Seeing spots.....lens flaw?

[AndrewMcD]

Camera: Sony NEX-6
Lens: Sigma 19mm, f/2.8
I was inspecting some images of sky and clouds when I noticed a small shaded orb in the picture that certainly wasn't present in the sky. On close inspection of some other images I noticed the orbs were not present at lower f settings. Anything above about f/11 and the flaws in the image became noticeable. I shot a series of sky images and found the shadowy orbs, which I assume to be some sort of optical flaw, increased in number and visibility as I stopped the camera down. The attached sample was shot at f/22, ISO 100, 1/60 seconds.
Can anybody provide any insight or explanation to what this novice is seeing.
Note that this is only the second time I've used the lens and a visual inspection shows nothing that I can see on the glass surfaces.
Thanks,
Andrew

[PixByMarti]

It is not your lens, but rather the camera's sensor that causes this issue. It is quite common, and usually can be cleared by cleaning the sensor. You can either read up on how to do this yourself, or take your camera into a camera shop, or perhaps Sony to have the sensor cleaned.

[AndrewMcD]

I have only had the camera for about one month and when I have changed the lens it has always been done in a controlled (indoor) environment. I thought I handled the camera in a manner that precluded anything touching the sensor. I'm surprised that the sensor would need cleaning already. Is the sensor going to need cleaning frequently and is it a consequence of changing the lens?

[DanK]

Sensor dust is common, unfortunately. In the film days, you didn't worry: every shot was a fresh piece of film, and the film wasn't electrically charged. the sensor stays put, and sooner or later, it will get dirty.

There is dust in the air, so yes, removing the lens increases the odds of getting dust on it.

As for how frequently it happens: it depends on lots of things: conditions, the camera (some have an anti-dust cycle when the camera is turned off and on), and what you shoot. You will be more likely to notice it if you have an area with no detail,like a sky, or if you shoot at a small aperture. You did both.

If you have dust already, it may have arrived dirty. Such things can happen. Maybe Sony will clean it for free.

Many folks clean their own. i do. Just read up first, because you will want to be careful. I use Copper Hill materials (they have good tutorials too), and follow this sequence:

1. Air from a rocket blower (NOT canned air)
2. If #1 does not work, a static brush
3. If #2 does not work, a wet cleaning

It's only the last that is nerve-wracking the first few times.

With my gear, I end up doing wet cleanings infrequently, probably once a year or so, but I do the others more often (but only as needed)

[AndrewMcD]

Thanks for the replies!
I dread the idea of a wet cleaning but as a research technician in a solar cell development lab I have confidence that if I follow the instructions I should be able to manage it (if it comes to requiring a wet cleaning) without catastrophic results.
The camera does have an anti-dust cycle and a "cleaning mode" which I will further investigate.
What was non-intuitive to me was that the spots appear so round and regular. I naively thought that dust or a dirty sensor would have produced something other and what appears to my eyes as circles. It does occur to me that the spots have the appearance of drops of condensation on glass that have dried.
It appears that some further reading on sensor technology is in order.
Thanks again for the help.
Andrew

[Mike Buckley]

I have only had the camera for about one month and when I have changed the lens it has always been done in a controlled (indoor) environment. I thought I handled the camera in a manner that precluded anything touching the sensor. I'm surprised that the sensor would need cleaning already. Is the sensor going to need cleaning frequently and is it a consequence of changing the lens?

Clean the sensor when it needs it. It may need cleaning soon and it may be a long time before it needs cleaning.

Even if you never change a lens after cleaning a sensor, dust can still get on it. That's because the dust may have been residing elsewhere in the camera and eventually got onto the sensor.

[DanK]

The dust is actually on the surface of an anti-alias filter and hence not right on the sensor itself. That is why it looks soft and (often) circular.

You can check your sensor easily by shooting a uniform surface at a small aperture. I use this: http://www.pbase.com/copperhill/image/95174363/original

[Donald]

Just like the guys have said, Andrew. Unless you always change your lenses in clinically clean, sterile environments, you're going to get dust in there. It's just one of the joys of having a digital SLR.

All you cna do is try and ensure you do change lenses in as dus-free and environment as possible (says he who changes lenses out in the middle of fields etc!).

[Polar01]

Andrew:you have a mirror less camera, regular DSLR cameras have a mirror behind the lens and in front of the sensor so when we change a lens less change of dust getting to the sensor directly, however when you change a lens the dust has a straight line shot to your sensor. The only thing that you can do is as the others have said. Oh and welcome to the wonderful world of dust bunnies.

Cheers:

Allan

[inkista]

+1. Mirrorless compacts expose the sensor whenever you change a lens; dSLRs have mirrorboxes which tend to "protect" the sensor more. My micro 4/3 camera's sensor typically picks up more dust than my Canons and I have to clean it more frequently.

Turn the camera off if you're changing lenses. That way, current won't be running through the sensor, which could attract more dust. Also, bodycaps can come in handy to minimize exposure time.

A rocketblower is a good thing to have.

The dust typically won't show if you're using wider apertures.

