Can I use Circular Polarizer like a UV Filter to protect the lens?

Hi,


I am planning to get a circular polarizer for my 18-200mm f3.5-5.6 lens. I already mounted a UV filter on it since day 1 and I never take the UV filter off. I wonder what would happen if I leave a circular polarizer filter on the lens just like how I left the UV filter on it?

I am hoping I don't need to change filter (to save the hassle) and it can be on the lens to protect it and at the same time giving me polarizing function when I need it. When I do not need polarizing function, can I just turn it off? (for example, turn to a position where it behaves the same as normal see-through glass)

<span style="font-size: 9pt; color: black; font-family: Verdana;"]One problem you will find is that even when it is not "polarizing" it's acting very similarly to a neutral density filter robbing you of 1-2 stops of light. For an already "slow" lens that's no good! Keep the UV on and only use the CPL when you need it.<o:p></o:p>

I can tell you straight - that is NOT the way you use a CPL filter. The CPL is meant to do what its meant to do, not to protect your lens from dust or damage. As Mark said, you will loose 1-2 stops of light and that's not good for your lens or just every lens depending on what you're doing. Take off the UV filter and put the CPL on when you need it, then switch back again.

Ditto Ben's advice. Your CPL will kill you in any low light situation. I forgot mine was on one night at a high school football game and spent 10 minutes trying to figure out what was wrong with my camera.

Thank you for all the info. I have further questions:

Can I stack the CPL in front of the UV filter? Will it affect the output if I can do so?

I am trying to find a way to not take off the UV filter when shooting outdoor to avoid exposing my lens to dust.

Under most conditions, you don't want to stack the filters.


If you are working in harsh environments, such as salt spray from an ocean mist, then leave it on.

You should not. You'll most likely end up seeing color desaturation caused by flares and other light artifacts on your image. That happens when the light enters and bounces back and forth between the multiple layers of your filters' reflective surfaces.

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Originally Posted by csphua

Can I stack the CPL in front of the UV filter? Will it affect the output if I can do so?
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Yes, physically you can as long as you are not using the super slim UV filters which does not have a screw on the outer side. And YES, that will affect your output. You will likely see vignette on your lens when shooting at 18mm or around wide angle range. Flare will likely to exist when shooting in bright sunlight (i guess that's when you use the CPL the most right?) especially when the sun is in front of you or is part of your image. Sharpness and contrast can be reduced too, depending on what kind of UV and CPL you're using. Try to get multi-coated filters, that makes a noticeable difference. But DO NOT stack filters.

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Originally Posted by csphua

I am trying to find a way to not take off the UV filter when shooting outdoor to avoid exposing my lens to dust.
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Dust is not avoidable in reali life shooting. As long as there isn't extremely too much dust, you IMAGE WILL NOT BE AFFECTED. Some dust involved when changing filter is not a problem for me, and it does not harmful your lens in any degree - blow them off afterwards if you need to, I'm too lazy to do that as long as I don't see them on my pictures. I know some people they like to keep their eqipment completely clean as just out of the box, i respect that too.

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Originally Posted by csphua

Can I stack the CPL in front of the UV filter? Will it affect the output if I can do so?
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Yes, physically you can as long as you are not using the super slim UV filters which does not have a screw on the outer side. And YES, that will affect your output. You will likely see vignette on your lens when shooting at 18mm or around wide angle range. Flare will likely to exist when shooting in bright sunlight (i guess that's when you use the CPL the most right?) especially when the sun is in front of you or is part of your image. Sharpness and contrast can be reduced too, depending on what kind of UV and CPL you're using. Try to get multi-coated filters, that makes a noticeable difference. But DO NOT stack filters.

