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Old Oct 22, 2008, 1:03 PM   #1
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I know there are differences of opinion about whether a filter is even necessary for lens protection. But when I bought my Canon XSi last month, the salesman convinced me that I should have something between my lens and potential debris. So I bought a UV filter. Since then I've also purchased a polarizing filter, which I love.

My questions:
  1. Did I make a mistake buying the UV filter? Is it necessary?[/*]
  2. Can I leave the UV filter on all the time? For indoor photos, etc? Or should I have purchased just a clear glass filter?[/*]
  3. Would leaving the polarizing filter on all the timebe wrong? Forindoor photos, etc? Probably a dumb question, but I took a few test shots the other day and the photos looked fine, then shots I took at a wedding reception later that night turned out horrible.
[/*]

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Old Oct 22, 2008, 2:07 PM   #2
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There are two arguments. The argument supporting the use of a filter is that replacing a damaged filter is simpler and cheaper than replacing a damaged objective lens. The argument against is that any additional optical element will adversely affect sharpness, color, and possibly even vignetting.

Good filters will have less adverse affect on image quality than cheap filters, and the difference in image quality between a good filter and no filter is probably imperceptible. And thin filters won't cause vignetting, but your lens cap probably won't work any more.

And UV filters may help with purple fringing, but they block UV light which prevents fungus from forming (something a clear glass filter wouldn't do.)

And polarizing filters are only good at reducing light reflected from non-metallic objects, and while, as a consequence,they can increase color saturation, they don't do well when there is limited light.
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Old Oct 22, 2008, 3:29 PM   #3
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TCav wrote:
Quote:
Good filters will have less adverse affect on image quality than cheap filters... And thin filters won't cause vignetting, but your lens cap probably won't work any more.

And UV filters may help with purple fringing, but they block UV light which prevents fungus from forming (something a clear glass filter wouldn't do.)

And polarizing filters are only good at reducing light reflected from non-metallic objects, and while, as a consequence,they can increase color saturation, they don't do well when there is limited light.
Thank you for the feedback TCav. But now I have a few more questions:

How do I know if I have a "good" UV filter? The brand is Optex, made by a company called Gentec, but I can't find my specific filter online (their website really blows). I paid approximately $28 CDN for it.

What's this about fungus!?

Also, if anyone has specific answers to my questions, that would be great. Can I leave the UV filter on all the time? Or should I take it off for indoor/low-light photography? Could the polarizing filter be what screwed up all the photos I took at a wedding reception?

Thanks.
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Old Oct 22, 2008, 4:43 PM   #4
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Boldstar wrote:
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The brand is Optex, made by a company called Gentec, but I can't find my specific filter online (their website really blows). I paid approximately $28 CDN for it.

What's this about fungus!?

Could the polarizing filter be what screwed up all the photos I took at a wedding reception?

Thanks.
Optex and/or $28 would not be the mark of a good filter. I'd take it off and throw it away unless I expect to take pictures in blowing sand occasionally (and the lens might be the least of your worries in that case.)

UV kills fungus so it might be slightly more likely to grow with a UV rather than without. As the glass of the lens blocks some UV I'd the risk difference to be slight.

A polarizing filter will cause a two to four stop loss in light and we generally need all the light we can get in indoor or low light situations.
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Old Oct 22, 2008, 10:34 PM   #5
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Thank you for the input ac.smith. I had a feeling that my $28 filter was low end. But being a newbie and not having priced a bunch of them, I wasn't sure.

style="BACKGROUND-COLOR: #000000""... take it off and throw it away..." I had to laugh at that comment. I pictured myself giving it a football spike into the garbage can.

style="BACKGROUND-COLOR: #000000"So can I assume that you're one of the people who thinks "a filter for lens protection" is B.S.? To be honest, I'm starting to think that way myself. In 3 years of using my S2, I've never had a lens-scratching incident (knock on wood). And I've dropped that bad boy a few times.

style="BACKGROUND-COLOR: #000000"I think I might lose the UV filter and just use the polarizer when I need to. Now I just have to figure out the best way to keep my lens clean. I used one of those cloth things made for glasses on my S2, but I'm not sure that's the best option.
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Old Oct 23, 2008, 8:20 AM   #6
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I think a good UV or lens protection filter is a good idea. It will protect the lens without appreciably reducing image quality. Good filters have clear, polished glass, flat, parallel surfaces, and uniform, polished coatings. (I invite others to commenton this list.)Companies that produce good filters are B+W (Schneider Optics), Heliopan, Hoya/Kenko & Tiffen. (I also invite others to commenton this list.) You can leave a good filter on your lens all the time to prevent damage to the lens, and it won't perceptibly impact image quality.

