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Filter Factor & Exposure Compensations


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#1 deepak srinivasan

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Posted 15 November 2010 - 01:34 AM

Hi Friends , I would like to know a very important thing from your point of view it is
"THE FILTER FACTOR & ITS EXPOSURE COMPENSATIONS"

My Questions are :
1. What are the filters a d.o.p can use ?
2. What are its purpose?
3. How much stops i must open in my lens to use a specific filter / what asa should i change in my meter in order to get the right exposure with specific filters ?

"Kindly answer these questions friend , i know i can google it and learn or go buy some books read them and learn this but i always feel it is better to learn through ppl who work in the industry so i get practical knowledge & theoritical knowledge as well as i can be sure that this particular thing ppl post here are the true fact so i dont h ave to cross check the source so pls share your views friends :)"
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#2 Adrian Sierkowski

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Posted 15 November 2010 - 04:00 PM

There are literally hundreds which are manufactured not to mention all those DoPs make themselves. You will either need to be more specific as to which filter or we can't help you. You will need to read up on filters, there is a good book
Image Control: Motion Picture and Video Camera Filters and Lab Techniques, Second Edition which gets into this. On top of that you will need to make some tests to understand how the filters work for you.

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#3 Michael Kubaszak

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Posted 15 November 2010 - 05:36 PM

you can make your own filters??? tell me more tell more. is it expensive??
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#4 Adrian Sierkowski

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Posted 15 November 2010 - 05:42 PM

Depends on the filter you want to make, but essentially anything can become a filter. The most common examples would be diffusions, different materials between white water glass, or just over a frame; but you could also take some white water glass and "paint it," with clear nail varnish for effects, or streak it with some colors, or another interesting idea is a little bit of tooth paste (white) which'll look like a low cloud/fog bank. I also saw someone take a CD cover, the plastic kind, and cut into it with a knife, after making it 4x4, so as to make a cheap-o anamorphic streak filter (found that link on here, iirc).

Now of course optical quality won't be that great on a "home made," filter and I don't advocate trying to make your own 85; but go nuts with diffusions etc; never know what you might cook up.
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#5 K Borowski

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Posted 15 November 2010 - 10:30 PM

You are making your own filters, Michael, every time you punch out an 85A for a behind-the-lens filter slot on a Panavision :P



I don't know if these truly count as filters, but I know some photographers and DoPs that have/had their own collection of different kinds of ladies stockings to stretch behind the rear element of the lens as diffusors.
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#6 deepak srinivasan

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Posted 16 November 2010 - 12:44 AM

I want to know the compensations for
nd3,nd6,nd9,ultra p.l.,85 n3,85n6,85,80,nd grad filters

i would like to know basicallly what all should we take in count while reading the light with a meter like what all should be in his(one who reads light) mind while reading the light with meter ????

Read more: http://www.cinematog...?#ixzz15QBZbytT
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#7 Adrian Sierkowski

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Posted 16 November 2010 - 12:49 AM

Well the NDs are pretty easy, it's base 3, so ND .3 is -1 stop, ND .6 -2 etc. For the ND Grads you generally don't compensate your iris as you're trying to control a local area of the image (such as the sky). For the Ultra Pola, I seem to recall a 2 stop compensation, but some of that does depend on angles. Still 2 stops hasn't led me wrong.. yet. 85 N.3 would be a normal 85 (2/3rds of a stop) plus an ND .3, so 1 and 2/3rd stops etc.. 80 (really an 80a) is -2 stops. All of this should also be readily available on the filter when you buy them or at the manufactures website. Also, if unsure, take 2 reflected readings off of a gray card, one w/o the filter over your meter, and the other with.
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#8 deepak srinivasan

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Posted 16 November 2010 - 01:23 PM

From your reply i understood that "we dont have to think too much about the compensations we can just read with filter over the meter and kknow what the correct exposure must be ????
am i right ? i have seen my seniors change asa in the meter to compensate like if they are using nd3 in 5201 stock they will set 25 asa in meter and keep the exposure for 25 asa
which is easy & safe ????
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#9 Adrian Sierkowski

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Posted 16 November 2010 - 01:30 PM

It's more like if you are unsure of the filter factor, then you use your meter to determine the stop compensation. Also, using an ND .3 and adjusting the ASA on your meter from 50 to 25 is the same as opening up the iris 1 stop. The reason for setting the meter to 25 is to save you from having to do the math (not that it's that hard) to know to open up a stop and to keep things simpler. It's the same as when you're shooting on 200T and throw an 85 filter on it and the can -o- film tells you to set your meter to 125 (hence plugging in a 2/3rd stop compensation for the filter).
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#10 deepak srinivasan

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Posted 17 November 2010 - 12:32 AM

Thanks for the reply sir it was very informative :)
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