Balancing The Light - Graduated Neutral Density Filters

The Fish River Canyon photographed using a Nisi 2 stop Hard filter on the Laowa 12mm ultra-wide with it's dedicated filter holder (Nisi also makes a filter holder for this unique lens)

Despite the incredible gains in photographic imaging over the last 20 years, one of the problems that photographers still have to contend with is the way that the visible range of tones in an image is recorded on a sensor (or film for that matter). Nowadays we talk about dynamic range as the range of tones that a digital sensor can faithfully reproduce without either blowing out the highlights in a burned out explosion of white, or sinking the shadows into unfathomable inky blackness. The way we have gotten round this for the last 30 to 40 years is through the use of graduated neutral density filters (or GNDs for short). These are particularly important for landscape photography as it is in this genre of that we most come across the problem of bright skies against a dark foreground.



Essentially a GND is a filter that is part clear and part tinted (like sunglasses). The idea is that the photographer can place the filter so that the tinted portion sits over the sky in the imaging frame and the clear portion over the foreground. The tinted portion blocks a certain amount of light from passing through, effectively balancing the exposure between the bright sky and the dark foreground.

To illustrate this, set a camera to spot metering mode and point it at the sky. Imagine the reading comes back as 1/125th of a second at f11. Now point the spot meter at the foreground in the image. In all likelihood the reading will come back somewhat darker, possibly something like 1/30th of a second at f11. The idea is then to place a GND that is the equivalent of two stops of light over the sky, while allowing the foreground to remain unfiltered. This would mean that the sky would now require an exposure of 1/30th of a second at f11 - the same as the foreground. The exposure has been balanced.

Balancing an exposure was particularly important in the days of color transparency film as these films had an extremely narrow exposure latitude - essentially the same concept as dynamic range. Fuji Velvia, a staple for many photographers had a published exposure latitude of +/- 1/2 stop. This is different to what most photographers referred to as exposure latitude being the range of light that the film could handle, which was closer to 4 stops at it’s extreme (most of the photographers I shot with thought 2 stops was about the limit for usable imagery unless you were going for pure blacks in the shadows). Either way, colour transparency film was a lot harder to work with than the digital sensors of today with their dynamic range of up to just under 15 stops of light (DXO Mark tested the Nikon D850 to a 14.8 Ev dynamic range https://www.dxomark.com/Cameras/Nikon/D850).

An image shot by my wife, Jackie, on a photographic trip into the Drakensberg using the Sirui ND8 Soft filter in a Nisi V2 holder.

So, with ever increasing dynamic ranges, why is using a GND even necessary anymore? Surely we can shoot and simply apply a filter effect in our post-production workflow? The principle reason is pixel quality. A digital sensor requires a certain amount of light to capture optimum data for the image. Too little light and noise in the shadows starts to become an issue of concern in the image. However, increasing the exposure so that there is better data in the shadows means that the potential to clip our highlights increases. The answer, at least if we want single image capture (as opposed to an exposure blend or High Dynamic Range Image of multiple exposures), is to still use GNDs in order to balance the overall exposure.

 

Understanding the Types of Graduated Neutral Densities

In the previous article on Neutral Density Filters (ND for short), the range of light blocking densities was described. GND filters work in the same way in that we have a range of light absorbing/blocking densities available to the photographer. Additionally photographers can choose from a range of sizes and transition effects between the neutral density portion of the filter and the clear portion of the filter. Putting together a filter set means understanding the differences between Soft, Medium, Hard, Reverse, Blender and Strip filters. For clarity I have included the same table below that was used to illustrate the difference between the various brands of filters available. If you are using a Lee filter, the nomenclature 0,9GS would stand for a 3 stop soft graduated filter. A similar Sirui would be marked GNDS8 and Soft ND8(0,9) while the same Nisi filter would be marked Soft GND8 (0,9). Old time users of the Lee system are usually the most comfortable with the nomenclature, but usefully, new comers to the market, Sirui and Nisi, mark their filters pretty thoroughly making it fairly simple to understand what each filter does.

