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05-18-2011, 06:13 PM   #1
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News flash: I'm an idiot - it's sensor dust!

I got the da35 ltd 2 wks ago and it went straight from box to the k7. It's been a great learning process on a great lens. Only in the last few days have I tried macro w/ it.

And that's when I noticed something weird...f/16 & beyond, I was picking up what I thought was sensor dust. But the filter runs, the dust alert is blank. I pulled the lens off and took a look - no spots on the glass.

Here's what I'm talking about (center, 2/3 down & upper right corner):


So now I know its the lens' fault that I'm getting declined in PPG.

Here's a shot from the k7 - no lens, no specks:


Fortunately I bought it from BH. Really fortunately, I was informed that they have a free shipping 15 day exchange policy. The guy on the phone was really helpful, said to stick it in the box, mail it back & they'd replace.

The weird thing is that I'd probably never go beyond f/16 for a non-macro shot and if I did (landscape) may never have seen these spots. They show up at long focus as well.

I have a few questions for you guys because I'm new to new lenses:
1. Where could these specks be in the lens? Why do they only show with small apertures?
2. Is my return unreasonable for this (or any quality) of new lens?


Last edited by John Araki; 05-18-2011 at 08:01 PM. Reason: title change
05-18-2011, 06:22 PM   #2
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Look like sensor dust to me, nothing to do with the lens. The dust alert feature in Pentax cameras is a total joke giving loads of false positives and false negatives. It is useless and best avoided.

Also, it is very very hard to spot dust on your sensor with your naked eye, almost impossible unless it's a nice big spec which most aren't.

Believe me, I have a bit of experience (and a few scars) dealing with sensor dust, I'm not making this up, this is from first hand experience.

Also, you cannot take a pic with no lens and spot any sensor dust, you need a lens on the camera stopped down all the way to f22, pointed at a clear blue sky or a white wall, ISO 200 and take the pic, dont worry about camera shake in fact a bit of shake is good. Then you need to open it in your photo editting program, flip the image vertically, and do an auto levels adjustment on it. Only then will you see whether you have sensor dust and where exactly on the sensor that dust is.

Last edited by twitch; 05-18-2011 at 06:43 PM.
05-18-2011, 06:37 PM   #3
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I probably should have mentioned what you should do about the sensor dust. You’ll find many differing opinions on this with all sorts of people swearing black and blue that their method is the best method.

About the only common ground is the first 2 steps of the process which are
1) run the sensor clean function built into your camera if it has one
2) use a rocket blower (not canned compressed air) to blow directly onto the sensor to remove the dust

However after this point you get wildly differing opinions. My own is that the inventor of the Pentax sticky sensor cleaning lollipop should get a knighthood, while the inventor of the SensorKlear sensor cleaning pen should be brought before a firing squad. I haven’t done wet cleaning but I have had to clean up after a botched attempt of a camera shop trying to wet clean of my sensor, complete disaster. Lets just say there’s more ways to get it wrong with wet cleaning than to get it right. IMHO the pentax lollipop is a killer solution that is super effective at removing dust, and doesn’t have the potential nasty downsides of a wet clean.

Good luck…..

Last edited by twitch; 05-18-2011 at 06:43 PM.
05-18-2011, 06:41 PM   #4
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Wow - the more I think I know the less I know I know.

I will stick another lens on the thing to verify, I hope you're right (at least if it's on the sensor, I'll have the lens for baby's first birthday and graduation parties this weekend (separate parties, of course).)

Will be calling on that luck as well....

05-18-2011, 07:16 PM   #5
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You will NEVER see dust on the lens in pictures unless you are doing macro work that extends the lens far enough out to focus on the glass itself.
Also, I've been using canned gas (Dust-off specifically) for routine sensor cleaning since I bought my istD in September 2003.
I really don't understand the hysteria about using it, just make sure you don't blast the sensor with liquid propellant.
05-18-2011, 08:03 PM   #6
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QuoteOriginally posted by Wheatfield Quote
Also, I've been using canned gas (Dust-off specifically) for routine sensor cleaning since I bought my istD in September 2003.
I really don't understand the hysteria about using it, just make sure you don't blast the sensor with liquid propellant.
That IS the hysteria, blasting the sensor with liquid propellant.
05-18-2011, 08:04 PM   #7
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Yep, it's sensor dust. Yep I'm an idiot.

