1

The Nikon Noct 58mm f/1.2 from 1997 is famous for having excellent coma control wide open. Sources generally credit this to its being one of the first lenses that used an aspherical element, which had to be hand-ground at the time (making it very expensive). Comparisons to recent lenses still show that it has better center sharpness wide open and less coma.

But aspherical lenses can apparently be produced very cheaply now. Even Nikon's 35mm f/1.8 has an aspherical element, and it's just about their cheapest modern lens at $200. Is there any reason that the same cheap aspherical lens manufacturing techniques could not be used to produce the same design that had to be hand-ground in 1997? Did the Noct's aspherical element use such an exotic shape that it still could not be made with a machine today? I assume there must be a technical reason that such lenses are not produced because there's a huge market of astrophotographers that want large apertures and low coma.

  • 1
    What makes you believe that there's a huge market? – null Aug 8 '16 at 12:52
  • 1
    Or maybe they just released a 58mm f/1.4 lens? What makes you think that it was specifically designed for your astrophotography needs? – null Aug 8 '16 at 13:21
  • 1
    @null Nikon's marketing copy states "excels in low-light and nighttime applications" and "Virtually no sagittal coma flare". I don't think I've seen a single review that doesn't compare it to the Noct at some point. – 0x5f3759df Aug 8 '16 at 13:27
  • 1
    Now this makes more sense to me. – null Aug 8 '16 at 13:32
  • 1
    @CarlWitthoft, whole-sky astrophotography? – Chris H Aug 9 '16 at 11:39
1

The Noct-Nikkor has earned its reputation on the wings of the community of internet photographers who don't know what coma is. Coma is the formation of comet-like shapes away from the optical axis. Coma has not been the dominant aberration limiting the performance of consumer lenses in a very long time. The Noct-Nikkor has a large amount of both axial and longitudinal chromatic aberration. Freeing these design variables allows the correction of the astigmatism that typically limits the performance of these lenses off-axis.

Additionally, the placement of the asphere on the front surface, as far from the aperture stop as possible, indicates that its role is to reduce off-axis aberrations. This asphere placement could be used in other designs, but having the front element be aspheric is very undesirable; it is the largest element, which makes it expensive to aspherize, and it is also the most exposed element, making it the most likely to be damaged. An aspheric surface is more sensitive than a spherical one, and it is highly preferred that it be protected in some way.

  • So you are saying that the effect making blurry, un-round messes of point light sources with extreme contrast (found in urban nightscape and astrophotography) when photographed through a very large aperture spherical lens (eg the Minolta MD 50mm f1.2) is astigmatism, not coma? – rackandboneman Dec 10 '18 at 22:22
  • Unround is not specific. If the blur looks at all like lines, that is Astigmatism. If it looks like a snowcone, it is coma. If it looks like both, it is both. – Brandon Dube Dec 11 '18 at 21:29
  • My point was: Does this apply both to internet and nighttime photographers, or is coma a very valid concern for the latter? – rackandboneman Dec 11 '18 at 22:59
  • In short - both. You will see these blurs on any point-like object. – Brandon Dube Dec 13 '18 at 0:09
  • The 35mm/f1.8G mentioned probably actually uses a similar strategy, though not as hardcore as the Noct ... compared to spherical 35mm lenses it is quite good in coma performance, but spherochromatic as all hell :) – rackandboneman Oct 16 at 21:54
0

It is my understanding that introduction of an aspheric element can improve spherical aberration, but it will throw the other aberrations. The lens designer needs to handle that. If this is a cheap lens, the chances are that the available means are limited and he/she will have to cut some corners and deliver a lens that is not perfect in all aspects...

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.