Help me calculate shutter speed with ND filters

[zamanakhan]

Ok i am looking for a formula or somesort of quick method to calculate shutter speed when i am using my 10stop ND filter.
Usually when i take pictures with my 10 stop filter i simply just GUESS exposure, and if its over exposed i use less time and vice versa.
I also occasionally add a Cir PL ontop of the 10ND for the extra stoping power, i read somewhere that this makes it a 20 stop filter and not a 12, i am not sure if this is true but it does kinda make sense 2x10=20.

Guessing exposure with 10 and 20 stop filters is now getting extremely annoying, If i miss exposure on a 10min exposure and find out i only had to go anther 15, i've now just spent 25min.

So i am wondering if there is a formula i can use, while out to calculate exposure by using the unfiltered metering off of my camera's meter and putting it in the formula to find out what a 10stop shutter speed and a 20 stop shutter speed would be.

 

[TheBiles]

The "formula" would be basic math. Each stop doubles your shutter speed. For quick calculations, I'd grab a smartphone app like "Exposure Calculator." And a CPL is 2 stops. You add the effect of stacked filters instead of multiplying.

Sent from my Galaxy Nexus

 

[zamanakhan]

The "formula" would be basic math. Each stop doubles your shutter speed. For quick calculations, I'd grab a smartphone app like "Exposure Calculator." And a CPL is 2 stops. You add the effect of stacked filters instead of multiplying.

Sent from my Galaxy Nexus

that is what i first thought but when you think about it, you are taking 2x of 10x and it makes sense, i am still on the fence about this, the other thing is, it usually takes twice as long to expose the same thing off of a 10 stop filter.
I am looking up some apps available for iphone, any hints on which app?

 

[jamesbjenkins]

Remember that each full stop is a doubling or halving of the amount of light you're letting in. You can manipulate the exposure triangle however you want by doing a little simple math. If you add the CPL on top of a 10 stop ND, you're only adding 2 stops, to make it a total of 12 stops down from a naked lens. I wouldn't try to guess off the meter reading though. If it were me, I'd either meter in camera and then put the filters on and modify your exposure triangle according to the math, or just use a light meter to take the right exposure. Just remember, for each stop you "stop down" via a filter, you have to double the shutter speed to keep the exposure consant, assuming ISO and aperture remain constant. Hope that helps!

 

[zamanakhan]

Remember that each full stop is a doubling or halving of the amount of light you're letting in. You can manipulate the exposure triangle however you want by doing a little simple math. If you add the CPL on top of a 10 stop ND, you're only adding 2 stops, to make it a total of 12 stops down from a naked lens. I wouldn't try to guess off the meter reading though. If it were me, I'd either meter in camera and then put the filters on and modify your exposure triangle according to the math, or just use a light meter to take the right exposure. Just remember, for each stop you "stop down" via a filter, you have to double the shutter speed to keep the exposure consant, assuming ISO and aperture remain constant. Hope that helps!

yes that all helps, i also added a iphone exposure calculating app which would make the calculations alot easier as well. Thnx for all the help everyone.

 

[Compaq]

If you're using a 10 stop neutral density filter, you'll have to increase your exposure by

2^10 = 1024

That basically means that your lens will be gathering 1024 times more light with the ND filter than without.

If you were at

f/11
1/20th
ISO-100

before putting on your filter, a possible new exposure could be

f/8 (1 stop difference from f/11)
30 seconds (apprx. 9 stop difference from 1/20th)
ISO-100

 

[ann]

perhapes this will help, comes from b&h website

ND.3 (exposure adjustment = 1 stop, reduces ISO 1/2)
ND.6 (exposure adjustment = 2 stops, reduces ISO 1/4)
ND.9 (exposure adjustment = 3 stops, reduces ISO 1/8)
ND 1.8 (exposure adjustment = approx. 6 stops, transmits 1% of light,)
ND 3.0 (exposure adjustment = 10 stops, transmits 0.1% of light)
ND 4.0 (exposure adjustment = 13-2/3 stops, transmits 0.01% of light)
ND 6.0 = (exposure adjustment = approx. 20 stops)

*

 

[zamanakhan]

perhapes this will help, comes from b&h websiteND.3 (exposure adjustment = 1 stop, reduces ISO 1/2) ND.6 (exposure adjustment = 2 stops, reduces ISO 1/4) ND.9 (exposure adjustment = 3 stops, reduces ISO 1/8) ND 1.8 (exposure adjustment = approx. 6 stops, transmits 1% of light,) ND 3.0 (exposure adjustment = 10 stops, transmits 0.1% of light) ND 4.0 (exposure adjustment = 13-2/3 stops, transmits 0.01% of light) ND 6.0 = (exposure adjustment = approx. 20 stops) *

Lol I am aware of those already, I was just wondering if there was a quick way to judge exposure while out in the field, the exposure calculators for iPhone helped tons. I was actually out today but forgot my goddamn shutter release, I simply made sure that the triangle had shutter speed at 1/125th which meant 30sec exposure with 12 stops, took shots with mup and exposure delay with tripod instead, I think I may have get more nd filters to go truly long, or better yet get to these places for the golden hour.

 

[mikeduk]

Best Kept Secret have a handy reference chart that you can print off and take with you:

http://photoink.org/wp-content/uploads/2012/03/BKS_ND_Chart.pdf

 

[Dao]

Just wondering, is your camera has a in camera light meter? And will the light meter work with the ND filter?

 

[Village Idiot]

Just wondering, is your camera has a in camera light meter? And will the light meter work with the ND filter?

How well will that matter with 12 stops of light blocking filters on it? I know with 9 I can barely see anything out of the lens.

 

[Mike_E]

Just wondering, is your camera has a in camera light meter? And will the light meter work with the ND filter?

This, more or less.

Take a reading with your camera and then adjust the aperture one stop up for every stop down (in manual) you want to set your shutter speed. Using that as a base adjust your aperture from there for your desired actual exposure.

 

[480sparky]

How well will that matter with 12 stops of light blocking filters on it? I know with 9 I can barely see anything out of the lens.

Does the filter make the meter hard to read?

 

[Village Idiot]

How well will that matter with 12 stops of light blocking filters on it? I know with 9 I can barely see anything out of the lens.

Does the filter make the meter hard to read?

I know it makes it impossible to focus.

 

[480sparky]

I know it makes it impossible to focus.

Focus before installing filter. Install filter, then meter.