Flashing twice

[girmann]

How do you get a camera to stop flashing twice?

All of the cameras that I have owned have always flashed twice (really fast) when taking a picture with flash, regardless of flash setting (red-eye, auto,slow sync). The first and second flashes are much less than a second apart and varies from camera to camera. I always assumed that this is because the camera is trying to meter the scene correctly for the flash. I don't remember film cameras doing this way back when.

The reason this is an issue is that recently my daughter started closing her eyes on the second flash. If we need the flash, we can't get a decent shot of her with her eyes open.

Recently we were considering getting a DSLR, but even those flash twice. They are faster than the p&s we have now, but we still can't get the shot. (Tried D40, D5000, XSi, T1i, A330)

Any ideas on how to just get one flash out of a camera? Thanks!!!

 

[fatman_br]

It´s an annoying feature. Many times, when taking pictures of people, they think the picture's already taken at the first flash, and look away. But for children, it works in the opposite way: they look to where the bright light is coming... and then comes the second! , I used a lot this to take pictures of my children, back when I was a SLR owner, I use the manual "test" button on my flash.

But seriously, I also didn't find a way to get rid of it. I believe that´s along with the camera using the first flash to measure exposition, there is an energy issue, the tiny flashes can't deliver the power needed to correctly expose the scene, and you need two (or more) discharges.

But, then you see more powerful units with this same behaviour, so i´m not certain.
--
Fabio Leoni, from Brazil
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[ChefZiggy]

The preflashes are used to meter the scene in order to determine how much to flash on the actual exposure and with some systems measure the distance to the subject. To get rid of them you can either learn to expose manually with the flash, or with most modern DSLR's, fire the metering pulse before actually taking the shot. (Usually called something like "Flash Exposure Lock")

That lets the camera figure out it's exposure and flash setting, then the next press of the shutter button uses that information.
--
Chefziggy
http://www.pbase.com/chefziggy/lecream

 

[mike703]

There might be two reasons for this

1. Red-eye reduction is switched on. This fires a first flash which makes people's pupils contract, so when the photo is taken on the second flash - about half a second later - there is less chance of red-eye. My old compact camera had this 'red-eye reduction' mode which could be switched off.

2. DSLRs with through-the-lens flash metering will fire a pre-flash to assess how much light is reflected back, and use this to set the exposure for the photo to follow. In these cases the pre-flash and the main flash are very close together (like 1/20 second). It is annoying because the pre-flash often causes a blink and then the main photo shows people with eyes closed or half closed ('lazy eye'). The only thing you can do about this is to bounce the flash or use a diffuser which helps prevent the blinking.

This used not to be an issue with film cameras because the through-the-lens flash metering was done during the main exposure: a sensor in the camera measured the light reflected off the film surface and cut the flash off when the exposure was correct, so no pre-flash was necessary. DSLRs can't do that because (I think) the surface of the sensor doesn't reflect light in such a predictable way so this cannot be used as the basis of metering - hence the pre-flash. It is a retrograde step IMO for precisely the reason you mention.

So you may be able to switch the effect off if it is red-eye reduction. if you are talking about a pre-flash for metering on DSLR you're stuck with it (but try a diffuser).

Best wishes
--
Mike

 

[ilminsterpete]

The first flash is sometimes to assist with autofocus. Some cameras, the Olympus E-1 for example, use a red beam instead.

 

[girmann]

Nope. Had the guy behind the counter shut off the red eye reduction for all of these DSLRs before we tried them. Since we're a p&s family, we wanted to make sure someone knowledgeable worked the controls.

Sucks that it works this way. Can you get a diffuser for the built in flash units, or does it require an external flash?

We tried some Oly's too and they do the same thing. Oddly, the Cannons use a red for focus assist, but still fire the flash twice. Do the low end models have flash exposure lock? How easy/hard is it to use?

 

[mike703]

Sucks that it works this way.

Yes!

Can you get a diffuser for the built in flash units, or does it require an external flash?

You can make one very easily from an old plastic film canister or a table-tennis ball

http://www.instructables.com/id/SZND122FCHYOAAD/
http://www.dpchallenge.com/forum.php?action=read&FORUM_THREAD_ID=702380

... but you will lose some intensity and pop-up flashes are pretty feeble to start with. If you get an external flash with a bounce/swivel head the results are much better...

http://forums.dpreview.com/forums/read.asp?forum=1018&message=33272116

Best wishes
--
Mike

 

[ChefZiggy]

OK. I know my typing sucks right now (one hand bandaged up) and my explanation yesterday may not have made a lot of sense (pain meds), but you can shoot without the preflash. You either don't use TTL flash metering or you take control of the pre flash and make it go off when you want to. Thus preventing people blonking during the main exposure.

It will be hard to tell you exactly how until you have made a choice.

Oh, and anymore, just because a person works in a camera store doesn't mean they know diddly about cameras.
--
Chefziggy
http://www.pbase.com/chefziggy/lecream

 

[girmann]

Contrary to your ailment, your explanation was very good! Let's say we wanted to see how this is done int he D5000 and the T1i. Is there a quick way of doing this on either of these cameras? Which one is simpler? I think DW could be sold if this could be done in 1 or 2 button presses.

What about going to P&S cameras? Any of them offer flash exposure lock?

 

[AbeFriedman]

I'd be really surprised if a P&S camera has flash exposure lock. That's not really a point-and-shoot sort of thing. OTOH, you never know. Maybe somebody has added it as a feature. I know that my Sony DSLR doesn't have it -- although it would be nice.

Abe

 

[vuPeak]

Let's say we wanted to see how this is done int he D5000 and the T1i.

The D5000 can't do flash exposure lock, but you can set the flash manually and avoid the pre-flash that way.

What about going to P&S cameras? Any of them offer flash exposure lock?

Not that I know of...

--
Hans-Emil

 

[ChefZiggy]

Not being familiar with either of those bodies, I can't say. I can say that on my D70 and D300 it is a single button press. (Memory may be fuzzy on the D70.)
--
Chefziggy
http://www.pbase.com/chefziggy/lecream

 

[vuPeak]

To be a bit more constructive: The D90 can do flash exposure lock (FV-lock), and has the FUNC button assigned to it by default. (But it's a bit more expensive as well...)

--
Hans-Emil

 

[chuxter]

There might be two reasons for this

1. Red-eye reduction is switched on. This fires a first flash which makes people's pupils contract, so when the photo is taken on the second flash - about half a second later - there is less chance of red-eye. My old compact camera had this 'red-eye reduction' mode which could be switched off.

2. DSLRs with through-the-lens flash metering will fire a pre-flash to assess how much light is reflected back, and use this to set the exposure for the photo to follow.

Actually, almost all cameras, regardless of what type they are use TTL flash metering...it's not reserved for dSLRs.

In these cases the pre-flash and the main flash are very close together (like 1/20 second). It is annoying because the pre-flash often causes a blink and then the main photo shows people with eyes closed or half closed ('lazy eye'). The only thing you can do about this is to bounce the flash or use a diffuser which helps prevent the blinking.

Cameras differ greatly in the timing between the pre-flash and the main flash. Often, the internal flash will have a very small delay, but the external flash will have a very long delay. This is possibly due to slow communications with the external flash. Having a slow processor in the camera also causes a big delay.

If the delay between flashes is below some value (that I don't know), the human eye doesn't have time to blink. This should be a parameter that is specified! It would also be really nice to have a camera that allowed the photographer to vary this delay (obviously only useful if the minimum delay time is quite small).
--
Charlie Davis
Nikon 5700, Sony R1, Nikon D300
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