Neutral Density Nomenclature as on filters
Light Loss	1 Stop	2 Stop	3 Stop	4 Stop	6 Stop	10 Stop	15 Stop
Shutter Speed (example)	1/8th	1/4th	1/2	1 sec	4 sec	1 min	30 min
Lee / Nisi	0,3	0,6	0,9	1,2	1,8	3,0	4,5
Sirui / Nisi / Cokin-Formatt	ND2	ND4	ND8	ND16	ND64	ND1000

If you understand the table above, the density of the filter is fairly easy to understand. The gradient itself is what confuses a lot of first time users. Simply put, a Hard filter is one that has a very short transition between the ND and the clear portion of the filter. A Soft filter has a larger transition area, hence ‘soft’ gradient. The idea is that one would choose a gradient dependent on the type of landscape you are photographing. Seascape photographers tend to gravitate towards the Hard type of GND as they are often photographing a dead straight horizon. Using the same filter on a building though would mean having the top portion of your building underexposed since the building would be under the ND portion of the filter. This is where a Soft filter is more useful. Photographers capturing cityscapes, mountains or areas where there is gradual change or varying change between the sky and the foreground would opt for Soft GNDs. Out of interest Cokin/Hitech tried to meet in the middle by creating what they called ‘Medium’ filters. Most of the cheap Chinese generic 100mm filters that are on the market are also ‘Medium’ filters rather than Soft or Hard. Lee have such a strong following that they have also developed Very Hard filters which are only slightly more graduated than simply using the edge of a conventional ND filter.

 To complicate matters for the photographer starting into a filter system are the Blender, Strip and Reverse filters. The Blender essentially goes from full ND to clear over the entire length of the filter. It is used when there is a gradual change in the light you are photographing, such as a fog or  mist encased forest (I have never had one so have never had the chance to experiment with it). Strip filters, also known as Horizon filters, have a thin strip of ND tinting in the horizontal centre of the filter. The idea is that they can be used for the band of sky between the horizon and the cloud base, particularly during sunrise and sunset. They are tricky to use and require careful placement as well as zoom/lens choice as the band of ND must match the band of bright sky in the image.

The Soft grads that were used in this article are from left, the Sirui, Nisi (both glass) and Lee filters (resin). Despite all being of the 'soft' type, the differences in the gradation of fairly obvious.

The Reverse grad is more interesting and useful than the previous two in my opinion. This is a special type of GND that has a hard edge, that then progressively lightens towards the top of the filter almost like an upside down Blender filter. It has been designed specifically for early morning late afternoon/twilight photography. Just before and after the sun crests the horizon there is a brighter band of light along the horizon, but the light dims as you look above and to the zenith. The filter tries to compensate for this.

Types of hard edge: On the left is the Nisi 0,6 Hard grad with an almost discernible two step gradation. The Lee 0,6 Hard grad to the right of it has a more even gradation. The reverse grad (second from the right shows a distinct two step hard edge and then a gradual and smooth transition to the top. The hard edged horizon filter on the right seemed promising, but I ended up not being able to use it as the band was simply too broad for the lens set that I work with.

 

The Brand Decision

For those who have read the previous articles on the 100mm system, it will have become evident that I had at my disposal three filter systems to try out: a full Lee system (that I have personally built up over the years), a Sirui system (courtesy of Willem Foster at the The Sunshine Company) and a Nisi system (courtesy of Hougaard Malan at Landscapegear.co.za). Unfortunately I didn’t have a full system of either Sirui or Nisi, so have had to look at only the comparable filters that were available, in this instance, the 3 stop soft grads. Along with the soft grads I also had a 2 stop hard grad from Nisi which I bought to replace a Lee filter of mine that was scratched, and was also sent a 5 stop Soft grad from Sirui and the horizon filter from Nisi. So no, not a full set of each brand, but enough to get an idea of how the various brands compare.

Photographed with the Laowa 12mm ultra wide and it's dedicated holder Sirui 10 stop solid neutral density and Lee 0,3 Hard grad.

 

 Sirui

The Sirui filters are glass filters with a very slight and angular bevel to the edges. There is a distinct pinkish sheen to the surface of the glass which I suspect is a type of multi-coating. The coating itself also makes the surface quite slippery. Slippery enough in fact that the Sirui filters will slide out of the Lee holders and the Nisi simple V2 holder (very slowly, but it will slide and fall out). They do fit neatly into the Sirui holder and the Nisi V5 pro holder though. The fact that the filters slip out of the Lee and basic Nisi holders is a serious cause for concern. While shooting a time-lapse in the Berg with the Sirui I discovered that the filter had slid almost completely of the holder. If I hadn’t discovered this the filter would probably have fallen out and smashed on the rocks below the tripod (I have a solution to this below).

