels, the flash duration would be longer. Were you firing the strobe at full power? If not, then a shutter speed of 1/250 would cause the 2nd curtain to start closing before the strobe light has completely died out. And this could cause the darkening along one long edge of the frame depending on the power level the strobe has been set to. This is something you can easily test for yourself. Shoot a couple of frames at 1/250 with the strobe power level varying from full power to the lower power levels (adjust the aperture accordingly for the power output). :)