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Working With Filters (1 reply and 3 comments)

Alex2II2
4 months ago
Alex2II2 4 months ago

Hi All,

I'm going to be DP'ing a film on 16mm, ASA 500, Tungsten stock soon, with some exteriors. I'll be using an 85 Filter to change the 3200K stock to 5500K. Here's where things get tricky for me...The 85 Filter has an ND factor of 2/3 (two thirds) of a stop - I'd like to expose everything at a constant T stop - either 2.8 or 4.0 depending on the day. 

I've tried to create a 'cheat sheet' for each possible aperture and the closest I can get to the desired stop.

I'm hoping someone can check my working - and correct me if i've made a mistake.

I'm sure it's obvious but for arguments sake i'll mention that the 85 ND.6 cuts out two and two thirds (2 2/3) of a stop, the 85 ND.3 cuts out one and two thirds (1 2/3) of a stop, the 85 filter cuts out two thirds (2/3) of a stop, and the pola filter i'll be using cuts out 2 stops.

So if I wanted to expose everything a T2.8 or as close as I can get with the filters I have, is the following correct?

The equation is: Correct Stop = (comes down to) New Stop - Filters Used

22 = 5.6 1/2 - 85 ND.6 & Pola

22 1/3 = 5.6 2/3 - 85 ND.6 & Pola

22 1/2 = 8.0 - 85 ND.6 & Pola

22 2/3 = 8.0 1/3 - 85 ND.6 & Pola

 

16 = 4.0 1/2 - 85 ND.6 & Pola

16 1/3 = 4.0 2/3 - 85 ND.6 & Pola

16 1/2 = 5.6 - 85 ND.6 & Pola

16 2/3 = 5.6 1/3 - 85 ND.6 & Pola

 

11 = 2.8 1/2 - 85 ND.6 & Pola

11 1/3 = 2.8 2/3 - 85 ND.6 & Pola

11 1/2 = 4.0 - 85 ND.6 & Pola

11 2/3 = 4.0 1/3 - 85 ND.6 & Pola

 

8 = 2.0 1/2 - 85 ND.3 & Pola

8 1/3 = 2.0 2/3 - 85 ND.3 & Pola

8 1/2 = 2.8 - ND.3 & Pola

8 2/3 = 2.8 1/3 - ND.3 & Pola

 

5.6 = 2.0 1/2 - 85 & Pola

5.6 1/3 = 2.0 2/3 - 85 & Pola

5.6 1/2 = 2.8 - 85 & Pola

5.6 2/3 = 2.8 1/3 - 85 & Pola

 

4 = 2.8 1/2 - 85

4 1/3 = 2.8 2/3 - 85

4 1/2 = 2.8 - 85 ND.3

4 2/3 = 2.8 1/3 - ND. 3

 

2.8 = 1.4 1/2 - 85 ND.3

2.8 1/3 = 1.4 2/3 - 85 ND.3

2.8 1/2 = 1.4 - 85 ND.3

2.8 2/3 = 1.4 1/3 - 85 ND.3

Like wise, if I wanted to expose everything at T4.0 or as close as I could get.

22 = 5.6 1/2 - 85 ND.6 & Pola

22 1/3 = 5.6 2/3 - 85 ND.6 & Pola

22 1/2 = 8.0 - 85 ND.6 & Pola

22 2/3 = 8 1/3 - 85 ND.6 & Pola

 

16 = 4.0 1/2 - 85 ND.6 & Pola

16 1/3 = 4.0 2/3 - ND.6 & Pola

16 1/2 = 5.6 - ND.6 & Pola

16 2/3 = 5.6 1/3 - ND.6 & Pola

 

11 = 2.8 1/2 - 85 ND. 3 & Pola

11 1/3 = 2.8 2/3 - 85 ND. 3 & Pola

11 1/2 = 4.0 - 85 ND . 3 & Pola

11 2/3 = 4.0 1/3 - 85 ND.3 & Pola

 

8 = 2.8 1/2 - 85 ND.6

8 1/3 = 2.8 2/3 - 85 ND. 6

8 1/2 = 4.0 - 85 ND.6

8 2/3 = 4.0 1/3 - 85 ND.6

 

5.6 = 2.8 1/2 - 85 ND.3

5.6 1/3 = 2.8 2/3 - 85 ND.3

5.6 1/2 = 4.0 - 85 ND.3

5.6 2/3 = 4.0 1/3 - 85 ND.3

 

4 = 2.0 1/2 - 85 ND.3

4 1/3 = 2.0 2/3 - 85 ND.3

4 1/2 = 2.8 - 85 ND.3

4 2/3 = 2.8 1/3 - ND.3

 

If anyone can manage to make sense of these ramblings and can help, i'l; be very grateful.

Thanks

Alex

dmullenasc
4 months ago
dmullenasc 4 months ago

It seems that you are giving a 1/2-stop loss for the 85 filter in some of these, not a 2/3-stop loss.   As for a Pola being a 2-stop loss, then if you combine it with an ND.3, for example, it's the same as using an ND.9 without a Pola.

Truth is that if you measure some of these filters, you find that an 85 loses a bit more then 2/3-stop and many Polas are more like 1.5-stops, not 2-stops... but color negative film has enough latitude to cover minor fractions of difference.

A good rule of thumb to remember is the "Sunny 16" rule, which states that the f/stop in direct sunlight on a clear day is f/16 when the shutter speed 1/x is the same as ASA rating of x.  So for 24 fps with a 180 degree shutter, which is 1/48th, you can round that up to 1/50th and say that with 50 ASA film, you'll be at f/16 in direct sunlight on a clear day (most meters give you around f/16.3-ish.)  It's just a rough guide but it gives you an indication of how much ND you'll need.

Alex2II2
4 months ago

Thanks David!
I can see that some of my working is following a pattern, would you mind pointing out on which variations I've miscalculated as I'd imagine it'll effect all of the other measurements and be an easy correction?

Thanks

dmullenasc
4 months ago

The first item in each section uses a 1/2 figure and the rest use a 1/3 figure.

dmullenasc
4 months ago

For example, if an 85 is 2/3-stop and an ND.3 is 1-stop, then it would convert an f/4.0 to f/2.0 and 1/3, not f/2.0 and 1/2.

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