
Lens Aberrations Explained - luu
https://phillipreeve.net/blog/lens-aberrations-explained-part-1/
======
freepor
As someone who’s been photographing for a few decades now, it looks like the
recent iterations of lenses from the big brands are basically “perfect.” 70s
and 80s lenses had tradeoffs... with today’s lenses from Canon/Nikon/Sony,
those made in the last 5 years or so, the optical quality after digital
correction is so high that for any non-extreme form of photography they can be
considered perfect. And that goes from lenses like Canon’s 35 1.4 ($1800) down
to their 10-18 ($250). The gearheads can natter online but the returns here
are now nearly fully diminished.

~~~
GuiA
Many lenses from the 80s/90s hold their own compared to modern designs. We’ve
been at the plateau of the S curve for a while. The really exciting stuff is
happening in smartphones, where miniaturization is the driving variable - for
instance the latest folded optics designs.

~~~
DagAgren
I'd say the really exciting stuff happening in smartphones are the things
going on with computational photography, like Apple's Deep Fusion. This is
moving beyond the limitations of single lenses and single sensors and enabling
some pretty impressive things.

------
01100011
About 15 years ago I participated in a study of wavefront lenses(I think it
was by Zeiss). The glasses were single prescription and they were hands down
the best glasses I've ever owned. Great vision and low chromatic aberation.

I've never seen the tech offered for single prescription lenses since then. I
really wish they continued with the technology.

~~~
amluto
Is this a fancy version of the horribly named “digital single vision” lenses
that you can buy? Zeiss has a product called “i.Scription.”

~~~
01100011
Probably, but there may be some important difference I'm missing. I did the
study quite a while ago, and it was around the time I did another study
involving 'programmable' lenses where the prescription was set using a process
"similar to how writable DVDs are made", or so they explained it at the time.
Those lenses were shit, IIRC.

I really miss those wavefront lenses. I kept them for years before dropping
them on a hike. I'd gladly pay extra for them again.

I remember the machine which mapped my eyes only took a minute or less to take
my prescription. Nothing like a phoropter, which I feel is subjective and
error prone. They also used a camera system to fit the lenses, similar to what
LensCrafters used when I got a pair of Rx sunglasses a month or so ago.

~~~
jakeogh
Take a look at the iProfilerPlus, it's description is an 'ocular wavefront
aberrometer', by Zeiss. I believe
[https://clearviewvisioncare.com](https://clearviewvisioncare.com) (in Tucson)
has one, they are open (I know cuz they called me last week), I bet they can
answer your questions.

[https://www.zeiss.com/vision-care/us/for-eye-care-
profession...](https://www.zeiss.com/vision-care/us/for-eye-care-
professionals/products/zeiss-instruments-and-systems/i-profiler.html)

[https://www.zeiss.com/vision-care/us/search/find-an-eye-
doct...](https://www.zeiss.com/vision-care/us/search/find-an-eye-doctor-near-
you.html)

------
rubatuga
In case you ever wanted to _add_ chromatic aberration to a perfect image, I
made kromo:

[https://github.com/yoonsikp/kromo](https://github.com/yoonsikp/kromo)

As a side note, isn't it ironic that games now resort to adding aberrations to
make it seem more real?

~~~
s9w
And every gamer hates it :( just like lens flares, motion blur, DOF, bloom,
...

------
thdrdt
I've got a smartphone with a not so good camera. Some time ago I heard about
an app that could take a picture of a template and then would calculate the
distortions of your camera and fix those (with ML).

Does anyone know what app/research this is? I can't imagine why smartphone
maker don't use this for their crappy camera's so they can still embed cheap
camera's but enhance the picture quality.

~~~
jimfleming
This functionality is built into OpenCV[0]. If you're using a reference image
(or if you know the lens properties) it doesn't require ML. It's mostly just a
matrix transform.

[0]
[https://docs.opencv.org/2.4/doc/tutorials/calib3d/camera_cal...](https://docs.opencv.org/2.4/doc/tutorials/calib3d/camera_calibration/camera_calibration.html)

~~~
thdrdt
Ah yes! It looks like this is related to what I was looking for. It was a long
time ago that I saw a demo about this and I was under the impression that ML
was used to calculate the correction matrix.

------
CarVac
My favorite site for explaining lens aberrations (unfortunately, it's
currently under construction in a new URL) is here:

[https://web.archive.org/web/20090204211139/http://toothwalke...](https://web.archive.org/web/20090204211139/http://toothwalker.org/optics.html)

It's a fantastic resource.

------
m463
Since the recent (2019) mathematical discovery allowing elimination of
spherical aberration[1], I've wondered if lenses will either be simplified, or
redesigned for better optical performance.

