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07-31-2009, 05:14 PM   #1
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Filter, New Cap for DA 40mm prime lens

I just bought a like new DA 40mm limited prime lens for KEH for $289 and am very happy with it so. I would like to know whether I should buy a filter and new cap for this lens. I assume I will need a 49mm UV filter with this lens. How would I find a cap for this lens?

Generally speaking is it a good idea to buy a filter for the Pentax prime lenses? I have filters on my tamron lenses.

07-31-2009, 05:31 PM   #2

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The sole purpose of a UV filter is to prevent dirt, finger, ...., to touch the front element of the lens.

For the DA40, the hood does that job very efficiently. The opening of the hood is so small (31mm) it keeps most if not all foreign objects from touching the lens. If the lens did not come with the hood, you should buy one.

There's no need for a UV filter.

Once you have the hood, the cap is easy. The thread below contains some info about the cap:

Pentax DA40
07-31-2009, 05:38 PM   #3
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I think the hood is probably sufficient. I did get a plastic lens cap to substitute for the screw on one. I am very afraid of losing it and anyway, it isn't very convenient to take it on and off. It certainly doesn't hurt to screw the lens hood on to a filter, but I don't think it is necessary because of the small opening in the hood.
07-31-2009, 05:42 PM   #4
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If it's "like new", it should have come with a cap, no? the little quarter-sized piece of metal that screws into the hood?

As for whether you "should" use a filter, do a sesrch of this forum, dpreview, or just Google 0 you'll find a pretty much weekly debate on that very topic. Some people like them because they are worried about scratching their lenses. Others don't like them because they are worried about loss of image quality. In reality, they probably really have very little effect either way (that is they don't protect a lens against very much, nor do they affect IQ very much). As far as I'm concerned, the only point of buying a filter is to lighten your wallet, but the filter will weigh more than the cash you spent. So I consider that a net loss.

Last edited by Marc Sabatella; 08-03-2009 at 11:26 AM.
08-01-2009, 12:35 PM   #5
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Thank you all for your advice. I realize now that the lens came with the hood and the tiny screw on cap -- very odd. I didn't realize that the hood was attached to the lens -- so different from my other lens. I'll take it out for a test practice.

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