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10-21-2007, 05:20 PM   #1
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Why lens filter do I need?

I think I should get a UV lens filter to protect my lens from sticky fingers and dirt, but I didn't know they came in different mm's. For example, I saw them listed on Sigma's website as 52mm, 55mm, 58mm, 62mm. etc. If I have the standard kit lens that comes with the K100D super (18-55mm), a Sigma 70-300mm F4-5.6 APO DG Macro and Pentax 500mm f/1.4 lens, do I need different filters or does one size fit all? Thanks!

10-21-2007, 05:29 PM   #2
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You need different filters for each lens. If you want to do this the theory is that you make sure that the front lens element is perfectly clean and essentially seal it with the UV filter never taking it off unless another filter is going to be added. It is good protection but many will opt for always using the lens hood when the lens is on the camera and always keeping the cap on unless you're shooting. The hood should provide all the protection you need except for a direct impact to the front glass. But for others it's a good and cheap piece of mind.

If you look at the underside of each lens cap for the lenses you own the filter size is stamped there. I have a 50mm and it's 49mm but I'm not sure about the others. Kit lens 52mm? And I'd guess the 70-300 is around 58mm but check to be sure.
10-21-2007, 05:39 PM   #3
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Welcome to Pentax Forums momof4

Just doing a google search it looks like you'll need a 58mm filter for the Sigma 70-300mm F4-5.6 APO.
Although I might be wrong.

The 18-55mm lens requires a 52mm filter, like Peter said.
When you have a filter on at the 18mm side you'll notice that the corners are dark
This is normal for the lens. It's called Vignetting.

Sorry I can't help you with the Pentax 500mm f/1.4 lens.
I think that you may have added a digit. I'm pretty sure that it should be
Pentax 50mm f/1.4 lens

If you bring the lenses into a local store they'll try on the filters and make sure that you get the right ones.
If you plan on buying I guess that this won't work.
10-21-2007, 05:44 PM   #4
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If its the SMC A 50mm f/1.4 manual its 49mm. and you are one lucky sob. auto im not sure.

if you're looking for a polarizer for the kit lens 52mm, i have a used one im looking to sell. PM me an offer.

James

10-21-2007, 07:54 PM   #5
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The diameter of the front screw/lens retention nut is usually stamped on the bottom side of the lens barrel; it looks llike a slashed zero and a number. On older lenses the front element diameter may also be stamped in the lens retention ring inside the barrel.

QuoteOriginally posted by momof4 Quote
I think I should get a UV lens filter to protect my lens from sticky fingers and dirt, but I didn't know they came in different mm's. For example, I saw them listed on Sigma's website as 52mm, 55mm, 58mm, 62mm. etc. If I have the standard kit lens that comes with the K100D super (18-55mm), a Sigma 70-300mm F4-5.6 APO DG Macro and Pentax 500mm f/1.4 lens, do I need different filters or does one size fit all? Thanks!
10-21-2007, 11:33 PM   #6
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No stinkin' filters

QuoteOriginally posted by momof4 Quote
I think I should get a UV lens filter to protect my lens from sticky fingers and dirt
Many say that you don't need any filters except a circular polarizer at all. Just protect your lens by always keeping on a lens hood. The SMC coatings are a dream to keep clean. Any filter degrades picture quality, is something else to keep clean and costs money. Lenses can also be repaired if you really damaged the very front optic by scratching it. I agree with the many...
10-22-2007, 05:43 AM   #7
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And, momof4, just be sure that you aren't confusing focal length and filter thread size. Both are in mm, but they have very little to do with each other. Your 18-55mm kit lens (as others have mentioned) uses a 52mm filter. You'll find this number on the front of the lens, where it says 52mm. On the Sigma, the same information is found on the zoom ring...if you keep following the numbers as they get smaller, and keep going past 70 for a bit, it says 58. As for the 50mm, where this might be listed depends on the model, whether it's an FA, A, etc. But for example: my FA 35mm f/2, which takes 49mm filters, doesn't say so anywhere on the body of the lens. The lens cap does say "49mm" inside, but that's about it. If your 50 is an FA lens, it may be the same way. But, in that case, it also takes the same 49mm filter.

Keep in mind that for things like polarizers, infrared filters, etc., you don't need one of every size. You just need to match your biggest lens. Than you can get step-up rings to convert those threads to the smaller threads of your other lenses. It's best to match the biggest lens you own because putting a smaller filer on a bigger lens can result in vignetting when it blocks the field of view (although I use a 55mm filter on a lens with 58mm threads with no problem). Of course, if you want to keep a UV filter on semi-permanently, you'll need one for each lens. But I don't do that, nor do many (most?) users.
10-22-2007, 06:15 AM   #8
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Can anyone recommend a good quality multi-coated UV filter for my 86mm sigma 170-500mm lens? I want to protect this baby, but don;t want to lose out on image quality.

I like the Hoya PRO1 Super HMC filters, but they don't seem to be available in 86mm.

A good bang for buck alternative would be good - what do you recommend and where can I get one?

Thanks

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