ND Filters Long Exposure Quick Reference Charts and Cheat Sheets

Choosing the right exposure time when using ND filters like Lee Big Stopper or when stacking a couple of filters can be difficult sometimes. For years I was using a piece of paper with a ND filters cheat sheet that I kept in my wallet. Now we are using mobile devices more and more in our photography life so I created a mobile application - an electronic version of my ND filters cheat sheet (or long exposure calculator if you prefer) for mobile devices like Apple iPhone, iPad, iPod touch and Android devices.

I've got two versions of the neutral density reference charts to assist you in calculating exposure times when shooting with ND filters: 'lite' and 'pro' versions. They all are free. Yes, even the pro version is free. Personally I'm using the lite versions and not the pro one. These lite versions of the long exposure calculators are exactly what I had on a paper in my wallet. They are designed for using with one or two ND filters only as most of the time photographers are using maximum one or two 'favourite' filters in photography. I created a few versions of 'lite' calculators for most common combitations: 3- and 10-Stops ND filters, 6- and 10-Stops ND filters and just for 10-Stops ND filter like Lee BigStopper or B+W 110.

There is much confusion about numbers for ND filters. Some manufacturers specify filter numbers in F-stop reduction, other manufacturers specify filter numbers in optical density and third manufacturers specify filter numbers in filter factor. Just to clarify it a bit here is a simple reminder:

If you are using other ND filters like 5-stops Singh-Ray Mor-Slo or Singh-Ray Vari-ND/-Duo/-Trio filters you need to use the 'pro' version of the calculator. The 'pro' calculator also has a chart with all F-stop reductions, optical density and filter factors so you can easily find an equivalent to any filter. For example look at the chart and you'll see that 2 stops filter is ND4 and had 0.6 optical density. Same applies to any other filter.

How to use calculators? It's very simple.

First of all visit the following links using your mobile device or use QR-codes at the bottom of the page to access the links:

When you first access ND Filters Cheat Sheet from your Apple iPhone, iPad and iPod touch it will ask you if you want to 'Add to Home Screen' doing so will turn ND Filters Cheat Sheet into a Mobile App for you. On Android or other mobile devices you have to add bookmarks by yourself. For the first time you need an Internet connection, but after the first visit it is cached on your mobile device and will be available even without Internet.

Do a light metering with your camera without the ND filter. Set your camera to aperture priority, select the aperture you want to use and take a note of the shutter speed.

For one- or two-filters 'lite' calcs find the closest shutter speed to your reading in the left hand column and then read across to column which has the amount of ND filtration you are using ND8/ND64 or Lee Big Stopper - this gives you your exposure length.

For the 'PRO' calc find the closest shutter speed to your reading in the table header and then go down the number of stops that your ND filter filters. For the convenience on the left hand side of the table you can find your filter names.

Bear in mind all charts use full stops so if your shutter speed is a fraction of a full stop then you need to adjust it accordingly. However on really long exposures slight variations do not affect the exposure that much so you can use the closest value from the charts.

If you prefer to use non-electronic versions you can also print the charts out and laminate them to keep in your camera bag for reference.

In theory these charts should give you accurate exposure. However that's not always true with very dark filters and very long exposures. For the ND filters up to 5- or 6-stops these charts works perfectly but the darker the ND filter, the less reliable these charts get. For example, if my camera calculates an exposure of 1/60 without my 3- and 10-stops stacked ND filters, I would need to use an exposure of 2 minutes with two stacked filter. This is true in theory, but doesn't always quite work out right in real life. If I expose at 2 minutes, the image will be very underexposed. So I recommend going 2 or even 3 stops further, using 4 or 8 minutes of exposure time. I'm not sure why the 2 minutes don't produce the correct exposure, but I suspect we have two possible scenarios (or both of them). First of all manufacturers aren't that precise when describing the filter factor of their ND filters, especially when the filter factor gets big. A manufacturer could say that their 9-stop filter has a filter factor of five hundred twelve or five hundred or simply four hundred. The second possible option could be due to some kind of digital equivalent to 'reciprocity failure', which is a phenomenon experienced when shooting extra long exposures with film. The reason for such reciprocity failure with film is that the longer the exposure, the less effective the film is in recording the light and so the exposure length needs to be increased. Taking into account both possible options I simply increase exposure to be 2 or even 3 stops longer.