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MPB ND2-400 variable ND filter review

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Review: MPB ND2-400 variable ND filter

Using a variable neutral density filter


What does it do and how you use it.

Carrying lots of neutral density filters is both expensive and inconvenient, particularly for larger filter sizes. What about just one that adjusts over a range of densities?

In this short review, Keith looks at a filter that offers a continuously variable range of densities, needing anything from 1 to 8 stops of additional exposure.

We've reviews of many MPB products. See the MPB Category in the dropdown menu at the top of the right column.

82mm nd2-400 filter

What do you get with the filter

The filter here is an 82mm MC ND2-400 multicoated glass filter (£59.99)

Costs of filters vary considerably, and the 82mm is the largest in this range of filters.

One of the reasons I tend not to use filters that often is that a lot of my work architectural work uses big wide lenses like the EF11-24mm and TS-E17mm, neither of which are designed for front fitting filters.

The 82mm does however fit on my TS-E24 f3.5L mk2 lens, and is thin enough that even at full shift there is only the smallest signs of vignetting at the corners most shifted – it took some care to see this and for most use of the lens there is no obvious vignetting.

I’ve never been a great fan of filters in general, with occasional use of a polariser for product photography.

An area though, where I have looked at ND filters before is to allow me longer exposures in busy well lit areas, where I want to emphasise the space and slightly blur people in it. This is sometimes for creative reasons, but sometimes because the image needs to have no obviously recognisable people in it, but not look deserted.

One thing I’m not personally interested in is massively blurring waterfalls and the sea… I may look for slightly longer exposures sometimes to give a bit of a sense of movement for waterfalls, but I’m looking for a feeling of falling water, not fog.

Photos of a seashore where the sea looks as if someone has gone nuts with a dry ice machine fall into the same category as luminous trees in infra-red photography, and ‘model world’ tilt/shift shots (“Oh, that’s interesting. Next idea please.”)
[YMMV as ever]

Using the filter

The filter is composed of two glass disks, with the front one freely able to rotate.

Both disks are linear polarising filters, which combined together, pass an amount of light dependent on their relative orientation. The amount of attenuation in this case can vary from 1 to just over 8 stops.

One stop means you need to double your exposure (with aperture and ISO unchanged) or open your lens aperture by one stop (keeping shutter speed and ISO the same).

Let’s say a particular daylight scene needs 1/125s exposure at f/8 (@100 ISO)

Adding the filter (at it’s lightest setting – 1 stop reduction) means we now need 1/60s at f/8 (or 1/125s at f/5.6 if only changing aperture)

[Note that I’m approximating exposure values to normal camera settings]

At the darkest filter setting (8 stops), let’s step further down through exposures (from 2 stops to 8 stops)

1/30s … 1/15s … 1/8s … 1/4s … 1/2s … 1 second … 2 seconds

So, I can now take a photo with a 2 second exposure at f/8 – more than enough to blur anyone in the scene not pretending to be a statue.

In lower light, I could stretch from 1/30s at f/8 to 8 seconds at f/8

1/15s (1 stop) … 1/8s … 1/4s … 1/2s … 1s … 2s … 4s … 8 seconds (8 stops)

Here’s a late afternoon shot (0.6 seconds) of a bus near my home, slowing for a red traffic light

long exposure showing movement

The lens in this case is my TS-E24mm f/3.5L mk2 on a Canon 5Ds.

Zooming in shows how LED brake lights (and the amber bus destination sign) all flicker at high speed.

detail of image showing movement blur

Yes… this is a nuisance when wanting to show car light trails in a night time shot.

Any filter can effect the quality of images taken through it. Looking carefully at some of the exterior shots, I could see a slight loss of detail in my images from the 50MP 5Ds. However, looking at the indoor shots (liveview and a hefty studio camera stand) I’d put much (but not all) of the loss of detail down to using long exposures on a windy day, when not using my heftiest tripod.

The filter has settings marked on it, but take these as a rough guide at best. Neither the darkest or lightest transmission of the filter matched up too closely with the ‘min’ and ‘max’ markings on the filter, the the solid bars should be used for indicative purposes only.

82mm filter mounted on lens

If you add in the effect that polarising filters can have on the metering (and AF) systems of cameras, then such filters are distinctly more reliable to use with fully manual settings for your camera.

Colour cast

The filters also add a slight warming effect to your images. This is best shown in the series of photos I took using my small portable product photography light table.

The photos were all taken, tethered using live view and EOS Utility, with a Canon 5Ds. All were white balanced before shooting, using my ColorChecker Passport.

