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85+ND3 filter?


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#1 Richard Vialet

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Posted 14 October 2005 - 01:06 AM

Alright, I don't want to be hoodwinked...!!!

I'm a film student in DC and im shooting a project this weekend...the director is really putting his confidence in me and I don't wanna mess anything up! I've reserved a set of 85 and ND filters from the school (shooting 7218 500T)...one of the filters is an 85+ND3 filter, now from research I know that the 85 filter cuts down 2/3 of a stop and an ND3 cuts 1 stop. So I concluded that using this combined filter, I would add these two factors together and get a 1 and 2/3 stop cut off. But the equipment guy at school told me that the 85+ND3 filter cuts down 1 stop of light (that the combined factors of the filter just added up to 1 stop)

Now I just read on the kodak website that 85ND3 cuts down by 1 and 2/3...whew!!!

So, I just wanna know from all you great DP's...how much light does this filter really cut?

And also how would I calculate the factor by doubling up and using a seperate 85 and seperate ND filter on the lens?
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#2 Dominic Case

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Posted 14 October 2005 - 02:14 AM

Very easy!

You add the ND values of all the filters together: or you ad the stop-correction values of them all together.

An 85 is indeed worth 2/3 stop. AN ND3 (0.30neutral density) is worth one stop.

An 85N3 is therefore worth one and two-thirds stops.
An 85 and a separate ND3, put together, are worth 1 2/3 stops.

But be careful. Another way of thinking of the effec of the 85 colour temperature filter is to consider the EI rating of the film emulsion.

You are shooting 7218 which is rated at 500EI in tungsten light. In daylight, WITH AN 85 on the lens, you rate it at 320EI. (That is, it's 2/3 stop slower). You don't correct twice. That's what your equipment guy was thinking of.

In practical terms, let's say you set your meter to EI500. If you shoot with an 85, you need to open up 2/3 stop from the meter reading. If you shoot with a 85N3, open up 1 2/3 stops from the meter reading.

Alternatively, set the meter to 320EI and expose exactly as it says, if you use a plain 85.
And set the meter to 160EI and expose exactly as it says if you use the 85N3.
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#3 Max Jacoby

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Posted 14 October 2005 - 03:06 AM

To find out how much you have to compensare for each filter, simply take an incident light reading, then put the filter in front of the lightmeter and take another reading. The difference will be how much light the filter cuts.

Simple as that.
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#4 Richard Vialet

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Posted 14 October 2005 - 09:11 AM

Thanks guys!!! I thought you would just add the values together, but i was starting to get confused, but thanks for great replies!

Annd audiris, wow i never even thoguht about that test, thanks alot!

Richard
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#5 dbledwn11

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Posted 17 October 2005 - 12:58 PM

Very easy!

You add the ND values of all the filters together: or you ad the stop-correction values of them all together.

An 85 is indeed worth 2/3 stop. AN ND3 (0.30neutral density) is worth one stop.

An 85N3 is therefore worth one and two-thirds stops.
An 85 and a separate ND3, put together, are worth 1 2/3 stops.

But be careful. Another way of thinking of the effec of the 85 colour temperature filter is to consider the EI rating of the film emulsion.

You are shooting 7218 which is rated at 500EI in tungsten light. In daylight, WITH AN 85 on the lens, you rate it at 320EI. (That is, it's 2/3 stop slower). You don't correct twice. That's what your equipment guy was thinking of.

In practical terms, let's say you set your meter to EI500. If you shoot with an 85, you need to open up 2/3 stop from the meter reading. If you shoot with a 85N3, open up 1 2/3 stops from the meter reading.

Alternatively, set the meter to 320EI and expose exactly as it says, if you use a plain 85.
And set the meter to 160EI and expose exactly as it says if you use the 85N3.



hi dominic,

i understand the explaination but i was just wondering if you could clarify the maths involved. i can't quite figure the equation. the way i see it is as follows:

500ei/0.64 (2/3rd stop change) = 320ei (if using an 85filter)

but i can't quite work out how to apply the equation to your 2nd example of 160ei if using 85n3 filter(1and2/3 stop change). my maths isn't too good.

also i was wondering why you set a preference for changing the meter ei setting rather than leaving it rated 'normal' (i.e. 500 or 320 depending on stock) and adjusting the stop from this reading???

any help appreciated.
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#6 John Pytlak RIP

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Posted 17 October 2005 - 03:11 PM

hi dominic,

i understand the explaination but i was just wondering if you could clarify the maths involved. i can't quite figure the equation. the way i see it is as follows:

500ei/0.64 (2/3rd stop change) = 320ei (if using an 85filter)

but i can't quite work out how to apply the equation to your 2nd example of 160ei if using 85n3 filter(1and2/3 stop change). my maths isn't too good.

also i was wondering why you set a preference for changing the meter ei setting rather than leaving it rated 'normal' (i.e. 500 or 320 depending on stock) and adjusting the stop from this reading???

any help appreciated.


Just take it in two steps:

The 85 filter has a 2/3 stop filter factor: EI-500 becomes EI-320.

The 0.3 ND is another stop: EI-320 becomes EI-160.

Remember, EI (exposure index) is normally specified in 1/3 stop increments:

25
32
40
50
64
80
100
125
160
200
250
320
400
500
640
800
1000

(every third number is a full stop, and therefore twice the EI)

If you set the meter to the effective EI for the film with the filter in place, you don't need to calculate the exposure change for each meter reading, since you've already "derated" the film for the filter factor.
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#7 Tom Yanowitz

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Posted 19 March 2015 - 07:13 AM

Hello everyone,

I re-up a topic that's 10 years old !

 

So, I have some 85 filters for a 35mm outdoor shoot at my school and decided to spot meter them.

Found this :

 

Filter, expected loss, measured loss :

  • 85, 2/3, 2/3 (6 tenth on the meter)
  • 85N3, 1+2/3, 1+2/3 (1 stop + 5 or 6 tenth)
  • 85N6, 2+2/3, 2+1/2 (2 stops + 5 tenth)
  • 85N9, 3+2/3, 3+1/3 (3 stops + 3 or 4 tenth)

 

What do you is more probable in that sort of test : the filter is "off", or I failed at measuring them properly ?

I can't remember the brand of the filters.

 

Thanks guys !


Edited by Tom Yanowitz, 19 March 2015 - 07:16 AM.

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