Currently Sirui only offer soft grads (at least to the South African market). This does limit the scope of the Sirui system for prospective users. This is a pity as I found the glass of a very high quality, good enough in fact that I actually prefer the Sirui to my original resin Lee filters (with some caveats).

The filters come packaged in a velvet finished pouch of a very high quality. The only issue I found with the pouches is that they are actually a little tight for the filters, meaning it is quite difficult to remove the filter from the pouch. With practice this gets easier, but it can hinder your speed when you are setting up for a shot.

 

Nisi

Nisi round the corners of their glass filters which I really liked. The bevel on the edge of the filter also looks more rounded than angular, which gives a very high-end feel to the filters. The rounded corners and edges also made it very easy to slide the filters into any of the holders that I used. The quality of the filters is simply superb. Like the Sirui filter they seem to have a muli-coating, but it isn’t quite as reflective or slippery.

The Nisi filters come in a very nice slim faux leather pouch with a soft velvet inner (in 18% grey even). I think I liked these pockets the most as a filter pouch as they were easy to access, slim enough to fit several in a bag and sturdy enough to actually protect the filters.

Nisi offer pretty much the whole gamut of filter types including Reverse grads and Strips (Horizon filters). They don’t do as many ND options, but offer the grads in Hard, Medium and Soft. In reality their Medium is more like the Sirui and Lee Softs, while the Nisi Soft is closer to the old Cokin/Formatt Blender. The holders are exceptionally good quality and value, offering both a simple holder and a more complex ‘pro’ version with included polarizer. 


 

 Lee

The primary difference between the Lee and the other filters that I tested is that the Lee filters are made of optical resin. This makes them significantly lighter than the glass filters from Sirui and Nisi. Being resin, they are also less prone to breakage. I have personally been using Lee filters for the last decade and have only managed to actually break one resin filter in that time, and it happened to be attached to the lens when a strong gust of wind knocked my tripod over. It wasn’t just the filter that broke. In another similar incident while shooting amongst the quiver trees in Namibia, a rock was accidentally dislodged and my whole camera went smashing into the ground. On this occasion the resin filter took the brunt of the impact and didn’t actually break (but was badly scratched and saved the Lens from any damage). The point is that the filters are really tough.

Unfortunately, being resin, although the the Lee filters are tough, they are prone to scratching. I regularly find myself replacing filters, not because they are broken, but because of fine scratches that do show up in the final images. The scratches are particularly obvious when shooting anywhere into the light (or even obliquely for that matter). Lee do make glass filters (evidence by the fact that their solid neutral density filters are all made from high quality coated glass), however these filters are extremely expensive. At least here in South Africa, they are also a special order item. So if you are using Lee, or are considering investing in their filters, you are likely using or thinking about their resin filters.

For years Lee have been considered the ‘quality’ choice against the likes of Cokin and Formatt/Hitech  (of which the latter ultimately bought out the former). In particular, Lee was seen as being more optically neutral than the Cokin/Hitech filters. Note, I say more neutral, not completely neutral. All photographers used to using Lee filters have come to accept the slight strange greenish cast to the neutral density portion of their GND filters. Still, the cast wasn’t anything as strong as the purple magenta cast found on the Cokin/Hitechs, so most photographers have opted towards the Lee and learned to deal with any color inaccuracies that they came across.

Lee offer the most comprehensive range of neutral densities covering even half stops of light between 1 stop and 4 stops in their GND range. Recently they have also introduced a range of reverse Hard grads similar to Nisi’s. On top of the Reverse grads, Lee offer all of theia GND filters as the usual Hard and Soft options, but also as Medium and Very Hard. Their commitment to the needs of photographers is truly exceptional with filter sizes beyond the 100mm filters being the excellent Seven5 (75x90mm and similar to the original Colin P series) for small cameras and the enormous and pricey SW150 (150mm on the short side) for ultra wide lenses (Nisi have also introduced a 150mm system).

The 100mm holder is due for a refresh though. It does show it’s age when compared to the Nisi V5 Pro and Sirui holders which both incorporate a special polarizer that can sit between the 100mm square filters and the front of the lens. The Lee still requires a 105mm thread adapter that sits in front of the filter stack. Considering that the Seven5 system has it’s own excellent polarizer, I suspect that it is on the to do list for the Lee engineers.

In Use  

Before discussing the filters in use it is useful to look at the comparison images above which show any potential colour shift in the neutral density portion of the filter. The images were shot under controlled studio lighting (Elinchrom BRXi) with the neutral density covering the full front element of the lens. RAW files were processed in Adobe ACR using the unfiltered image as a 'controller' from which White Balance was set (click on the image for a larger view).

