NOTE: THIS TUTORIAL IS OUTDATED, CHECK THE MOST RECENT AND MORE EXTENSIVE LONG EXPOSURE GUIDE HERE
Last week’s Part 1 of this series was just some basic information about long exposure photography. Today I’m going to discuss some more technical subjects.
The difference between light and dark ND filters
There’s a wide range of ND filters to choose from. There are ND filters starting from 1 stops to 10 stops. But when do you use what filter and why?
Ok, first of all, you’ve got to ask yourself the question: What do I want to achieve?
I’ll illustrate some scenario’s.
1. You live in a place with enormous amounts of sun, like Australia, Vegas or the Sahara desert… Shooting with wide apertures can be a big problem, because the sunlight is so intense that even at ISO 100, f/5.6 and 1/4000s the picture is still overexposed. In this scenario a 2 or 4 stops ND filter can be very helpful.
2. You’re living in a average country, with average weather (most European countries) and you like to make some long exposures at daylight. You should try the darker ND filters, like the 6 or 10 stops.
Two minute and 30 seconds exposure at broad daylight. These kinds of exposure times can only be done by using a
very dark ND filter, like the 10 stops.
4. Or maybe you want to create a spooky scene. Using a long exposure at daylight in the middle of the street can create ghosts like in the picture below. Depending on where you live (how intense the sun is where you live), you’ll need a light to medium ND filter.
5. To eliminate moving subjects. You can make the Taj Mahal look completely deserted, or make a crowded beach look empty. If you use a long enough shutter speed, moving subjects that only stay a few seconds in your frame won’t be recorded by your camera.
I shot this picture in broad daylight at the Scheveningen beach, Holland. This beach gets lots of visitors every day, especially on hot and sunny days like the day when I shot this. There were actually dozens of people walking in and out of the frame, but you don’t see any of them in this picture – all because of the long exposure.
Removing the human element (or any moving objects, like cars) requires a long exposure. You probably are going to need a 10 stops ND filter.
6. To reduce an image to just curves, lines and tones. When making very long exposures, not only moving objects will disappear. Clouds turns into stripes, crashing waves into smooth surfaces… After a while your image is down to its true essence: lines, curves and tonality. To achieve this, you’ll need a very dark ND filter – 10 stops at least.
I’m not sure if polarizers are commonly used for long exposure photography, but I use it. The great thing about polarizers is that not only does it gives a little colorboost, but also reduces the light with 2 extra stops.
There are two types of polarization filters: the circular polarizer (CP) and the linear polarizer (LP). There is some talk that a LP filter isn’t suitable for DSLR’s, it seems to disable the auto focusing of your camera and the built in light metering. I can’t say for a fact whether that is true or not. But why risk it? Just use a CP. Besides, most polarization filters are CP.
Step up/down rings
A lot of people who use screw-in filters will encounter the problem that one size doesn’t fit all. So your freshly bought 10 stops ND filter worth $ 100 or more, does fit your wide-angle, but not your zoom lens.
There’s actually a quick and easy fix for this (and a cheap one!): step up/down rings.
A step up/down ring is a thin ring that you mount onto the front of your lens. You can screw your ND filter into the ring.
Step up ring
You use a step up ring to fit a filter onto a lens that has a smaller diameter than the filter. For example: using a 77mm ND filter on a 58mm lens. There won’t be any vignetting, since the filter is bigger than the lens.
Step down ring
You use this ring to fit a filter onto a lens that has a bigger diameter than the filter. For example: using a 58mm ND filter on a 77mm lens. These will cause vignetting. Like I said, it’s a quick and easy fix. But don’t expect any miracles for that kind of price.
Vignetting and stacking
Most long exposure photographers use multiple filters at once. They might use a ND8, ND4 and a GND. Using multiple filters at once is called stacking. Now, there is nothing wrong with stack. I even encourage this and I myself do a lot of stacking. There’s however a disadvantage to stacking: vignetting.
I can’t recommend using more than 2 or 3 filters simultaneously. Especially ultra wide angle lenses at their furthest reach encounter this problem.
There are many people out there complaining about color cast in their images when shooting with a ND filter.
This has happened to me also. I’m not sure who or what to blame. This colorcast can be caused by several reasons.
– Your camera might be “leaking” light. Holes in your camera causes light to fall through it and mess up your pictures pretty badly. The longer the exposure, the more light falls through the holes and the bigger the color cast. Note: with holes I mean very small cracks, usually in the corners of your camera.
– Extreme light fall on your viewfinder. Never shoot directly into the sun when making long exposures. Don’t even shoot directly into the sun with very fast shutter speeds. It can ruin your sensor. However…it’s also bad to shoot with the sun directly behind you when shooting long exposures. Exposing your viewfinder to the extreme brightness of the sun for several seconds or minutes can also cause color casting. Cover the viewfinder by standing behind the camera while making the long exposure. That way, the sunlight hardly goes through the viewfinder.
– Stacking multiple filters. Again, I’m not sure why or how, but stacking multiple filters usually cause more color casting that just using a single filter.
So, who to blame? I simply do not know. Most of the color casting can be explained due to light falling into your viewfinder. I don’t have any hard evidence that the color casting is caused by poor ND filters.
In next week’s last part of this series I’ll discuss how to
calculate the exposure time
when shooting long exposures. I also made
an overview with the most used filters and all their specs, like price, diameter, f-stops
etcetera. So please join me next week in the final part of The Ultimate Guide For Long Exposures.