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ND2 and ND4?


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#1 James Steven Beverly

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Posted 26 April 2008 - 01:08 AM

I know the 3 primary ND filters are ND3, ND6 and ND9, of which I have an ND3 and ND6 (still need a 9). Are ND2s and ND4s ever used on movie cameras? If so when and why are 3,6 and 9s more common and if not, why not? Thanks-Steve
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#2 Jonathan Bowerbank

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Posted 26 April 2008 - 02:08 AM

ND's .3, .6 and .9 are in full stop increments, so they're just easier to work with. So having those three, you're well taken care of as far as ND's go.

They're mainly used if you wanna be able to work at a lower f-stop and maintain a shallow depth of field while staying within the mid to lower range of the lens' iris.
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#3 Satsuki Murashige

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Posted 26 April 2008 - 02:29 AM

James, are the filters you're referring to possibly NDx2 and NDx4 and not ND.2 and ND.4? I've never come across the latter, but occasionally come across the former for newer filters that are made for still photography use. A filter marked NDx2 refers to it's filter factor - a x2 filter factor means the filter cuts light transmission by 1/2 (or 1 stop). Thus, it is the same thing as an ND.3 or ND 0.3 (sometimes incorrectly referred to ND3). An NDx4 filter would cut light by 1/4, or 2 stops. This is the same as an ND.6. I don't think I'm alone when I say that this is extremely confusing!

Edited by Satsuki Murashige, 26 April 2008 - 02:30 AM.

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#4 David Auner aac

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Posted 26 April 2008 - 02:32 AM

Second that. I have never seen .2 or .4 but ND2 and ND4 are quite common in still photography, IIRC I have a couple of these sitting somewhere around here (52mm NDs for my Nikkors).

Cheers, Dave
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#5 Jonathan Bowerbank

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Posted 26 April 2008 - 02:51 AM

Just lookin' at B&H, they do seem t come in 4x4 & 4x5..65, etc

So I guess they're only really useful if some DP is REALLY particular about the grades of ND he/she wants on hand.
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#6 Satsuki Murashige

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Posted 26 April 2008 - 03:11 AM

So I guess they're only really useful if some DP is REALLY particular about the grades of ND he/she wants on hand.

Yeah, because making us ACs juggle another filter makes so much more sense economically than just stopping the lens up or down by 1/2 a stop. :P Maybe they're for student DPs who insist that the lens stop must always, ALWAYS be T4!
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#7 Damien Bhatti

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Posted 26 April 2008 - 10:16 AM

James, are the filters you're referring to possibly NDx2 and NDx4 and not ND.2 and ND.4? I've never come across the latter, but occasionally come across the former for newer filters that are made for still photography use. A filter marked NDx2 refers to it's filter factor - a x2 filter factor means the filter cuts light transmission by 1/2 (or 1 stop). Thus, it is the same thing as an ND.3 or ND 0.3 (sometimes incorrectly referred to ND3). An NDx4 filter would cut light by 1/4, or 2 stops. This is the same as an ND.6. I don't think I'm alone when I say that this is extremely confusing!


actually i picked up a x4 from a strange lot i won on ebay - for my bolex, i want to get some really shallow depth of field with it, so open up 2 stops should do the trick?/ how does cutting the light by a 1/4 correspond to the 2 stops lost?/ would a filter cutting the light by 1/2 = 4 stops loss? thanks
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#8 Chris Keth

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Posted 26 April 2008 - 10:49 AM

actually i picked up a x4 from a strange lot i won on ebay - for my bolex, i want to get some really shallow depth of field with it, so open up 2 stops should do the trick?/ how does cutting the light by a 1/4 correspond to the 2 stops lost?/ would a filter cutting the light by 1/2 = 4 stops loss? thanks


Hi, Damien. The NDx4 corresponds exactly with opening the lens by two stops. A 1 f/stop changes represents either halving or doubling the amount of light that reaches the film.

The NDx4 will quarter the amount of light (L/4) and you counteract this for exposure by opening 2 stops, or doubling the light twice (Lx2x2=Lx4).
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#9 Damien Bhatti

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Posted 26 April 2008 - 11:08 AM

Hi, Damien. The NDx4 corresponds exactly with opening the lens by two stops. A 1 f/stop changes represents either halving or doubling the amount of light that reaches the film.

The NDx4 will quarter the amount of light (L/4) and you counteract this for exposure by opening 2 stops, or doubling the light twice (Lx2x2=Lx4).


hey there - thanks, you know my maths is awful so any talk of fractions etc i run away//!but i think the penny hath dropped
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#10 Leo Anthony Vale

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Posted 26 April 2008 - 01:28 PM

ND's .3, .6 and .9 are in full stop increments, so they're just easier to work with. So having those three, you're well taken care of as far as ND's go.


It's a logarithmic scale. Every 0.3 doubles in value. It's the the same scale that's used for the exposure
scale on a characteristic curve.
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#11 Jonathan Bowerbank

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Posted 26 April 2008 - 08:45 PM

Yeah, because making us ACs juggle another filter makes so much more sense economically than just stopping the lens up or down by 1/2 a stop. :P Maybe they're for student DPs who insist that the lens stop must always, ALWAYS be T4!


Ha ha, good one Sats. I remember in lighting classes some students being so concerned with having to stop down or open up just fractions of a stop, beginners insecurity I guess...funny how everyone seemed to like T4 :/
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#12 Chris Keth

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Posted 26 April 2008 - 08:53 PM

hey there - thanks, you know my maths is awful so any talk of fractions etc i run away//!but i think the penny hath dropped


I suggest you get comfortable with at least a little math. A lot of things will be much easier if you can do the calculations in your head.
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#13 Satsuki Murashige

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Posted 28 April 2008 - 05:41 PM

...funny how everyone seemed to like T4 :/

Because the only lenses we had access to back then only started to get really sharp around T4...
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#14 Michael Collier

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Posted 28 April 2008 - 06:23 PM

I had a kit once that only had an ND8, when I needed ND9. Took a bit of work with the light meter, but found its 2 2/3 stop loss. I assume there are filters ND1-ND9, each incriment being 1/3 of a stop. I haven't run into any oddball ND filters since then however to confirm that assumption. Like Satsuki says, there normally no pressing need to be so inflexible, especially with all the other pressing matters at hand. Maybe when I have bigger crews I will call for an ND8, but it would only to establish my reputation as a tyrant. :P
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#15 Dominic Case

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Posted 28 April 2008 - 08:47 PM

You can (or could) get gelatin Wratten filters in 0.10ND increments - traditionally used in the lab for fine-tuning the light balance on printers.

Correct, every 0.10ND is one third of a stop.

As for maths, I posted this message last week - it summarises all the different scales that affect exposure.
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