Neutral Density Filter for D90

[banksy]

Hi everyone,

Can anyone please explain the difference between ND4 and ND8 in these filters? Thanks

[tclune]

ND4 provides 2 full f-stops worth of light reduction (one quarter the unfiltered light); ND8 provides 3 full f-stops worth of light reduction (one eighth the unfiltered light).

[banksy]

Thanks for the post.
I am a newbie at this - would D4 be used when you need a little more light and D8 when you need more light (eg dusk or early morning)?
We want to photograph waterfalls and ocean surf. Cheers

[TCav]

Can you not get the shots you want now?

Can you post some samples of what you are getting?

[frank-in-toronto]

I can see how you can get confused. The first link that shows up using google is
http://www.cs.mtu.edu/~shene/DigiCam...filter-ND.html
and, oh boy, do they make it difficult. perhaps the to and fro here will make it clearer for you.

tclune said it exactly. then your reply showed up. you appear to have things backwards. lemmee try.

waterfalls. you're looking for a slow shutter speed to give that blurred effect. so perhaps 1/15 second. on a bright day at iso100 you'll be somewhere near 1/125 at f16. you'll need to slow down the shutter. if you can stop down further, that'll help. say 1/50 at f22. still too fast. add an ND4. That's 2 stops. so 1/10 or so at f22. might be ok. an ND8 instead would allow you to use 1/5 at f22.

see? the additional ND filter in front of the lens allows you to keep the shutter open longer and still obtain correct exposure.

if you haven't got the nd filters yet, you might like to investigate the cokin system. i got that as it allows me to have up to 3 filters in front of the lens. i like fewer restrictions and i really don't like screwing filters on and off. they get stuck or my finger will smudge one.

the shutter speed to use actually is open to debate and experiment. some suggest 2 seconds even. it'll depend on the effect you're looking for, speed of the water etc. while you're set up on your tripod using mirror lock up or remote release or self timer, take varying exposures. review later and see how things look.

hmmmmmmm. i don't know if what i typed helps. what do you think?

[banksy]

Thanks TCav. I will trawl through our photos and attempt to upload a couple.

[banksy]

Thanks frank-in-Toronto, we will look into this.

[banksy]

TCav here are a couple of photos I thought might be better with a filter??

[rjseeney]

Originally Posted by banksy

TCav here are a couple of photos I thought might be better with a filter??

ND filters will allow you to use longer shutter speeds by reducing the amount of light entering the lens to give moving water the silky look. This is especially helpful on bright days. Another advantage is they also allow you to use larger apertures on bright days to give a smaller DOF to isolate your subject from the background (the blurred background effect). So to address your earlier question, you'd use ND filters when you want to reduce the amount of light, not when you need a little more light.

One caveat...when using more aggressive nd filters you will likely need to use a tripod

[banksy]

Wonderful information.
Thank you to everybody for their posts - this is a great forum!