I've shot with three lens brands already, Nikon, Ricoh, and Tokina. I noticed that on my nighttime shots of the city skyline, each lens has different characteristics in rendering the starlights (or sparkles) coming from bright lights. The Nikon exhibits a 14 pointed-star, the Ricoh 6, and the Tokina 8.

My question is, what lens characteristic determines the number of starpoints? Would such a characteristic be a determining factor in identifying if one lens is better than the other? This is something that is of no significant importance to my photo objective, but I'm just curious.

-- Ronald R. Gregorio (gregorio@ksc.th.com), July 11, 2000

Answers

The number of aperture blades. Even numbers of blades produce the same number of star points; odd numbers of blades produce two points per blade (one in each direction). So, in your examples above, your Nikon lens has seven aperture blades, your Ricoh has six, and your Tokina has eight. Stopping down more accentuates the effect.

-- John Kuraoka (kuraoka@home.com), July 12, 2000.

Interesting. Any reason why odd numbered aperture blades display two starpoints per blade? I wonder of lens manufacturers take this into account when deciding how many apertures to put in their lenses.

-- Ronald R. Gregorio (gregorio@ksc.th.com), July 13, 2000.

FWIW, I've noticed that Nikon original issue AI and pre-AI lenses typically have six aperture blades (with the exception of late AI lenses like the 50 f/1.8, introduced in 1979 with seven aperture blades), AIS lenses typically have seven aperture blades, and the newer AF-D lenses have nine aperture blades. Just a generalization. I don't know if it's universally true.

-- DJSoroka (DJ2SOROKA@msn.com), July 13, 2000.

To answer Ronald's follow-up question: Each aperture blade produces two starpoints -- one in each direction. With even-numbers of blades, the starpoints merge. For example, with eight blades, you'll see the outward starpoint caused by blade #1, but the inward starpoint will run into the outward starpoint caused by blade #5, immediately opposite blade #1. With odd-numbers of blades, the starpoints are staggered, so you can see both radiants.

-- John Kuraoka (kuraoka@home.com), July 13, 2000.

Does the sparkle have anything to do with how round the aperture hole is? I mean if the aperture blades fits together in such a way as to produce a round hole, why would there be any preferential direction for a sparkle to form?

-- olenbeck (chaohui@msn.com), July 13, 2000.