There are dry cleaning methods as well as wet ones. You could use a LensPen instead--in fact, it's rumored that that's what Canon Service uses to clean sensors. And unlike volatile cleaning fluids--you can fly with a lenspen.

[rpcrowe]

Many folks clean their own. i do. Just read up first, because you will want to be careful. I use Copper Hill materials (they have good tutorials too), and follow this sequence:

1. Air from a rocket blower (NOT canned air)
2. If #1 does not work, a static brush
3. If #2 does not work, a wet cleaning

If you are traveling by air with a Rocket Blower, place it in your checked baggage. The security folks seem to think that the Rocket Blower is some type of hand grenade and often will not let you carry one aboard the flight...

[Dave Humphries]

Surely even a mirror-less camera will have a mechanical shutter curtain between the sensor and lens throat?

I always hold the camera with lens throat down towards floor when changing lenses, gravity assisted removal (and bar to entry) is my theory
I also always have it go through the cleaning cycle at switch on and switch off.
... and I prepare everything for a quick swap to leave it open for minimum amount of time.

[Mike Buckley]

I also always have it go through the cleaning cycle at switch on and switch off.

I must be doing something wrong. I put the camera through the cleaning cycle -- not the spin cycle -- of my washing machine with the camera switched on and I then put it through with the camera switched off. The sensor still had dust bunnies on it. But the outside of the camera was really clean.

[Glenn NK]

Surely even a mirror-less camera will have a mechanical shutter curtain between the sensor and lens throat?

I always hold the camera with lens throat down towards floor when changing lenses, gravity assisted removal (and bar to entry) is my theory
I also always have it go through the cleaning cycle at switch on and switch off.
... and I prepare everything for a quick swap to leave it open for minimum amount of time.

Further to your first comment, and in support of this, I don't recall ever being able to see the film in an SLR when I took a lens off. As you say, surely all cameras have a shutter in front of the sensor/film?

EDIT - APPARENTLY NOT - SEE KATHY'S POST BELOW.

Likely the most problematic "dust bunnies" are from the moving parts of the camera - shutter and mirror. The moving parts are lubricated (lubricant is sticky but does fling off), and when parts wear (they actually do), where to the bits go?

I suspect that one could leave one lens on the camera forever, and the problem would still appear.

Glenn

[inkista]

Surely even a mirror-less camera will have a mechanical shutter curtain between the sensor and lens throat?

Here's the NEX-6 (body only) product image off Amazon.



And my DMC-G3:


Not seeing a mechanical shutter curtain covering the sensor. Which makes sense, since while you're composing in liveview, you're doing it with data from the sensor, so it has to be exposed.

...also, the register distance on these cameras is thin; < 20mm. vs. 42mm for EOS and 46mm for Nikon F. So, not only is it uncovered--it's closer to the lens throat by more than half the distance.

[Glenn NK]

So with the sensor easy to see, I suppose the NEX and Lumix will be easy to clean. Don't even have to go through mirror lockup procedure.

Just carry a can of Dust-Off (being careful not to shake it), and you're good to go - anywhere.

And because the register distance is so small, it's easy to get at.

Completely off topic, but there is an inherent advantage of the small register distance - many other lenses can be fitted with an adapter that doesn't require optics. Nikon having about the largest RD of the larger bodies cannot use many other makes of lens if any without optics.

Glenn

[wobert]

Saw a Pentax film SLR owner once that had literally destroyed the front lens element surface-trying to get rid of the dust spots he saw through the eyepiece viewfinder- Of course, it was dust on the frensel focusing screen within the camera- never affecting his images!
Thanks all for an interesting thread!

[shreds]

Of course you can set up to PP remove dust using software, as it will always be in the same place. Not ideal and better without in the first place, but it is a means of dealing with it.

I clean my DSLR about once every three months, but it does get into some filthy environments and even with excellent weather sealing, changing the lenses frequently on the hoof, does result in muck getting in there. Personally I dislike blowing muck around and prefer to ensure it is removed entirely rather than being possibly temporarily relocated.

[Nat]

It's also very important to keep your lenses and back lens caps(the ones where the camera attaches) clean. Any dust on the lens caps may transfer to the lens and then to the sensor later. I cleaned the sensor of my old Fuji S2 Pro many times....with the proper lens cleaning kit....and after the first time, I felt confidant that I could do it. Unfortunately, dust is among us always.

[jcuknz]

I must be doing something wrong. I put the camera through the cleaning cycle -- not the spin cycle -- of my washing machine with the camera switched on and I then put it through with the camera switched off. The sensor still had dust bunnies on it. But the outside of the camera was really clean.

If we are permitted humour rather than helpful comments on this thread I will tell you that my answer to the problem is in the first place have a long zoom lens and secondly an editor to clone out things I dread the day when I need a rocket, got to find one first, let alone wet swabing URRRGH!.

Just because one has an ILC doesn't mean you have to change lenses and I gave that away when I started digital along with the the associated problem of carting a bag of lenses around for my SLR.

But sadly the business is promoted by all the twin lens specials rather than a single long zoom.