Flash photography


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Feb 2, 2006
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#1
Hi,

Ive been reading on flash photography lately. Have a question in mind..... Lets say im using an external flash in Shutter or Aperture pirority, and then I wanna illuminate the foreground and the background is dark.... lets say at night. So, the camera will probably give me a setting for low ambient light, which means slow shutter speed. The thing is lets say the picture I am taking contains people in the foreground, it doesnt make sense cos the low shutter speed means the people in the foreground will have to stay still for a few seconds??? Is there anyway to get around this?

Also, I also read that flash output levels can be adjusted. Just want to know how much to adjust? Is it based on experience? Lets say the ambient is already quite bright but I wanna do fill flash. How much lower to adjust the flash output?

Anyone knows about this?

Thanks
 

catchlights

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#3
duhduh83 said:
Hi,

Ive been reading on flash photography lately. Have a question in mind..... Lets say im using an external flash in Shutter or Aperture pirority, and then I wanna illuminate the foreground and the background is dark.... lets say at night. So, the camera will probably give me a setting for low ambient light, which means slow shutter speed. The thing is lets say the picture I am taking contains people in the foreground, it doesnt make sense cos the low shutter speed means the people in the foreground will have to stay still for a few seconds??? Is there anyway to get around this?
yes, they have to stay still. else some lights will "cut" into the person body
or you can try high ISO, so the time of exposure will be shorter.

duhduh83 said:
Also, I also read that flash output levels can be adjusted. Just want to know how much to adjust? Is it based on experience? Lets say the ambient is already quite bright but I wanna do fill flash. How much lower to adjust the flash output?
Yes, by experience, and your taste,
No hard and fast rule, but I would use one stop to two stops less on flash output.
 

Feb 2, 2006
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#4
catchlights said:
yes, they have to stay still. else some lights will "cut" into the person body
or you can try high ISO, so the time of exposure will be shorter.


Yes, by experience, and your taste,
No hard and fast rule, but I would use one stop to two stops less on flash output.
wow... i must say photography has real limitations..... im trying to think of a way round this... cos it makes no sense to keep a person perfectly still for more than a second..... i was thinking if the aperture is too small.... then slight movements wont be recorded on the film provided the flash has already been fired out and the reflection of light has already been recorded on the film since its really low light? dunnoe.... just thinking anyone got ideas?
 

catchlights

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#5
duhduh83 said:
wow... i must say photography has real limitations..... im trying to think of a way round this... cos it makes no sense to keep a person perfectly still for more than a second..... i was thinking if the aperture is too small.... then slight movements wont be recorded on the film provided the flash has already been fired out and the reflection of light has already been recorded on the film since its really low light? dunnoe.... just thinking anyone got ideas?
Since you want to record the backgound, so there is some lights, flash with register the image of the person, but the light of the backgound need more time to be register on film or sensor, so the subject need to be still to enable perfect register the outline of the subjest.

If the backgound has no lights, what is the perpose of take long exposure for this?

The is not the the limitation of photography, is simple law of physics.

to brake away from law of physics, can always try photoshop.
 

waileong

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#6
No, they don't have to stay still. Flash photography is independent of your shutter speed.

They only need to stay still if you want to balance the foreground and the background scene, which is lit by ambient light only. In your example, it will probably be too slow to handhold.

On your 2nd question, with a good flash system (eg Nikon), the camera will do all the calculation and adjustment for you. Typically people adjust by -1.7 stops, but that's a personal preference.


duhduh83 said:
Hi,

Ive been reading on flash photography lately. Have a question in mind..... Lets say im using an external flash in Shutter or Aperture pirority, and then I wanna illuminate the foreground and the background is dark.... lets say at night. So, the camera will probably give me a setting for low ambient light, which means slow shutter speed. The thing is lets say the picture I am taking contains people in the foreground, it doesnt make sense cos the low shutter speed means the people in the foreground will have to stay still for a few seconds??? Is there anyway to get around this?

