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shooting 200t with a ND4


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#1 Joshua Dannais

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Posted 20 September 2007 - 11:05 PM

is exposure adjustment for 200T with an ND4 as simple as exposing for 200T and just opening up 2 stops, or do I have to calculate the iso film speed after the filter is on and take a meter reading using the new effective iso film speed?

thanks
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#2 Bobby Shore

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Posted 20 September 2007 - 11:18 PM

is exposure adjustment for 200T with an ND4 as simple as exposing for 200T and just opening up 2 stops, or do I have to calculate the iso film speed after the filter is on and take a meter reading using the new effective iso film speed?

thanks



Adjusting the ISO on your meter is simply an easier way to work the calculation into your light readings as opposed to leaving the rating at 200, taking your readings, then calculating in your head the stop compensation of the filter. Did you mean ND.6 though (you mentioned 2 stops)? An ND.4 would mean a stop and a third of light loss. If you're shooting 200T and using an ND.6, then you would adjust your ISO to 50 to work the compensation into your readings (assuming you wanted to rate the 200T at 200 in the first place).

If you're using ND's, I imagine you're shooting outside... any 85 correction, or are you planning on letting the scene play cold?

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#3 Joshua Dannais

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Posted 20 September 2007 - 11:48 PM

Thanks for the quick reply, I need to figure this out tonight for something I have to shoot tomorrow. We mean the same thing when it comes to the filter, Filter Factor (NDx) of 4/ Filter Optical Density .6, I just called it by the filter factor.

Great, I'll set the readings for 50 iso... but more importantly how did you figure that out? is there a simple math formula?

Yes, it's outdoors... and I wasn't planning on using an 85, just having it corrected during the telecine transfer. I was told it can be done in color correction.

since it'll be the same rating as 50D, what would be the visual difference between the two?

thanks again
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#4 Adam Thompson

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Posted 21 September 2007 - 01:37 AM

Thanks for the quick reply, I need to figure this out tonight for something I have to shoot tomorrow. We mean the same thing when it comes to the filter, Filter Factor (NDx) of 4/ Filter Optical Density .6, I just called it by the filter factor.

Great, I'll set the readings for 50 iso... but more importantly how did you figure that out? is there a simple math formula?

Yes, it's outdoors... and I wasn't planning on using an 85, just having it corrected during the telecine transfer. I was told it can be done in color correction.

since it'll be the same rating as 50D, what would be the visual difference between the two?

thanks again


ND filters are rated .3, .6, .9, etc. Each. ".3" is the same as one stop of light loss. Use a ND.9, and that's 3 stops you can open up.

Yes, you can adjust for the color in post. Otherwise you'd adjust stop for the 85 which is about 2/3 stop.

The visual difference? The reason you use ND's, for the most part, is to get a more shallow depth of field since the more open your iris is, the smaller the area is that's in focus. There is no other visual differences.

The best way to set your meter is to spot a grey card, record the reading, then spot in the exact same way but while shooting through your filters. This will true your measurements. To save possible confusion, dial down the meter asa to match the readings you got.

This is cinematography 101 stuff that is well covered in any of the cinematography books or classes.
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#5 Alessandro Machi

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Posted 21 September 2007 - 01:53 AM

Might as well rate the ASA a bit under 200 ASA as well, somewhere between 150 ASA and 100 ASA.
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#6 Patrick Neary

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Posted 21 September 2007 - 08:17 AM

Hi-

Figuring out the asa is very simple- just doubling or halving, so you start with 200, cut 2 stops with your nd and you're down to 50. One stop nd and you'd set your meter to 100.

If you're asking about visual differences compared to 50D stock, then there'd be a noticeable difference in grain with the 50D. Because 50D is a slower, sharper stock, much less grain.

Lenses tend to perform better if they aren't stopped down to 16 or 22, and NDs are also useful in opening up your stop for that as well.
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#7 Joshua Dannais

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Posted 21 September 2007 - 01:45 PM

Hi-

Figuring out the asa is very simple- just doubling or halving, so you start with 200, cut 2 stops with your nd and you're down to 50. One stop nd and you'd set your meter to 100.

If you're asking about visual differences compared to 50D stock, then there'd be a noticeable difference in grain with the 50D. Because 50D is a slower, sharper stock, much less grain.

Lenses tend to perform better if they aren't stopped down to 16 or 22, and NDs are also useful in opening up your stop for that as well.


Ahh... the grain, didn't even think about that. I'm leaning toward the 50 now.

thanks for all the input.
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