# Trying to figure our the required ND

Started 2 months ago | Discussions thread
Re: Trying to figure our the required ND
2

JohnPhotoP wrote:

Hi guys,

I'm new to video and I understand I need an ND filter for the 180 rule.

I'm currently using a Full Frame and wish to shoot on apertures between 1.8-4.0.

If I understand correctly, each stop of light of an ND filter equals to 1/f of the aperture?

For example If i was filming in F/14, in order to not change shutter/ISO settings, and to film in f/4, I have to get a 10 stops ND filter, correct?

I don't understand why in this video:

At 4:20 he is using:

f/14, ISO 100, shutter speed 1/50

And at 5:47 he got a DARKER image, when using
f/4, ISO 100, shutter speed 1/50 and a 5 stops filter
Shouldn't it be equal to 4 + 5 = 9? how is it darker than the f/14?

Also, which ND would you suggest me using for 1.8-4.0/f at bright sunlight? 6-9 VND?

Thanks!

Five stops darker than f/4 is f/22. So shooting at f/4 with a five-stop ND filter would be darker than f/14 (with no ND filter).

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