Fiilter recommendations

BasilFawlty · Oct 23, 2012

Newbie here with my first real DSLR camera. I just bought a Canon 7D with a 28-135mm lens. I want to purchase a UV filter and a polarizer (72mm). I want good quality but don't want to spend a fortune either. (I'm a hobbiest who wants to learn and get better, not a professional shooting for National Geographic) I went to a local Camera shop and the Polarizers in that size ranged in price from $35 - over $200! Ok, so what should I look for in buying filters from my new 7D? Any recommendations or sources for good deals on reasonably good-quality filters?

Thanks in advance,

Basil

Scuba · Oct 23, 2012

See this thread that is currently active.

http://www.thephotoforum.com/forum/photography-beginners-forum/300230-filter-question.html

UV filters are thought by some to be a waste and degrade quality. A polarizer is another story. You want to get a high quality multi coated filter. It is going to run you ~$100 or more for a good one.

TCampbell · Oct 23, 2012

Whether or not you use a "UV filter" is up to you. Just be aware that the _only_ reason to use a "UV filter" is to offer some form of protection for your glass (and there are consequences for this.) One reason that you should definitely NOT use a UV filter is to block UV light. Your camera already has a UV filter in it. It also has an IR filter.

If you were to remove the lens, and use the menus to put the camera into a manual sensor cleaning mode (in that mode it will lock the mirror up and hold the shutter open so you can inspect the sensor), what you are actually looking at (what your finger would touch if you tried to touch the sensor) is actually two filters located in front of the sensor.

This is required for digital cameras because a digital sensor is sensitive to more wavelengths of light than film. The filters constrain the wavelengths of light that can pass so that the sensor can only "see" human visible light.

A UV filter actually did improve the image quality back in the days of film. This is because every lens technically has some level of dispersion (which we call "chromatic aberration" or "CA".) As light refracts through a lens, the lens behaves a bit like a prism and splits the light into it's constituent parts -- like a rainbow. Optical engineers attempt to keep this to a minimum, but they can't completely zero it out. Since UV is at one extreme of the spectrum and IR is at the other extreme, these wavelengths will diverge the most (compared to the optical wavelengths which will still disperse a little.) That can result in some "fringing" on the edges of things that should be sharp and softens the image quality. By blocking this unwelcome wavelength, you eliminate something that contributes to fringing and you get sharper images. But that's for a FILM camera. A digital camera is already filtering the unwelcome wavelengths. So what once was taken for granted on a film camera as "of course you have one of these" is now viewed as a "why are you putting a UV filter on your lens?"

When you add a UV filter to your lens, you're just being redundant. Really high quality UV filters will always block _some_ visible light and will block most (nearly all) UV. In essence that means they sort of work like clear glass in front of your lens (because the internal UV filter would already have filtered the UV.) But low quality UV filters can actually block much more visible light while failing to block most of the UV (not that the UV matters because the camera would already have handled that with the internal filter.) Basically the glass in front of your glass should either be high quality glass... otherwise don't bother.

SOME lenses suggest a clear filter to complete the weather seal (very few, but it is one reason why you might want a filter.)

The glass on the lens is actually pretty strong. It's hard (though not impossible) to scratch it. But the only way you're going to scratch it is by dragging around something capable of scratching it ... generally because you're using too much pressure and poor cleaning technique. LOOK at your lens before you clean it. If you see any obvious bits of debris that could scratch a lens, carefully remove it before dragging it around the lens with a cleaning cloth. Make sure the cleaning cloth is, in fact, "clean".

The filters you SHOULD have are a circular polarizer (buy this in the largest thread diameter for any lens you own. You can buy "step up rings" to adapt it to fit any smaller diameter lens threads.) For example, I own a 77mm polarizer which fits two of my lenses, but have a 67-77mm "step up ring" which allows me to use the same polarizer on another lens which only has 67mm diameter threads. This $10 adapter saves me from spending $150 on yet another high quality CPL.

