Screw in filters are probably the most widely used filter type, they are simple to use, (open box, line up screw thread with end of lens, screw in, simples!) and everyone who gets into DSLR photography will inevitably be told by someone sooner or later that they should put a UV filter on all their lenses to protect them. There are many manufacturers of such filters, the most commonly used are probably Hoya, who are a respected brand and have grades of filters ranging from cheap and cheerful, to pretty expensive. B+W are another oft recommended brand, generally pricier than Hoya but many people claim them to be better than Hoya, personally I have never used B+W so can’t offer any direct comparison.

Now slot in filters, they’re a bit more of an unweildy setup and take more considered planning, but can be much more useful in my opinion. There are various manufacturers of filters and holders, Cokin being one of the most well known at the cheaper end of the market and Lee being widely regarded as the best, albeit at a much higher price (and suffering massive supply and demand issues at time of writing). There are some other brands out there as well which I’ll get on to shortly

All slot in systems comprise roughly the same setup, a metal adapter ring that screws into your lens’s normal filter mount, a plastic or metal holder that slots on to that ring, and then the filters themselves that fit into 1 or more slots in the holder, things get complicated from the start though with a wide range of differing sizes. Cokin do several sizes which have become industry standards, designed to fit different size and focal length lenses, their ‘P’ range being one of the most popular and readily available and able to fit on lenses with up to a 77mm thread size, the filters themselves being 85mm width. They also do a Z range designed to fit larger lenses that uses 100mm filters, the same size as the Lee system. To further complicate matters most manufacturers do a standard holder with multiple filter slots so that filters can be stacked, and a wide angle one for only 1 or 2 filters to make it feasible for use on wider angle lenses without introducing vignetting.

With so many options it can be difficult to know what will and won’t work for your own lenses and the best advice I can offer in that respect is to do what I did when I first considered a slot in system and take a trip to ebay, particularly if you are considering the Cokin P range, where there are a myriad of cheap copies of filters and holders available for you to try as proof of concept. I personally picked up 2 adapter rings, a standard and wide angle holder and 4 filters for all of about £30, knowing full well that they wouldn’t be much cop quality quality wise, but sufficient enough to test what would and wouldn’t work with my lenses, and to decide whether I would get the use out of the system to warrant splashing out on good quality ones

For me the answer was yes and the Cokin P system was just feasible with my 12-24mm landscape lens with the wide angle holder, I then subsequently switched to a Hitech Wide angle 2 slot holder to enable me to stack filters where necessary, with the caveat that it does have a little vignetting at 12mm, but none if zoomed in a touch. Bear in mind that while they look identical to the real deal, the cheap copy wide angle filter holder I originally bought was a bit loose on the adapter ring and was clearly of cheap quality plastic as I managed to accidentally shear off some of the surface layer of plastic quite easily, the official Cokin one I later bought was still a fraction loose, but was a much better fit and hasn’t suffered any damage despite extensive use, so it is worth investing in the official kit if you decide you like the setup. The adapter rings you can pick up off ebay however seem perfectly fine for Cokin holders and I see no need to buy official ones when it’s just a thin ring of metal, although if you do go for a more solid filter holder like my aforementioned Hitech one, you will need to buy the associated manufacturers filter holder ring as it is a slightly different shape

As for filters themselves, as mentioned before Lee are widely regarded as the best of the best, but this does come at a cost, and at time of writing with a considerable wait as they struggle to keep up with demand. Cokin are the cheaper alternative but I see many reports of unsightly colour casts from their filters, particularly if stacked. After much research I eventually opted for Hitech filters, as general opinions seem to be that they offer the best of both worlds, they’re not far off the price point of Cokin, so are pretty affordable, the 85mm filters neatly in the Cokin P size filter holder, they seem to lack unwanted colour casts, and all importantly they are easier to get hold of, albeit there aren’t many suppliers that stock them so there’s a limit to how much you can shop around.

What filters you need is a question that will inevitably vary from one person to the next, but there are a few commonly used filters that most people entering into this realm are likely to want and that I personally own, so I will go into a bit more detail on what I use

UV

I have long followed the standard advice and used screw in UV filters to protect my lenses against scrapes. I favour Hoya Pro-1 Digital filters as they are the upper tier grade of the Hoya range but are not as bank breaking as B+W and some other less well known high grade brands. Whether or not to use UV filters is a debate that rages the internet with no clear answer, I have always used them on the basis that I can afford to replace a £60 filter more readily than an £800 lens, however there is a counter argument that if a lens is dropped and the filter shatters, the resulting broken glass could scratch a lens front element more than the original impact would have.

