To me, this is my least understood topic when talking about photography. Sure, I’ve put UV filters in front of my lenses whenever possible, but do I know what it really does? And what with the different brandings and versions, it gets complicated really fast.
There’s two divided camps when it comes to using UV filters. As it does nothing really to drastically change the images taken, (unless you’re using a really, really inferior UV filter), the debate comes down to lens protection. One side claiming it’s better to leave in on to protect the front element, and it’s easier to clean a relatively cheap filter than a lens; another side claiming it degrades image quality, and even if the filter breaks upon impact, it might scratch the lens anyway.
I fall in the former camp, because I do preach what they say as well. But do remember not to choose a filter that degrades the image quality so bad that there’s no point to have it on. Any coating is better than no coating as this will allow more light to pass through, and of course multi coating is better than single coating, denoted famously by Hoya’s HMC or SHMC lines. I have a UV(N) HMC on my 50mm f/1.4, and I have to say, I love the colors it lets through. On the other hand, I have a UV Guard Coated on my 77mm thread lenses, and sometimes the colors are disappointing once in a while. And if pixel peeped really, really close, the image quality is seriously degraded if you know where to look. Made me regret not to choose a 77mm filter carefully, as that was all I could find when my 80-200mm arrived. Will rectify that soon with a new filter purchase.
Here’s an example listing of UV filters, and as you go down the page, the price drops and the coatings become less and less, making for a lot less light to pass through, and generally worsening image quality. Generally, the more coating the better, and also be on the lookout for vignetting effect on your images when attaching a filter when going into your widest setting. This is why there are other options such as Thin filters, purposely engineered if you experience vignetting effect going wide.
Oh, remember, for night shooting, when shooting directly at lights, if you’re getting ghostings and flares, just take the UV filter off. It will reduce it immensely.
Another set of filters that help in digital photography are Circular Polarizers. Why? Linear polarizers will sometimes mess with your Through The Lens (TTL) metering system employed in dSLRs and give a wonky reading. And that is why Circular Polarizers are selling for top dollars, and this spurred me to write up this article to get a better understadning how it works. While other filters can be emulated in post processing, this filter type has the most unique charasteristic that can’t be emulated in post. Basically it removes the extra light that has been reflected off of surfaces, such as foliage, water surfaces and windows.
I know there are certain angles which makes the Cir PL filters more effective, but reading through Wikipedia doesn’t offer much help in illustrating this fact. This page explains it the best as I have found out, and makes me can’t wait to go shooting in bright sunlight to see the effects myself. Basically the maximum effect of removing reflection is when the reflection is incident at 30 degrees, and you are pointing 30 degrees from the opposite side of the incident. Another way is to have the sun perpendicular to where you are pointing the lens, to get the maximum effect.
Now we get to the “Hard to Swallow” part. As I said, the more coatings it has, the more expensive it becomes, so much so, for instance, a Pro 1 Digital HMC Circular Polarizer filter can reach upwards of USD200. That’s why sometimes people, including yours truly, will skimp on this vital thing until we know what’s the true purpose of these extra bits of glass. But if possible, get the best you can. You can skimp on other things, you shouldn’t really skimp on something that goes infront of that thousand dollars lens.
And now for the fun part, using filters to alter the colors and exposure in your photograph. While there’s times you just want a cool effect of the sky looking a different color with a Skylight 1B filter, there will be times when using a filter is important to get that shot otherwise impossible to get. Some might be familiar with using a Neutral Density filter to bump down the exposure of a scene while retaining a slower shutter speed than otherwise normal, or allowing the aperture to open up without overexposing the entire scene. Now imagine that effect for part of the frame.
Graduated ND filters are a godsend to landscape photographers the world over. A brief overview of the wonders of Grad ND filters are found here, allowing you to compress the dynamic range into something manageable for a dSLR. You might remember exposing for a shadow area in bright sunlight giving you overblown surroundings, while exposing for the sunlight might leave dark harsh shadows on your subjects. Imagine this for landscape photography, where the sky might be too bright while your foreground subjects are in the shadow. Rotating the ND side to the sky and the clear part for the foreground will make exposure for both to be correct.
Grad NDs come in 1, 2 or 3 stop variants and either in hard or soft gradation between the ND side and the clear side. Singh Ray has a complement of these for the Cokin P filter holders, so that may be on my wishlist for the time being. These are not cheap mind you, and for a specific purpose, you better be taking a lot of landscape pictures to be investing in the Cokin P system and a bevy of Singh Ray filters. B+W has a selection of these in normal, filter ring form, which to me, a 77mm 1 stop soft ND filter might be nice to invest in, as I’m not really gonna be doing landscape shots, that often, but it will be nice to have for the occasional hikes-up-a-hill-at-4-am-to-catch-the-sunrise.
There are a slew of other kinds of filters, such as diffusion filters or cross screen filters, but you will rarely come across these unless you’re specifically into that kinda thing. I believe UV and CirPL are the most important filter knowledge you need to have, and at least I can give you a bit of reading jump off point so you can learn more how to effectively use filters.
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