Also, I also read that flash output levels can be adjusted. Just want to know how much to adjust? Is it based on experience? Lets say the ambient is already quite bright but I wanna do fill flash. How much lower to adjust the flash output?

Anyone knows about this?

Thanks
 

Feb 2, 2006
495
0
16
#7
so, the subject has to stay still if i do a 30sec exposure?? this would be seemingly ridiculous.... so the law of physics limits photography.... :dunno:
 

waileong

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#8
I only said they needed to stay still because I thought your ambient exposure was something like 1 second. If they moved during that one second, you would get shadows and forms resulting from their movement.

For a 30 sec exposure they don't need to stay still. The flash actually lasts only 1/1000 of a second or so, ithat's all it takes to capture their image onto the camera. If you want to blend in such a dark background using ambient light, all you need to do is after the flash, cover the lens with a black card or something, then ask the subjects to exit the frame, and open the lens again for the remainder of the 30 seconds. In fact, even if you did not use a black card, their movement would probably not register on the camera if the light level is so low.


duhduh83 said:
so, the subject has to stay still if i do a 30sec exposure?? this would be seemingly ridiculous.... so the law of physics limits photography.... :dunno:
 

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#9
duhduh83 said:
so, the subject has to stay still if i do a 30sec exposure?? this would be seemingly ridiculous.... so the law of physics limits photography.... :dunno:
If u need 30sec exposure to capture the background, the background is probably too dark to begin with.
 

Feb 2, 2006
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#10
ok la maybe 30 sec is overexaggerated but how about a 8 sec exposure for a normal 7-8pm shot? So I suppose if the aperture is above f/16 AND at such low light levels then movements wont be registered? still, the black card trick is a clever idea.... thumbs up:thumbsup:

next question, how low is low light? i mean how do you tell whether the light level is low enough such that movements will not be registered???
 

LittleWolf

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#11
duhduh83 said:
this would be seemingly ridiculous.... so the law of physics limits photography.... :dunno:
Did you assume photography was based on some kind of supernatural magic?
 

Feb 2, 2006
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#13
LittleWolf said:
Did you assume photography was based on some kind of supernatural magic?
well.... yes and no..... ive seen some seemingly impossible to take pictures.... maybe its just PS, but i just want to find out what i can do with a film camera without any PS. eg double exposure is quite cool. and this flash photography is a mind-boggling one as its hard to figure a way out..... or maybe there is no practical way at all......
 

#16
duhduh83 said:
well.... yes and no..... ive seen some seemingly impossible to take pictures.... maybe its just PS, but i just want to find out what i can do with a film camera without any PS. eg double exposure is quite cool. and this flash photography is a mind-boggling one as its hard to figure a way out..... or maybe there is no practical way at all......
Actually, the preview is an advantage of a Digital SLR/compact. You will know if there shot is ok, or need to make adjustments to the shoot.

With film, its mainly trial and error and through experience of previous shoot. so the only way is really to keep shooting in different settings/bracketing.
 

#17
wildstallion said:
hang on a sec, why not just use a faster shutter speed and a brighter flash? would this not solve your problem?
NO flash is strong enough to flood the entire scene unless its a super hugh floodlight...;(

Perhaps another way would be to take 2 shots, one of the background with the long exposure, and another with the person using flash, and PS them together. This is similiar to using double exposure for film.
 

Feb 2, 2006
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#18
i found a loophole in the black card method..... firstly if the person moves away and the black card is removed, the area where the person is standing will start to become exposed.... this will cause a ghosting effect??!??

a brighter flash will not illuminate the background thats for sure....

maybe its just not possible.....
 

Ah Pao

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#19
Glad you found out the 'loophole'.
The only solution is to pump up the ISO and get fast lens. That's about it.

You don't need 30s exposure to capture the ambient light of the 7-8pm dusk, that's for sure, unless you are using ridiculously small f-stop with ISO 100.
 

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