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A Question about NDs


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#1 Andy_Alderslade

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Posted 04 December 2005 - 05:42 PM

I've just finished filmschool several months ago where I was taught that in reducing light NDs worked as:

ND 3 = 1 stop, ND 6 = 2 stops, ND 9 = 3 stops

The other day I was doing focus pulling/ac on a short film shoot for one of the UKs best film schools on super 16, when we needed to reduce light input by another two stops. We already had an ND 3 in the Aaton's matt box and I was going to insert the ND 6 in the free slot.

However one of the school's tutors (a directing teacher) was supervising and told me to take out the ND 3 and use the ND 9 alone, saying that each filter alone added another half stop and using two together would take out an additional stop.

Was he right? Or am I completly lost?

Please Help :blink:
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#2 Hans Engstrom

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Posted 04 December 2005 - 06:06 PM

Never heard that one before. I often use several ND´s together and have never calculated in loosing any extra light based on that.
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#3 Brad Grimmett

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Posted 04 December 2005 - 06:31 PM

However one of the school's tutors (a directing teacher) was supervising and told me to take out the ND 3 and use the ND 9 alone, saying that each filter alone added another half stop and using two together would take out an additional stop.

Was he right? Or am I completly lost?

Please Help :blink:

He was wrong. At least he was wrong for the reason he gave you. But it is a good idea to cut down on how many layers of glass you put in front of the lens. The more layers of filters the more chance you'll have flares or reflections. I don't know where he came up with the extra 1/2 stop thing......never heard that one before.
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#4 Andy_Alderslade

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Posted 04 December 2005 - 06:49 PM

Phewwww! I hate it when you find out you've given false information.

Cheers Hans and Grimmett

Now I can sleep... actually i only thought of putting the extra ND 6 joint with the ND3 because the sun was behind a cloud and knew when it was out again we would only need the ND3 alone - dam that british weather

Thanks
Andy
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#5 Chris Keth

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Posted 04 December 2005 - 09:40 PM

The two options really should cut the same amount of light. On the other hand, it's really better to only have one place of glass in front of your lens than to have two. Also, having 2 pieces of glass increases the chance of having nasty reflections, bad lens hits, etc. So, what he told you was good in practice but not for the reason he gave.
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#6 beanpat

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Posted 05 December 2005 - 03:09 AM

I've just finished filmschool several months ago where I was taught that in reducing light NDs worked as:

ND 3 = 1 stop, ND 6 = 2 stops, ND 9 = 3 stops

The other day I was doing focus pulling/ac on a short film shoot for one of the UKs best film schools on super 16, when we needed to reduce light input by another two stops. We already had an ND 3 in the Aaton's matt box and I was going to insert the ND 6 in the free slot.

However one of the school's tutors (a directing teacher) was supervising and told me to take out the ND 3 and use the ND 9 alone, saying that each filter alone added another half stop and using two together would take out an additional stop.

Was he right? Or am I completly lost?

Please Help :blink:

That doesn't make any sense. except as mentioned, only the reflection problems. you can easily verify whats happening by shining a light source towards a light meter and placing filters in front of it and then you'll instantlly see how many stops you are loosing.
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#7 Stephen Williams

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Posted 05 December 2005 - 03:14 AM

I've just finished filmschool several months ago where I was taught that in reducing light NDs worked as:

ND 3 = 1 stop, ND 6 = 2 stops, ND 9 = 3 stops



Hi,

Be very careful if you work with people who shoot timelapse. ND 3 is 10 stops not 1! You mean ND 0.3!

Stephen
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#8 Andy_Alderslade

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Posted 05 December 2005 - 06:19 AM

Hi,

Be very careful if you work with people who shoot timelapse. ND 3 is 10 stops not 1! You mean ND 0.3!

Stephen


I follow, I learnt that when learning how to use a contact printer and noticed the ND 3 i was familiar with was the same as ND 0.30 for the contact printer.... for some reason the camera filter kits i've seen have always been labled ND 3, ND 6, ND 9
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#9 Kevin Zanit

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Posted 05 December 2005 - 06:51 AM

I can third (or fourth) the above. Misinformation.

I tend to try and use less glass as a rule.
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#10 Stephen Williams

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Posted 05 December 2005 - 09:06 AM

I follow, I learnt that when learning how to use a contact printer and noticed the ND 3 i was familiar with was the same as ND 0.30 for the contact printer.... for some reason the camera filter kits i've seen have always been labled ND 3, ND 6, ND 9


Hi,

I was recently working with a 1st, I asked for a ND 3, he put a 3 on and smiled!

Stephen
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#11 John Pytlak RIP

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Posted 05 December 2005 - 08:33 PM

Always go with as few filters in the image light path as possible -- they do add flare.

While NDs do generally add up in their effect (ND 0.3 + ND 0.6 = ND 0.9), in reality, there is additional slight light loss due to internal re-reflections between surfaces. Usually negligible, but that is the "lost" light that produces the flare.

Bottom line: Don't gang too many filters, if you have the ONE that does the job, use it.
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#12 Dominic Case

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Posted 05 December 2005 - 11:38 PM

for some reason the camera filter kits i've seen have always been labled ND 3, ND 6, ND 9

Not everyone can handle decimal points, so some people just discard them :(

Also, the combined colour temp & ND filters are called 85N3, 85N6 etc. That's a "name" not a specification, so they could call them what they like (85N1, 85N2 for one and two stops would be no more and no less confusing!)

A 3.0ND filter is pretty black - it cuts out 10 stops of light - so it's unlikely anyone would confuse it with a 0.30ND if they had their mind on the job.
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#13 Nick Mulder

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Posted 06 December 2005 - 06:30 AM

Polarizing filters can do odd things like this (and be used as simple ND as well) - but polarizing filters usually dont live in matte boxes, nor are they used much in cinematography (compared to stills, where I have more experience)
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#14 Mitch Gross

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Posted 06 December 2005 - 01:00 PM

I don't know where you got the idea that Polas are not used much in cinematography. Certainly they are not used as much as ND filters, but they are in just about every kit that I've ever seen.
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#15 David Mullen ASC

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Posted 06 December 2005 - 03:08 PM

I use Polas all the time when shooting movies outdoors.
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#16 Adam Frisch FSF

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Posted 06 December 2005 - 04:48 PM

My bare minimum filter kit usually consists of: 85, ND0.3,0.6,0.9 and ND0.9 Grad Hard Edge and Soft Edge (sometimes called blenders) plus a Polarizer. Without that I don't get out of bed... :D
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#17 Nick Mulder

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Posted 09 December 2005 - 12:39 PM

from what i've seen so far in cine/video work (which isnt very much at all) i have never seen one used - i should maybe have said 'not used as much as in stills' ... in my experience (which isnt very much at all) :huh:
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#18 Mitch Gross

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Posted 09 December 2005 - 05:43 PM

from what i've seen so far in cine/video work (which isnt very much at all) i have never seen one used - i should maybe have said 'not used as much as in stills' ... in my experience (which isnt very much at all) :huh:



No offense, but perhaps if you have not seen much at all and your experience isn't very much, the making of sweeping statements should be avoided.
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