Lately I have had the opportunity to travel around Scotland, capturing some of the wonderful landscape around me. Like this shot at Cashmore beach where I enjoyed a lovely day with my friend and fellow Photographer, Lea Tippet.

Besides the Camera, Lens and Tripod that were used to create this image there is another piece of equipment which helps give the smooth water look. That is the humble little ND filter.

What is an ND filter?

It is a bit of optical glass (or resin) that reduces the amount of light going into your lens/camera. Just as sunglasses do for our eyes. If the ND Filter is made well it should do so without affecting the quality or colour of your images.

Why would you need to reduce the amount of light?

Here are a few reasons listed below.

1: You want to use flash but are limited to 1/180s shutter speed. Normally you have to stop down the lens losing that lovely out of focus background but with an ND filter you can keep the aperture of the lens wide open and bring your shutter speed down allowing you to use flash. While you can also get around this by using High Speed Sync on a modern flash it is less efficient than using ND filters. Although can be often more convenient.

2: When shooting video you typically want to keep your shutter speed at double that of your recording speed. So if you are shooting 24fps you want a shutter speed of 48 (or as close as you can get) to add some movement into the frames helping the motion to blend better. Doing that without ND filters in bright sunlight can be almost impossible.

Left is 1/4000 at 24fps while right is 1/50 at 24fps

3: The most common use for an ND filter is to enable longer exposures, allowing you capture to more movement in your image. For instance, making a waterfall appear smooth and milky instead of freezing individual droplets of water.

ND filters come in various types, sizes and strengths. Quite a common quandary being should I get square (Which would require a holder) or circular ones which screw directly onto the lens.

In my opinion and If your budget allows you to, you should go for the square system as they offer better stacking. where you can use multiple filters and have the capability to use graduated filters and fine tune how they affect your image. If you do prefer circular filters then you could buy the size for your largest lens and use step up rings to adjust it for smaller lens.

One of the benefits of filter holders is that you can often quick release them. This can help frame the shot. Quite often it can become hard to see. In particular this happens with the super dark filters attached. You can get magnetic circular filters which solve that issue too.

Another benefit of square filters are specific holders for super wide lenses like the Sigma 12-24 f4 ART that don't have screw in threads so they could be your only option.

Square filters come in many different formats.

Resin filters are often cheaper and tend to have a larger effect on image quality, they can also scratch easily which would further reduce the quality of the images though them.

From my experience I have found Glass filters offer the best image quality but are more expensive. While less prone to scratching they are not immune as the ND part is normally a coating on the glass. There are a few exceptions though like the Formatt-Hitech Firecrest range which use two layers of bonded glass with the ND material in the middle offering better durability.

Glass filters can at times have the added bonus of smashing (oops) if you drop them like I did with this one! so care is definitely needed!

Filters come in all different strengths from 1 stop all the way to 24 and possibly more if you look around.

For every stop of strength the filter has you lose half the available light going to your camera. For example at 1/1000 of a second shutter a 1 stop filter will take you to 1/500, a 2 stop to 1/250 and a 10 stop will take you all the way to one second.

How strong a filter you need will depend on what you are doing, I tend to use a 4 or 6 stop quite often for flash and landscape use but sometimes 10 or more can be needed just depending on the light level and what you are trying achieve.

I have been using the older Formatt-Hitech Firecrest 100mm filters for the last few years and they have done me well particularly on the 14mm f4 Sigma dp0 helping me create images like this at Tobermory on the Isle of Mull.

I'm still perfectly happy with them as with wide angles and normal resolutions they are fine but when I borrowed the Panasonic S1R (article here) the 147mp mode combined with longer focal lengths I was losing a lot of detail. So I reached out to some friends in the industry to see if this was common with using filters and the great guys at Formatt Hitech and Benro uk sent me a some stuff to test.

First up Formatt-Hitech.

Their Pro and Ultra range are newer than my old Firecrest kit and the first thing I noticed is the difference in packaging. I just love the new pouches supplied with the felt inside and magnetic clip. The added cleaning cloth is a nice bonus.

As I was testing the filters I found that the Formatt Pro was pretty much the same as my older Firecrest kit. Whilst great for wide-angle lens it struggles with longer lens, so I would skip these and go directly for the Ultra version, (unless you know for sure you will only ever use wide angle lens).

The Ultra version was just great with only a slight degradation in image quality at 147mp using longer focal lengths. The Formatt filter is a more complex design though and offers a more durable filter where you can't scratch the ND coating unlike most other glass ND filters I've come across.

Next is Benro

Normally known for their tripods. One of which I've been using for a while now, they have also released a nice looking filter system. While I do prefer the pouches supplied by Formatt, the Benro case is a hard plastic box which has foam inserts and will fully protect the filter. There is also an included small felt pouch which is lovely.

Surprisingly the Benro Master filters had almost no effect on image sharpness at all. Colour cast which can be another side effect of using filters was very minimal on both sets of filters. The Formatt-Hitech was a little cooler while the Benro was a little warmer and both are easily fixed.

Here's the test image from the filters.

There is a small difference between the filters. I shot these on the Panasonic S1R using the 147mp muti-shot mode with the new Sigma 70-200 DG HSM Sport lens at 137mm f5 so not your typical settings and its pushing both the lens and filters.

For standard day to day use you are not likely to see much if any difference at all especially on lower resolution cameras and using wider focal lengths, where even my older filter produces great results.

It is good to see Formatt-Hitech have improved their filters with the Ultra versions but starting at a whopping £165 per 100mm filter when the the Benro start at £99 for 100mm filters is quite a difference. Considering you would be hard pushed to tell the difference between both in everyday use! Although that more complex design of the Formatt-Hitech Ultra filter should make it more durable in challenging conditions.

Hopefully this helps someone. Please stay tuned. As I was finishing this article some nice variable ND filters popped through my door. These can allow you to change how much light passes through to the lens on the fly. After some testing we will see if they can really offer you the quality along with flexibility in one package.