Landscape is one of my favorite, and anyone plays landscape will sometime got into a will to shoot in slow shutter speed. Probably one of the most common case is shutting water, such as wave, river stream, or waterfall into cotton-like soft image by shooting it in an extremely low shutter speed.

The challenge here is light, because most landscape shoots are taken in daylight, where fast shutter speed is needed to control overcast. Even after you close the aperture down to the smallest size – means largest f-stop mark – you are still running at 1/n speed, whilst desired blur the water movement to cotton soft requires at least 30 seconds or even a few minutes.

The tool to overcome this problem is neutral density filters, widely known as ND. In simple way, usage of ND filters is like using a sun glass to block the light. ND filters work the same way, blocking part of the light from reaching the sensor, making the sensor “feels” and then records the image in darker situation than it actually is. The difference of ND filters is in its optical specification. The glass is designed to block the light without interfering clarity and color.

ND filters are available in various light-blocking capacity, in shops we can find 2, 4, 8 f-stops. These numbers mean that the filter blocks the light by n stop. If you for example use ND-2, then you can shoot two stop slower if you are prioritizing aperture or two stops wider if you are prioritizing speed. As it covers the lens, usage of ND filters is responded correctly by automatic metering system of the camera.

Logically you can stack as many ND filters as you need to get desired light-blocking capacity. However, bear in mind that no mater how high the optical quality is, putting slices of glass in front of the lens compromises image quality. The more you put the filter the worse the effect. Technically the hollow space between filters can bring negative impact too. On the other side, stacking many filters may result in vignetting effect especially when ultra-wide lens is in use.

The catch of using ND filters is practicality. If you have ND-2 attached and you find that you need it darker, you have to either put another ND-2 or replace the ND-2 with ND-4. Vari-ND filter is the solution to this situation. You only need to bring and attach one filter, if you need it lighter or darker, you just need to twist the dial. Unfortunately this luxury is quite expensive. The only brand that I know is offering this product is Singh-Ray sold at about $400 for 77mm thread. I will have to spend at least another $200 to ship it to my country and pay the custom bill.

If I buy three ND filters at different powers of 2,4, and 8, I will only have to spend something between $100-$200 depending on brand, and do not have to pay for shipping and custom as it is available here. But I am interested in owning one and therefore seeking for chance to get one at the most affordable cost.