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03-22-2012, 08:27 PM   #1
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Pentax K or A 15mm F3.5 built in filters?

This lens fascinates me since I collect A lenses and its the widest prime they made in that series (or anything before I think). I see that it apparently has 4 built in filters and that has me rather baffled, can someone explain to me how all the odd features of this lens work?

BTW someone took this amazing picture with this lens that made me totally want to have one:
http://www.pbase.com/wlachan/image/33830849
I'm thinking its the K version based on the shape (number of aperture blades) of the flare that is the sun.

03-22-2012, 08:38 PM   #2
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The filters were mostly useful on film cameras- you won't see much use for them on digital.

Don't get this lens if you're looking to get cool wide-angle shots, as it's sharpness is much lower than that of the DA 15mm F4 limited, and it distorts more. Also, it tends to underexpose on digital (K version - 1 stop, A version, 0.5 stops), at least for me. I tested it with the super program and MZ-S and got the correct settings.

With that said, it does make for a great collector's item!
SMC Pentax-DA 15mm F4 ED AL Limited Reviews - DA Prime Lenses - Pentax Lens Reviews & Lens Database

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03-22-2012, 09:11 PM   #3
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Actually it would be a good excuse to pull the Super Program out again. Though I'm sure it would find its way onto the K20D. For digital id probably go the sigma 10-20 route.
I was more curious as to how it has 4 built in filters and how you switch them, do they just screw on behind that massive lens hood? That would make them rather not built in so I assuming there's funny business involved.
Also yes I totally just want to own one just to have it as part of my A lens set too.
03-22-2012, 09:42 PM   #4
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QuoteOriginally posted by PPPPPP42 Quote
Actually it would be a good excuse to pull the Super Program out again. Though I'm sure it would find its way onto the K20D. For digital id probably go the sigma 10-20 route.
I was more curious as to how it has 4 built in filters and how you switch them, do they just screw on behind that massive lens hood? That would make them rather not built in so I assuming there's funny business involved.
Also yes I totally just want to own one just to have it as part of my A lens set too.
The K&A15/3.5 has a built-in filter ring that you turn to select a specific filter. Other Pentax lenses also have a filter ring: the 17/4 Fisheye, K28/3.5 Shift and K18/3.5.

Phil


Last edited by gofour3; 03-23-2012 at 07:41 AM.
03-22-2012, 09:56 PM   #5
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You can see the ring on this image. You just turn it to engage the filter you want to use. On the photo the ring is in the 'no filter' position. I'm also attaching a photo taken with the K version.
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03-22-2012, 10:27 PM   #6
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The built in filter system was used because the design of the front element on some lenses prevented the use of screw on filters. Not a huge problem with digital but on film you needed those filters to get the color correction right. Quite an innovative solution. My 17/4 fisheye has that system. But outside of messing things up when I accidentally engage a filter I have not found a use for it.
03-23-2012, 08:25 AM   #7
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So how does rotating the ring change filters? I guess I just don't understand how they built that into one layer when there is no room for a filter to get out of the way and another to move in.

And I hate all of you even more every time I see another pic from that lens, I WANT!
03-23-2012, 08:47 AM   #8
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QuoteOriginally posted by PPPPPP42 Quote
So how does rotating the ring change filters? I guess I just don't understand how they built that into one layer when there is no room for a filter to get out of the way and another to move in.

And I hate all of you even more every time I see another pic from that lens, I WANT!
To make it more clear, you're asking about the mechanical action that moves one filter out of the way (to where?) and another into place.

03-23-2012, 08:47 AM   #9
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QuoteOriginally posted by PPPPPP42 Quote
So how does rotating the ring change filters? I guess I just don't understand how they built that into one layer when there is no room for a filter to get out of the way and another to move in.

And I hate all of you even more every time I see another pic from that lens, I WANT!
I do not know how it works but this page shows where the filter fits into the optical formula of the lens. I would really like to see a directed model to understand how it works.

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