Exposure compensation and Flash compensation

[ast]

just want to ask, what is the difference (the effect on the photo) between Exposure compensation and Flash compensation?

when do you use Exposure compensation and Flash compensation?



TIA!

[Onyx]

Basically, these two factors apply when you're shooting with the flash (no point adjusting flash compensation when you're NOT using the flash!)

Exposure comp controls how brighter or darker you want the whole scene to be (+ and - respectively). Flash compensation controls how much brighter or darker you want the flash to be, from what the camera determines to be "correct" amount.

Example: person standing in a room indoors, for the sake of simplicity say the room is lit with a standard lightbulb, and you're taking the picture using the onboard flash.

Exposure comp will make the person and the room lighter or darker when you dial in +/-.

Flash comp will make only the person lit up by the flash lighter or darker.

When you dial in exposure compensation, whatever it lit up by the flash will also be altered. Exposure comp affects everything in the scene, hence all light, regardless of whether it came from the flash or not, is altered. Flash comp basically controls the light output from the flash only.

[ast]

thanks for the reply!

i think i tried using Exposure compensation without flash, i shoot a person and the background is the blue sky, metered on the sky but the person darkened. so, adjusted exposure compensation (+), then got the photos i want. with my example above, i don't think it lit up the 'whole scene' as you stated. Maybe that will apply on 'matrix' metering mode.

[sirhc55]

thanks for the reply!

i think i tried using Exposure compensation without flash, i shoot a person and the background is the blue sky, metered on the sky but the person darkened. so, adjusted exposure compensation (+), then got the photos i want. with my example above, i don't think it lit up the 'whole scene' as you stated. Maybe that will apply on 'matrix' metering mode.

When using exposure compensation, in let’s say Aperture mode, by using + compensation you are slowing the shutter speed down thereby letting more light in. Conversely, if you use - (negative) compensation you will increase the shutter speed thereby letting less light in.

The question is why would you be metering the sky if you are trying to shoot a person. Surely you would want to meter the person!

[ast]

thanks for the reply!

i think i tried using Exposure compensation without flash, i shoot a person and the background is the blue sky, metered on the sky but the person darkened. so, adjusted exposure compensation (+), then got the photos i want. with my example above, i don't think it lit up the 'whole scene' as you stated. Maybe that will apply on 'matrix' metering mode.

When using exposure compensation, in let’s say Aperture mode, by using + compensation you are slowing the shutter speed down thereby letting more light in. Conversely, if you use - (negative) compensation you will increase the shutter speed thereby letting less light in.

The question is why would you be metering the sky if you are trying to shoot a person. Surely you would want to meter the person!

thanks for the pointers!

so, when shooting a subject with bright background, we meter on the subject then use negative compensation?

[phillipb]

No, when shooting a subject with a bright background, you must decide which one you want exposed correctly. You can meter for the subject and the background will be blown out or you can meter for the background and the subject will be dark.
The solution is to use fill flash in which case you meter for the background and the flash fills in the shadow on the subject.

[ast]

No, when shooting a subject with a bright background, you must decide which one you want exposed correctly. You can meter for the subject and the background will be blown out or you can meter for the background and the subject will be dark.
The solution is to use fill flash in which case you meter for the background and the flash fills in the shadow on the subject.

Interesting! Thanks so much for all you replies!

anyway, i'm just having some trouble with my indoor shots, the photos don't 'snap'!

i'm using my D70 with kit lens and SB-800...and still... doesn't 'snap'

[Mj]

Whilst on the subject of flash photography, thought I'd throw this question into the ring... am guessing that Onyx has the answer to this one?

When using the SB800, it seems you can adjust flash compensation both on the camera and on the SB800 itself... which setting wins? I haven't been playing with the flash much lately but I seem recall noticing that I could adjust both independently yet I would have expected that the two settings would synch with each other somehow.

Michael.

[xorl]

When using the SB800, it seems you can adjust flash compensation both on the camera and on the SB800 itself... which setting wins?

You need to add both values together to get the actual compensation value used. Usually you would just leave either the body or the flash at 0 comp to keep things simple.

[Onyx]

When using the SB800, it seems you can adjust flash compensation both on the camera and on the SB800 itself... which setting wins?

