Coma Example (Noctilux)

I'll have to post the detail shot oversize. Apologies to those with dial-up, but I kept the file size as small as possible. This is a detail from the upper left quadrant.

Note that over to the right (the center of the original picture) we have a bunch of bright highlights from small light bulbs. They are round, as they should be.

But at the left, we see, apparently, a swarm of butterflies moving in. But on closer inspection, they are not really butterflies. The lights approaching the frame edge are distorted into the shape of butterflies. This is coma.

The closer we get to the edge, the more pronounced is the butterfly shape. I rarely see this, even with the Noct at f/1. Just happened to catch it in this shot.

I have seen those oval highlights on many Noctilux samples posted here.

Not unexpected as mentioned in past technical reviews of this lens. If you want to practically eliminate coma, then get the 50/1.2 Noctilux with it's twin aspheric surfaces. To put it in pespective, the coma of the CV 40/1.4 is far worse than the 50/1 Noctilux.

I must say I have been unaware of this effect on my Noct. Now I will be looking for it! Does it only occur with specular highlights, or does the whole image get affected?

I must say it is still the best working tool at f1.0 despite the aberration. Maybe just accept the fact as part of the price for being able to shoot at f1.0.

Here I bought my Noct used for 400 bucks in the late 1970's. The tradeoff for a super speed lens like this is vignetting off axis versus abberations like coma. Vignetting is PURPOSELY added to a design to reduce abberations. In practice the F1 Noct lens here has very little flare, and has excellent wide open performance. It has a radically better performance than any of my F1.4 Nikkors in F mount, my Leica Canon 50mm F1.2

The older Noct F1.2 is today more of a collectors lens. There is one right now on Ebay at 5600 US dollars, the starting bid was 5500, it has 1 day + to go.

Doesn't look like coma. Coma should extend along a line between the point and the center of the image - and it should be Coma shaped!

Could be tangential astigmatism or possible (but less likely) out of focus highlights modified by the shape of the iris which is distorted by vignetting and/or oblique viewing near the edge of the frame.

Maybe ROB has weird shaped lights too! :)

Interesting picture. Can we really say this is coma?

First question: What is the shape of the tiny light bulbs? Are they round or are they pear shaped, sort of like the older larger Christmas lights? If pear shaped, some of the lights in the upper left appear pear shaped. However, for many the shape is clearly distorted no matter what they started out as.

Second: Coma makes a commet shape out of a point source. It would take small round lights and make commets with a dull (rather than pointy) front end. Also, due to the mathematics of third order coma, it would appear as having the brightest and smallest feature pointed towards the center of the field (the optical axis) and the outer edges away from the center would get wider and fainter. The butterflies in this picture do not behave this way.

The butterflies appear to be elongated tangentially rather than radially. This is a feature of astigmatism (different planes of focus for the tangential VS sagital rays).

I could not see any clear signs of coma but Rob's image shows definite signs of astigmatism.