Your plan to "lose the UV filter and just use the polarizer when I need to." is good, but remember that the surface of the objective lens element on a dSLR is a lot bigger than the one on your S2, and therefore, more likely to get damaged. And that dSLR lens is also likely to cost more to replace than your S2. That Canon EF-S 18-55mm f/3.5-5.6 IS Auto Focus Lens that came with your XSi will cost $165 to replace.

But it's up to you.
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Old Oct 23, 2008, 9:43 AM   #7
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Boldstar wrote:
Quote:
... Now I just have to figure out the best way to keep my lens clean. I used one of those cloth things made for glasses on my S2, but I'm not sure that's the best option.
The first thing to do is blow on the lens with something other than your breath (mouth blowing is likely to spatter some mucus). That avoids touching the lens at all so there is no chance of damage. High pressure air is also not a good idea, it can mechanically damage the lens.

There are all kinds of opinions/options about what to do if a blower doesn't do the job. Whatever you use, start out very gently. Do not touch whatever you are rubbing your lens with: that can transfer oil to the cloth/brush/thingee so dirt/sand/grit sticks to it making it act like sandpaper.
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Old Oct 23, 2008, 10:44 AM   #8
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On filters:

I started out with filters on all my lenses, now I use none. I just always use a lens hood.

There is no sense debating the issue - some believe it's completely necessary others that it's BS. All I would echo is that if you do decide to use them you use high quality multiple coated - Hoya Super HMC or B+W (whatever their version is). Everything you put in front of your lens will degrade image quality - you just want to do it as little as possible.

Whether you use a filter or not sooner or later you need to clean the front of the lens:

I recommend the following order:
  1. Blower (I recommend getting a rocket blower because you can also use it on the sensor)[/*]
  2. if that doesn't work a brush[/*]
  3. if that doesn't work - an appropriate lens cleaning solution for coated lenses with appropriate lens paper
[/*]
The idea being you always want to do the least invasive approach to get the job done.

Copperhill makes a nice little kit - they also incidentally make a kit for cleaning the sensor which you'll eventually have to do as well.

Bottom line - you spent a lot of money on a camera - buy the right cleaning products - splurge and spend the $40 (or whatever it is I don't remember) - rather than spitting or using alcohol or other homemade cleaning remedies.

Having said ALL that - don't become anal about it. Clean your lens when it NEEDS it not because you inspect it daily looking for a dust mote. A couple particles aren't even going to be noticable in many instances. I easily take 20,000 shots a year and probably need to clean each lens about once a year.
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Old Oct 23, 2008, 1:12 PM   #9
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I'm in the "don't use 'em" group.

For some purposes, a filter can be helpful. But, I wouldn't keep one on a lens used with a dSLR, unless the conditions were very extreme.

The most common issue you see with UV and "Haze" filters is loss of contrast from flare when shooting into brighter light sources, even when it's not very obvious that's what's happening (since you may not see any ghosts from it with a more evenly lit light source).

In other words, they can cause the very thing some users are expecting them to help with. This type of loss of contrast is known as "veiling flare" (that washed out/hazy look you sometimes see with photos shooting towards the brighter side of the sky, even when the light is more diffused. This is caused by light scattering and reflecting between optical elements. In more extreme conditions with brighter light sources, you may also get more severe flare causing streaks of light and ghosts (where you may have a bright light in an image and see a reflection of it in a different area of the frame) You will also tend to get vignetting with some lens/filter combinations. The lower the filter quality, the more chance you'll see these types of issues, and the lens one is being used with can also influence it.

As already mentioned, using a Polarizer all the time is a bad idea, since you'll have significant loss of light through one (making it more difficult to get sharp photos in lower light conditions because slower shutter speeds will be needed for proper exposure at any given aperture and ISO speed). That loss of light can also impact your Autofocus (since the camera's AF sensors can't see as well to focus).


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Old Oct 23, 2008, 2:25 PM   #10
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Thanks for all the input. This is great, I'm glad I started the thread. Of course I might experiment a little more, with and without the filter, but I have a feeling I'll end up joining the "don't use 'em" group too.

I'm rarely in situations where I'd have to worry about something hitting or scratching the lens. And I have a feeling I'll be using the polarizer for a lot of my outdoor photography.

I wonder if this "filter as protection" is one of the bigger dupes that retailers throw at the noobs.
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