How much dirt will degrade image quality?
How much of dust and surface scratch on the lens front element is enough to cause visible image degradation? And how much will render my 1000$ lens useless?
These were the questions bugging my mind today – Not accidentally though; I had a rough working day involving animals… obviously curious ones tried to grab my camera, and few even managed to leave a nice nose print on the filter – at the end of the day, when I came home and set for a complete clean-up (including a nice shower for me) I noticed few slight, but noticeable scratches on the UV filter.
I must say I’m a paranoid type when it comes to my camera, I cherish it like a baby… So any mishap makes my mind run in circles, and wonder about limits of photography equipment.
Obviously, first thing I did was to plunge into a comprehensive ‘scratch and dust’ internet research – which didn’t give any satisfying results. It appears this topic is not researched properly.
Highlights of my research:
“I have a Yashica 124g with a few dust specs internal, and a Vivitar series one 28-90 with bad scratch on front element, with no apparent problems. In fact, they are among my favorites.”
“Some years back I bought a 50mm Zenzanon S lens(Bronica) and on close inspection with a magnifying glass, I noticed that the coating on the front element looked like crazy-paving. It was really bad. Somebody must have cleaned it with Harpic. The crazy thing is. It was clearer and sharper by far, than the two other examples of this lens I had previously used.”
And my favorite:
“Insect in the lens and few nasty scratches, doesn’t affect image quality at all!”
General consensus among photographers is that minor dust and scratches don’t affect image quality. In fact, damage caused by cleaning and over obsessing are far worse than few finger marks. But, severely dented lenses are prone to; lens flare, loss of sharpness in the area of damage and visible halos when photographing direct light.
Final notes
Findings of the research correlates with my experience: photos taken with really dirty filter / lens produce images that lack sharpness and contrast.
Take a look at the example picture below. First crop is shot with UV filter on, and second one without.
There is a huge difference between these two crops in terms of quality and detail reproduction. First sample is obviously less detailed, exhibits strange glowing effect and it’s less sharp. It seems poorly focused, but in reality there is dirt on the front element that distorts light and destroys detail.
If you are wondering what happened to the filter while shooting the candle, I will tell you this: DON’T take your DSLR to the seaside when there is a wind – standing in few hundred meters away from the water doesn’t help, salt still ends up on the front element – result is what you see in the sample photo.
Answer to my question: “How much dirt will degrade image quality?”, is “allot”. It takes more than usual amount of dirt to achieve same effect as in the example photo.
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