Despite unstoppable technological progress, unfortunately, our camera is not yet able to see like our eyes, especially when it comes to dynamic range (the ability to see details in bright areas and dark areas at the same time). Surely we all remember the disappointment of our first sunset photo: our eyes saw a magic moment, but the pictures we got showed a white ball with black all around it.
Sure, at first we were quite happy with the idea of the silhouette effect, but soon we wanted something more.
Fortunately today there are several techniques to help our camera to see as we do, and in the end, everything can be summarized in two categories: Advanced Post Production and Photographic Filters. Today we will talk about the second technique.
Before we begin
Before we start, I want to answer a question I often hear: “why do you use filters instead of making everything in post production?”
This is a bit like trying to find an answer to the age-old Canon vs Nikon debate..for me the answer is actually very simple: first of all, I really suck at post-production; and second (and I think most of all), I really love to spend as much time as I can in the field struggling to get my shot in-camera with a single exposure.
If you want to put a little bit of technique in this answer, as we will see later, it’s also because there are filter effects that cannot be reproduced in post-production.
Maybe this is not the best method, but it is the one I use, and I will now try to share the experience I’ve gained over the years in order to let you choose and use your filters to the best of their ability!
Screw-On or Slot-In?
In order to choose the filters that suit us best, it’s necessary to understand the different types of commercially-available filters.
The first great division that needs to be explained is between the screw-on filters and slot-in filters.
The screw-on filters are screwed to the thread in front of your lens. They don’t need additional mounting accessories, just a lens with a thread to allow filters to screw in. The only lenses that cannot use these types of filters are ultra-wide angle or fisheye lenses, where the curvature of the first lens element is very pronounced.
The biggest advantage of these kinds of filters is that they prevent leakage of light between the filter and the lens, a problem that may affect the slot-in filter (but we will talk about this later).
Almost all of these filters allow stacking one above the other to use them simultaneously, but this is not advisable for two reasons:
- You will find that stacking is not practical in the field, because when you’re taking pictures, any changes you want to do, you’ll want to do them really quickly.
- Stacking filters (or using thick filters) will introduce the issue of vignetting on wide-angle lenses. For that reason “Slim” filters are available: they lack of front thread in order to reduce thickness.
When you buy a screw-in filter you must choose the size according to the size of your lens. As you can easily understand, another disadvantage of this kind of filters is that you need one filter for every size of lens you own.
Tip: You can buy an adapter ring called a “step up.” This allows you to mount filters with a diameter greater than your lens. For example, if you have a lens with 82mm filter size and one with 77mm, with this adapter you only need to buy the 82mm filter!
The slot-in filters are the second big family of filters. The main characteristic lies in the fact that they cannot be screwed onto the lens, and instead require two special accessories: an Adapter Ring and a Holder.
The Adapter Ring is a special threaded ring that mounts onto the thread of your lens (the same place you install the screw-in filter). The purpose of this ring is to allow the Holder to be mounted on the camera, not to attach filters.
Slot-in filters (and the adapter ring and holder) are generally more expensive compared to the screw-in solution, but they introduce a few advantages that make the choice of this family almost mandatory for landscape photographers:
- You can install many filters without having the vignetting issue
- Replacing filters in the field is really fast and comfortable
- Some slot-in filters are not available as screw-in
- If you are using ultra-wide lenses you can still use filters with a special holder system
The most common slot-in systems support 100mm filters: these are designed mainly for DSLR with lenses from wide angle to telephoto. Recently, specially sized systems for mirrorless cameras and ultra-wide lenses have been introduced on the market, allowing you to use filters up to 180mm in size.
There are many manufacturers of Adaptor Rings and Holders, but I would certainly push you to focus on quality and longevity.
As we finally know something more about the two main families of filters, let’s have a look at them!
Types of Filters: UV Filters
Before starting, an introduction is mandatory. The goal of this tutorial is not philosophy, but to give you elements to let you buy the filters you need. But if you have a $3,000 camera and lenses that cost you thousands dollars, do you really want to put a coke bottle filter in front of them? I didn’t think so.
