# Thread: Cokin type third party filters

1. ## Re: Cokin type third party filters

Originally Posted by Octarine
Don't use decimal fraction.
ND2 halves the amount of light. Therefore the calculation is 1/60 / 1/2 = 1/30. This, converted into a decimal fraction, is 0.03.
ND2.. the 2 is the attenuation factor. Just multiply the shutter speed by the attenuation factor and you are done.

1/60s exposure without filter:
ND2 shutter speed = 1/60 * 2 = 1/30s
ND4 shutter speed = 1/60 * 4 = 1/15s
ND8 shutter speed = 1/60 * 8 = 1/7.5s round up to 1/8s
ND400 shutter speed = 1/60 * 400 = 6.667s around up to 7 seconds
assuming ISO and aperture stays constant.

That is the simple way to calculate.
If you want to think of stops, then each addition stop of ND will extend shutter speed by a factor of 2 (double the exposure time). So you have:
ND2 = 1 stop ND, double the exposure time
ND4 = 2 stop ND, twice double the exposure time 2^2 = 4 times
ND8 = 3 stops ND, three times double the exposure time = 2^3 = 8 times.
You will realize the calculation is already stated in the attenuation factor...

2. ## Re: Cokin type third party filters

Originally Posted by romeo tango
I check my camera this morning and discovered that I can set the EV to 1, 1/3 or 1/2. It is currently set at EV1 so from 1/60s, 1 click brings me to 1/30.
So can I say that the table you provided is EV1 stop ?
Stop, EV settings are a different story. They do something similar, in the end. But adjusting shutter for ND filter usage is a 'manual EV' that it techncially not related to the click settings for in-camera EV.
Since the click setting can be changed and I have seen dials that cause settings to 'jump' due to contact issues I would not recommend counting clicks. Check the display, do the simple Maths.

3. ## Re: Cokin type third party filters

Originally Posted by daredevil123
ND2.. the 2 is the attenuation factor. Just multiply the shutter speed by the attenuation factor and you are done.

1/60s exposure without filter:
ND2 shutter speed = 1/60 * 2 = 1/30s
ND4 shutter speed = 1/60 * 4 = 1/15s
ND8 shutter speed = 1/60 * 8 = 1/7.5s round up to 1/8s
ND400 shutter speed = 1/60 * 400 = 6.667s around up to 7 seconds
assuming ISO and aperture stays constant.

That is the simple way to calculate.
If you want to think of stops, then each addition stop of ND will extend shutter speed by a factor of 2 (double the exposure time). So you have:
ND2 = 1 stop ND, double the exposure time
ND4 = 2 stop ND, twice double the exposure time 2^2 = 4 times
ND8 = 3 stops ND, three times double the exposure time = 2^3 = 8 times.
You will realize the calculation is already stated in the attenuation factor...
Hi daredevil123,

Thank you so much for your patience in typing the above details. Really appreciate that

4. ## Re: Cokin type third party filters

Originally Posted by Octarine
Stop, EV settings are a different story. They do something similar, in the end. But adjusting shutter for ND filter usage is a 'manual EV' that it techncially not related to the click settings for in-camera EV.
Since the click setting can be changed and I have seen dials that cause settings to 'jump' due to contact issues I would not recommend counting clicks. Check the display, do the simple Maths.
Hi Octarine,

Thank you for your patience too. Really appreciate it

5. ## Re: Cokin type third party filters

Hi all,

Thank you guys so much for your patience and guidance

I think for the time being, I will stick to the ND calculator apps while trying to understand the formulae

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