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08-15-2010, 09:07 PM   #1
Pentaxian




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Location: launceston
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Curved Asahi filters?

Hi everyone. Just wondering if anyone knows anything about curved filters?

I was rifling through my mum's 35mm Pentax gear the other day and came across an old film-era Asahi Pentax UV filter, which has a convex element... I've never seen anything like this before and it has me intrigued.

Would this hypothetically work better, as the curvature of filter element would match the front element of the lens? Or would it just cause erratic flare and so on? I know they try and match curvature for underwater fisheye ports, but I don't know if it would work the same for a filter?

The filter reads: Asahi Pentax 49mm UV Ghostless

Anyone got any info?

08-15-2010, 09:13 PM   #2
Pentaxian
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Join Date: Feb 2008
Location: Waterloo, Ontario
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Posts: 4,444
Hey Nick

This might help.

Die Cast Pro - Asahi Pentax Filters

I have one and it seems to work as far as I can tell. It is not SMC.

Tom G
08-15-2010, 09:46 PM   #3
Pentaxian




Join Date: Dec 2008
Location: launceston
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Original Poster
Thanks Tom!

Mine doesn't have SMC printed on it but it does have a purplish cast to the reflections... Hmmm interesting.

Do these have any known downsides compared to normal UV filters?
08-16-2010, 07:34 AM   #4
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Join Date: Feb 2008
Location: Waterloo, Ontario
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Nick,

I can't really see any downside to these filters. The concept actually makes sense to me. The front element of any lens I have ever seen has always been curved to optimize performance. I've often wondered why we put flat filters in front these convex surfaces. Other than protection it doesn't make sense. I suspect Pentax quit making them (ghostless filters) not because they didn't work but because they were more expensive to produce than a flat filter.


Tom G


Last edited by 8540tomg; 08-16-2010 at 01:46 PM. Reason: typo
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