Exposure Compensation

ams99

ams99

Messages
1,058
Name
Alan
Edit My Images
Yes
Hi all,

I've been playing around this evening using the flash indoors. I've been experimenting with Exposure Compensation and want to understand how the camera is adjusting the exposure without seemingly altering the settings.

Each image EXIF data shows 1/60s, F5, ISO 800. However, the exposure is obviously different when ive applied exposure compensation.

Question is, what is the camera adjusting to alter the exposure given the constant shutter speed, aperture and ISO ?:shrug:

Nikon D5000 and std kit lens

Thanks
 
Basically, the camera is saying 1/60s at f/5 but you are overriding it with + or - settings that equate to full, half or third stop increments of over/underexposure. So if +1 is applied, it's actually now got a shutter speed of 1/60th + 1, which equates to 1/30s ('+' is overexposure on my Nikon). I was sure that the EXIF showed the EC value as the shutter speed though. Might be wrong....

In Av it's the shutter speed that's the variable; in Tv the aperture changes.

All sounds confusing I know, but all you're doing is overriding the camera. It's a halfway house between an auto mode and manual that allows additional user input..
 
Are you dialing Exposure Compensation or Flash Exposure Compensation? If the latter, then you are increasing flash power hence the different brightness
 
That's where i'm struggling with the understanding. I have been shooting in Aperture Priority as well as shutter priority to see the difference and understand how the exposure compensation adjusts the other settings.

In good light in Aperture priority i can visually see the change to the shutter speed when i apply EC. However, indoors with dull light with the std pop up flash the exposure is changing when EC is applied but none of the main parameters are changing. I expected to see the shutter speed or ISO change when i'm in Aperture priority. But yet, none of these appear to change but the exposure does.

I may be being a bit simple but just can't apply the logic at the moment.

Also, as an aside, the flash compensation isn't increasing / decreasing either so it's not that.

Can i presume that for some reason the camera is adjusting the exposure without showing me what it is actually doing. If so, why does it show me the changes in good light situations? Bizarre
 
There is no way camera would 'hide' that from you. I suspect that EC simply changes the flash exposure. May be this is how builtin flash works on Nikons?
 
I suspect that Alex is almost certainly right and that you are adjusting FEC and not exposure.
 
Is this due to the Balanced Fill Flash ?
Using flash the camera emits pre-flashes before the actual exposure to determine how much flash is needed, together with the ambient light, in order to prevent the flash overpowering the ambient. This gives a balanced light which looks natural while still adding flash light to dark/shadow areas.
The control of the flash is acheived by cutting off the flash when enough flash light has illuminated the scene.
If you use Exposure Compensation the camera may be adjusting this Fill Flash and leaving Shutter Speed, Aperture & ISO alone.
AFAIK this only occurs in Matrix Mode so if you change to Spot Mode you should see the Shutter Speed change if you are in Aperture Priority.
 
I think between you chaps the solution is there somewhere.

Without the flash, adjusting the EC when in aperture priority does indeed reduce / increase the shutter speed.

With the flash switched on, adjusting the EC does not actually change the shutter speed nor ISO. Yet, the image is visibly brighter / darker. This must therefore come from the power emitted from the flash. However, this is not indicated on the EXIF data other than showing the EC has been altered +/- 2 EV.

When i adjust the Flash compensation this is actually shown on the EXIF as built in flash, TTL +/- 1.

As a reply to Kev, this happens in matrix, centre weighted and spot metering modes.

So, there we have it. It must be changing the light emitted from the flash unit
 
You must log in or register to reply here.
Back
Top