There can also be some degredation in picture quality if you use cheap filters, hence me using the upper tier Hoya models to avoid this. Presently the only lens I don’t use a UV filter on is my 12-24mm so as to avoid vignetting, but I have debated many times taking them off my long zooms as well and just relying on their lens hoods for protection unless I’m in a particularly dusty and/or windswept environment

Circular Polariser

In addition to UVs, I also have a screw in Hoya Pro-1 Digital Circular Polariser for my 18-200mm lens which I have used a few times for landscapes. If I’m honest, I don’t really consider it to be particularly essential, it’s primary uses are cutting down or eliminating reflections and bringing out the colour in the sky, but the former I find little call for and the latter is something I can do in Lightroom in about 5 seconds so isn’t a big deal. Also worth noting is that Polarisers can cause some strange effects on ultra-wide angle lenses so they aren’t particularly practical there. Honestly the most useful thing I’ve done with it has been using is as a substitute for a Neutral Dentisy filter prior to owning one, as it does cut down the amount of light entering the lens. All in all, if you do particularly feel the need to take photos through water or glass where you need to reduce the reflections, or really don’t want to do any colour touch up in post processing then they do the job, personally though it’s something I rarely use and wouldn’t lament the loss of. Polarisers are also available for slot in systems with the right holder, all the same points apply.

Neutral Density

Neutral Density filters are widely available in both screw in and slot in format. I do own a Hoya screw in ND filter for one of my lenses, however I have never used it much as I prefer using my slot in filters in general. Neutral density filters come in varying densities, confusingly with 2 different naming conventions used by different manufacturers. The conventions followed are either that of 2x, 4x, 8x, 16x, designating the relative reduction factor in shutter speed the filter will grant, or 0.3, 0.6, 0.9, 1.2, designating a 1, 2, 3 or 4 stop reduction of light (to be honest I don’t get it either!). All you really need to know though is that an ND 0.3 is the same as an ND 2x, an ND 0.6 is the same as a ND 4x etc. Personally I see little point to 2x and 4x filters, the main use of an ND filter is to allow slow shutter speeds in daylight for shots like flowing water, so to my mind you want the maximum reduction of shutter speed possible, you can always raise your ISO a notch if for some reason you want a slightly shorter shuter speed than the filter is giving you, so the only ND I use is a Hitech ND 1.2

Some manufacturers including Lee and Hitech also do what is generally known as a big stopper, a filter allowing up to 10 stops of light reduction. I personally don’t own one as they’re pretty pricey and thus far my ND 1.2 has served me well enough, so I’m not really in a position to comment on how essential or otherwise they are. Big stoppers do have their own quirks, such as an unavoidable colour cast and the fact that they cut down light so much that autofocus is basically a no go, but they do allow for extremely long shutter speeds in even very bright weather.

Graduated Neutral Density

These are probably the main reason most people buy in to a slot filter system. They are designed to help solve the age old problem of cameras being unable to capture the same range of light the human eye can resolve. Many times, particularly in bright weather, you’ll come across a scene where there is simply too much contrast between highlights and shadows and if you take a picture straight out of camera, it’ll be impossible to capture all the detail. graduated filters come in because they allow you to effectively split the scene and darken the camera’s view of a section of it in order to try and balance the contrast enough to capture all the detail

Neutral grads come in two main types, soft and hard, the difference being the abruptness of the transition between clear and ND ends. I started out with soft grads as I guessed that a soft transition would create a less noticable effect on shots and that unless you do something like seascapes with a very clear line on the horizon that the hard grad would be too obvious. I was later proved wrong when I attended a seminar day with some professional landscape photographers who clearely demonstrated that with digital SLRs, the transition line on a hard grad really doesn’t show, and that in fact soft grads are not entirely effective because of the length of their transition, so I have since swapped to hard grads myself. I again own Hitech grad filters, best balance of cost and quality, plus at time of writing they are one of the only filter manufacturers able to largely keep up with demand! I use 0.6 or 0.9 grad filters, the way I see it if you need less than a 0.6 you probably don’t really need one at all, and if you need more than a 0.9, you’re probably looking at a scene where a single filter isn’t going to cut it so you need to be looking at either stacking filters (which adds more chance of image quality degredation with the addition of another optical layer) or going down the HDR/exposure blending route.

Others

There is a range of other filters available, most being for applying a variety of colour casts or corrections to scenes, and whether or not they are useful is, as with all of the above, largely down to the individual. Personally I’m of the opinion that ND, Graduated ND and Polariser filters all have their practical uses as they enable you to do things that you can’t really do in post processing, (long exposure effects, capturing more dynamic range, cutting down reflections), meanwhile anything that deals with colour cast, can be fairly easily corrected later on. Coloured filters were more of a big deal back in the days before digital, when you pretty much had to get it right in the first place, these days most colour related adjustments can be easily done in post processing. That said clearly plenty of people must still find use for coloured filters or there wouldn’t be a market for them, having entered into the world of photography in the digital era and not explored that side of filters myself, I’m not really qualified to judge