measuring ND filter value in stops

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#1 Christian Schonberger

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Posted 25 March 2016 - 10:20 AM

Hi group members,

Just a quick question: My K-3 is finally on its' way (after customs paperwork). It comes with all the usual filters. One is very important for me: the ND filter. Here in Portugal sunlight is very bright and intense.

I couldn't find any information about how many stops I will 'lose' with the neutral density filter. Online translated K-3 instructions only mention the filter, but no value is provided.

I thought about using the spot metering in my analog Sekonic, pointing it at a bright wall (or various objects for that matter) and compare the f-stop readings with and without the filter held over the meter. Does this method work?

Any input highly appreciated,

Christian

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#2 Jay Young

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Posted 25 March 2016 - 10:29 AM

Yes, that method will work: hold the filter in front of a spot meter.

I believe that ND filter in the set is ND.6 (2 stop reduction) but my memory is a bit fuzzy on that subject.

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#3 Christian Schonberger

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Posted 25 March 2016 - 10:37 AM

Yes, that method will work: hold the filter in front of a spot meter.

I believe that ND filter in the set is ND.6 (2 stop reduction) but my memory is a bit fuzzy on that subject.

Thanks Jay!

Didn't know about the ND value numbers (.6 = 2 stop reduction). Will look into that.

Two stop reduction would be just perfect.

Thanks again,

Cheers,

Christian

Edited by Christian Schonberger, 25 March 2016 - 10:39 AM.

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#4 Ari Michael Leeds

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Posted 25 March 2016 - 11:18 AM

Basically the number that follows the "ND" drops the period/full stop or comma depending on the language and the leading zero.

ND [0.]3

ND [0.]6

etc.

What this refers to is transmission value.  Status A transmission goes down 50% (or 1 f/stop) every 0.3 of visual density increase in a filter.

Just a different scale way of saying the same thing.

Also, 0.15 is a half stop, 0.1 is a third of a stop.

Hope this helps!

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#5 John E Clark

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Posted 25 March 2016 - 11:28 AM

I have seen two ways that ND filters are listed... one is the 'log' method where .3 differences correspond to 1 stop, and one in terms of powers of 2... so ND2 is 1/2 or one stop... ND4 is 1/4 or two stops... etc.

As a note, for some digital cameras, as one increases the ND factor, one may experience Infrared 'pollution' as many ND filters are not IR filters as well, so for higher values of ND, one may have to spend more to get ND + IR filtration.

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#6 Christian Schonberger

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Posted 25 March 2016 - 01:53 PM

Ari and John: Thanks a lot for the information. Great!

Well I can see a system here: The old DIN standard for film sensibility uses an increase by three whole numbers for each stop: 100 ASA = 21 DIN.  200 ASA = 24 DIN (one stop gained).

Yep, the UV and IR issues. Will need to check with the film stocks I am planning to use (not that much choice anyway as we speak). Got 3x 100ft  E 100D (E-6) in my fridge - waiting to be used for something more than just test footage... Quite the challenge nailing the exposure with reversal stocks (moving images!). Let's see how it turns out.

Thanks a lot,

Christian

Edited by Christian Schonberger, 25 March 2016 - 01:54 PM.

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#7 Ari Michael Leeds

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Posted 25 March 2016 - 02:37 PM

Yes, that's right, Christian.

10 12.5 16 20 25 32 40 50 64 80 100 is the ASA progression.

Then DIN is every 3 is a stop.

This 0.3 is a stop.

With E6 you don't need to worry about IR (it doesn't see it) just UV.  A standard UV filter works great, and think they have some that may combine that with other filters, so you don't have to stack too many.

If you get UV that mostly just shows up as exaggerated blues (they see UV but you end up with cyan + magenta = blue dyes rendering it).  So you won't have to worry about IR filtration with ND filters.

I will say that, some NDs are better than others.  I'm lucky, I have a densitometer so I can actually read them to see if they are purely neutral, same with gelatins.

So just a standard UV will work fine for you, and ND filters you'll have no issues as-is.  Good luck.

And thanks, John E. Clark, for pointing out what I shouldn't have left out.

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#8 John E Clark

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Posted 25 March 2016 - 04:20 PM

With E6 you don't need to worry about IR (it doesn't see it) just UV.

I didn't pick up on K-3 in the original post... must mean Krasnogorsk-3... a 16mm film camera... so yeah, UV is the thing to protect for in Film film cameras... whereas for current digital cameras IR is a more prevelant polluting part of the spectrum.

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#9 Christian Schonberger

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Posted 25 March 2016 - 05:28 PM

I didn't pick up on K-3 in the original post... must mean Krasnogorsk-3... a 16mm film camera... so yeah, UV is the thing to protect for in Film film cameras... whereas for current digital cameras IR is a more prevelant polluting part of the spectrum.

Yep, the Krasnogorsk-3. It's meant to be my entry model. Let's see. Opinions are mixed and I know its limitations all too well. If excessive UV radiation alters the film's hue, it can be re-graded in post (I know, film is about getting it right in-camera). I will delve a little deeper into UV protection. Summers are hot where I live (Portugal, Atlantic coast) and UV radiation is strong here.

Cheers,

Christian

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