Filters

[Claff]

Just placed an order for a new lens and I see among the various accessories being offered are filters. I have one on my Nikon but it came with the (second-hand) camera, know nothing about it, what it does, what the difference between the different kinds are, and if they’re necessary in the first place.

The two choices are “polarized” and “multi-coated”. Should I get one or the other or maybe both? This is for a camera that is mostly doing sports photography during afternoon daylight.

[staplermofo]

Polarizers are always a good idea. They cut down on glare and make contrast a bit more pronounced. You might even want to use a lens hood if glare is a problem. They make you look cooler to boot, you know, turning stuff, having stuff protrude.
I’ve never heard of multi-coat being used to describe a filter by itself, usually it’s “a mutli-coat _____ filter”, and as it usually doubles the price, so I assume it’s a good thing, though I’ve never used one. The coatings are supposed to cut down on flare and other uglies I think.

They aren’t necessary, but it’s nice to know that if a sudden sand storm pops up or children throw rocks at you or what not, your lens will be protected by an easier and cheaper to replace filter.

Unless you’re really anal about image quality, a polarizer is really the only filter that’s going to make a difference that you couldn’t get in photoshop. If people are wearing shiny helmets or driving shiny cars it would be more dramatic, but it can make the sky a whole lot prettier which is always nice.
If the front of your lens rotates you have to correct the polarizer every time you change focus, which would make it pretty useless for fast paced sports I would guess.

I’m by no means an expert or anything, just replying because no one else has.

[schnee]

Polarizers were sort of discussed earlier. In a nutshell, they are useful to control reflections. For a mid afternoon sports shooter, this could be beneficial. Are you talking water sports? Have you ever had a lot of reflection off the water? A polarizer could stomp that out. Similarly, if you’ve ever taken a photo of a racetrack where the asphalt is all shiney, that shinyness is due to reflections. Grass reflects, too.

A big drawback for polarizers is that they steal 2 stops of light – this means that it would be harder to stop action -> more motion blur as the athletes hit the ball (or whatever). Can be artistic, but… I have a polarizer on whenever I’m doing landscapes. Not so much when I’m doing portraiture or photos of the kids.

Multicoating. Hmmm. Was is a “UV” or a “Skylight” filter? Those filters are supposed to reduce a blue cast due to light being reflected by atmospheric particles. Supposed to be helpful in mountain photos where you have gobs of landscape going through tons of atmosphere. I’ve never noticed the difference (but I’ve never done a controlled test, either). I put my skylight filter on when I give my camera to someone who probably won’t treat the optics nice – it acts as a physical protector.

“Multicoating” as a term is something very desireable for a zoom lens or a filter for a zoom lens. It has to do with the “characteristic impedance of free space” – as light travels through space and hits a glass surface, an uncoated surface will reflect (due to impedance mismatch). A coated surface tries to better match the impedance, reducing the relfection, leading to more light hitting the imaging device (film, CCD). Multicoating just does it better. For a concrete example, have you ever seen someone’s eyeglasses that reflect gobs of light? Those glasses are not coated. Ones that don’t reflect are coated.

Note that I wrote “zoom lens”. Zooms tend to have many optical elements which all introduce light loss. Coating those elements mitigates that loss. Prime focus lenses are simpler and not as susecptible to light loss.

(I really like “characteristic impedance of free space” as a phrase and try to work it in whenever possible. Its harder than you may think)

[Claff]

The sports photography is motorsports, if there’s water involved that’s usually a bad thing.

I’ll pick up a polarizing filter and (assuming the lens shows up this week) I’ll give everything a good thorough test drive over the weekend.

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