rcirr Loc: Gilbert, Arizona

Being a technician I find I can use equipment better when I understand how it works. I have been trying to find out how a camera and flash work together but have not been able to find answers to my questions. When you take a picture without a flash, I assume the camera just opens the aperture to the specified opening for the specified time. I would like to know if the camera controls the flash power and duration or does the flash just go off and the camera closes the aperture when it has recieved enough light. When you set the power on a flash are you actually setting a power level? If not, is the flash always full power and you are simply manipulating the duration of the flash which adjusts the amount of light reaching the camera? Does the camera monitor the amount of light it sees and adjusts on the fly or does it assume the amount of light according to the settings? I guess what I'm looking for is a theory of operation. Any information would be appreciated. Thanks in advance.

Wahawk Loc: NE IA

WOW! What a question.....

I don't care "HOW" it does it, all I care is that it gets done!!!

rpavich Loc: West Virginia

The flash power is controlled by the flash. The aperture stays open for a particular duration no matter what the flash power.




The flash power doesn't change, it's the duration that changes.





I think (but I don't know) that the camera's settings are constant, but the ETTL system sets the flash duration according to the subject distance via an invisible "preflash"




There is a good video on youtube by mark wallace about this...I don't remember any specifics but you could go to youtube and search "mark wallace flash sync" or something and probably find it.

EstherP

Assuming your camera has an on-board flash, you will likely find some information in your camera's instruction manual.
I think it will actually discuss more things like "when" (the flash goes off, or when to use it) than it will tell you where the electrical impulse goes when you press the shutter-button, but still will give you some interesting ideas.
EstherP

Quicktee Loc: Finger Lakes

Try reading Mastering Canon EOS Flash Photography. Sold at Amazon. I am in the process of reading it now. You will be most impressed by all the technical information.

Tom

rcirr Loc: Gilbert, Arizona

thank you for the suggestion. I'll check it out.

rcirr Loc: Gilbert, Arizona

Thanks for the suggestion. I've already checked out a couple of his videos. They fill in a lot of the holes in my understanding of photography.

CaptainC Loc: Colorado, south of Denver

Assuming you are using the iTTL/E-TTL system, here it is:
You press shutter button - flash sends out a flash at a known setting - camera meter reads the reflection and since it KNOWS how much light was sent, it knows how much to increase or decrease the REAL flash - camera brain sends this information to the flash - shutter opens and flash fires at the setting the camera brain told it to fire.
Remember, just like ALL meter readings, the meter assumes 18% gray for the reflectivity, so if the preflash sees too dark, you may overexpose and vice versa.

AS far as flash operation goes, you don't need to know more than that. You may think you do, but you don't.

iTTL/E-TTL is smart, but not smarter than a human that understands how the metering system works and how to vary subject exposure and background exposure. THAT is what is helpful to understand.


There are tons of books and internet posts/blogs on how all this works.

FilmFanatic Loc: Waikato, New Zealand

And just to add to the complication - I shoot Olympus OM 35mm. They have a neat TTL OTF flash system (Thru the Lens Off the Film) which works by measuring the light reflected off the film to determine when it has enough light. Gives awesome flash exposures. I believe that is only possible with film sadly.