Variable ND Filters.

A few week's ago I wrote about the creative benefits of using ND (Neutral Density) filters in photography. This can be viewed here. Although I love ND filters they can require a larger initial investment which could be a barrier for people who want to play around with long exposures photography.

What if there was another option that let you adjust the strength of the light reduction which costs less and still offers decent image quality?

I know it all sounds a little too good to be true and I did try such a filter many years ago, granted a £30 version from ebay and it degraded the sharpness of my images so much I found it was better as a tea coaster!

Fast forward many years and K&F Concept were kind enough to send a few Variable Neutral Density Filters through my door and I can honestly say I am really surprised at how good they are.

The filters come in two strengths, the ND2-ND32 which offers a 1 to 5 stop adjustment and the ND8 to ND128 which offers a 3 to 7 stop adjustment. Both filters come with hard stops on minimum and maximum settings to stop you going too far and reducing the image quality.

Personally I find the ND8 to ND128 offers the better range as it blocks more light allowing smoother water like in this shot with the Sigma sdQ-H and 50-100Art of the river Luggie on a very cold day.

Luggie River - Sigma sdQ-H with 50-100 f1.8 Art and K&F Concept ND 8-ND128

Although at lower light levels the ND2-ND32 might be what you need. I used it for this shot at the Loup of Fintry with the Sigma fp and 45mm f2.8 Contemporary lens.

Loup of Fintry - Sigma FP with 45mm f2.8 and K&F Concept ND2-ND32

Unlike a traditional ND filter that is made of a piece of glass or resin and blocks a particular amount of light, Variable filters are made up of two circular polarizer/linear (CPL) filters as you can see via the reflections in this image.

ND filter top, Variable ND bottom.

The variable ND filters work by adjusting the polarization of the light as you rotate the front element, This creates a similar effect as a traditional ND for reducing light. They are not exactly neutral though as the CPL filters that make up the ND will be having an effect on your image. To help understand why I took this photograph of the same scene with CPL filter set to maximum and one without a CPL to demonstrate the difference it can have.

no cpl left - max cpl effect right

As you can see the CPL filter only lets light traveling in a particular direction enter the lens, blocking out reflections This not only helps add contrast to images by darkening the sky or removing reflections on small items like leaves but can allow you to see past surface reflections into water or even car windows.

I feel CPL filters are one of the most useful filters you can buy as the effect isn't something that can be replicated in post but it might not be an effect you always want and unlike a CPL filter that gives you control over this effect the Variable ND filters don't. K&F Concept do offer a +CPL version of the ND2-ND32 that let's you have control of the CPL effect directly via an extra leaver but sadly their is no ND8-ND128 version

The first thing I wanted to test with the filters was color cast, so I grabbed my Sigma sdQ-H with 50-100mm f1.8 Art and proceeded to create the same image with out filters, with a normal ND (benro 6 stop) and the K&F Concept Variable ND's which I tested at the minimum and maximum settings.

Surprisingly for me the weaker ND2-ND32 actually had the strongest colour cast but the good news that both Variable ND's were consistent throughout the range so it should be an easy fix in post with a slight white-balance tweak.

Next up I wanted to test the sharpness, Sadly I don't have the Panasonic S1R around anymore to do the 147mp test like I did in my last article but the Sigma sdQ-H is very good at resolving fine detail and using a longer focal length tends to puts a bit more stress on the filters.

I honestly couldn't see any difference in sharpness between the Variables, regular ND and no filter except for the ND2-ND32 which at the maximum setting did lose a little contrast and sharpness but even with this 100% crop its very slight.

No filter - K&F Concept ND2-32

Costing around £55 for the 82mm version's where a normal ND filter will often cost more than double that. It is hard not to be impressed with how well these are doing considering the cost and I can see me using these for many shots particularly when I want to travel light.

Are they better than a traditional set of ND's?

Well that depends on what you are doing. Traditional ND filters will offer better image quality particularly during very long exposures as they are also designed to block Infrared light that can start to contaminate the scene and let's not forget a truly neutral light reduction without any CPL effect unless you add one into the mix. There are also the square filter kits that offer many more options of filter types like graduated filters giving much more control over an image. The down side to this system is that it requires a larger investment, extra bag space and a longer time required to change filters means it is not so great for fast adjustments.

Variable ND filters on the other hand give you around 5 stops of light adjustment in one filter saving time, money and space so it is really up to each user if the compromises are worth the benefits for either system.

Kirkintilloch - Sigma fp with 45mm f2.8 and K&F Concept ND2-ND32

I am pleasantly surprised with the K&F Concept Variable ND filters in particular the ND8-ND128 as it offers tremendous value for money for anyone wanting to try some long exposure shots or have more control over shutter speeds when shooting video. I wish that they would offer a ND8-ND128+ CPL version as I feel having control over the CPL effect would benefit everyone.

A good tip when buying filters is to get one that fits your largest lens in my case 82mm and use step-up rings to fit the filter onto smaller ones. This also helps if using an ultra wide as there's less chance of the lens seeing the frame of the filter.

K&F Concept filters have kindly given me a code to share with you all to save a bit of money if these are something you are interested in so check out the links bellow.

Amazon purchasing ND2-ND32 , ND8-ND128 and lastly the ND+ CPL with the 5% discount code: 97L8OU4N valid till 15th Jan 2020.

K&F Concept directly ND2-ND32ND8-ND128 and ND+CPL with a 10% OFF code: KF10UK valid till 20th of Dec 2019

I hope this has been helpful, any questions feel free to catch me on Instagram  or Facebook and I would love to see what you create with them if you do grab one.

Created By
Paul Monaghan