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How does auto-exposure work with slave flash?
I see these slave flash units for sale on eBay and elsewhere. If I were to use these with a small digital (I'm considering the Panasonic TZ5), how does the automatic exposure system in the camera deal with the extra light? Do I have to jump through hoops to get an appropriate exposure?.

Color me clueless here..

Thanks,Topher..

Comments (8)

Tgeliot wrote:.

I see these slave flash units for sale on eBay and elsewhere. If Iwere to use these with a small digital (I'm considering the PanasonicTZ5), how does the automatic exposure system in the camera deal withthe extra light?.

Put simply, Auto Exposure doesn't deal with it at all! The extra light comes as a big surprise, and arrives much too quickly for the camera to adjust in any way. .

For control of auxiliary flash units you need flashes which are more sophisticated that talk to each other, and that listen to the camera, as it were. This is done by a pattern of coded pre-flashes and all sorted out BEFORE the exposure is made for real..

Do I have to jump through hoops to get anappropriate exposure?.

Although the simple slave control method is not so sophisticated as in the dedicated flash systems referred to above (slaving just triggers the flash and doesn't tune it's exposure) it could be be considered that simplicity is a bonus..

Mostly it is a matter of doing a test shot or two (so easy with digital, and something you'd likely be doing anyway) and adjusting individual flash powers (higher/lower) after viewing the LCD..

This is the big benefit of digital. It is NO LONGER necessary to pre-determine everything about the exposure. Now everybody can afford to do test shots to see almost exactly how things will turn out.Regards,Baz..

Comment #1

Thank you for your reply..

I'm still a bit confused as to how I would adjust the camera and/or flash. I can understand the flash having some sort of intensity control, but if it's putting out any significant amount of light, I would think the resulting photo would be overexposed unless some appropriate adjustment were made on the camera. What would the appropriate adjustment be? What exactly should I look for in a camera's specifications to know that I could accomplish this?.

Thanks again,Topher..

Comment #2

On D200 if you use flash, Auto ISO turns off and the ISO set by the ISO control is used. Instead of Auto ISO blinking in viewfinder, it is now steady..

FINE PRINT: I reserve the right to be wrong. Should you prove me wrong, I reserve the right to change my mind...

Comment #3

Tgeliot wrote:.

I'm still a bit confused as to how I would adjust the camera and/orflash. I can understand the flash having some sort of intensitycontrol, but if it's putting out any significant amount of light, Iwould think the resulting photo would be overexposed unless someappropriate adjustment were made on the camera. What would theappropriate adjustment be? What exactly should I look for in acamera's specifications to know that I could accomplish this?.

You can't use auto mode anymore with this slave flash that will surprise your camera (she didn't know the slave was there)..

Switch your camera to manual mode. Set the shuttle speed, aperture and ISO that you want. Set your built-in flash to always on (because the slave need it's signal). You might need to set it's compensation to the lowest one (-1EV in most P&S) since you don't want it to cast directly to your subject..

With the slave turn on, set it's power to anything according to instinct. Test shoot. Then adjust it's power accordingly...

Comment #4

Tgeliot wrote:.

Thank you for your reply..

I'm still a bit confused as to how I would adjust the camera and/orflash. I can understand the flash having some sort of intensitycontrol, but if it's putting out any significant amount of light, Iwould think the resulting photo would be overexposed unless someappropriate adjustment were made on the camera. What would theappropriate adjustment be? What exactly should I look for in acamera's specifications to know that I could accomplish this?.

After viewing the LCD and evaluating whether the test image is correctly exposed or not, control of flash intensity is achieved by one or more of the following .....

Winding the intensity control (if it has one) up for brighter, or down for dimmer..

Moving the flash closer for brighter, or further away for dimmer..

Setting the camera to manual exposure control and adjusting the lens aperture wider for brighter, or narrower (stopped down to a higher f/number) for dimmer..

Having made your adjustments, take another test shot, rinse and repeat! .

Alternatively you could invest in a flash meter to measure the test flashes and recommend exposure settings. However, such meters are quite expensive, so I wouldn't get one until a need had been established, say, when you have multiple [non-dedicated] flash units, or monolight type studio flash units..

