Sunstars are the star shaped rays of light you get from a point source, when shooting a wide-angle lens stopped down. I recently did a short test on most of my wide angle lenses to see which gave the best sunstars. I included the 70-300mm as well just to see. I used a small LED torch as the light source about 2 metres away, focused on it, and took shots at f/8, f/11 and f/16 with each lens, except the Zeiss 50mm which ash f/8, f/16 and f/22. The number and shape of the blades that make up the diaphragm should determine how many points the star has, with straight bladed diaphragms giving the most defined stars.
First up is the Nikon 14-24mm f/2.8 lens. I use this for most of my wide landscape work. I wasn’t expecting anything to be honest as this lens has 9 rounded blades. What we get is 36 point sunstars. Well, not quite, its more like two 18 point sun-stars, one rotated a few degrees on from the other.
Next up is the little Nikon 20mm f/2.8 AIS I use when I need to use the full catalogue of Lee ND filters (I only have 2 and 3 stop hard grads for the 14-24mm). Nice, clean 14 point stars from the seven straight blades
Now we have the Sigma 24-70 f/2.8 EX DG. It gives nice sunstars at both ends of the zoom range (the right-most one is at 24mm):-
Here’s an old Zeiss Flektogon 50mm f/4 MC. This is a massive 50mm lens from an old medium format (6cm square) Pentacon 6 camera. It’s mounted on my D800E via a tilting adaptor. Despite this being the “multi-coated” version of this lens, it does create some really unattractive flare artefacts when pointed at a light source. The 8 pointed sun-stars it creates from it’s 8 slightly rounded diaphragm blades are indistinct at f/8. They look pretty good at f/16 and f/22
Last – and just for fun, I tried my Nikon AF-S 70-300mm f/4.5-5.6 VR. It’s not totally unattractive at 70mm, especially at f/16
So there you have it – if you want attractive sun-stars in your landscapes, or from small light sources in the studio, check out the construction of the aperture diaphragm. Straight blades are best – hard to find on modern lenses now as the rounded ones give nicer out of focus highlights. You can still get nice sun stars out of rounded blades, but you may have to stop down so much your image goes soft. Incidentally, you can tell how many blades the aperture diaphragm has by counting the rays on the sun star – 14 points, 7 blades – except for some oddballs like the 14-24 which makes 36 points from 9 blades. Almost all Nikon lenses have an odd number of blades – so you can also take a good guess at camera brand 🙂