The general advice is: focus on quality
The UV filter is generally the first filter we come across during our photographic career. Even if it’s available also as slot-in, this filter is widely used as a screw-on version.
The main point I should make about this filter is that, in the digital era, it’s absolutely useless.
The benefit of the filter was to protect the film from UV rays, but today this function is already integrated in your camera. For this reason, this filter is often used only as lens protection from scratches and dirt. It may be a reasonable choice, and I confess I’ve used it for several years, even after I started using slot-in filters.
After some time, however, I also came to the conclusion that they are perfectly useless for these reasons:
- We do not need to protect the lens. If you are reading this article it is because you want to use other filters, and the lens will be protected by whatever filter you happen to be using this time.
- Although only slightly, each filter we use reduces the overall quality of the image, so it makes no sense to place a useless piece of glass in front of our lens.
- Every filter you install increases the possibility of vignetting issues, and believe me, every millimeter can make a difference.
- The front element of your lens is the easier and cheapest one to replace in case of damage. In addition to this, a small scratch on it will not affect the image quality.
I’ve just mentioned UV filters, but the exact same thought applies to variants that are called Protector and Skylight. If you have money to invest in filters, we will find a better way to spend it.
In my bag: none
Types of Filters: ND Filters
ND (or Neutral Density) filters are the first example of filters that cannot be recreated in post-production. They have a different use depending on the applied field, but in landscape photography their task is to decrease the shutter speed. Yes, if you love long exposures, you cannot live without them.
These filters are sold both as screw-on and slot-in, and the choice between the two depends only on your needs. We can compare the two filter families for hours and hours and it will still be difficult to find an absolute truth, so my advice is as follows:
- If you don’t need to use Graduated ND filters (we will discuss about them shortly), the screw-on solution is for you. This solution is great if you only photograph waterfalls, rivers in forests, or, generally, in places where there is no big difference in the exposure between different areas of the scene.
- If you are going to use GND filters, the slot-in solution is recommended as the use of a screw-on ND with a slot-in GND is uncomfortable in the field.
Each filter, both slot-in and screw-on, is characterized by a fundamental parameter: namely, the ability to reduce the passage of light. The higher is the value, the longer it takes for the sensor to get the same amount of light.
Manufacturers express this value in different ways: f-stop reduction, optical density, and ND filter factor. Below you can find an example of correlation between the aforementioned classifications.
The most obvious question is: it is good to have them all? And the answer is really simple: no.
First of all, having all the possible gradations in our backpack is impractical, as it would require a dedicated backpack, in addition to being a very costly solution!
My advice is to select two or three filters at most, according to your photographic habits. You will see that using say, a 6 filter stop properly (i.e. not to push to the limit the settings of your camera to get a correct exposure), you’ll be able to move from 5 to 7 stops just by changing your camera’s basic settings (ISO/shutter speed/aperture).
As I am a lover of seascape long-exposures, my choices are: 3, 6, and 10 stop. Three filters, and with these, I can handle all of the situations I run across.
As we’ve seen, both screw-on and slot-in filters have advantages and disadvantages. If you are entering the world of filters for the first time and have no idea if you will love it or not, the choice could be complicated.
My advice is not to immediately buy all the filters that you believe you need: start with a good quality screw-on filter with a good price tag. In this case, my advice is to focus on the ND64 (6 stop).
Another highly debated topic is the choice between resin and glass filters. From my personal point of view, if you are following the advice in this guide, do not bother even a minute, because in terms of quality the glass offers the excellence.
Just keep in mind that a glass filter will almost certainly break if you drop it, unlike those made of resin. On the other hand, the filters in resin are extremely sensitive to scratches and more likely to have a color cast.
But be careful, all that glitters is not gold! Many manufacturers state that they are selling optical glass filters when they are not. I mean, there are thousands of optical glass types, but just a few of them are made for high precision optical applications. For example, don’t trust too much those are selling you an optical glass filter made of a B270 glass..
