Neutral density filters. They are one of the mainstays of modern outdoor photographers. Look in any pro’s or serious hobbyist’s gear bag and you’re virtually assured to find at least one, if not more, ND filters.

I like a good analogy as much as the next person, and one of my favorites concerns calling ND filters “sunglasses for your camera.” Feel free to use that line.

ND filters block out light which allows us to use longer exposures in conditions which would normally be far too bright. This enables motion blur and other dynamic characteristics to be present in your photos when they otherwise might not be possible. But not all ND filters are created equal. Generally, the case exemplifies the “you get what you pay for” notion that with higher cost comes a higher grade product in terms of build and optical quality.

A couple years ago (has it been that long?) I reviewed the X3 line of ND filters from Breakthrough Photography. I was blown away by their quality and considered them to be virtually the best ND filters I had ever handled.

Now, the folks over at Breakthrough have introduced an updated version of the X3 line.

Aptly named the X4 Series. As with the previous review, I was hard pressed to find any negative points to mention of this new generation of filters. Still, let me show you the in’s and out’s of the X4 3-stop ND filter as well as a little bonus… we’ll also take a look at the brand new “Dark” CPL 3-stop. Hang onto your hats! Or… whatever you might happen to be wearing on your head.

X4 ND Build Quality

The X4 ND filters continues the same extreme performance as the X3 Series. For this review, I evaluated X4 ND filters with darkening grades of 3-stop, 6-stop, and 15-stop in a 77mm size. The majority of the images shown here display the 3-stop filter.

The construction of the X4 ND consists of a brass housing which holds a SCHOTT Superwite B270® optical glass element. There is a heft and solidity to the ND that is completely comforting. It is seemingly built for consistent professional use. The outside circumference of the filter sports deep cut “traction” ridges that superb gripping of the filter wet conditions or with gloved fingers.

And also, the extra grip makes it easy to attach the X4 to your favorite 4×5 large format camera when you ecstatically realize the filter size is the same… if you’re into that sort of thing.

Each side of the element is layered with eight coats of MRC (multi-resistant coating) which is an ultra hard hydrophobic substance that reduces glare and protects the filter element from dirt and moisture intrusions. The MRC16 (8+8 coats) nano coating is stated by the manufacturer to be physically harder than the glass of the filter itself. In my tests the water drops and dust particles can essentially be “blown off” the filter easily without the need for a lens cloth*. The MRC16 coatings, at least from a practical standpoint, seem to produce the kind of results stated in the product description.

*Important: never wipe dirt/grit/sand from a filter or lens. Use a blower to avoid damaging your precious gear.

X4 ND Sharpness, Color Cast, and Vignetting Results

It’s somewhat paradoxical that some of the strongest attributes of the X4 ND give me virtually nothing to write about at length. Breakthrough Photography market’s these as the “Worlds Sharpest ND Filter. 100% Guaranteed” and also as “…the most color neutral ND filter for the discerning landscape photographer”.

That simply is what the X4 delivers. There is no evident color casting observed in my tests. The sharpness? Every filter I’ve used in the X3 line up, and now the X4 Series, has offered incredible sharpness. The image quality produced by the X4 ND is quite literally second to none.

With X4 ND 6-stop
With X4 ND 3-stop
With X4 ND 3-stop

Vignetting is a common problem when using any type of light blocking photography gear. Darkening at the peripherals in both filters and lenses is just an accepted downside to our tradecraft at times. That being said, the X4 ND filters seem to be completely free of vignetting while being used with my semi-wide angle test lens (Sigma 24mm f/1.4) and full frame camera (Sony a7R Mk1). Even with the darkest X4 ND (15-stop) currently offered, there was virtually no discernable darkening at the edges of the frame caused by the filter. Here are three unedited images showing the 15-stop X4 ND in use.

No filter
15-stop at 10 second f/1.4
15-stop at 30 second f/16

The company states that these filters are completely free of vignetting at focal lengths 16mm and longer with full frame cameras. And I have to say, at least with a 24mm, that assertion is accurate.

X4 Dark CPL

Life occasionally offers us little bonuses. At the time I was being sent the X4 ND filters for this evaluation, Breakthrough Photography was developing a brand new “Dark CPL” filter. As a result, I was fortunate enough to also be able to include this prototype 82mm Dark CPL as part of this review.

CPL stands for circular polarizer. Just as with the ND filters, a quality polarizing filter is a mainstay of the professional outdoor photographer’s tool set. Polarizing filters essentially straighten lightwaves so that reflections and glare are minimized. Polarizers also serve to darken skies and make color tones appear more vibrant. Circular polarizers take this a step further by allowing the user to literally dial in the amount of polarization desired simply by rotating the bezel of the filter housing.

The X4 Dark CPL combines the effects of a polarizing and ND filters. The model I evaluated was the 3-stop version with 6-stop and 10-stop models also being available. At the time of this review, the per-orders of the X4 Dark CPL were being shipped out to customers according to the product’s Kickstarter page.

X4 Dark CPL Build Quality

The X4 Dark CPL features the same utilitarian traction housing as the X4 ND along with the same type of SCHOTT Superwite B270® optical glass and nano coatings. The construction of the X4 Dark CPL is exceptionally robust. What’s more? The X4 Dark CPL looks downright sexy with it’s contrasting polished and matte black design. That’s right. I called a filter sexy.

This is where the similarities between the X4 ND and X4 DCPL end. Where as the former sports a housing built from brass, the X4 DCPL is constructed from titanium. This makes the X4 Dark CPL lightweight yet astoundingly durable. Even the 82mm frisbee test filter felt quite nimble.

X4 Dark CPL Sharpness, Color Cast, and Vignetting Results

Great for those brighter days when you need a longer exposure time, the Dark CPL allows you to darken up a scene without the need to stack an additional ND filter with your CPL. The sharpness was again superb with no vignetting observed nor color cast.

Dark CPL with about half the amount of possible polarization applied
Dark CPL with full polarization applied

As a side note that is worth mentioning, I again used the Dark CPL with the same 24mm lens I used with the X4 ND filters. This meant that a step up adapter ring was needed for the 77mm filter thread to match the 82mm filter supplied. The adapter ring furnished by Breakthrough Photography was as well-engineered and sturdy as the filters themselves.

Final Thoughts on the X4 Series

Breakthrough Photography has consistently impressed me with their product. They offer extremely high grade filters with innovative designs which cater to the true photographer. As observed since the last time I reviewed their filters, Breakthrough continues to refine what i consider the best filters available for serious photography hounds.

The X4 ND filters along with the Dark CPL offer wonderful sharpness in a well made and usable package. Take into consideration the 25 year warranty the company places on their wears and the price tag (around $140US) becomes, if not a bargain, a well spent investment for those who want the absolute best in terms of image quality from their filters.

I can honestly say that I have found nothing but positive things to say about every filter I have ever evaluated from Breakthrough Photography.