Lens Cleaning

<p>I have a Canon 70-210 f/3.5-4.5 that I brought second hand. The previous owner sold the lens as-is as they dropped the lens in water. Luckily the lens' auto-focus motor works fine. But thanks to the water residue, it leaves any picture I take with it soft, especially at 210mm.<br>

<a title="Boston Mug by Duy Nguyen, on Flickr" href=" src="https://farm6.staticflickr.com/5585/15016017918_7f5b23b38b_z.jpg" alt="Boston Mug" width="427" height="640" /></a><br>

This picture taken with my Canon 70-210mm at f/4.5, ISO100, 210mm at about 6' from the mug. The left side of mug is fairly sharp, but the right side where flash comes in is soft.</p>

<p>While I was able to remove and clean the two front elements and clean the rear element, I was unable to access the insides of the rear elements. Here's how the rear elements look like.<br>

<a title="More Water Residue by Duy Nguyen, on Flickr" href=" src="https://farm4.staticflickr.com/3875/15016089828_a927d74d78_z.jpg" alt="More Water Residue" width="640" height="427" /></a><br>

You can see the residue under the catch light on the glass.</p>

<p><a title="Possible Fungus by Duy Nguyen, on Flickr" href=" src="https://farm4.staticflickr.com/3914/15016091557_bec9c52552_z.jpg" alt="Possible Fungus" width="640" height="427" /></a><br>

I'm not sure if this spot is fungus on the element.<br>

Can anyone provide advice for cleaning the lens' inner rear elements?</p>

<p>Thanks,<br>

Duy</p>

<p>The sharpness problem is unlikely to be the dirt/fungus/whatever. It's probably a tilted/decentered element.</p>

<p>LensRentals wrote up some notes on cleaning dust out of lenses that might be useful. These are specific examples, none of which are this lens, but still illustrates how lenses are disassembled and reassembled.</p>

<p>http://www.lensrentals.com/blog/2013/05/a-few-easy-lens-dustings</p>

<p>Thanks for the reply Alan. I'll give this a try. I may need to buy a lens spanner.</p>

<p>You may need to send your lens to a factory service center and have it professionally cleaned and adjusted.</p>

<p>That lens has been out of production for at least 15 years, I doubt they'll service it.</p>