Nikon 50mm f/1.2 Coma
Nikon 50mm f/1.2 AI-s (52mm filters, 12.5 oz. /354g). enlarge. You can get these brand-spanking-new at Adorama, B&H Photo-Video and Amazon. It helps me keep adding to this site when you get yours from these links, too.
Coma is when bright points of light in the corners become weird blobs at large apertures.
Let's see what happens at night:
This looks like a perfectly nice moonlit shot, but it's also at f/4, where there is no coma.
Let's open up to f/1.2 and see some coma:
Wow! Look at the moon! Look at the lights in the lower left!
Let's now look at crops from these 12MP FX Nikon D3 images. If you enlarged the entire image this far at the standard 100 DPI of most computer monitors, the prints would be 42 x 28" (100 x 75cm).
Here are crops from the lower left:
As you can see, there is a load of coma at f/1.2. f/1.4 looks the same since the corners are so vignetted that they don't see close to f/1.4, even at f/1.2.
Coma is pretty much gone by f/2, and the lens gets sharper until f/4.
The 18-pointed stars are sunstars caused by the 9-blades diaphragm.
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