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12-23-2010, 05:39 AM   #1
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Need a check with owners of the FA*24mm f2.0

I had just acquired a pre-owned copy of this lens. Upon closer inspection of the lens through bright light, I'd realise that there is a very faint concentric circle within one of the lens group. Yes, it looks like the boundary of an element that had been glued on to another. There also appear to be very minute bubbles/spots appearing evenly over that element's surface if I am right. It isn't really all obvious but faint enough such that it can only be observed through a bright light source at certain angles (within the shadows). It's rather hard to be photographed and I hope my description is good enough here.

To clarify, the observations were made by looking from the rear at wide open aperture (ok, obviously).

I am wondering this this is a sign of element separation or just normal for this lens. I have checked with some of my other lenses and do not quite observe this. Can some kind souls check theirs or advise accordingly? Thanks!

P.S. I really love this lens.


Last edited by scorpioh; 12-23-2010 at 06:12 AM. Reason: Clarifications
12-23-2010, 05:51 AM   #2
axl
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I'm on my way to work. Don't have the lens on me and won't be home anytime soon with busy tomorrow. I'll try to check over Xmas and will let u know. Although when I was examining my copy before purchase I haven't noticed anything like that. But will double check and let you know.
Regards
12-23-2010, 05:54 AM   #3
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QuoteOriginally posted by axl Quote
I'm on my way to work. Don't have the lens on me and won't be home anytime soon with busy tomorrow. I'll try to check over Xmas and will let u know. Although when I was examining my copy before purchase I haven't noticed anything like that. But will double check and let you know.
Regards
Hey, thanks axl! I had you in my mind while posting this thread. Ha.
12-23-2010, 06:03 AM   #4
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Ok, I am trying to find out more on the net and came to this:

The Mamiya 50mm f4 for M6, A shocking observation! - Photo.net Medium Format Forum

To quote:

"True separation of lens elements can usually be seen by transmission (i.e. looking through the lens) as well as reflection, and appears as slightly grey, less clear patches of roughly circular shape." (Pete Andrews)

In my case, the bubbles/spots are uniformly spread across and the "concentric" circle/lens element outline/boundary is perfectly circular with no "broken lines". Maybe its a poorer glue job than separation?

12-23-2010, 06:45 AM - 1 Like   #5
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My FA*24 shows no similar problem if that helps. But it is also quite worn and Pentax service says they miss the spare parts to replace weakened mechanic components.
I really wish for a DA* replacement of this lens. I'd gladly sacrifice 1000euros for one.
12-23-2010, 06:45 AM - 2 Likes   #6
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QuoteOriginally posted by scorpioh Quote
I am wondering this this is a sign of element separation or just normal for this lens.
Yes, this is a typical problem with this lens. The aspherical lens element is a piece of plastic glued on a glas element. There have been reports of separation and yellowing of this piece.
That's the reason why this "star" lens is not as highly regarded as the other star lenses.
12-23-2010, 07:05 AM   #7
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QuoteOriginally posted by blende8 Quote
Yes, this is a typical problem with this lens. The aspherical lens element is a piece of plastic glued on a glas element. There have been reports of separation and yellowing of this piece.
That's the reason why this "star" lens is not as highly regarded as the other star lenses.
I see... Thanks! Plastic?! No wonder... But I think it is nothing to worry about at this stage since it's really very mild, perhaps like this ever since it left the factory and hopefully doesn't worsen.
12-23-2010, 07:05 AM   #8
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QuoteOriginally posted by elho_cid Quote
My FA*24 shows no similar problem if that helps. But it is also quite worn and Pentax service says they miss the spare parts to replace weakened mechanic components.
I really wish for a DA* replacement of this lens. I'd gladly sacrifice 1000euros for one.
Ironically my copy is pretty minty. Guess I'll live with it. Thanks for your help! Merry X'mas!

12-24-2010, 01:24 AM   #9
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Well, I managed to check mine. No such problems. On a side note, my copy is in great shape so I hope it'll last. But yes, the DA*24 would be nice!
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