This article is missing a huge factor: aperture. If you go higher than f/11 the debris will start to get much more visible. All of the pictures in here are at f/5.6 or less.

Each pixel basically takes a weighted average of all the light that travels from a pixel-sized area in the world to the lens. As the picture with the dark area shows, this makes the debris form a dark area over a large part of the image. As the f number increases, the weighting gets stronger until 100% of it is a single line from scene to lens to pixel. At this theoretical f/infinity, you'll see all the lens's imperfections in perfect detail since the camera is essentially a pinhole.

This is true for lower apertures, but at higher apertures they become much more noticeable especially at high magnification. This is especially annoying for telescopes (it tends to look like this https://farm9.staticflickr.com/8679/16584213212_5b33222d6e_c...), which why astrophotographers use a trick called flat calibration to remove any artifacts from dust or smudges in the optical train. The trick is surprisingly simple: take a picture of an evenly illuminated surface (usually a flat box or a clear sky) and make sure your ADU is in the linear phase of the sensor (ergo, don't clip the highlights or darks). Then divide your original image by the flat ($T * mean(flat) / flat). This is of course easier with a monochrome sensor and works best with RAW data, but it can definitely be done with a color CMOS as well. In case you ever find yourself with hard to correct dust on the sensor: this trick might save an otherwise poor image.

Huh.

Optics are modeled by differential equations. They describe a massively parallel phenomenon, light waves passing through and being modified by layers of media that, essentially, performs calculations using them. Warps and scales and so on. Clearly these particular differential equations are highly robust to architectural changes.

There's a parallel there to something else I've read about on Hacker News... what are those things called? Oh yeah, deep networks.

Are there any deep nets out there that attempt to mimic optics? or is anyone applying ideas from robust differential equations to deep nets?

I took some photos of Mt Fuji from a distance with a 28-70 at prob something like 60mm f8. To my horror when I got home and fired up Lightroom there were several, very visible, dark blotches against the bright clouds around the summit.

I learned my lesson and will often use an air spray squishy thing to get rid of dust from the lens.

I had dust inside a push pull zoom. I never noticed anything. I think the main issue with dirt is if sunlight hits the dust on the lens it can do some additionaly flaring.

I don't use lens caps either, but put a clear filter on the lens. Resale value is hurt with scratches...

On the other hand, a finger smudge on your cell phone camera lens will destroy contrast and the resulting picture, especially is there is any degree of backlight in the image.

Make sure you wipe the lens with your t-shirt every once in a while.

I live in the tropics, and have fungi growing inside my lenses. They leave visible spots all the time, but photoshop takes care of that.

What I find fascinating about articles like this is that they demonstrate the high quality of common objects (well, maybe not too common for those that do not like to take photos with DSLRs, but anyway).

For some reason, I have almost been 'conditioned' to adopt a 'Everything that we manufactured is really crappy' philosophy---maybe this comes from working too much with software---so it is really nice when you learn about these things.

Also, as an owner of a DSLR, this is news to me, making me less anxious about now having the best equipment for cleaning everything with me all the time.

I wonder how oily/fatty smudges behave. Because on eyeglasses, they are either very noticeable, or, if you try to wipe them off but only end up smearing them all over the place, not really noticeable but extremely tiring (probably from subtle degradation and dispersing light coming from the side across what you see).

dust on the sensor shows up a lot more than lens scratches