Lens Cleaning, worth it?

wmstumme

I have a Canon 28-135 3.5-5.6 USM/IS kit lens that is now about 5 years old. It has some dust on the inside elements -- it appears to be on the back side of the front element. It is leaving really noticeable spots on pictures. Otherwise, the lens clarity/sharpness has been good. Does anyone have experience/recommendations of having this repaired? Should I just start looking for a replacement?

ziggy53

Dust on or in the lens will cause dispersion, but not well defined spots on the image. Well defined spots on the image are generally shadows cast by a combination of dust on the sensor array and use of small apertures. (The image sensor is generally a stack of Anti-Aliasing (AA) filter and Infrared cutout filter, both in front of the sensor and both protecting the sensor as well.)

Generally, there has to be a lot of dust in the lens to cause any troubles at all and those troubles mostly relate to simultaneous loss in contrast and some loss in sharpness.

It sounds like you need to clean your image sensor array. We have several threads describing that task.

http://www.dgrin.com/showthread.php?t=221922
http://www.dgrin.com/showthread.php?t=183351
http://www.dgrin.com/showthread.php?t=151358
http://www.dgrin.com/showthread.php?t=2556

pathfinder

Like Ziggy said, a few dust motes within a lens array will have little to no effect on the image whatsoever, and any effect they will have will be limited to a loss of contrast or very limited diminution of sharpness. Canon will clean the lens but it costs ~ $150.00. (I just had my 18-55 cleaned by CFS but it had a LOT of dust in it )

Spots in your images come from dust on your anti aliasing filter when shooting at smaller aperture - typically f11 or higher.

wmstumme

Looks like I came to the right place. I usually am shooting sports with as wide of an aperture as possible. The shots with spots were virtually "snapshots," shot with in full auto and which kicked up the aperture to to f/18.

So, based on your comments I took some shots with different lenses (including the "dusty" one) at different aperatures. Wide open--no spots. Tight--plenty of spots!

So, I'll be heading out to get some supplies to clean the sensor.

Thanks again.

pathfinder

The smaller apetures collimate the light beam such that the dust motes on the anti aliasing filter are sharply outlined, while larger apertures allow a wider light beam that prevents the dust motes from being as sharply defined on the sensor array.

Try a Rocket blower bulb and see if that helps before going to a wet mop treatment. The goal is to decrease the motes, not eliminate them entirely.