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Originally Posted by csphua

I am trying to find a way to not take off the UV filter when shooting outdoor to avoid exposing my lens to dust.
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Dust is not avoidable in reali life shooting. As long as there isn't extremely too much dust, you IMAGE WILL NOT BE AFFECTED. Some dust involved when changing filter is not a problem for me, and it does not harmful your lens in any degree - blow them off afterwards if you need to, I'm too lazy to do that as long as I don't see them on my pictures. I know some people they like to keep their eqipment completely clean as just out of the box, i respect that too.

<p class="MsoNormal" style="margin: 0in 0in 10pt;"]<span style="font-family: Calibri; font-size: small;"]csphua
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<p class="MsoNormal" style="margin: 0in 0in 10pt;"]<span style="font-size: small;"]Most filters are obsolete with today&rsquo;s camera and software. <span style="mso-spacerun: yes;"]Filters are from the film and pre computers period when you had to modify color/effect at the point of image capture.
<p class="MsoNormal" style="margin: 0in 0in 10pt;"]<span style="font-size: small;"]When you add a filter to the optical path you increase optical distortion, flare, etc. <span style="mso-spacerun: yes;"]If you want to protect your lens from everyday hazards use a lens hood.
<p class="MsoNormal" style="margin: 0in 0in 10pt;"]<span style="font-size: small;"]When you put a filter on a wide angle lens the outer edges of the image will become softer due to the higher angle of light travel as compared to the center of the lens.<span style="mso-spacerun: yes;"] Thus, increasing the travel path of light through the glass of the filter and causing the image to be unfocused. <span style="mso-spacerun: yes;"]
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Originally Posted by Bob

<span style="font-size: small;"]Most filters are obsolete with today&rsquo;s camera and software. <span style="mso-spacerun: yes"]Filters are from the film and pre computers period when you had to modify color/effect at the point of image capture.

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Can you really replicate a CPL filter during post processing? Sure you can saturate/ underexpose the sky and increase contrast across the image but at the end of the day (my personal opinion is)it's better to capture the right image from the word go... i.e straight out of the camera. Just my 2 bob, Bob. [:P]

I'd have to agree with btaylor. Some filters are still quite relevant in today's digital age. The circular polarizer, in my opinion, is one. I don't think the results can be easily replicated in post, if even at all. And even if you could, it'd probably take more time than I'm willing to spend editing my images.


Another filter that's still quite relevant is the ND filter. There are things you can do with an ND filter in place that you certainly cannot do in post-processing.


Whether or not you need a UV filter on your lens at all times is a matter of personal preference. Yes, any filter will degrade the image to some degree. Whether or not it's worth that sacrifice to protect your investment is up to each individual user to decide based on his/her needs.

I'll be with btaylor too. The CPL and ND do have their job to do even with digital. ND lets me shoot with f1.4 in bright sunlight without my speed go all the way up to 1/8000. I will need to use UV because I actually do shoot film. Just for the sake of protection I also will need them to stay on my glasses all time.

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Originally Posted by Bob

When you add a filter to the optical path you increase optical distortion, flare, etc.

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From what I believe, since the filters discussed here are not concave nor convex, they will always perform the same, regardless of their position in the optical system. Therefore I wouldn't believe distortion to be a problem - unless you are using very cheap filters. Flare, on the other hand, may be present when using these filters, but don't let that bother you too much. Use a lens hood [:)].


Advice that I recommend (and previously discussed):

• Don't stack your CPL and UV filters. You'll notice vignetting at the wider focal range. Also, with more reflective surfaces, I wouldn't be surprised if you noticed more flare, too.
• Don't keep the CPL on your lens constantly. Going outside? Out on the lake? Make use of the CPL. But indoors, or any low light situation for that matter, will be problematic with the CPL - You lose a few stops of light.
• Remove filters for long exposures. Do not be concerned about dust, unless you're using the 50 1.8 II (which is a great lens!)[:)].
  

Hope I helped you out...


- Alex

I only use my circular polarizer when the need arises....otherwise, I keep the UV filter to protect my lens.

UV has stayed on my lens from day 1 as well, only change it toa CPL as and when you need to.