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Old Nov 3, 2009, 9:55 PM   #1
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Default Filter size?

I want to buy a polarizing filter for my Sony Alpha A230. How do I know what size will fit, how do I know if I'm buying a "good" one, and whats a good price for one?

Thanks.
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Old Nov 4, 2009, 3:36 AM   #2
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I want to buy a polarizing filter for my Sony Alpha A230. How do I know what size will fit ...
Filters go on the lens, not the camera, and since your A230 has interchangeable lenses, you need a filter that fits each lens. Since the A230 comes with at least the DT 18-55mm, and since it takes a 55mm filter, that's at least one filter size you'll need. If you've got other lenses, they may or may not use the same size filter. You can tell what filter size a lens takes by finding the filter size engragved in the lezel or barrel of the lens. It usually starts with a "Ф" symbol followed by the filter size. See the attached image of the front bezel of a Minolta 135mm f/2.8 lens, which also takes a 55mm filter.

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... how do I know if I'm buying a "good" one, and whats a good price for one?
All you can really go by is price and reputation. Cheap filters will have inconsistant coatings, or coatings that can be easily damaged. There are a number of brands that make good filters, while the cheap ones are the house brands or the ones they give away when you buy something else.
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Old Nov 4, 2009, 12:03 PM   #3
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get a multicoated filter from Hoya or B+W.

if you are using the kit lens with a 55mm filter size, this one is a good choice.
http://www.bhphotovideo.com/c/produc...zer_Super.html

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Old Nov 4, 2009, 4:04 PM   #4
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Thanks TCav for that post on filter size.

Now Hards80, what is the advantage of having a multicoated filter? That Hoya filter you linked me costs $65, and I found a non multicoated Hoya filter that was $30.
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Old Nov 4, 2009, 4:09 PM   #5
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the multicoat helps to prevent flare and reflections. its worth the investment to get a coating.
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Old Nov 4, 2009, 4:11 PM   #6
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Man, I never thought that a tiny plastic coating would cost so much...

How much better does it work that a non multicoated filter? All the other non multicoated filters claim to prevent flare and reflections as well.

Thanks.
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Old Nov 4, 2009, 4:12 PM   #7
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well you can think about it this way. you spend all your money on a camera and lens to capture the very best in image quality. do you then want to shoot through a cheap piece of glass?
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Old Nov 4, 2009, 4:28 PM   #8
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well you can think about it this way. you spend all your money on a camera and lens to capture the very best in image quality. do you then want to shoot through a cheap piece of glass?
Good point.

edit: Another dumb question. Does the filter stay on all the time and act as a lens cover, or would I take off the filter when I'm done using my camera and put my lens cover on?

Last edited by adamvk; Nov 4, 2009 at 4:32 PM.
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Old Nov 4, 2009, 5:18 PM   #9
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Another dumb question. Does the filter stay on all the time and act as a lens cover, or would I take off the filter when I'm done using my camera and put my lens cover on?
Not dumb. You can leave the filter on, or not. The lens cap will attach to the filter the same way it attaches to the lens. There is something else to consider, however. The kit 18-55 has a wide angle of view. A conventional filter has filter mounting threads on it, just like the lens, so you can stack filters. The problem is that a lens with a wide angle of view could have some of it's view blocked by the filter and its threads. If you'll be doing a lot of shooting at wide angles (landscape, , cityscape, architectural, groups, etc.) you might want to skip the filter altogether. And while some filters are made specifically for wide angle lenses, some of them don't have their own filter mounting threads, so there's no place to mount the lens cap.

So a filter can protect the lens, but reduce image quality (especially if you don't get a good one) or you can go without to get the best image quality and hope for the best.
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Old Nov 4, 2009, 5:35 PM   #10
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Good point.

edit: Another dumb question. Does the filter stay on all the time and act as a lens cover, or would I take off the filter when I'm done using my camera and put my lens cover on?
well a circular polarizer, which i thought you were referring to in your original post is a rather specialized filter, mainly used in landscapes to boost saturation and give you nice blue skies. so this filter would not stay on your camera at all times as "protection". the version i linked you is a thin version, since your kit at 18mm is pretty wide. i am not sure the standard cap fits these thin versions.

if you are looking for a protective filter to keep on at all times to protect your lens. well first, i would advise against this practice unless you are in shooting environments with alot of traveling debris etc. instead protect your lens with the cap when not in use, and a lens hood while in use.

then just use the circular polarizer for your landscape days.
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