2nd curtian question? 20d

[kawter2]

When I use seccond curtian on the 20d I get 2 flashes (have only tried this with external flash). One on open and one on close. Is that how 2nd curtian should work?

If so, than ok.. If not, does anyone else get this with the 20d?

TIA!!

[robertwgross]

You will see that kind of effect with a long shutter time.

With a very short shutter time, the same thing happens, but it is a low-power pre-flash and then the main flash that both pop within a small fraction of a second.

---Bob Gross---

[kawter2]

You will see that kind of effect with a long shutter time.

With a very short shutter time, the same thing happens, but it is a low-power pre-flash and then the main flash that both pop within a small fraction of a second.

---Bob Gross---

Is there any way to only get a pop on the shutter close of a long exposure?

[slin100]

With the built-in flash, not really. There's no way to disable E-TTL, so you will always get a preflash. If you are taking a picture of a static setting, you can use FEL to fire the preflash earlier. You, then have something like 16 seconds to release the shutter.

With an EX flash, you can disable E-TTL and therefore eliminate the preflash.

[kawter2]

With the built-in flash, not really. There's no way to disable E-TTL, so you will always get a preflash. If you are taking a picture of a static setting, you can use FEL to fire the preflash earlier. You, then have something like 16 seconds to release the shutter.

With an EX flash, you can disable E-TTL and therefore eliminate the preflash.

I think you are talking about "PRE"plash. I am refering to 2 flashes that happen while the image is being exposed #1 as soon as the shutter opens, #2 right before it closes. I would like it to only fire right before closing

[slin100]

I think you are talking about "PRE"plash. I am refering to 2 flashes that happen while the image is being exposed #1 as soon as the shutter opens, #2 right before it closes. I would like it to only fire right before closing
#1 is the preflash and occurs just before the shutter opens.

[hmhm]

I am refering to 2 flashes that happen while the image is being exposed #1 as soon as the shutter opens, #2 right before it closes.

The E-TTL system sends out a "pre-flash" automatically just before opening the shutter. This is a "low power" flash, the system uses this as part of flash metering, sort of a "let's send out a little flash and see what comes back, this will give us an idea of how close the primary subject is, and will tell us how much power we should use for the 'real' flash". Once this is done, the mirror is flipped up and lens aperture set, then the shutter opened, and the main flash is sent out, either with the first curtain or second.

The pre-flash has to go out before opening the shutter, while the mirror is still down, so that the lens is projecting its image via the mirror to the exposure meters.

When using first curtain flash, or when the shutter speed is short, you don't notice the two flashes as distinct, but with second curtain and a longish shutter speed, you can notice the time between the flashes, and see them as two distinct flashes.

For more information than you'd ever want to know about how Canon flash metering works (and yet somehow still not enough), look here:
http://photonotes.org/articles/eos-flash/
-harry