To be fair I have been using Lee 100mm filters for quite some time now, so I tend to view Lee as the benchmark in terms of use (the older Cokin/Hitech fails dismally in my opinion due to the holder design which has admittedly been markedly improved with the new ‘Firecrest’ range, but still falls behind the designs by Nisi and Sirui). True to form the Lee holders were still the simplest to use in the field. Apart from the Nisi V2, they were also the lightest.

Interestingly all three types of filters that I tested had very different tactile feel to them. The Sirui is genuinely slippery to the touch, while the Lee felt the most matt and were also the least reflective. The Nisi are the heaviest in the hand, but also have the nicest edges as they are carefully rounded, even at the corners. The result of the rounded corners on the Nisi filters is that they are the easiest to insert into any of the holders that I used. Not so the Lee and Sirui which both have hard corners. Here the usually exemplary V5 Pro holder shows a slight quirk. The V5 grips the filters on the edge rather than having deep rails like the Lee and Sirui (and Laowa) holders. Due to the design you have to watch how the filter slides in otherwise the edge can jump between the first and second slots. It’s only really an issue with the slightly flexible resin Lee filters though. There are no similar issues with the glass Nisi filters, nor the Sirui filters.

Holders
Filters		Lee	Nisi V2	Nisi V5 Pro	Sirui
	Lee	YES	YES	YES	NO - The edges of the GND scratch and the ND won’t slide past the holder’s light baffle
	Nisi	YES - be aware that there have been reports of the filters gradually slipping out of the front filter slot	YES	YES	MOSTLY - No problems with the GND, the ND won’t slide past the holder’s light baffle
	Sirui	NO - The glass slips out of the holder	MOSTLY - The glass GND does gradually slide out of the holder. Can still be used though with caution	YES	YES

All of the filters had a slightly different effect on the color of the light. In use I actually found the Sirui to possibly be the most color neutral with the Nisi very close on its heels. The Lee reduced contrast the most and also had a noticeable greenish cast over the ND portion of the filter. However, both the Lee and the Sirui were simpler to position as the Nisi Soft grad was more like a blender than the other two. I suspect that the Medium filter from Nisi is closer to the Soft filters from Lee and Sirui, so be aware of this when selecting filters.

I wasn’t able to test the Hard grads properly, but was able to look at the differences at least between the Nisi and Lee 0.6 Hard GND filters (remember, Sirui don’t make a Hard filter). Nisi have a slightly different approach to the actual edge of the ND. They do almost two sections of translucence whereas the Lee has a more uniform gradient look to the edge (ironically looking at their recently announced Reverse grads they have done the exact opposite whereas Nisi do a gradual gradient across the whole upper portion of the filter). The same color cast was evident in the Lee 0.6 Hard as was the 0.9 Soft that I used for the test*.

A seeming loss of contrast was also evident in the neutral density portion of the Lee filters (see the images of the colour checker passport above). Most photographers probably won’t even notice this in their day to day shooting. It was only when I compared the results of the Lee to the Nisi and Sirui glass filters that I even became properly aware of it to be honest. Essentially, the same issues that plagued the old Big Stopper from Lee filters down, although in not as pronounced a fashion, it the GNDs.

Finally, as evidence that no single manufacturer seems to be able to produce the perfect system, although I would heartily recommend the Nisi v5 Pro holder as the best holder, I’d probably replace the adapter threads (i.e step-up rings) with the Sirui step up rings which are easier to take on and off and seem to have more thread with which to work.

Image shot without any filtration

Sirui 0,9 Soft Grad

Nisi 0,9 Soft Grad

Lee 0,9 Soft Grad

Something to be very aware of is also how the filters fair in the different holders. I have mentioned before that the Sirui filters literally slide out of the Lee and Nisi V2 holders. Initially I thought that this didn't happen with the Nisi filters and that it was unique to the slippery coated Sirui grads coupled to the heft of the glass compared to resin. Then, while shooting at the Fish River Canyon while the temperature soared to just below 40 degrees centigrade, I noticed that my Nisi filters were also slipping! This didn't happen shooting in the Drakensberg where the ambient temperatures were significantly cooler. My theory is that the plastic Lee holder becomes a little more flexible in the heat, with the result that it can't firmly hold any glass filter!

