Go Back   Steve's Digicams Forums > Digital Cameras (Point and Shoot) > Kodak

Reply
 
Thread Tools Search this Thread
Old Jan 11, 2008, 11:57 AM   #1
Junior Member
 
Join Date: Jan 2008
Posts: 1
Default

My new Kodak Z812IS flashes twice, despite of the position of the "red eye correction" selector.

My old Kodak Z740 flashes once when the "red eye correction" is off and makes a correct synchronization with auxiliary flash lights in the studio.

How may I solve this trouble with my new Kodak Z812IS?
dtomeysoto is offline   Reply With Quote
Sponsored Links
Old Jan 12, 2008, 9:25 AM   #2
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

Most digital cameras will not allow you to disable the preflash (although some models have manual power settings for flash that can be used to get around it).

This metering preflash is used so the camera can determine the length of the main flash burst needed, based on reflected light seen from the preflash.

Because of the reflectivity of digital camera sensors versus film, manufacturers don't meter during a flash exposure the way newer film cameras worked with off the film metering. A metering preflash is used instead with most digital cameras.

From time to time you'll see a digital camera with a separate sensor built in that can measure the flash during the exposure (the same way many auto thyristor type models work). But, they're relatively rare anymore.

As for triggering strobes via the camera's built in flash, you can get digital aware slave triggers designed to ignore a preflash. Here are some examples:

Wein Digital Peanut Slave Triggers at B&H

JimC is offline   Reply With Quote
Old Jan 14, 2008, 5:18 PM   #3
Senior Member
 
Join Date: Dec 2006
Location: Davenport, IA
Posts: 2,093
Default

Jim:

If P&S life were simple it wouldn't be any fun would it. When I first acquired my Z612 a year ago I did some tests with the 612 and one of my old Honeywell Strobinar 200 slave strobes. I was able to attain synchronization as soon as I raised the ambient light level enough that no focus assist was required. Preparing for this answer I took a number flash pictures and this is where the camera behavior showed itself to be much more complicated than I'd imagined.

The first several shots, taken at office level lighting but still within the range to require flash showed no preflash having another person directly observing the flash. I then lowered the light level see if I could find a point at which the camera would use the flash rather than low-light illuminator. I found no point at which the low-light illuminator was not used and no preflash. To verifyno preflashI again set up a Strobinar, setting it to illuminate the room across the hall which because of distances would receive very little illumination from camera flash. Results, no preflash and the Strobinar synced.

I next changed the setup to have the Strobinar illuminate the same subject as the cameras flash (over exposing the subject.) The Strobinar synced twice and then the preflash appeared eliminating the the sync. At none of the numerous settings and setupI tried could I get the preflash to cease and it was now directly observable as well.

The camera however does not seem to be using any exposure information gathered during the preflash as the exposures were about the same with and without the Strobinar, behaving as a "thyrister" controlled flash. If it had been using the preflash information it should have seriously under exposed the subject in at least one of my test setups.

The first photo is without Strobinar and no observed preflash.
Attached Images
 
ac.smith is offline   Reply With Quote
Old Jan 14, 2008, 5:20 PM   #4
Senior Member
 
Join Date: Dec 2006
Location: Davenport, IA
Posts: 2,093
Default

This is with the Strobinar and no preflash. It can be seen that the Strobinar is illuminating the room across the hall.
Attached Images
 
ac.smith is offline   Reply With Quote
Old Jan 14, 2008, 5:21 PM   #5
Senior Member
 
Join Date: Dec 2006
Location: Davenport, IA
Posts: 2,093
Default

Overexposed showing the Strobinar still synced.
Attached Images
 
ac.smith is offline   Reply With Quote
Old Jan 14, 2008, 5:23 PM   #6
Senior Member
 
Join Date: Dec 2006
Location: Davenport, IA
Posts: 2,093
Default

The preflash appears, no sync.
Attached Images
 
ac.smith is offline   Reply With Quote
Old Mar 13, 2008, 12:07 AM   #7
Junior Member
 
Join Date: Mar 2008
Posts: 9
Default

In the menu, on the camera plus tab to the right of the main one, there is a Redeye preflash menu, if you turn that off it should do the trick.
anyaonly is offline   Reply With Quote
Old Mar 13, 2008, 7:51 AM   #8
Senior Member
 
Join Date: Dec 2006
Location: Davenport, IA
Posts: 2,093
Default

The Z812 menu option may or may not do the same thing as flash control button. The manual doesn't indicate any difference but I can't test. The option doesn't exist on either the Z612 (I physically checked on the camera) nor the Z712 (according to the manual).
ac.smith is offline   Reply With Quote
Old Mar 13, 2008, 9:00 AM   #9
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

Interesting. I missed your tests in January for some reason. I must have been pretty busy that day. My apologies.

A metering preflash can be very hard to observe. With a DSLR, it's a bit easier if you know what to look for.

That's because a separate metering sensor is used in a DSLR, and the preflash occurs just before the mirror flips out of the way to allow the main sensor to see the TTL image. This process normally takes around 100ms, and if you watch carefully, you'll see the preflash through the viewfinder. It's not contributing to the main exposure, because the mirror is not flipped out of the way yet (which is why you can see it in the viewfinder on a dSLR). I've seen more than DSLR owner argue that their camera didn't have one (because the delay was so short). But, when they looked closer they could see the initial preflash in the viewfinder (before the mirror is out of the way to fire the main flash burst).

But, with a non-DSLR model, there is no mirror to worry about. So, the time could be shortened between a preflash and main flash, provided the camera's processing has time to analyze it, making it appear like one burst to the human eye. Also, it's not unusual to see a bit of inherent delay using some triggers (often so much that it significantly reduces the maximum sync speed you can use with a DSLR without seeing part of the frame dark). That could be what's happening here (the delay is allowing the strobe to fire while the camera is still capturing the image).

Another theory is that it may be using only focus distance, aperture and ISO speed to set the flash burst length (just like you'd do with a manual type flash using a distance scale). Most modern cameras are capable of determining focus distance to your subject after focus is locked.

Many DSLR models use a combination, provided newer lenses are used. For example, Nikon and Minolta's D series lenses are designed to provide focus distance information to the camera that it uses in combination with a preflash to give better flash exposure.

JimC is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 1:30 AM.