manual flash settings

[robster]

OK, this is embarasing, though, it's my first time with the flash, so be gentle on me

I've a 580EX Speedlite and, plugged into the 30D set to full auto, I get the 1/60 at 1.8 (using a 1.8 50mm prime lense). Great! Smile

But... when I swap to say, Aperature Priority, I can't for the life of me get the thing to 1/60 at 1.8 without the meter telling me I need either a wider aperature (fat chance ) or a slower shutter speed.

The question is, how can the camera do it on auto, then when I go to AE mode it won't let me get those same settings?

Any help really appreciated

Rob

[Yi-P]

Rob,

I cant answer this question directly in Canon's terms.


But generally what I know from camera and flash exposure comm is done via the camera's internal meter CPU, lens CPU and flash CPU at the same time. Each provides little bits of information relay for the final flash output.

Say in your situation at 1/60 and f/1.8. You set the manual setting for it, and will force the camera flash to compensate any light that is needed to get that exposure. Information such as lens focus distance and camera metering info is transfered to the flash and it does all the calculation for you on the final output based on the complex formulae they got inside.

On AP mode, the camera will suggest you with the aperture and shutter that matches the 'exposure' it is needed, without flash. On the Nikon Cameras, there is an option that restricts the slowest shutter speed with flash onboard, which it will then use flash to compensate the left-over underexposre.

Back to your question, I dont really use Aperture priority in with flash anyway if I gonna leave it on Auto mode. Manual in setting aperture and a shutter which you can hand-hold the lens is best left there and let the flash exposre itself to the right way.

Another way to correct this is increasing/decreasing in-camera exposure vs on-flash exposure, they compensate each other and will make up another exposure method.


For the actual "Manual flash" I suggest you do some readings at using GN (Guide-Number) for flash exposure calculation. Its a formula based on distance to subject, aperture vs shutter and ISO on film/sensor. I cant pull the formula out from my head now, but im sure other members can help you here and/or just google it, should give you plenty of results and good readings. PS. Pls correct me if Im wrong.

Good luck

[Antsl]

Hi Rob,

Make life easy for yourself when doing the studio thing and put the camera in manual mode and then put the flash in manual mode too.

Set the camera in manual mode to 1/60 or 125th of a second and manually set your aperture to whatever you are hoping to work at (f4 or f5.6 is good for hair). Next set the flash to the manual and adjust the power output to a suitable increment (full power, half, quarter etc) until you start getting the exposure looking right. Once you start shooting a look, assuming you do not move the lights to dramitically, everything should remain reasonably constant. This is the approach most serious photographers use.

Cheers, Ants

[robster]

Thank you (both). That's some great advice. I just got this great link from the other forum: http://photonotes.org/articles/eos-flash/ a VERY long read but well worth it, it's demystified flashes for me.

I'll do the whole manual thing like you described and get back with my results.

Thanks again

Rob