[1] [https://arxiv.org/abs/1811.03792](https://arxiv.org/abs/1811.03792)

~~~
freepor
Doubtful. Those mathematically optimal surfaces look like a complete nightmare
to manufacture out of optical glass.

~~~
londons_explore
Unless the lenses have bits that 'overhang' it would seem possible to simply
CNC mill the whole thing?

A lens needs accuracy to ~the wavelength, so 400nm. That seems doable with not
so specialist CNC tech.

~~~
fsh
Sub-µm accuracy is not at all easy for a CNC mill and the surface quality is
way to bad for optics.

Commercial aspheres are polished with special CNC grinders, but achieve
nowhere near the quality of spherical lenses. Only recently magnetorheological
finishing became available which allows getting a bit closer in quality.

In most applications, it makes more sense to stack a few spherical lenses
instead of manufacturing a super expensive custom asphere which cannot even
compensate for chromatic aberrations.

------
_pmf_
Slightly topical: there's a steam game "Umurangi Generation" that aims to be a
realistic photography simulator.

------
jacobush
Wow, I have a lens with noticeable Focus Shift. I thought it was just some
mechanical play in the mechanism, but Today I Learned it's a Thing.

------
dan-robertson
I wear glasses and recently significantly increased the power on one of the
lenses (weirdly, not in the other). I also got larger lenses (so distortion
that happens in the corner is increased because the corner is farther from the
midpoint than before).

The main issue with the new lenses which I noticed was chromatic aberration.
Unfortunately my brain can’t fix this in post though it has gotten used to it
a bit. Something that I suppose I already knew was that the lens material
would affect how much of this distortion you would see. I thought different
refractive indices would give different amounts of dispersion, though maybe I
should not have thought that as lower indices would mean thicker lenses so
more distance to disperse in which might cancel out the lower disposition. In
the end it doesn’t matter what I thought, the Lens material does affect the
dispersion.

The thing I was more surprised by was that dispersion wasn’t something that
came up when making the choice of lens material. Thinking back though, perhaps
the only qualities discussed were “thickness” and cost. I put thickness in
quotes as maybe the weight was discussed too. I feel like dispersion is quite
an important thing I care about and I wonder why it wasn’t discussed. Perhaps
it is hard to explain to people (I guess all the material properties are hard
to explain), or perhaps it is difficult if the lenses don’t necessarily get
better in every way as cost goes up.

There are no glasses lenses which can correct for their chromatic aberration
like camera lenses, presumably because they would be too thick and delicate.

In a more general sense, I’m surprised that there’s so little variety in
optometrists (at least in the U.K.). Basically wherever you go you get the
same precision of prescription and are then given the opportunity to buy some
glasses. Some studies have shown that the accuracy of the prescription you get
from the subjective refractometry exam can vary a lot between practices but
there is no way to know if a practice will be good or bad. I’m also surprised
that there is not really a way to get a more accurate or precise prescription
than the standard, as I would think that if such a thing existed it would be
able to find customers at least in larger population centres. Maybe it would
be impossible to improve on the status quo because of the lack of economies of
scale or because glasses won’t be in a consistent enough position or because
the rich people who would be expected to pay floor the service opt for eye
surgery instead.

This comment is so far mostly unrelated to the OP though so I will make
another comment: I wish the article had mentioned some of the physics behind
the different aberrations, for example the reason longitudinal aberration is
hard to correct in post is that it os an effect where different colours are
focused to different distances and it of hard to make a colour less out-of-
focus to fix it. The reason a bokeh light circle is a certain shape is that
that is the shape of the lens aperture (hence usually a circle or many-gon).
The misshapen bokeh effects tend To come from light coming in at more acute
angles and from those angles the lens is a different shape.

~~~
unishark
If you're seeing annoying color effects it could also be the anti-reflective
coating that is bad. Or just that you're not used to having it.

There are alternatives to the phoropter exam called autorefractors and
wavefront sensors which use lasers to measure your eye. I'm pretty sure the UK
must have clinics who use them. Startup companies in the US are trying to make
"kiosks" for eye exams based on such technologies, but run into state laws
that restricts prescribing lenses to licensed optometrists. Also there are
startups trying to scale such technologies for the developing world where they
don't have sufficient eyecare so people with bad refractive errors are
basically just left blind.

~~~
dan-robertson
It’s true that these exist but they are rare and not typically advertised.
Studies have also shown that one doesn’t necessarily get better outcomes from
the kind of objective refractometry that an autorefractor gives (because
eyesight is a combination of the optical properties of the eye and things
happening in the brain/optical nerves)

