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03-15-2009, 07:54 PM   #1
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fault in front lens

I have a DA 70mm ltd lens and from the day I bought it I have had a uv filter on mainly just to protect the lens. Recently I cleaned the front glass and have noticed what appears to be a bubble it can't be a scratch. I am wondering what effect this will have on my photo's. I have had this lens for six months now and think it performs well. I recently took a photo at infinity with lots of blue sky and noticed a mark in the sky - easily removed in editing. Should I return the lens under guarantee or because the lens performs well in all other situations, ignore the fault stick with the lens???

You can see the mark on right in the image attached.

Any advice on this would be greatly appreciated.


K10D Pentax DA70mm Ltd, 50mm f1.4, Sigma 17-70mm

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03-15-2009, 08:11 PM   #2
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You have a bit of splooge on your sensor. It's time for a cleaning. It's not the lens.
03-15-2009, 08:12 PM   #3
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If it really is a bubble, I would exchange it. Sometimes there are odd little reflections though, that appears to be a flaw in the lens but are not, so make sure it stays in the same place as your rotate the lens at difference angles and inspect.

The mark in your photo though, looks to be from sensor dirt, not a lens flaw.
03-15-2009, 08:57 PM   #4
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Lens elements occasinally have tiny bubbles. According to common wisdom a bubble in a glass element doesn't affect the picture at all (I have not confirmed that myself, I have never seen a bubble in a lens). For peace of mind you might want to exchange the lens, if possible.

03-15-2009, 09:00 PM   #5
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If it's a bubble, then the spot is probably not caused by it, and you probably want to check your sensor. However, I've had the rare experience where there was a tiny ant stuck on the rear of the primary element of my 10-17 Fisheye; never knew it was there till I shot one day @ F22 and noticed a black blob that would not go away after sensor cleaning, and most importantly will disappear when I put on another lens (so do a check like that). I bet the ant got in there during assembly (assembled in Viet Nam). Needless to say, I got it replaced pronto :-)
03-15-2009, 10:12 PM   #6
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Do you think you could get a photo of the "bubble" using another lens? I know that's tough, but It might help.

Could be some sort of lens coating separation. I'd return it if it was going to drive me nuts.

03-15-2009, 11:53 PM   #7
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you could put a spot of blue tak the size of a pin head on your lens and not notice it unless you stop the lens down all the way.
03-16-2009, 08:42 AM   #8
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The only thing the spot will hurt is (possibly) resale value. It will have zero affect on your images.

The spot you posted is sensor dust.

03-16-2009, 07:29 PM   #9
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Original Poster
Thanks for all the comments

It is good to hear that a bubble in the glass will not affect image quality. Infact I have just read an article on the internet that confirms this and even suggests that a bubble is considered an indication of high quality ( I doubt this). It seems that I have to clean the sensor. Something I have been avoiding for fear of c***ing it up!

So if the bubble has no affect on image quality and the lens performs up to scratch, and I think it does then there is no reason to return it to Pentax apart from a possible affect on resale value.

I paid good money for a new lens with a fault in the glass. Therefore it is not worth the money I paid for it. It should be perfect. I returned this lens to pentax twice for checks relating to front focusing problems and play in the barrel. They didn't notice the fault in the glass? Or maybe they did see it but it's within their tolerances or they knew it would not have any affect on image quality so they said nothing. This annoys me!!!
Perhaps I should pay Pentax a visit.

Thanks again for your comments

03-24-2009, 12:12 AM   #10
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I actually changed my mind about going to Pentax about the fault but now after close inspection of the rear glass I have found a bubble in that too!!! I really think that this is rediculous considering this lens is advertised as being high quality and made to high tolerances. I can't see any effect on my images and according to others I wouldn't but even so after finding a second bubble I think as I live near Pentax I will go to their office and see what they say.

Thanks again for your comments


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