effect of an nd filter

[albedo_0_39]

hello all. I am a beginner and I have a little perplexed by filters. Can someone please help me?. Assuming I have a shot of a sunny landscape (without filters) such that the sun is out, sky is blue, green fields etc. Now if I take a 'snap' of the view and then take the same view with an Nd4 grad filter (grey) added over the sky part. what exactly would be the result with respect to the difference in the general exposure value between them both?

thanks in advance
Gaz

[theMusicMan]

ND filters as far as I am aware, simply lower the amount of light entering the camera and thus they affect a combination of the exposure, aperture value and shutter speed.

With a grad ND, it depends where you are taking your meter reading from. If from the bottom of the image, then the sky will appear darker and the bottom of the image will be correctly exposed.

[Messiah Khan]

If the settings were left the same as the shot without the ND grad, you would end up with a picture where the sky was darker. If the shot was balanced to begin with, ie the sky was a perfect blue and the ground a perfect green then there wouldn't be much need to use a ND grad filter. However if the origional shot resulted in the ground being perfect, but the sky far too pale or even blown out then this is where you would use a ND grad to balance the exposure. Hope that helps.

[milou]

Grads are sunglasses for the sky: http://www.leefilters.com/CPEF.asp?PageID=77

[albedo_0_39]

ah ok. so, if an nd filter was used for the shot, such as an ND4 grey grad filter, this would slow down the light getting into the shot from the sky area. presumably, this would have teh same effect as dropping an aperture setting of f4 to f16 for the sky area only ?

Gaz

[Messiah Khan]

ah ok. so, if an nd filter was used for the shot, such as an ND4 grey grad filter, this would slow down the light getting into the shot from the sky area. presumably, this would have teh same effect as dropping an aperture setting of f4 to f16 for the sky area only ?

Gaz

Thats correct. Sometimes you get scenes with a dynamic range (The difference between the blackest black and the whitest white) too wide to capture on a camera sensor, so you need to use tricks such as a ND filter to reduce this dynamic range and end up with a well exposed scene.

[CT]

ah ok. so, if an nd filter was used for the shot, such as an ND4 grey grad filter, this would slow down the light getting into the shot from the sky area. presumably, this would have teh same effect as dropping an aperture setting of f4 to f16 for the sky area only ?

Gaz

You've got the general idea Gaz, you're just a bit out with the maths.

An ND4 filter means it has a filter factor of X4, in other word it will increase exposure time by 4 times, so in the example you give, it would be the equivalent of changing to f8, not f16.

Have a read of this article which will probably help. :)

CLICK (http://www.ephotozine.com/article/Using-a-Neutral-Density-filter)

[Messiah Khan]

You've got the general idea Gaz, you're just a bit out with the maths.

An ND4 filter means it has a filter factor of X4, in other word it will increase exposure time by 4 times, so in the example you give, it would be the equivalent of changing to f8, not f16.

Have a read of this article which will probably help. :)

CLICK (http://www.ephotozine.com/article/Using-a-Neutral-Density-filter)

That's one area I still get confused with. What are the 'full' stops? 2.8, 4, 5.6, 6.3?...

[CT]

2.8, 4. 5.6, 8, 11, 16, 22, 32.

You can go further at either end. :)

[moomike]

Whilst on the subject of apertures, I thought I'd share a really easy way to memorise apertures that I use.
Just times the alternate apertures by two to arrive at the next number.

http://www.talkphotography.co.uk/gallery/data/1154/Aperture_guide.jpg

Never know when it could come in useful (makes me almost sound like I know what I'm talking about too :lol:)

[jork45]

Good thread guys,it helped explain things,:thumbs: