# Help me calculate shutter speed with ND filters



## zamanakhan (Apr 7, 2012)

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.


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## TheBiles (Apr 7, 2012)

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


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## zamanakhan (Apr 7, 2012)

TheBiles said:


> 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?


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## jamesbjenkins (Apr 7, 2012)

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!


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## zamanakhan (Apr 7, 2012)

jamesbjenkins said:


> 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.


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## Compaq (Apr 7, 2012)

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


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## ann (Apr 7, 2012)

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) 

*


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## zamanakhan (Apr 7, 2012)

ann said:


> 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.


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## mikeduk (Apr 17, 2012)

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


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## Dao (Apr 17, 2012)

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


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## Village Idiot (Apr 17, 2012)

Dao said:


> 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.


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## Mike_E (Apr 17, 2012)

Dao said:


> 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.


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## 480sparky (Apr 17, 2012)

Village Idiot said:


> 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?


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## Village Idiot (Apr 17, 2012)

480sparky said:


> Village Idiot said:
> 
> 
> > 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.
> ...



I know it makes it impossible to focus.


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## 480sparky (Apr 17, 2012)

Village Idiot said:


> I know it makes it impossible to focus.



Focus before installing filter.  Install filter, then meter.


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## mjhoward (Apr 17, 2012)

TheBiles said:


> And a CPL is 2 stops.



Most decent CPL's are 1.3 stops.



Compaq said:


> 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.*



No it doesn't.  The lens will *always *be gathering less light with an ND filter in front of it.  If you've adjusted the exposure to compensate for the filter, then the *sensor *will receive roughly the *same *amount of light.


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## dlmvegas (Mar 15, 2014)

I realize it's been awhile since this thread was updated but here is a link that should help everyone in using a 10 stop ND filter.  Scroll down a little to view the table they have for the 10 stop or 6 stop filters they sell.  No more math.

Big Stopper and Little Stopper long exposure filters from LEE Filters.


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## TCampbell (Mar 16, 2014)

Keep in mind that CPLs are variable -- so there's no one-size-fits-all answer for them.  I have metered, put the filter on, tuned it, and metered again, and have had CPLs take as few as 2/3rds of 1 stop.  But 2 stops is also common.  

This is because a CPL doesn't just cut light equally... it cuts light based on the polarity of the light waves hitting the came as compared to the tuned angle of the polarizer.  If you use an ultra-wide angle lens, put a CPL on it (which I would not normally recommend that anyone do when using an ultra-wide angle lens), shoot a photo of a blue sky and look at the result, you'll see very distinct brightness banding with a dark zone where a lot of light was cut, but this fades to a weak zone where only a little light was cut.  

When I use my CPLs, I don't necessarily tune them to the highest amount of light cut I can get.  I usually want subjects to offer some reflection (I don't want it to cut everything), but I don't want obnoxious reflections... so I'll tune up the CPL, then back it off a touch to offer a pleasant hint of a reflection.  The light cut is all all in how you're using it.

A 10 stop ND, however is usually plenty and I would not recommend stacking a CPL on a 10 stop ND.  Metering and focus have to be done prior to putting the 10-stop filter on the lens... at which point you want to *know* how much light you've just cut and not be guessing at it.  When you add the CPL to the mix, you're now at the point where you're probably going to have to take several shots and guess at the exposures.  I also carry a 2 stop and 3 stop ND.  So if 10 stops is ever not enough... I can add more.  

Suppose you're outside on a bright sunny day in the middle of the afternoon and thus get to assume that it's a "sunny 16" exposure (although you'll get better shots near sunrise and sunset during the "golden hours") ... since the point of the 10 stop ND is usually to slow the shutter speed, you're probably already using settings that slow the shutter speed as much as possible even without the ND.  So... ISO 100 and f/16 probably are good choices.  Now your shutter speed is 1/100th, but I'm going to round up to 1/125th because that's a "whole" stop (1/100th is 1/3rd stop down from 1/125th).  As you add the 10 stop ND, you have to increase the shutter exposure by 10 stops.  

1/125th -> 1/60th (1 stop)
1/60th -> 1/30th (2 stops)
1/30th -> 1/15th (3 stops)
1/15th -> 1/8th (4 stops)
1/8th -> 1/4th (5 stops)
1/4th -> 1/2nd (6 stops)
1/2nd -> 1s (7 stops)
1s -> 2s (8 stops)
2s -> 4s (9 stops)
4s -> 8s (10 stops)

Now... I did round the 1/100th sec exposure time (which is not on a full-stop boundary) to 1/125th (because that is on a a full stop boundary).  But in reality 1/100th is 1/3rd stop slower... so if you want to go 1/3rd stop slower from 8 seconds you end up at 10 seconds -- which is 10 full stops slower from 1/100th.

Something else to keep in mind is that most digital cameras are set to 1/3rd stop increments each time your shutter speed wheel moves by 1 "click".  That means 3 clicks of the dial is 1 full stop reduction.  And THAT... means that you could just turn the shutter speed dial 30 "clicks" and that would be 10 stops.

But before you assume the 30 "clicks" is good, do make sure... set the camera at say, 1 full sec shutter speed and rotate the dial to 1/2 second exposure and make sure you had to turn it three "clicks" to arrive there.  Many cameras have a setting... I can set my cameras to 1/2 stop increments if I want via the customization settings (in which case it would be 20 clicks instead of 30 clicks to change the exposure by 10 full stops.)


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## garrywillson (Mar 18, 2014)

Great information... As per my experience the easy way is to multiply your shutter speed times, using a calculator to get the shutter speed with the filter on. i.e. 2 multiplied by 2, 13 times (or 2^13)

Regards,


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## pgriz (Mar 18, 2014)

I use this table:




Left is the time value without the filter, right is the value with the filter.


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