Dirty Lens - Photo Jottings

Dirty Lens

Equipment used for this article; the Sony A900 and Minolta AF 28-85mm F/3.5-4.5 lens.

Here’s a typical scene from a tourist trap destination, usually somewhere in the southern US: an older guy wearing sandals, dress socks and a Madras or Guayabera shirt, carrying around a Nikon or Leica camera outfit and taking snapshots at high noon.  After every few shots, he takes out his handkerchief or lens tissue and cleans the front element of his lens, removing all dust and any possible smudges.  Sound right?  Take a hard look next time if you don’t know what I’m talking about!  But more importantly, does this do any good?  Will dirt and dust really show up in pictures?  Is it necessary to clean minor dust and fingerprint smudges from the camera lens?

Your colorful host will unveil the truth to these questions and more using a combination of technical knowledge, downright stupidity, and some good old fashioned brute force!

Check the images and text below for results.

Let’s start off with a nice clean front element.


Clean front element

The lens has been cleaned properly, with no smudges, dust or cleaning streaks.

Full shot with clean lens

Above is the full resized image taken with the clean lens.

Two large scratches on lens, at the one o’clock, and four o’clock positions.

In this shot, notice the two large and deep scratches at the one o’clock and four o’clock positions.  The scratches could be felt by the fingers.

Image with scratches, not visible even at large viewing sizes.

No evidence of the front element scratches in the picture above.  Even though the image I’m showing you here is small, when enlarged, there are no signs of image degradation attributed to the scratches.

Scratches show no reflections

There doesn’t appear to be any noticeable signs of the scratches even when the sun is in the frame.  I waved the lens around in the sun at different angles, zoom lengths and apertures, and saw no signs of scratches.  I’d venture to guess that the angle and depth of the scratches may produce different results at different zoom lengths, but in my test, I saw no traces of the scratches.

Five spots of masking tape, plus lots of dirt and finger prints.

Now let’s get crazy and add some real dirt and dust to the front element.  In this test, I’ve added a few small bits of masking tape, threw in a handful of dust, and some fingerprint smudges to see how this would effect actual pictures.  The bits of masking tape can simulate small bugs or chunks of mud.

Image with tape on lens

There is only one area I can see that has been altered by the masking tape.  Check out the area in the middle/left of the sidewalk, by the window reflection, there’s a small, dark circular blob appearing here, not visible in other shots.  If I hadn’t pointed it out, would you have noticed?  The only way I noticed it was by flipping through the different images quickly, and looking for just this type of issue.  This image was taken at F/5.6, 28mm.  At F/3.5, 28mm,  the spot didn’t show.  If you shoot the clear blue sky at wide angle, you’ll see faint dark spots where the tape is, especially when stopped down hard.  At 85mm, the tape doesn’t show, at least with the placement of the tape as you see it.  Also remember; the front element turns when focusing so that effects the results, as the tape may show in a clear blue sky depending on the front element orientation.

To sum up the results; in regular picture taking, large blobs and a whole lot of dust on the front element aren’t noticeable.

Now let’s get super crazy with the next “messed-up” lens test!

Massive front element obstructions.

There’s a huge obstruction covering about half the front element, but things look ok still!  This image was taken at 28mm, F/5.6.

Contrast loss on middle/right lower image

Obvious contrast loss here, this time coming at 85mm, F/5.6.

Yes, we have a problem this time!

What the crap happened here?

Even with the busted front element, the images aren’t all that bad in my opinion.  With careful framing, you could actually keep taking pictures with this lens, instead of just going home and missing out on the action, especially while on vacation.

Bad things don’t stop here, read on for more destruction!!

Broken front element removed

Now the entire front element has been blown out!  This eliminates the ability of focusing beyond a few inches, but turns the lens into a good 1:2 macro or slightly larger.  The front element is clearly very important; it helps control distortion, color fringing, and makes focusing possible beyond macro range.

Full image of usual stamp shot
Detail of lower middle

This is a shot of the usual stamp macro.  It actually shows more detail than the original review shot with the front element intact.  The detail above comes from the bottom center-right of the full image on top.  This close focus shot is much larger than the original, but has contrast loss which makes it look not-so-sharp.  For you bargain conscious people; I’d recommend paying for a regular macro lens instead of breaking out the front element of your non-macro lens just to save money.

Full macro image with broken front element removed
Detail of macro above.

Here is a shot of a refrigerator magnet, that should have straight lines on the sides.  This is an indication of how important the front element is for controlling distortion.  There’s massive pincushion distortion, and very soft corners present.  In the middle everything looks pretty sharp.  There’s quite a lot of color fringing present, most likely caused from the different angle of light coming in as a consequence of the loss of the front element.  Image taken at 28mm, F/5.6.


Based on my un-scientific testing, I’d say there isn’t any noticeable reduction in image quality as a result of normal dirt, smudges and small scratches on the front element.  My dirt, smudges and scratches presented here are clearly more numerous and larger than what I’d consider “normal,” but as I’ve shown, they have little effect on image quality.

Finally, I bet you’re wondering why I smoked a perfectly good lens for this article.  So I’ll tell you why.  I bought this lens on eBay.  After receiving it I put it away without really looking at it.  A couple of months later I made time to review it, at which time I inspected it—oops, I got ripped off.  I noticed the filter ring was mangled up, most likely from a screw-on hood that someone got rough with.  I also noticed numerous scratches all over the body, especially underneath as it would be mounted on the camera.  Optically and mechanically it was fine.  I decided I didn’t want to try and resell it, as by disclosing all the defects, it would only bring a fraction of what I paid, less than $100.  I then remembered the habitual dirty lens cleaners I saw at a recent photo outing and at that point decided on a glorious use (and ending) for the lens.

Although this lens lost its life, it was not in vain.  I destroyed this lens so I could better understand how it worked, and the limitations of any possible amateur repair.  I like to share my knowledge so that other people won’t have to destroy their lenses only to come to the same conclusion.  I would encourage more people to consider buying lenses with front element scratches, or to keep using the lens they have with scratches, instead of putting it away, or trying to sell it.  I’ve seen great bargains out there for scratched lenses, often going for half the cost of an “unblemished” front element lens.  Before I whipped up this article, I would’ve shied away from a scratched lens, but not now.  Hopefully, with this article, I’ll save a few lenses from death, or extended the life of a few lenses with minor defects such as small front element scratches.

Go here to see the lens taken apart, and how I smashed it up due to ignorance.


Scroll to Top