My past experiences were of "big" specks, what can I say. I changed the lens, it's still there, these small little things. I went back to the blower again, they're not moving.

Thanks, twitch, and phew. Now off to get some sticky lollipops from an e-tailer....and just stick below f/16 until then.

Better send a retraction to b&h. They're awesome, btw.

John
(stepping away sheepishly)
05-18-2011, 08:37 PM   #8
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QuoteOriginally posted by John Araki Quote
Yep, it's sensor dust. Yep I'm an idiot.

My past experiences were of "big" specks, what can I say. I changed the lens, it's still there, these small little things. I went back to the blower again, they're not moving.

Thanks, twitch, and phew. Now off to get some sticky lollipops from an e-tailer....and just stick below f/16 until then.

Better send a retraction to b&h. They're awesome, btw.

John
(stepping away sheepishly)
Better to find out now than after you've sent back your 3rd lens for the same problem

I mentioned it in my first post, but make sure when you take the picture prior to cleaning your sensor you follow what I said carefully, including flipping the image vertically on import. The lollipop isn't to drag all over the sensor (in fact you just gently but firmly press it onto the sensor and lift, no dragging!), you want to be a bit targetted with where you press it into the sensor, and so you need to know roughly where the dust specks are. I can see at least 3 specks from the pic you posted. If you do an auto levels adjustment you will see the specks a bit clearer.

Good luck.

05-18-2011, 09:00 PM   #9
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Thanks again twitch. Anthony Bourdain was right about how cool Melbourne folk are.

I'm sending an email to the mod to change the title of the post so as not to speak badly against my awesome lens.
05-19-2011, 06:49 PM   #10
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QuoteOriginally posted by DogLover Quote
That IS the hysteria, blasting the sensor with liquid propellant.
I've heard of rocket blowers shooting sticky junk onto sensors too.
Does that possibility make people hysterical?
I challenged this forum a few years ago to come up with one verifiable instance of a person wrecking a sensor by freezing it, and got nothing but an anecdote about some guy who knew some guy who thought he might have or something to that effect.

A quick puff from the nozzle of a canned gas container away from the camera before cleaning the sensor is all that is required. That and not holding the can upside down.
A little common sense goes a long way.
05-19-2011, 06:54 PM   #11
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QuoteOriginally posted by twitch Quote
Better to find out now than after you've sent back your 3rd lens for the same problem

I mentioned it in my first post, but make sure when you take the picture prior to cleaning your sensor you follow what I said carefully, including flipping the image vertically on import. The lollipop isn't to drag all over the sensor (in fact you just gently but firmly press it onto the sensor and lift, no dragging!), you want to be a bit targetted with where you press it into the sensor, and so you need to know roughly where the dust specks are. I can see at least 3 specks from the pic you posted. If you do an auto levels adjustment you will see the specks a bit clearer.

Good luck.
Wait a sec, do I really flip vertically or do I do a 180* rotation?
05-19-2011, 08:59 PM   #12
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QuoteOriginally posted by John Araki Quote
Wait a sec, do I really flip vertically or do I do a 180* rotation?
Yes you really do do a vertical flip, this is not the same as rotating 180 degrees (which is like doing both a vertical and horizontal flip)
05-20-2011, 07:05 AM   #13
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QuoteOriginally posted by Wheatfield Quote
A quick puff from the nozzle of a canned gas container away from the camera before cleaning the sensor is all that is required. That and not holding the can upside down.
A little common sense goes a long way.
+1 to this,
I've been using canned air on all my gear for few years now and never had a problem with it! Just use your common sense and you'll be fine
05-20-2011, 07:18 AM   #14
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QuoteOriginally posted by axl Quote
+1 to this,
I've been using canned air on all my gear for few years now and never had a problem with it! Just use your common sense and you'll be fine
I'm a canned air supporter as well. Again, so long as you don't shake the bottle or turn it upside down while you're using it, there shouldn't be any issues at all.
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