Effect of Star filter without star filter

[yjiang]

I took this photo in Paris late May. I did not use any star filter but there was kind of star filter effect.

I wonder why it could happen.

C&C is also appreciated

Exposure: 20
Aperture: f/22.0
Focal Length: 20 mm
Exposure Bias: -1 EV
ISO Speed: 100

[flipmode]

I'm not 100% sure but I think it's because of the small aperture you're using (f/22), similar to when you want to get a starburst effect. Someone correct me if I'm incorrect.

[Colin Southern]

I'm not 100% sure but I think it's because of the small aperture you're using (f/22), similar to when you want to get a starburst effect. Someone correct me if I'm incorrect.

Spot-on Chris

[yjiang]

I did google search and found similiar explanation as yours. Thank you very much! It is interesting to know.

[pwnage101]

Why are there more blades in the sunstar in colin's image that those of yjiang's? Surely the aperture doesn't have 14 blades.... isn't 6-8 blades the norm?

[Colin Southern]

Why are there more blades in the sunstar in colin's image that those of yjiang's? Surely the aperture doesn't have 14 blades.... isn't 6-8 blades the norm?

Good question Troy - my answer to which is "I don't have a clue"

[pwnage101]

welcome to the club

[Klickit]

Folks describing interference at edge of aperture are right, Light spreads out (diffracts) perpendicular to the edges of the blades, with star spikes at right angles to flat/straight edges of the aperture opening.

So (if you really care) a 5-blade iris will give a 10-point sun star, a symmetical 6 blade iris a 6-point star (because opposite edges are parallel, their points overlap), 7-blade iris a 14-point star, etc...And this effect may be less pronounced/more diffuse with rounded iris touted on some newer lenses

http://photo.net/medium-format-photography-forum/001uPA

[Sahil]

This was at f29