Filter for Canon L lense

[RCOONa]

I just got my first Canon L lense and after some research, I decided not to purchase a UV filter as protection for the front glass element.  Then I happen to read the (B&H) overview for the EF 16-45 mm F/4 L , which states that "when paired with an optional Protect filter, this lense also exhibits a dust and water resistant costruction to enable its use in inclement conditions". So now I am confused:  Why does a $ 1,200 L lense need a "Protect filter" ? What do they mean by "inclement conditions" ?  Should all L lenses be equipped with a protective filter?  What would be a recomended "protective filter" ?  I would really appreciate some guidence on this because I would want protect my investment in my L lense and would consider getting one if recomended. 

[Skirball]

A handful of Canon lenses require a front filter to complete the weather sealing.  That is, the gap between the lens front element and the cone isn't sealed, and requires the filter.   IIRC, most of them are wide angle lenses.  You can do a search and find the list somewhere.  But no, not all your lenses need it.

I don't know why it was done this way, but I'd guess that some part of the design required a front element and Canon decided to leave it optiona.  It might be because flat front elements on wide angle lens make it more prone to flare, but I'm just guessing at that point.

I would recommend getting one, but I keep them on all my lenses.  I simply take them off when I don't need them or I'm worried about flare (like when shooting in dim situations with bright points of light).  I don't care to get in the Filter vs Non-filter debate for the 1000th time, so I'll just leave it at that.

I use B+W filters, but there are plenty of other options out there.

Edit: btw, enjoy the 16-35 f/4, looks like a great lens.  I've been debating selling my 17-40 to get it for awhile now.

[TCampbell · Accepted solution]

Some "L" series lenses are weather sealed.  If you see a black silicone gasket at the rear mounting flange, then chances are it's a weather-sealed lens.  But you have to read the instructions for each specific lens to find out what that means.  A few lenses will indicate that they're only weather-sealed only if a protective filter is attached.

Weather sealing means the lens is generally been sealed against dust, rain, and spray -- but it's important to remember it does NOT mean the lens is "waterproof".  They are not sealed against water under pressure.  If you blast it with a firehose... you'll probably get water on the inside.  Likewise they will leak if submerged.  There are "underwater camera housings" available when you need the camera & lens to be ready to go underwater.

Also, just because a lens is weather-sealed does not mean the camera body is sealed.  Only some camera bodies get weather-sealing and the level of treatment varies.  Generally the mid-level and higher camera tend to have at least some weather-sealing treatment but even then there are some obvious gaps.  The memory card door and battery door being just two examples of places that do not have weather-sealed gaskets.

With that aside... there are some downsides to having a UV filter.  

First, the camera already has an internal UV filter, so the second filter doesn't really offer any help in that deparment.  

Second, being a flat-glass filter, it's able to create nice reflections that can be seen by the camera.  This can create "ghosting" reflections and other undersireable side-effects.  Using filters with anti-reflective coatings will substantially reduce this problem, but those filters cost a bit more.  Also they will simply "reduce" reflections considerable but wont guarantee that you don't get any reflections at all.

The glass itself is pretty durable.  Be gentle with it when you clean it and you'll never have a problem (use a "clean" soft microfiber cloth).  The lens hood (even if you aren't trying to shield it from glare) actually helps to keep anything from hitting the glass.  The hood is probably better protection than a UV filter.

[RCOONa]

Thanks for the advice, it helped me to make a decision. I understand the pros and cons of using a protective filter and I will probably never expose my camera and lense to harsh environment, but I think I will get one nevertheless. Thanks again for your thought and opinions.

[ebiggs1]

What the anti-filter guys seem to forget is, the filter can be removed as easily as it goes on.  If you are in a situation where it would hurt, remove it.  Otherwise it is cheap insurance and is required on certain lenses.

[ebiggs1]

Also, I suspect people that argue against using a filter, don't take photos of small children.  A hood in this case is just all the more tempting!  

[RCOONa]

ebiggs, I concur with your reasoning and I would add that the saying " an ounce of prevention..." may be applicable in this instance. Thanks for your comment.

[TCampbell]

I certainly wouldn't characterize myself as an "anti filter" guy.  I own a filter for every lens I own.  But I've learned to become aware of the trade-offs of using a filter.  Most of the time I don't use the filter and it only goes on when I think a situation warrants it.

Mostly I wanted to point out that I've seen people posting requests for help because of bizarre optical issues.  In one case, I had someone who thought they had identified a UFO (no kidding) and I showed them that their "UFO" which appeared on the upper right side of the image was actually the upside-down and dim reflection of a street lamp which appeared in the lower left side of the image and the two were precisely opposite with respect to the center axis of the lens.  

Those reflections & ghosting issues are something you'll just want to watch for. This is also why I highly recommend that whenever possible you would want anti-reflective coatings on any filter you buy.  Block any bright lights from shining on the face of the fitler (a lens hood is good for this, but if you don't have a hood, use anything as a "flag" to hold just out of frame to keep direct light from shining on the filter. 

[Skirball]

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@TCampbell wrote:

I certainly wouldn't characterize myself as an "anti filter" guy.  I own a filter for every lens I own.  But I've learned to become aware of the trade-offs of using a filter.  Most of the time I don't use the filter and it only goes on when I think a situation warrants it.

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Sure, and people need to learn these tradeoffs.  The problem is, usually when these discussions take place (on the internet) there is no in between, it's purely always on, or always off.  And the focus usually turns to things like image quality degradation, instead of more realistic issues like reflections and flare.

I'm similar to you, I know the trade-offs and adjust accordingly.  It's just that mine are on all the time, and only come off when I think a situation warrants it - like shooting at night or in the studio.