Exposing for Off Camera flash ??

[bigdazzler]

Darren, in your shots, the background is affected by the flash because it is so close to the subject..

yep ok Tom , i totally get that bit .. obviously the flash has a certain guide number distance and will only light so far into the frame front to back at any given power output/setting ..

what im trying to get (as in the two sets above) is why the shutter speed has no effect on the subject but the adjusted aperture has a great effect ??

the two sets of images above clearly support what you were saying earlier on about shutter speed and subject ..

[TOM]

precisely, because the flash is, in effect, your shutter and ambient light all rolled up into one little pop that happens at around 1/10000s. Now you shutterspeed is irrelevant and the aperture and distance are the only things that are controlling how much light gets to the film err.....sensor. the shutter speed will have a very minute affect on the exposure but only when we take two images at extreme shutter speeds will we notice this. it is best to work on the basis that shutter is irrelevant.

try a shot of a close object with the background far away. looking forward to some examples. determine the aperture, take one at max sync, then take one dragging the shutter, say four stops under ambient.

[bigdazzler]

ahhhhh ok .. i think im understanding ... so even at 1/10th, the slowest of the shots above, becasue the flash is still firing so quickly, at approx 1/10000th, the ambient light is never going to effect the exposure in the foreground within the flash guide distance .. ?? The burst of flash is simply too bright to be effected by any ambient light in the foreground/subject of the scene ??

am i getting this.. ??

[TEITZY]

Yes the flash will overpower the ambient light in the foreground, however @ 1/10 you should have a brighter background or less light fall off than you would at say 1/100 (that's assuming you are not in a completely dark room). Using low shutter speeds with flash is often referred to as 'dragging the shutter' and it provides a more natural looking shot (with some background detail) while the flash effectively freezes the subject in the foreground. You can also do this by bumping up the ISO as this has basically the same effect as dragging the shutter. So if you have a play with your flash just set the aperture and shutter in manual and change the ISO and see the difference it makes to the exposure.

Cheers
Leigh

[bigdazzler]

ok im getting the idea that the flash will expose the subject and the aperture and distance will determine the ambient light of your background ... handy to know next time I wanna shoot manual fill flash outdoors and want to maintain some background detail.

What about if i want to shoot portraits at say 2 metres with a black backdrop ?? From what i think ive just learnt, shutter speed will be irrelevant so I would set to max sync speed, 1/160th in my case, and then play with aperture until I get a correct exposure ?? Is this a good place to start .. ?? Bearing in mind of course, I dont have an incidental flash/light meter ..

Whilst on the subject of incidental meters .. How exactly do they work ?? Im assuming that you hold the meter in front of to read the light falling onto the subject. Does the meter then indicate to you a correct shutter speed and aperture and you just set your camera and strobes accordingly ?? Is it a matter of just replicating the numbers ... ??

[TOM]

Leigh has explained this better than I. Just remember that with flash photography there are two seperate exposures happening. This is the key to getting to grips with flash. One is the flash/aperture/distance exposing the subject (usually in the foreground unless you are using snoot or barndoors - forget about his for now), and the second is the shutter speed/aperture/ambient/ light exposure - just as you would expose a shot without flash.

The background is not epxosed by distance as your last post suggests. With you black backdrop scenario, you are right. Shutter has little affect on this shot. I would tend to go for max sync to try to underexpose the black background. This is opposite to my earlier post where I would overexpose for a white background. it is not so much a matter of the flash overpowering the ambient, which it does do, but the speed in which the flsh works. the flash (very fast) determines the exposure along with the aperture and it doesn't matter about the shutter speed as it is ALWAYS going to be slower than the flash.

when using a meter, you will pre set your flash at a power setting. Let's say 1/16th power. Your flash is two meters from the model. You get the model to hold it in front of themselves, and you fire the flash. the meter will then indicate to you the correct aperture. It will not give you a shutter speed as it is not required. These meters are incident meters and will only measure the light falling on them. as the background is under differnet lighting (ambient rather than flash) and some distance away, it has no way of determining this. it is something you will want to choose youreslf depending on your desired effect.

[bigdazzler]

ok yea i get the error with the distance/background thing .. now i read it back.

with the porttaits, in the absence of a flash meter, i would simply set SS to max sync and experiment with aperture/distance until the exposure looks good ??

was i right about how the meters work ?? Its been something ive been meaning to ask one of you more experienced flash guys.

EDIT: RE: The meters. I replied as you edited .. oops

[bigdazzler]

.

when using a meter, you will pre set your flash at a power setting. Let's say 1/16th power. Your flash is two meters from the model. You get the model to hold it in front of themselves, and you fire the flash. the meter will then indicate to you the correct aperture. It will not give you a shutter speed as it is not required. These meters are incident meters and will only measure the light falling on them. as the background is under differnet lighting (ambient rather than flash) and some distance away, it has no way of determining this. it is something you will want to choose youreslf depending on your desired effect.

ok thanks mate, its something ive always wondered, how you determined your settings using an incidental meter. So its only aperture that gets determined by the meter .. ok.

So.. if i was setting up an outdoor portrait shot and had my flash 2 metres from the model, I would test fire at the model and determine the required aperture, and set my camera accordingly. Then to expose for the background, lets say a beach scene at dusk, I would meter a seperate exposure off the sky or whatever part of the scene, and then set my shutter speed corresponding to the predetermined aperture from the flash test shot ?? Now this would in theory give me an even exposure and maintain ambient light and detail in my background. But If I wanted to underexpose the background slightly, to create seperation of model from bg, I would set the shutter speed so that my meter indicated a 1 stop underexposure ?? Am I on the right track ??

