First Flash for a noobi

I am thinking about getting a Nissin Di622 flash for my Canon xsi/450d.
Supposedly you can set it to TTL and everything is automatic, fine. But here is my question. If I am standing 15 feet from my subject, snap a picture with the flash pointing straight at the subject, the flash will get its readings from the camera and the exposure should be correct. The light traveled 15 feet. But what if I bounce the flash off of the ceiling? The camera will read that I am 15 feet from the subject, but the flash will travel 8 feet up to the ceiling and then 8 feet to the subject. Doesnt this cause a little less light hitting the subject? And what about the different angles I point the flash head? What if I aim it straight up to the ceiling instead of at an angle. Or bounce it off of a wall?

Thanks in advance.

marcheseg wrote in post #10247830
I am thinking about getting a Nissin Di622 flash for my Canon xsi/450d.
Supposedly you can set it to TTL and everything is automatic, fine. But here is my question. If I am standing 15 feet from my subject, snap a picture with the flash pointing straight at the subject, the flash will get its readings from the camera and the exposure should be correct. The light traveled 15 feet. But what if I bounce the flash off of the ceiling? The camera will read that I am 15 feet from the subject, but the flash will travel 8 feet up to the ceiling and then 8 feet to the subject. Doesnt this cause a little less light hitting the subject? And what about the different angles I point the flash head? What if I aim it straight up to the ceiling instead of at an angle. Or bounce it off of a wall?

Thanks in advance.

the flash emits a little flash before the big flash so it knows

for your XSi/450D also at the Yongnuo YN465 flash - ETTL, manual controls, works with the XSi camera menu, built-in white card and diffuser and "sto-fen" like diffuser - all for less than $70 !

I'm about to order a YN-468 for my first flash and then a 460 II for OCF later.

Distance is NOT the main parameter used in setting the flash power (and in fact is probably NOT used when bouncing)

Basically, the flash fires a pre-flash that gets to the subject via the same route as it would during the exposure. And the camera's regular metering sensor reads the pre-flash as it's reflected back from the subject and determines what power (taking into account the ISO and aperture set on the body) is needed to achieve proper exposure.

Thanks for the responses

So basically I can set my ISO, indoors, at 100? And the in-camera metering should do all thos calculations then.

marcheseg wrote in post #10249267
Thanks for the responses

So basically I can set my ISO, indoors, at 100? And the in-camera metering should do all thos calculations then.

You set your ISO to whatever you want...Using a higher ISO allows you to use less flash power. So if you're bouncing off of a high ceiling (or trying to use a narrow aperture) changing the ISO from 100 to 200 requires half the flash power (such as going from 1/1 to 1/2 power)

I've used ISO1600 and flash in certain situations. But yes, the camera will set the flash power needed when you're in E-TTL.

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