You should also probably own at least one neutral density filter... perhaps even two or three depending on your needs.

You may eventually wish to buy a "gradient" neutral density filter (perhaps a few variations on it) and these come in a rectangular slide form (not screw on). You buy a Cokin filter adapter which is a bracket with several slots on the front. You "slide" the filters into the slots. This allows YOU to choose how far in you slide the filter (where the line is that separates the clear vs. the tinted half of the filter.)

If you are using your camera in an environment where you think things may smack the end of the lens, put a lens hood on it (so that things hit the hood instead of the glass).

If something hits your camera so hard that it's going to break the hood... chances are it's going to damage the lens anyway and a "protective" filter wouldn't have saved you anyway.

BasilFawlty · Oct 23, 2012

Great reply! Thanks! To be honest, the only reason I was thinking of a UV filter was for precisely that reason - to protect the lens. Is there such a thing as a neutral filter that does nothing to the image but only serves to protect the lens? (Is that waht the "Neutral Density" filter you mentioned is for - just to protect the glass? ). What you have said makes sense, so maybe I will just invest in a good CP filter and a hood and forget the UV filter after all.

Majeed Badizadegan · Oct 23, 2012

BasilFawlty said:
Great reply! Thanks! To be honest, the only reason I was thinking of a UV filter was for precisely that reason - to protect the lens. Is there such a thing as a neutral filter that does nothing to the image but only serves to protect the lens? (Is that waht the "Neutral Density" filter you mentioned is for - just to protect the glass? ). What you have said makes sense, so maybe I will just invest in a good CP filter and a hood and forget the UV filter after all.

A neutral density filter is going to reduce the amount of light that reaches the sensor.

In effect, what TCampbell has so eloquently stated, is the UV filter is the redundant piece of glass to protect the front element. Remember, your photograph is only as strong as your weakest piece of glass. If you have great quality glass, and buy a cheap filter, your photographs will suffer. Filters are the worst place to cut costs. Buy the good quality ones, and buy them as big as your biggest lens (or the biggest lens you plan on owning in the near future).

When I purchased my 10 stop ND, I bought it in 77mm with a step up adapter, even though at the time I only had a 67mm thread. Lots of the Canon L quality glass is going to be in 77mm, so I wouldn't recommend buying any smaller than 77mm, even though right now I believe you have a 67mm thread. Use step-up adapters in the meantime.

johncam · Nov 1, 2012

I stopped using UV filters on a regular basis because unless you have a $2000 lens and $100 filter you are doing more damage to your image quality for no good reason than protecting anything. Plus, if you get a 400 2.8 with a 135mm ring, you can't put a protector on it anyhow.

Solarflare · Nov 1, 2012

A neutral filter that "does nothing" and "only protects the lens" will, just like an UV filter, reduce image quality, in pretty much the same way.

Basically the problem is that any glass surface will reflect light. Without coating, its about 4% of the light for ordinary glass - and every such piece has TWO surfaces. Thats why we still can see glass.

This is the problem with every glass in your lens, too. Thats one of the basic reasons why prime lenses have an edge over zooms - less pieces of glass in them, thus less loss.

Mind, the loss itself isnt that problematic. Its problematic that the reflected light will bounce and in the end still end up on the sensor - at places where its not supposed to be, reducing image quality.

Also, these reflections also make the lens darker than it could be, causing very substantial amounts of losses in light, forcing the photographer to use higher ISOs, slower shutter speeds or more open apertures than otherwise would have been necessary.

And high quality filters will use the same techniques used as for the glass modern lenses - coating - to reduce this loss. Very expensive glass might be "invisible" - you cant actually see the glass anymore, only its effects. Zeiss is famous for this.

Also, a high quality filter will of course use glass, not flexible pastic, so the filter itself is perfectly plane and doesnt distort the image.

Sources:
The confusion between T-stops and f-stops
Anti-reflective coating - Wikipedia, the free encyclopedia