They both do the same thing. The SB800 manual recommends going with the on flash one, simply to avoid confusion when the SB800 is not mounted and you use the onboard flash. Also note that they are cumulative - ie. -1FV on camera, -1FV on flash = total of -2FV which renders pretty much a dim flash output.

NB: tip - to cancel flash compensation, press + and - buttons on the SB800 together for 2 secs.

ast - you might also like to experiment with slow sync flash mode to balance both ambient and flash light output if that's one aspect you weren't happy with. Taping the 2 contacts for 1/8000th sync speed I found also defaults the flast mode from front curtain (normal) to slow sync.

[ast]

Taping the 2 contacts for 1/8000th sync speed I found also defaults the flast mode from front curtain (normal) to slow sync.

i'm sorry, what do you mean by 'taping the 2 contacts'? and also i think the 'slow sync' can only work with certain shooting modes? does it work with MANUAL and APERTURE PRIORITY modes?


Thanks again Onyx!

[the foto fanatic]

Just a word of advice when experimenting with exposure compensation on the camera and on the flash.
As Onyx says, the effect is cumulative and is very hard to control.
I would not use both at the same time.

[Onyx]

i'm sorry, what do you mean by 'taping the 2 contacts'? and also i think the 'slow sync' can only work with certain shooting modes? does it work with MANUAL and APERTURE PRIORITY modes?

Hi ast, perhaps I shouldn't have mentioned the taping 2 contacts bit - that's a separate issue. It's a trick or "hack" to override the 1/500s flash sync limitation of the D70. Ken Rockwell (http://www.kenrockwell.com ) has plenty to say regarding flash sync and its importance in photography. Then again he has alot to say about everything, and he's not always correct.

As for slow sync flash mode, I would imagine it is available in all the good shooting modes (P, A, S, M). I'm guessing the "idiot modes" won't allow it, as they don't allow changes to any other image parameters. Anyway, when you normally have the SB800 mounted on the camera and turned on (in A, S or P modes), there is a base shutter speed that the camera will not go below. Turn the flash off (or push the on-board flash down) and the camera gives you a different metered exposure reading. Slow sync basically uses the camera determined metered ambient light conditions. So you're exposing your image for ambient light. With the added bonus of flash for your main subject.

eg. If you're shooting in Aperture priority, at your chosen aperture you may notice the camera's metered shutter speed into the seconds if light levels are particularly low. This means if you fire the flash in front curtain sync, the default flash mode, which defaults to 1/60s shutter, you will get severe underexposure of everything that your flash does not illuminate.

In fact, I have some pics I took a long time ago that demonstrates the differences between normal (front curtain) flash and slow sync. Here they are -
Default flash mode: http://dr-cbtan.fotopic.net/p4990350.html
Slow sync flash mode: http://dr-cbtan.fotopic.net/p4990351.html

NB: slow sync had a 3 second shutter, so it's not ideal for moving subjects.

[ast]

Thanks so much the info and samples!! Greatly appreciated!

In fact, I have some pics I took a long time ago that demonstrates the differences between normal (front curtain) flash and slow sync. Here they are -
Default flash mode: http://dr-cbtan.fotopic.net/p4990350.html
Slow sync flash mode: http://dr-cbtan.fotopic.net/p4990351.html

actually, the two samples to showed is exactly my problem!

can i ask? will increasing the ISO help in these shooting and lighting condition? i know they will add noise, but will it help to put in more ambient lighting or does it all depend on 'longer' exposure (slow shutter speed)?

[xorl]

Default flash mode: http://dr-cbtan.fotopic.net/p4990350.html
Slow sync flash mode: http://dr-cbtan.fotopic.net/p4990351.html

can i ask? will increasing the ISO help in these shooting and lighting condition? i know they will add noise, but will it help to put in more ambient lighting or does it all depend on 'longer' exposure (slow shutter speed)?

In the standard flash mode increasing ISO will make the background brighter. When the background is very dark this may not be enough to get an even exposure.

In slow sync/aperture priority increasing the ISO will force the camera to use a faster shutter speed. You may still need to use a tripod to avoid blurring the background.

Personally, I prefer to use manual mode to balance the background and get the effect I want when doing flash work.