[TOM]

with the porttaits, in the absence of a flash meter, i would simply set SS to max sync and experiment with aperture/distance until the exposure looks good ??

difficult to answer. every situation is going to require evaluation and with time you will develop kind of like a fifth sense. you will intuitively know where to set your aperture and power. with digital, you have the ability to chimp. this is really going to be a task for you, not having the ability to manually adjust you power output. essential items for flash portraiture imho are at least one shoot through umbrella with stand. a decent softbox is going to be too limiting with the small power of a speedlight. if you look at the catchlight in my image above, you will see that this was taken with a flash and a bounce card. this type of catchlight is not very attractive.

edit: you snuck a post in on me. yes to get some nice seperation, I like to go about two stops under. This also applies to ttl flash as well, which you should use manual in - meter the scene, adjust your you meter displays about two stops under, and then fire. during the a daytime outdoor portraite session, you are going to be wanting fill flash - this is different again.

[bigdazzler]

with digital, you have the ability to chimp. this is really going to be a task for you, not having the ability to manually adjust you power output. essential items for flash portraiture imho are at least one shoot through umbrella with stand. .

ok well i have a shoot through brolly and stand so at least i now have a starting point where ill be able to have a play and see what i can come up with .. yea the limitations of my flash wont help me i guess. thats what i was getting at when i said before that my only real option is to set to max sync and then manipulate aperture until I can maybe get something that looks ok .. i took these with a shoot through brolly and my speedlight off camera .. difference here is i was triggering with the onboard flash. The light is soft enough, but broad and flat and has no shape .. thats the whole reason i bought the triggers., to see if i could improve these kinds of shots by not having to use the onboard flash as a tirgger.

[TOM]

yeah sure, but the max sync speed is not important, just don't go above it. more than likely you will be well below it. your choices are to adjust the aperture or the distance of the brolly. if you could get the brolly in really close, and wind down the power output of the flash (if required), you will get some nice wrap. Then another flash at the rear with a snoot to add a nice bit of backlighting on the hair........

All the best with your flash experimenting and be sure to post some samples along the way. If you get the chance, do pick up a nice little cheap flash unit ($100) and then you can really start experimenting.

[bigdazzler]

ok thanks mate, its something ive always wondered, how you determined your settings using an incidental meter. So its only aperture that gets determined by the meter .. ok.

So.. if i was setting up an outdoor portrait shot and had my flash 2 metres from the model, I would test fire at the model and determine the required aperture, and set my camera accordingly. Then to expose for the background, lets say a beach scene at dusk, I would meter a seperate exposure off the sky or whatever part of the scene, and then set my shutter speed corresponding to the predetermined aperture from the flash test shot ?? Now this would in theory give me an even exposure and maintain ambient light and detail in my background. But If I wanted to underexpose the background slightly, to create seperation of model from bg, I would set the shutter speed so that my meter indicated a 1 stop underexposure ?? Am I on the right track ??

I dont want this ^^^^^^ to get lost in the thread before it gets answered. Would this be the way to go about setting up and exposing for this kinda shot ??

[TEITZY]

^^^^ Sounds fine Darren. In these situations you will possibly need to use a shutter speed higher than the fastest flash sync speed (to expose the BG correctly) unless your aperture is quite small.

Cheers
Leigh

[bigdazzler]

ok thanks guys .. the info and help is much appreciated. Now that i got my head around this concept a little I might head on over to ebay and find a cheap manual flash to play with .. i guess all i need is a unit with manual power and a sync input .. brand is irrelevant yea ??

[TOM]

brand is irrelevant. as TEITZY explained above, you could use your camera in high sync special mode but i am not sure if that is available off camera. the other option, which will allow for greater controlof dof, is to use one, or a combination of nd filters to get your shutter below sync. using high speed sync comes at the detriment of power.

[TEITZY]

TOM, I assume the camera hot shoe adapter is similar to a PC cord connection (rather than TTL) which should allow Darren to flash sync at any speed. You can do this with Nikon speedlights/bodies that don't have FP Sync mode by simply taping over the outer (smaller) contacts on the camera hotshoe and just leaving the main centre contact exposed.

Cheers
Leigh

[TOM]

Tietzy, I don't understand your post. Are you saying that flash sync is irrelevant with the Nikon's under certain circtumstances other than FP?

[JM Tran]

wow I cant believe Sony is allowed to get away with selling a flash unit with no Manual control for flash power output!

in a studio shoot with backdrop, shutter speed has very little effect, but is much more evident when shot indoors or outdoors with a subject - the slower the shutter speed, the more ambient light is drawn in and gives the background a more natural look.

[TEITZY]

Tietzy, I don't understand your post. Are you saying that flash sync is irrelevant with the Nikon's under certain circtumstances other than FP?

No just saying you can fool the camera into thinking there is no flash connected. You can do this with PC cord as well but obvously you have to use the flash in full manual mode. This normally works pretty well up to 1/1000 on most Nikon bodies but is a bit more problematic on the Canons in terms of shutter blackout. Here are some D70s shots using the SB800 in the hot shoe with the contacts taped at 1/1000, 1/2500 & 1/8000

Cheers
Leigh

[TOM]

right no worries, thanks for clearing that up Leigh.