More ND Filter Questions

[AdamIsMyName]

So Ive been doing some research on ND and graduated ND filters since I'd like to start trying long exposure / landscape photography.

Can anyone explain what the different filter levels are used for / which would I actually need.

I've already come to the conclusion a 10 stop filter would be ideal for long exposure (minutes) to create a very silky water.

What are the 2 thru 9 stop reductions good for? An example of what you might use a 2, 4, 6, etc. for to achieve what type of affect would be very helpful.


I also ordered myself a cheap ND8 filter to test with (hasnt arrived yet)

Wikepedia had this chart that says a ND8 is a 3 stop reduction?

[TABLE="class: wikitable, width: 485"]
[TR]
[/TR]
[TR]
[TD]1/2[/TD]
[TD]0.3[/TD]
[TD]1[/TD]
[TD]50%[/TD]
[/TR]
[TR]
[TD]ND8 - 1/8[/TD]
[TD]0.9[/TD]
[TD]3[/TD]
[TD]12.5%[/TD]
[/TR]
[TR]
[TD]1/16[/TD]
[TD]1.2[/TD]
[TD]4[/TD]
[TD]6.25%[/TD]
[/TR]
[TR]
[TD]1/32[/TD]
[TD]1.5[/TD]
[TD]5[/TD]
[TD]3.125%[/TD]
[/TR]
[TR]
[TD]1/64[/TD]
[TD]1.8[/TD]
[TD]6[/TD]
[TD]1.563%[/TD]
[/TR]
[TR]
[TD]1/128[/TD]
[TD]2.1[/TD]
[TD]7[/TD]
[TD]0.781%[/TD]
[/TR]
[TR]
[TD]1/256[/TD]
[TD]2.4[/TD]
[TD]8[/TD]
[TD]0.391%[/TD]
[/TR]
[TR]
[TD]1/512[/TD]
[TD]2.7[/TD]
[TD]9[/TD]
[TD]0.195%[/TD]
[/TR]
[TR]
[TD]1/1024[/TD]
[TD]3.0[/TD]
[TD]10[/TD]
[TD]0.098%[/TD]
[/TR]
[TR]
[TD]1/2048[/TD]
[TD]3.3[/TD]
[TD]11[/TD]
[TD]0.049%[/TD]
[/TR]
[TR]
[TD]1/4096[/TD]
[TD]3.6[/TD]
[TD]12[/TD]
[TD]0.024%[/TD]
[/TR]
[TR]
[TD]1/8192[/TD]
[TD]3.9[/TD]
[TD]13[/TD]
[TD]0.012%[/TD]
[/TR]
[/TABLE]




So does this mean the ND8 filter I bought is actually a 3 stop reduction, and not close to a 10 stop filter?


How about stacking filters? - ND filter / graduated filter / polarizing filter (just for getting rid of reflections?)
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(Sorry for the screwy charts - tried copying and pasting and though it looked right initially it saved weird and I cant delete them... )

 

[paul85224]

I use an ND .9 for waterfalls and the like....it seems to work well.

 

[Big Mike]

Yes, I do believe that an ND8 is a three stop reduction. And in many cases, that should be plenty.

There is no formula for what you have to use in a certain situation. It will depend on the light that you are shooting in, at the time. For example, in the middle of the day, you might want 3, 4 or 5 stops of filtering...but if you just come back in the evening, you may not need a filter as all.

Also, keep in mind that there are three things that affect exposure. The shutter speed, the aperture and the ISO. So if it's your creative goal to use a long shutter speed, you can work toward getting a proper exposure by using a low ISO and/or a smaller aperture. For example, at ISO 100 and F22, your shutter speed is going to be slow in just about any lighting condition, without any filters. Add filters to that and you can get a really slow shutter speed.

When I am shooting running water, and want to get that 'ribbon' effect, I use a circular polarizer and an ND filter (ND4 I think).

Waterfalls ~ Mike Hodson Photography