D90 Aggravation

[chammer]

jimmy: shutter speed, aperture, and iso are the ways we have at controlling exposure normally.

however, under flash/strobes its the aperture which controls your exposure, and in this case how much of your background is seen or not seen.

these two i took today playing around while doing something else, but it shows what im talking about if you look closely...

the first shot was 1/160th @ f/16, and the second was at 1/160th @ f/8. if you look at the first the background is almost completely black (which is what the OP is going for). the second shot, because i used a wider aperture it allowed more of the background to bleed into the exposure.

had i left the camera at f/16 and simply increased the power of my flash, i would have gotten a nicely backlit plant with the black background.

*edit*
the two initial ones were way too dark, so i increased the ev +4 in lightroom to make it easier to see what im talking about

 

[JimmyO]

jimmy: shutter speed, aperture, and iso are the ways we have at controlling exposure normally.

however, under flash/strobes its the aperture which controls your exposure, and in this case how much of your background is seen or not seen.

these two i took today playing around while doing something else, but it shows what im talking about if you look closely...

the first shot was 1/160th @ f/16, and the second was at 1/160th @ f/8. if you look at the first the background is almost completely black (which is what the OP is going for). the second shot, because i used a wider aperture it allowed more of the background to bleed into the exposure.

had i left the camera at f/16 and simply increased the power of my flash, i would have gotten a nicely backlit plant with the black background.

*edit*
the two initial ones were way too dark, so i increased the ev +4 in lightroom to make it easier to see what im talking about

I obviously understand exposure and exposure's relation to flash. I think were talking about 2 seperate effects and we cant be on the same page without pics from the OP.

You said that aperture controls the value of the flash. Thats half true, iso does the same obviously. Also, upping the aperture doesnt effect the background as your describing. It will change the whole image but you also have to adjust the flash along side of it. With those pictures you posted the second one is being overexposed by the flash. So you could have just lowered the flash power and it looked normal, but instead you used a smaller aperture to bring the whole exposure down and that ended up taking out what was left of the ambient. So although it did take out the BG its not becuase of aperture completly. Had you had raised the flash power in the first one you would have also just overexposed it jsyk.

 

[chammer]

well, it wasnt overexposed before i did it on purpose to emphasize.

maybe we're not on the same page, but from reading the original post it appears to me this is exactly what he's wanting.

i respectfully disagree. my photos in general may suck (especially compared to yours), but i do read a ton and feel like i have a nice grasp on the technical side of things.

this is the way i understand it...

sample scene: it's 6pm in the evening, and there's enough ambient light where your camera is telling you to properly expose this flower it's going to need to be at 1/60th, f/4, and iso 100. you take the shot using ambient light only and it exposes the flower, and blurs the background ever so nicely with pretty blues and greens and pinks and reds etc etc.

now, switch the camera to manual. dialing in 1/60th at f/4 and iso 100 is obviously going to expose the picture the exact same way. now, simply change the aperture to f/5.6. now the entire image is underexposed by 1 stop.

ok, now the fun part. lets at some flash. we get our stuff out and point the flash at the flower we are wanting to photograph. we turn it on, set it to 1/8th power, and using our previous settings of 1/60th at f5.6 and iso 100 we take the shot. the background is STILL underexposed by 1 stop, but now the flower is nicely lit.

we want the background darker still so we set the flash to 1/4 power now, doubling its output from its previous value (+1 stop). if we left the camera alone at this point the flower will now be overexposed by 1 stop, and the background will still be underexposed by 1 stop. to compensate we stop down 1 stop to f/8. we take the picture again...

at this point we should end up with the background now 2 stops underexposed, and the flower is still properly lit.

...and so on and so forth until we either get our black background and nicely lit flower, or until we run out of flash power and curse at the gods before coming inside and ordering yet more stupid equipment.

but seriously, if im still missing something i'd be happy to find out what.