Dirt on Sensor!

[Buckeye]

I use a Sony A77 for wildlife photography. Being outdoors in Alaska means exposure to glacial silt blowing in the air. This is true even when conditions seem calm. We have a lot of dust too (when it's not under 3' of snow).

I use telephoto zoom lenses and have been so pleased with many wonderful pictures. I have a Sony 16-50 f2.8, a Tamron 70-210mm f2.8, and an older Minolta 100-400mm f4.5. Whenever I change lenses on site, I am meticulously careful about shielding the camera body from any wind, and sliding the body cap on to it so I can secure the lens I am putting away while getting ready the lens I want on the camera. The new lens then gets mounted with great care and attention to ambient conditions.

The bad news: I've had to have my sensor professionally cleaned in Anchorage twice in 6 months, and once now successively by myself with the proper cleaning tools and solution. It is a nuisance to have to deal with, but I understand there are others with this problem.

Does anyone think dirt on a sensor could be caused by a lot of zooming action. Each time the lens barrel slides in and out, air is being pulled in & out as well. I wonder if that is the source of particulate matter on my sensor. Does anyone experience this with zooms, or have any thoughts?

[FootLoose]

It depends on the lens in question, Anita. External focusing lenses (where the lens physically extends outside the body) do suck dirt in. Internally focusing lenses don't.

[RustBeltRaw]

If a lens isn't advertised as "sealed," then it probably sucks in a certain amount of dust regardless of the focusing action. Not sure how much of said dust might make its way back to the sensor. If your lenses have rubber focus rings that aren't glued down, see if you can lift them an have a peek underneath. You might be amazed by the size of the holes straight into the focus mechanisms and electronics. My Canon 28-135mm f3.5-5.6 IS USM has some truly gaping holes under the focus ring. A bit scary, but if you know they're there, you're more aware of how to protect them.

[Buckeye]

Thanks Greg and Lex. What you say makes sense and it is very helpful. I am curious how many folks have problems from time to time with dust on their sensors. I may re-post with a more simple question.

[Glenn NK]

Does anyone think dirt on a sensor could be caused by a lot of zooming action. Each time the lens barrel slides in and out, air is being pulled in & out as well. I wonder if that is the source of particulate matter on my sensor. Does anyone experience this with zooms, or have any thoughts?

I think it's quite possible, and in fact probable, but only with zoom lenses that change in length (and hence volume). When a telescoping zoom lens extends, the volume increases - air comes in - and dust with it. But I'm not sure if dust will come in on a "sealed" lens - to keep the kind of dust out that fouls a sensor might require a Hepa filter. When lens is shortened the air and some dust could be pushed out the back (if it can get in).

I just did an interesting test with my Canon 17-55 f/2.8: the rear opening is quite small - small enough for me to get my lips around it. When I breathed in, there was pretty well no resistance, and air just swooshed in - which means that dusty air could be sucked in easily.

Glenn

[rondd5]

....dust on sensor is part of the experience..over time you develop skills/familiarity with cleaning till....it's just 2nd nature cleaning.

[loosecanon]

Its well known that some lenses suck the muck in. Worst seem to be the push pull zoom lenses, often designed in film days when of course a new sensor surface came with every frame.

[RustBeltRaw]

I just did an interesting test with my Canon 17-55 f/2.8: the rear opening is quite small - small enough for me to get my lips around it. When I breathed in, there was pretty well no resistance, and air just swooshed in - which means that dusty air could be sucked in easily.

Glenn

Pics or it didn't happen.

[Glenn NK]

Pics or it didn't happen.

I just wasn't able to hold my 5DII and do a video while testing the lens.

What surprised me was how little resistance there was - I had thought that with the individual lens elements pretty securely mounted around their perimeter that no air would go through but it surely did.

Glenn

[GrahamS]

It helps to make sure that the camera is switched off during lens changes - if left switched on the sensor LP filter can have a static charge that will attract dust. It also depends on the environment and the type of dust - tree pollen is particularly "sticky" and sticks to the sensor like sh1t to a blanket. Any non environmentally sealed lens will suck in a certain amount of air and dust as the focus mechanism works, even an internally focussing lens. It helps to have a protective filter on the front and Canon recommend such a filter with the 17-55 f2.8 to avoid getting dust under the front element.

[C24]

Aren't we talking about two separate things? As I see it, movement of a zoom lens could/does ingest dust into the lens. Once in, how would it get past the inner lens and onto the sensor?
Most likely the dust gets in during lens changing, with or without the camera switched on. Switched on, as stated above, would aggravate the situation.
Just a layman's opinion.

[revi]

Quite often, the lens elements closest to the sensor move as well (during zooming or focusing, have a look at your lenses ). In that case, the air volume in contact with the sensor changes => dust can get sucked in...