They range from a shot without any filter (1/10 s) through the minimum setting of the filter, half way though the indicator marks, three quarters the way, and finally at the ‘Max’ setting (20s).

series of photos with different ND filter settigns

I’ve pretty much equalised exposures in the Adobe camera RAW settings here, since accurate exposure setting needs quite a bit of care – more precision I’d suggest than you will get from the settings on the side of the filter.

If you look at the white balance settings of the image taken at the minimum filter setting, you can see the change bought about by the filter itself.

I’ve needed to bring the colour temperature down from 5050K to 4800K

white balance settings

If you look carefully, you’ll also notice the very strong tint adjustment for this lighting.

The light table is lit with CFL lighting tubes, which have a distinct greenish tinge.

That’s not a problem in normal use, since I have custom DNG profiles for this lighting setup, for all of my cameras (made with the ColorChecker Passport).

If I was using this particular filter for work outdoors, I’d be inclined to take a shot including the ColorChecker Passport, just for later adjustment options. I generally do this anyway if there is a mix of lighting. It takes just a few seconds and can be invaluable.

Too dark

When you look through the filter, you’ll notice that it’s actually possible to get it to go very dark.

This is beyond the ND400 value.

However, in this 30 second shot, you get a strange cross shaped darkening. This is due to the angle light is coming through the filter elements, and small variations in this across the scene. The exposure in the cross area would have needed to be well over a minute to show the coloured patches.

polarising cross with wide angle lens

A less obvious version from outdoors shows the beginning of this effect.

Maximum density setting, uneven illumination

If you are looking to use the filter at its darker settings, I’d suggest trying a sequence of test shots to get a feel for where this effect starts to come in, with any particular lens.

The longer the focal length of the lens, the less visible this will be.

If you’re using the filter at any of its darker settings, you should also be aware of potential light leakage via the viewfinder of a DSLR camera. My old 1Ds series cameras had a small mechanical shutter built in to the viewfinder, but with my 5Ds I have a rubber cap (on the camera strap) that clips over the eyepiece.

Filter comparisons

There are a number of different notations used for ND filters.

This table shows a comparison between them and how much light reduction they offer.

ND1xx Notation
ND.xx Notation
NDxx Notation
Fractional Transmittance
Optical density
f-stop reduction
% transmittance
1 1 0.0 0 100%
ND 101
ND 0.3
ND2
1/2 0.5 0.3 1 50%
ND 102
ND 0.6
ND4
1/4 0.25 0.6 2 25%
ND 103
ND 0.9
ND8
1/8 0.125 0.9 3 12.5%
ND 104
ND 1.2
ND16
1/16 0.0625 1.2 4 6.25%
ND 105
ND 1.5
ND32
1/32 0.03125 1.5 5 3.125%
ND 106
ND 1.8
ND64
1/64 0.015625 1.8 6 1.563%
ND 2.0
ND100
1/100 0.01 2.0 6 2/3 1%
ND 107
ND 2.1
ND128
1/128 0.0078125 2.1 7 0.781%
ND 108
ND 2.4
ND256
1/256 0.00390625 2.4 8 0.391%
ND400
1/400 0.0025 2.6 8 2/3 0.25%
ND 109
ND 2.7
ND512
1/512 0.001953125 2.7 9 0.195%

More than just long exposures

Note that although I’ve shown examples here utilising long exposures, it’s just as relevant to use them on fast lenses, allowing you to shoot wide open in daylight. Great for portrait work where the benefits of a f/1.2 lens are irrelevant if your camera shutter won’t shoot fast enough.

If you shoot with flash in daylight, an ND filter also allows you to work at a wider range of apertures and to crank up the flash output (to match or exceed daylight) without running into sync issues.

Although I don’t do video, I should mention that such ND filters are very useful in bright conditions, allowing wider lens apertures to be used for more precise control of depth of field. Do watch for the colour shifts though.

Conclusions

The MBP filter is well made and performed well on some expensive glass and a high resolution camera.

The variable ND filter is a simple device that can be very useful when your camera ISO setting just won’t go low enough to get the exposure or aperture you need.

Watch out for slight colour shifts (easily correctable if you shoot in RAW) and don’t forget that a tripod that is great for quarter second exposures may be found wanting for 15 second ones on a windy day.

One other thing to remember is that you are using polarising filters, so just as at the darkest settings, there are some unexpected results, then at the lightest setting, you have a plane polariser on the front of your camera – watch out for unwanted contrast changes, visibility of reflections, and potential oddities with metering and autofocus.

Summary

Effective variable density neutral filter to reduce light by between 1 and 8 stops.

Available from MPB in their range of filters
Example 82mm £59.99

ND variable filters from B&H or Amazon.com in the USA.

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