Here a short list of the qualities you should look for:
- Made of optical glass (at least H-K9L)
- Color cast free
- Hydrophobic coating
- Vignetting free
Anything else is absolutely secondary. (I found a brand that makes fungus-free coatings..absolutely funny!)
But how to use these filters independently of the shape and material?
Actually, it is very simple: take your camera and make an exposure reading of the scene without a filter, and depending on the shutter speed that you got, calculate the shutter speed correction with the filter mounted. For example, if your reading tells you 1″ and you are going to use a filter of 3 stops, once you mounted the filter you will need to set a shutter speed of 8″.
Note: It’s almost impossible that the filters you buy have exactly the declared f-stop reduction. It’s always good to know the exact optical density of the filter you’re using because in a long exposure, even 1/2 stop of difference can cause minutes error!
To measure the exact intensity of your filter do the following:
- Choose a room in your home, turn on the lights and close the windows (we need a place where the lighting is perfectly constant).
- Mount your camera on a tripod and take a photo of the room until you get a shot with a good histogram. Note down all the parameter (ISO/Aperture/Shutter speed) of the shot.
- Mount the ND filter and compensate the shutter speed obtained before according to the f-stop reduction introduced by the filter.
- Take a picture with the ND filter
- Now look at the histogram of the photo taken with the filter and compare it to one taken without. If they are approximately superimposable, the filter intensity stated by the manufacturer is real; if the new histogram is shifted to the left, your filter has an intensity greater than that the one declared; if it is moved to the right, it has a lower intensity.
- If the two histograms are not superimposable, take another shoot changing the shutter speed to obtain a histogram approximately similar to the one of the picture without the filter.
Note: in my life I’ve never used a filter with the intensity stated by the manufacturer. This test will take away a bit of time but it will save you a lot of photos.
Tip: once you get the real f-stop reduction of the filter (that could be something strange like 6 ¾ for example), build your own shutter speed conversion table and fix it to your tripod! Another possibility is PhotoPills app for your iPhone, the only one that allows you to convert the shutter speed for non-standard f-stop reductions!
In my bag: NiSi Filters 100mm ND8, ND64 and ND1000
Types of Filters: GND Filters
Although formally you can find them in the screw-on version, these filters are an absolute prerogative of the slot-in world. (If someone tries to sell you a GND screw-on filter, run!)
GND filters, or Graduated Neutral Density, consist of a rectangular plate of glass or resin characterized by two distinct areas: an area completely transparent, and a dark area, which is nothing more than an ND filter like the one previously discussed.
Those filters are able to overcome the problem we mentioned at the beginning of this article: the human eye sees better than your camera, whatever it is.
As your camera is not able to see at the same time very bright areas (usually the sky) and very dark ones (normally the rest of the scene), you can use these filters to cover with the dark (ND) area the bright area of the scene, matching its brightness with the darker area of the scene.
The transition area on the filter, between light (transparent) and dark (ND) determines the type of GND filter you’re working with. There are four types available on the market: Hard, Soft, Reverse, and Medium.
- Hard edges filters are characterized by a clear boundary between the transparent and ND area. They are therefore used when the separation between the bright and the dark areas of the scene is very defined, such as the horizon at sea.
- Soft edges filters are characterized by a soft transition, and therefore are used where the transition between light and dark areas is not so clear. A classic example is a shot in a mountainous area.
- Medium filters are basically used as when neither the Hard nor the Soft filters suit the situation. They are extremely useful for example when you want to use a Hard filter but there is something that exceeds the horizon line. By positioning the transition area so as to match the part of the image where the skyscrapers or the promontory with the lighthouse exceed the horizon line and go into the sky, we will be able to balance the exposure in a very effective way.
- Reverse filters are nothing more than Hard Edge filters with the ND effect that fades away the more you move from the line of separation to the upper border of the filter. Basically, they were invented to better manage sunrises and sunsets, where the light is more intense on the horizon line.
Using these filters is very simple: make an exposure reading on a light area in the scene, then do the same for a dark area, and finally calculate the difference between them in f-stops.
