Why does this happen?

[powdork]

i'm using a different camera's flash towards the end of the 20 second exposure. every time i did it there would be an additional ghost image just before the more fully exposed image. is that just what happens with an unsynced flash or is that the result of some flash setting on her camera (red-eye reduction?)

[spook]

i'm a newbie and i haven't really delved into this site too much and it's probably not relevant to what you're asking, but it seems to have a lot of cool stuff related to lighting at least

http://strobist.blogspot.com/

[systemoverblow'd]

Think of the flash acting as your shutter. If it flashes twice, you are double exposing the image. It could be a focus assist flash and then the real flash but not much info was given.

An instance flash will give you a line where only some of the image was exposed because the curtain wasn't fully open.

[powdork]

i don't have her camera now and can't look at the results or properties of her pics yet to know. it wasn't focus assist because we had it in manual focus and that is usually noticeable anyway. my guess would be red eye redux since that is a quick flash to close the pupils prior to the real flash, right?

[Lonnie]

What you are seeing is the "pre-flash" from the first camera. Most cameras send out a weak"pre-flash" before they fire the main flash so the camera can calculate how strongly to fire the flash based on the camera settings. It fires the pre-flash and then does a through the lens (ttl) calculation based on the amount of light that is returned from the subject. Based on the amount of light that's returned, the camera then adjusts the power output of and fires the primary flash (and any wireless flashes is you have wireless TTL metering). Generally all of this happens so quickly that it's not noticed (the shutter doesn't open to capture the image until after the pre-flash metering is done). But a long exposure from a second camera captures the light from the pre-flash.

[powdork]

Thanks lonnie. That makes sense now that i notice one of the pictures of me jumping has both the flash lit exposures at the same opacity. Is this something that can be turned off usually?

[Lonnie]

Thanks lonnie. That makes sense now that i notice one of the pictures of me jumping has both the flash lit exposures at the same opacity. Is this something that can be turned off usually?

Maybe. Check your owners manual, but my first guess would be to try setting the camera with the flash you are using to light the subject to full manual mode. The other alternative is just to use a shoe mounted strobe hand held and pop it manually when you want to freeze the action.