My solution is inelegant, but it does work. Simply add a thin strip of black electrical tape to the very edge of the Sirui and Nisi filters and they suddenly work perfectly on the Lee holder system (trim using a sharp craft cutter). No, it's not perfect, but does mean that using the glass filters reliably is now possible on the older Lee system. this is important as many photographers already have a large Lee system, and cannot easily change the entire filter system for Nisi or Sirui. This fix means they can mix and match filters and holders to better meet their filter requirements. 

Image shot with a Sirui 6 stop solid neutral density filter and a 0,9 Stop Lee Soft grad

A Note on Carrying

 

As I have pointed out, I use filters a lot, which means I have a fairly large set of filters that I carry with me. Although I have commented on slip covers for each of the filters, none of them is ideal if you are carrying more than 3 filters with you. Nisi give you their filter carrier if you buy any of their advanced kits, and you can separately buy a filter box that holds up to 8 filters. Personally, I really disliked the Nisi carry cases. They are heavy and hard with sharp corners that make it impossible to carry comfortably. To date, the best filter carrying method I have come across is the Lee Field Pouch. This is an excellent canvas concertina style case that is light and tough and holds up to 10 filters. The strap could be better made admittedly (the stitching on the loop gave way on mine, but it’s easy enough to repair). The pouch has replaced my previous carrying solution which consisted of homemade sleeves (made from high quality felt and gaffer tape) that were carried in a home modified travel bag from Cape Union Mart. The point is that the sleeves that the filters come in are really not the perfect way to carry multiple filters.You tend to be fiddling with multiple filters when you are selecting the right one, meaning that opening and closing individual sleeves is a hassle, as well as taking up unnecessary space in the bag. If you are using filters, do yourself a favor and just buy the Lee Field Pouch. It is worth it.

Conclusion

Before delving into any meaningful conclusion, it is worth considering the current price of the three different filter brands:

Filter Pricing
Brand	Individual Filter	Set of Three
Lee Resin Filter	R1975	R4945
Nisi Glass Filter	R2295	- (n/a but some other kits are)
Sirui Glass Filter	R2040	- not available at writing, but will be shortly according to www.sunshine.co.za

Also worth considering is that www.landscapegear.co.za is currently running a massive promotion on Lee filters (some as much as 50% off!) and that www.studio22.co.za are also running a Sirui special of 20% and will also be doing a Black Friday deal on November the 24th (according to the good folks at the Sunshine Company who are the distributors of Sirui gear in South Africa). 

We really have amazing options available to us as photographers these days. It doesn’t seem so long ago that we had little choice, at least in South Africa, and were saddled with choosing between Cokin and…Cokin. The really good news is that for the most part the filters and holders are inter-compatible (to a certain degree), meaning that you can be brand agnostic.

I found it hard to select a favorite brand amongst the filters that I used. In fact the ability to be brand agnostic means that you can select the best from each range. If you are starting from scratch though it’s hard not to take advantage of the incredible pricing and quality of the Nisi kits (in comparison to the Lee kits).

So my takeaway, if you are starting from scratch, is to get the Nisi V5 Pro holder with the polarizer. This gives access to any of the filters that are available and provides a simply excellent polarizer into the mix. Next, if you need a 0.9 or stronger soft grad, go for the extremely well-priced Sirui filters which work well on the V5 (and are heavily discounted at the moment). After that it comes down to a preference between glass or resin in terms of which filters to get. On the face of it, Nisi offer better image quality than the old Lee resin filters, but at the expense of weight and potential for breakage.

If you have an existing Lee system it gets a bit more complicated. You cannot use the Sirui filters safely as they just slide out of the holder. A work around though is to add a tiny sliver of black electrical tape to edge of the glass. Do this and the filters work perfectly with the Lee holders. Apart from working in extreme heat, I found that the Nisi filters worked fine on my holders, but have heard others say that they also slip in the Lee holder, in particular in the second slot of the filter (furthest from the lens element). I am impressed enough with the Nisi glass that I have replaced a scratched Lee 0.6 Hard with a glass Nisi equivalent.I suspect as my Lee filters get scratched or broken I'll probably continue to replace them with Nisi equivalents.



*Bear in mind that my Lee filters are not new. The newest GND I have is a 0.9 Soft which is at least a year old (replacing a scratched 0.9 that was a good 5 years old).

Part 1 - The 100mm Square Filter System : Part 1 - The Filter Holder
Part 2 - Big Stoppers - Blocking The Light