Sorry this is only general advice. Unfortunately, the devil is in the detail, and we cannot be any more specific until you have settled on an actual camera and flash(s) combination.Regards,Baz..

Comment #5

So the critical point here is: you pretty much need to have a camera that allows you to set shutter speed, aperture, and ISO. If you can't set those things manually, using a slave flash won't work very well, if at all.True?.

The other message I get is that I'm just not going to be able to use such a setup to take quick, candid photos the probability of getting the exposure right the first time is too low. Or maybe I could do it with lots of practice. But it won't be easy. Again, do I have this right?.

By the way, I gave the SD200 to my son, because I was so frustrated with it's (lack of) low-light capability. I am now shopping for a replacement. So advice on what features I would need to use a slave flash is exactly in order here. If anyone has more detailed advice, I'm all ears..

(Skylark: from you writing, I guess that English is not your first language. Thank you for being willing to help me out anyway. As a typical mono-lingual American, I am repeatedly humbled by the rest of the world's willingness to work in English. OTOH if English IS your first language, no insult intended, but you have a few grammatical errors ... .

Topher.

Skylark_khur wrote:.

Switch your camera to manual mode. Set the shuttle speed, apertureand ISO that you want. Set your built-in flash to always on (becausethe slave need it's signal). You might need to set it's compensationto the lowest one (-1EV in most P&S) since you don't want it to castdirectly to your subject...

Comment #6

Tgeliot wrote:.

So the critical point here is: you pretty much need to have a camerathat allows you to set shutter speed, aperture, and ISO. If youcan't set those things manually, using a slave flash won't work verywell, if at all.True?.

Yes, you do need manual exposure adjustment if you want to use simple cheap slave flashes instead of expensive digitally controlled dedicated ones..

Manual exposure control allows all sorts of creativity that is otherwise very difficult or just plain impossible otherwise..

The other message I get is that I'm just not going to be able to usesuch a setup to take quick, candid photos the probability ofgetting the exposure right the first time is too low. Or maybe Icould do it with lots of practice. But it won't be easy. Again, doI have this right?.

Yes, again, you have understood very well..

Manual may not be the quickest way to set up to begin with, but, in combination with examining review images, it is ultimately reliable..

Also, when working without the crutch of auto flash exposure you do get to aquire an instinct for what works and what doesn't, which *feel* for the processes of lighting IS gained surprising quickly. Just practising across one weekend, and writing down what you did with the flash for each shot, will get you 1/2 way to expert status...which stage some people never reach if they rely totaly on auto flash techniques..

This in itself may help you to set up quickly when trying for spontaneous candids.Regards,Baz..

Comment #7

Tgeliot wrote:.

So the critical point here is: you pretty much need to have a camerathat allows you to set shutter speed, aperture, and ISO. If youcan't set those things manually, using a slave flash won't work verywell, if at all.True?.

Largely true for this. Because in auto or semi-auto (aperture priority and shutter priority) mode, the camera will try it best to get well-exposed shot. If the slave is there, it will cause over exposure..

However, if you can get the camera to always shoot under-exposed shot, then the slave extra light may turn it to well-exposed. I thought of a few solution here:.

(1) You can turn your camera exposure compensation to negative. Most P&S should allow you to get -2EV exposure compensation..

(2) You can bounce or diffuse your built-in flash. You reduce it's power in doing this and you should get underexposed shots if the slave is not there.(3) You can stand somewhere out of your built-in flash coverage..

The main idea here is that if you are able to get underexpose shots without the slave, you might be able to get well-expose shots with the slave..

(Skylark: from you writing, I guess that English is not your firstlanguage. Thank you for being willing to help me out anyway. As atypical mono-lingual American, I am repeatedly humbled by the rest ofthe world's willingness to work in English. OTOH if English IS yourfirst language, no insult intended, but you have a few grammaticalerrors ... .

Haha, you caught me here. English is not my first language. I always have some grammatical mistakes in plural/singular and past/present tense...

Comment #8

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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