Owning an expensive camera lens can be a nerve-wracking experience - the tiniest scratch can instantly decimate its value. As a result, the first thing I do after purchasing a lens is to fit it with a filter. For those of you unaware of a filter's purpose, it's basically a piece of glass which screws onto the front of your lens, providing it with a degree of protection. Of course, it's not all about protecting your assets, as different filters have different properties. The filters that I primarily use are of the 'UV' type, designed to screen out (or more aptly 'filter out') ultra-violet light, and reduce haze in sunny conditions. The good thing about UV filters is the fact that in most cases that they are completely transparent, meaning they won't change the amount of light entering the camera, and subsequently can be left on the lens at all times.
My favourite UV filters are of the 'Hoya Super HMC PRO1 Digital' variety, as I have found them to be by far the best mid-priced filters available (and I have tried a fair few, believe me). Currently, the 52mm size can be purchased for £31 from amazon.co.uk, although I generally pay in the region of £25 from eBay. If you're thinking that eBay's price is costly for a small piece of glass - it isn't - what would you rather damage, a £25 filter or an £800 lens!?
Holding up both a Hoya Super HMC PRO1, and a cheap filter in front of a light source will demonstrate a huge difference - with the cheap filter, you'll be able to see the glass, whereas with the Hoya Pro1 you probably won't. You see, Hoya's coating reduces reflections and chromatic aberrations, making it almost invisible to the naked eye. The cheaper filters are often lacking this special coating, and similarly use low quality glass - at the end of the day it's the photographic equivalent of looking through a dirty window - not something you want to do if you take your photography seriously.
In practice, the Hoya Pro1 will successfully cut a percentage of haze from your shots (you can never really eliminate all of it), and helps produce clean images without any deterioration of quality. There is no filter-factor, meaning you won't have to adjust the aperture or shutter speed to compensate for the filter's presence. The glass in the filter is surrounded by a screw-fitting black almite frame, featuring a satin finish that reduces reflection back onto the camera lens. It's also very thin (low profile) to stop it causing vignetting (darkness in the corners) of wide-angle shots.
In my experience, I have found the Hoya Super HMC Pro1 to be hard-wearing and durable, and my current Hoya has been on the front of my camera for a couple of years without showing any sign of marks or scratches. It should also be mentioned that the filter is splash proof - meaning it's perfect for those drizzly days when you find yourself having to take photos up a mountain without an umbrella (as you do!). The packaging is similarly good, and it comes in a small plastic case featuring foam padding. Overall, I can only give the Hoya Pro1 Digital 52mm a high recommendation, as it really is an excellent product which does exactly as it is supposed to.
*there are a number of fake branded Hoya filters on eBay, and you should be especially vigilant when buying from there.