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07-08-2011, 03:26 AM   #1
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Dust inside DA 40mm F2.8 SMC Limited

Hello dear Pentaxians,

Maybe someone can help me with this conundrum...

Some months ago, I acquired a brand spanking new DA 40mm F2.8 SMC Limited lens. Lucky me. And recently I have noticed a rather... let's say huge piece of dust:



Unfortunately for me, it turns out the dust is actually inside the lens. On simple lens switching, it goes away. And upon close inspection against a blank wall with aperture wide open, the dust is clearly visible with its unusual shape.

And here is the best bit of all. In order to clean it, my local service needs to send it to Germany, in order to realign the optics inside (they claim). The cost for this operation? A measly 100 euro. Estimated, not definite...

So before I chose this desperate option, did anyone open up such a lens? Is there a way to partially open it and try to blow away the air with compressed air without misaligning the inside optics? Any help would be greatly appreciated.

07-08-2011, 07:34 AM   #2
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100 Euro fix for a 2 month old purchase?!?!?!
not covered under warranty? I'd be massively annoyed!
Can you get the retailler to exchange?
07-08-2011, 08:23 AM   #3
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Could you have gotten it with the dust between the elements? You should be able to send it to Pentax for free cleaning under warranty, especially since so large a bit of dust must have got there during the production process. (It seems to me Pentax lenses haven't been so clean lately.)
07-08-2011, 08:24 AM   #4
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Acum vad ca esti roman Ai luat-o second hand?

07-08-2011, 08:56 AM   #5
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1) Unscrew the front retaining ring using a rubber tool.
2) Remove the filter ring which is held by 3 screws.
3) Unscrew the front lens group.
4) Flip open the aperture and blow off the dust.

Since the lens group is screw on, alignment won't be affected. However, I feel strongly the dust is on the sensor, not inside the lens, despite what you said.
07-08-2011, 08:57 AM   #6
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Hello all,

Yes causey, I'm Romanian, but let's keep this in english

The lens was bought on a business trip in Taiwan, on Taipei Camera Street. To the best of my knowledge, the lense was brand new. The evening I bought it I was with a local coleague who should have gotten for me the international warranty card. Until now it has not reached me and I don't think it ever will...

Unfortunatelly, a retailer exchange is quite out of the question. As it is, the local Pentax representative is a small company that can handle only the most basic warranty situations. For the most serious, Germany is the way to go.

Dear wlachan, thanks very much for your advice. I will give it a try. I triple checked that the dirt is not on the sensor, it was my earnest wish that it was so... Just to clarify, is this the front retaining ring? And does it unscrew normally, or clockwise?


Last edited by ender.wiggin; 07-08-2011 at 11:52 AM.
07-08-2011, 03:00 PM   #7
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The retaining ring is the outer shiny one with words on it. It's not very tight to unscrew (anti-clockwise, just like the way you remove the filter) but you need a good fit rubber to get a good grip. Be careful not to scar the matt black finish on the inner ring.
07-08-2011, 06:00 PM   #8
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Your lens looks squeaky clean compared to this one.

I'm counting 4 more specks with a similar point spread on the right side of your beach photo. The only times I have seen spots like this, they were from dust on the sensor, not from damage to the lens. Try this - when you switch to a different lens for comparison, make sure you take a picture in Av mode at the smallest aperture it provides (say f/22) against a uniformly bright surface. Don't worry about the long shutter time. If I'm right, you'll see small, crisp dots in the very same places where we see the blurry ones in the shot above.


Last edited by Ikarus; 07-09-2011 at 10:24 AM.
07-08-2011, 10:39 PM   #9
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Dear Ikarus & wlachan,

I am very glad to say that you were both right. Incredibly for me, the dust is actually on the sensor. I have never noticed it on my kit lenses, but on smallest aperture against the white refrigerator...



Thank you both for insisting

And yes, I have an incredibly dirty sensor. That's what you get for changing lenses on the run while chasing two small kinds. Going to buy a sensor cleaning kit right now.

PS to this lesson: Don't trust the in-camera dust detection system. It completely missed the huge ones.
07-08-2011, 11:29 PM   #10
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You may wish to invest in a Giotto Rocket Blower if you haven't done so.
07-09-2011, 04:30 AM   #11
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QuoteOriginally posted by wlachan Quote
You may wish to invest in a Giotto Rocket Blower if you haven't done so.
Just did. Also bought some wet/dry sensor wipes and a 49 mm lens cap to easily use the lens
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