This difference will tell you the f-stop reduction needed to balance the exposure.
Let’s assume that the light meter reading for the sky is 1/250” and the one for the rocks in the foreground is 1/60”. The difference between those readings is 2 stop, so to balance the exposure you must use a 0.6 (2 stop) GND.
Once the filter is chosen, you should insert it inside the first available Holder slot and cover the bright area of the scene (in the previous example that’s the sky) with the dark (ND) area of the filter.
Tip: A Holder is not mandatory to use a GND filter! You can just hold the filter with your hand in front of the lens! For a shot with a shutter speed up to few seconds, your only problem will be the correct alignment of the filter. For shots of minutes, even if your hand is not perfectly still, the final result will be more than great, try it if you don’t believe me!
The holder is required if we want to use multiple filters together (or when you start having cramps on your hand!)
As you can imagine, just like the ND filters seen previously, different sizes and gradations are available for each of these filters in order to meet the needs of all landscape photographers.
Again, if this is your first purchase, it is quite easy to go crazy.
Similarly to the ND filters, it’s not necessary (in fact it’s almost wasteful) to have all types and gradations of GND filters in your bag. I am convinced that more filters you have in your backpack, the more difficult it will be to choose which one to use when shooting, so as always, the advice is: few but good.
For example, in my backpack, you’ll find just a few of them.
But how do you choose between all the possibilities?
Regarding the typology, if you are a seascape lover, a Hard filter could be a perfect choice, but if it is our first purchase focus on a Medium filter.
If you had a look at my gallery you can easily guess that the Hard variant is my favorite, as almost all the horizon lines in my pictures are well defined. A good start may be given by a couple of filters, like a Hard and a Medium.
Regarding the gradation, I suggest you avoid the 0.3 (1 stop) filters because the situations when these are required are unusual and rare.
During a beautiful sunset, the difference in brightness between light and dark areas will be quite strong, so the 0.9 (3 stop) filters are probably the ones you will use the most. If you are a storm chaser like me and you love taking pictures even when the sky is overcast, the 3 stop filter can be too strong and a 0.6 (2 stop) filter may be a better ally.
Regarding the Reverse filter, I advise you to not go below 0.9 gradation.
Finally, when it comes to materials, the considerations are similar to ND filters: all of these filters are available in glass and resin, but if you are looking for quality, glass should be your choice.
In my bag: NiSi GND 0.9 Hard & Soft, NiSi GND 1.2 Reverse and Medium
Types of Filters: Polarizing Filters
The last family of filters I want to talk about is the polarizing filters family. Often undervalued, I think they are absolutely essential to every hardcore landscape photographer’s filter kit. This filter basically only allows light rays that are traveling in one direction to enter the lens
What does it mean in the real world? The following benefits:
- It removes glares from non-metallic surfaces such as water, glass, wet rocks, etc.
- It helps to get colors more vibrant and saturated (which is actually a consequence of the first point).
- It helps to add contrast to the clouds.
- Reduces haze.
Another feature of this filter is that it cannot be reproduced in post-production, so you should think twice before considering it unnecessary!
There are two types of polarizers on the market: circular and linear, but despite what you could think, the difference between them isn’t that one is round and the other it’s: it’s the working principle of the filter.
Without getting into technical details, it’s enough to say that linear polarizers do not get along with the autofocus of your DSLR. That’s why you’ll find almost exclusively circular polarizers on the market, which of course is the obvious choice.
Despite what you might think, polarizing filters are either round or square. The square version is recommended for studio use, or when no GND filters are required in additions to the polarizer, so we’ll only focus on the screw-in rotating version here.
A screw-in rotating polarizer is made of two metal frames and two glass surfaces. The first frame is screwed on the screw threads of the lens; the second (the outer one) idles on the first one. This allows you to modify the orientation of the polarization and control the intensity of the reflection reduction.
When using a polarizing filter, keep in mind that:
- The maximum effect of the polarizer is when the angle between you and the sun is 90 degrees (i.e. when the sun is on your left or right). The more the angle decreases, the more the effect of the filter drops… reaching zero when the sun is straight ahead.
