ND Filters?

hschlessphoto · December 1, 2008

So i want to get an ND filter for chrsitmas...but I am not sure what grade (or whatever the term is) I should get. .3, .6, .9? I see that as the number gets greater the filter gets darker, but how does it effect the actual outcome on the photo? does it make skies darker? water darker? Thanks so much.

-Hank

ziggy53 · December 1, 2008

hschlessphoto wrote:

So i want to get an ND filter for chrsitmas...but I am not sure what grade (or whatever the term is) I should get. .3, .6, .9? I see that as the number gets greater the filter gets darker, but how does it effect the actual outcome on the photo? does it make skies darker? water darker? Thanks so much.

-Hank

Ideally, a Neutral Density (ND) filter affects all light wavelengths equally. While it will affect the exposure of the skies, it will do it at the same rate as the rest of the image.

Commonly, an ND filter is used to reduce the effective sensitivity of the host camera and lens. Reasons to do this:

To allow a reduced DOF at a given exposure by allowing a larger aperture.
To allow a longer shutter duration which tends to smooth moving water and, at the extreme, may even allow moving subjects in a scene to "disappear".

If you want to selectively darken skies or reduce the reflection of water and glass, you are looking for a "polarizer", typically a circular polarizer (to preserve the proper operation of exposure and AF systems.)

catspaw · December 1, 2008

to add to this, some folks will get fewer ND filters and 'stack' them to get a darker filter. So rather than getting a .3 .6 and .9, you'd get a .3 and .6 and when you want a .9, just use both at once (.3 + .6 = .9)

Scott_Quier · December 1, 2008

The snide comment would be .... are you ready for it? .... "If you don't know what they do, why do you want one?"

OK, now that I have that out of my system

, here's your answer... The ND is a Neutral Density filter, meaning that it blocks light of all (visible) wave lengths equally. So that implies that there will be no color shift when one is used. They are most often used to cut the amount of light entering the lens, thus allowing the photographer to keep ISO and shutter speed constant and opening up the lens; opening the lens creates a shallower depth of field (all else held constant) or to slow the shutter so you can get creamy water in rapids.

The numbers represent how much light is blocked, with 0.3 == 1 stop, 0.6 == 2 stops, 0.9 == 3 stops. So if your exposure without the filter in place is ISO 100, f/8, 1/100 ... when you use the 0.3 filter your exposure would need to be ISO 100, f/5.6, 1/100 (for example) or ISO 100, f/8, 1/50.

hschlessphoto · December 1, 2008

thank you all so much for your answers. My one last question is if I can stack a polarizer with the ND filter? I assume I can...but just to clarify.

RogersDA · December 1, 2008

You can stack them assuming that they are the same size (unless you want to hand-hold the filters - which can be done for large plate filters for reasonably short exposures

). Note also that stacking of filters increases the risk of light artifacts that can show up due to the increased number of optical elements that the light is traveling through.

Also, it may be harder to see the effect of the polarizing lens when stacked with darker ND filters. You may have to compose and focus first, add and adjust the polarizing filter, then then add the ND filters. The more light you block the harder it will be for the camera's auto-focus to operate (in my experience).

cjmchch · December 1, 2008

I'm looking to purchase an ND2 and ND400, Given the lens I want them for (Canon EFS10-22) I can only really use one at a time, thus the ND400

hschlessphoto · December 1, 2008

thank you all so much for your help! I really appreciate all of the input you guys could give.

ND Filters?

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