- The effect of the polarizer is not uniform throughout the entire frame, and the wider the lens, the smaller the surface that is polarized. Often, this is seen as a defect and many are discouraged to use one on wide angle lenses, but this is absolutely wrong! The incomplete polarization is an incredible advantage as you can decide what to polarize. For example, we can decide whether to focus on the transparency of the water or let the reflection of a beautiful cloud at sunset color the surface! It’s up to you to make this “defect” a point of strength, so avoid halos and use this feature creatively.
- The polarizer absorbs part of the light acting as a 1 or 2 stop ND filter, keep this in mind when you calculate to achieve a correct exposure.
- If you have a lens that rotates while focusing, remember that the polarization should be made after focusing.
- Like any other filter that you add to your lens, it’s possible that a polarizer will introduce vignetting, especially on wide-angle lenses. Therefore, opt for the “Slim” filters (i.e. without thread in front of them). We’ll see really soon that it rarely (actually never) makes sense to buy a filter with front thread.
If you want to use a polarizer and you don’t use a slot-in system with Adapter Ring and Holder, the purchase is very simple: you should buy a polarizer that has a diameter equal to that of your lens or, if you are using step-up adapters, to the biggest screw-in filter you have.
On the market there are many manufacturers of polarizers and, as always, the advice is to focus on quality. A polarizer is a life-long purchase.
Also, remember to prefer the “Slim” filters to minimize the risk of vignetting, and if your budget allows for it, opt for the “Multicoated” versions: this means the company has applied a special treatment on the surface to minimize flare.
As usual, avoid “miraculous” filters; remember that it’s never a good idea to entrust the quality of a shot captured with thousands of dollars of gear to a €10 piece of glass.
If you want to use a polarizing filter with a slot-in system, things get a bit more complicated. In fact, if you have a normal polarizer, there are two cases:
- If you have bought a “Slim” filter, the lack of frontal thread will not allow you to mount an adapter ring.
- If you have a polarizer with frontal thread and you decide to mount on top an adapter ring and a holder for slot-in filters, you’ll find out really soon that every time you set the polarizing filter, it will rotate with the whole holder!
So how should we handle this? We have 3 possible solutions:
- 105mm polarizing filters: If you have an old generation filter holder, this solution allows you to mount the polarizer after the last filter mounted on the Holder. To do this you need to buy an additional special ring (that has to be mounted on the holder) and a polarizer with a diameter of 105mm. This is something that we used to do many years ago and actually is just something expensive and not needed anymore, so definitely not suggested.
- Square Polarizer filter: yes, polarizer filters are not just round shaped. You can buy it as a square filter to use in your filter Holder. Unfortunately, this brings you two problems: the first one is that you have just four possible orientation on the polarization (one per side of the filter) and not the 360° given by a round filter. The second one is that if you’re using it combined with a GND filter, it will be the GND filter that will determinate the orientation of the holder, so the polarization is even more limited. Until the beginning of 2018, this was anyway the only available solution for 150mm filters system (used for ultra wide angle lens). Luckily now NiSi Filters released the revolutionary S5 that will let you use a 360° orientable round polarizer on a filters holder.
- Holder with integrated 360° orientable polarizer. Since a couple of years, it’s possible to buy filter holders that have a special round shaped polarizer integrated into the adaptor ring. This system was invented by NiSi Filters and today was adopted by almost all the competitors. Without any doubt, this is the best solution to use a polarizing filter combined with ND and GND filters.
Round, square, screw-on, slot-in, glass, resin: the possibilities are almost endless, but if you apply the advice in this tutorial to your photographic interests, you’ll find that just a few of them are needed to enhance your photography significantly.
At the beginning using filters may seem complicated, but with time it will become as natural as setting the correct shutter speed and aperture in your camera.
As always, my main piece of advice is: have fun and gain experience in the field, perhaps with someone who can help you to get started in this wonderful world!