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Sun Stars :-) But why ?

Discussion in 'Native Lenses' started by ctc, May 26, 2014.

  1. ctc

    ctc Mu-43 Rookie

    20
    Nov 5, 2012
    Denmark, Copenhagen
    Claus Tom Christensen
    When I take pictures of the sun shining in the water, there are these stars as you can see in these photos ...? They are actually quite nice, but why do they occur? I don't use any special filter. The photos are just some ordinary snapshots taken with my beloved EM-5 with PL 25mm 1.4 ...

    :) Claus (-:


    #1: Shutter Speed 1/1250 s - Aperture f/6.3 - ISO 200

    Sun Stars-1.

    -----

    #2: Shutter Speed 1/1250 s - Aperture f/7.1 - ISO 200

    Sun Stars-2.

    -----
     
  2. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    Those are specular highlights. The surface of the water is uneven (ripples) and parts of the ripples are either reflecting sunlight from behind you back towards you or acting like a prism and bending light from the sun in front of you towards you. This light is much brighter than the water surface itself so it shows as a very white highlight. The reason for the rays giving the "star" effect is that the light for this highlights is being diffracted at the aperture blades within the lens so it gets "bent" is a radiating pattern within the lens. It takes a bright source of light within the frame to make this diffraction visible so you will also see it with bright lights at night under the right conditions.

    You can try stopping down to get rid of them but while that may work for some (probably a very few) of the "duller" highlights which aren't showing a strong star pattern, the highlights showing the strongest "starring" will probably end up showing the effect even more strongly because the smaller size of the aperture opening when you stop down will act to increase the amount of diffraction so one way of maximising this effect is actually to use a smaller aperture opening and longer exposure time. Another is to use a starburst filter in front of your lens. There are several versions of these and they are designed to increase the effect.
     
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  3. ctc

    ctc Mu-43 Rookie

    20
    Nov 5, 2012
    Denmark, Copenhagen
    Claus Tom Christensen
    Thank you, David :2thumbs: It is a clear and precise answer you come up with and I am now much wiser than I was ten minutes ago :rolleyes: I do not believe I will do anything to get rid of the stars as I usually am a street photographer and only rarely shoot nature photos. But it's nice to know your suggestions for the solution and a starburst filter I've never heard of before despite the fact that I have shot in over 30 years! :smile:
     
  4. LowriderS10

    LowriderS10 Monkey with a camera.

    May 19, 2013
    Canada
    Narrow aperture. Open up the aperture and they'll disappear (or at least be less visible).
     
  5. ctc

    ctc Mu-43 Rookie

    20
    Nov 5, 2012
    Denmark, Copenhagen
    Claus Tom Christensen
    A third "star"-photo from last week ...

    #3: Shutter Speed 1/800 s - Aperture f/5 - ISO 200

    Sun Stars-3.

    :smile:
     
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  6. stargate

    stargate Mu-43 Regular

    131
    Aug 14, 2013
    Greece
    I do not know the physical explanation but an interesting fact is that if the diaphragm has an odd number of blades, the sun stars have twice as many rays, and if the lens has an even number of blades, the sun star has as many rays as the blades. So for 6 blades, you get six ray stars and for seven blades you get 14 ray stars.
    Also the effect is more pronounced when the diaphragm has straight blades. Curved blades do not give strong rays effect.
    Modern lenses tend to use rounded blades for better bokeh but that diminishes the ray effect. Legacy lenses are better for this because of their staright blades and if the number of blades is odd the effect is more spectacular.

    Fom the OP's picture I deduce that the lens used has 7 blades.
     
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  7. ctc

    ctc Mu-43 Rookie

    20
    Nov 5, 2012
    Denmark, Copenhagen
    Claus Tom Christensen
    Stargate, thanks for your comment! :smile: And your good: 7 blades are correct! :smile: But it has rounded blades and apparently still some ray effect.

    The lens I use for the three shots is a Panasonic Leica 25mm f1.4 and a fast google search gives: "The aperture is controlled by a seven-blade diaphragm with rounded blades".

    The odd number of blades vs even number of blades theory is really interesting and deeply mysterious... Now I have to buy a lens with 6 or 8 blades ... :wink:
     
  8. tjdean01

    tjdean01 Mu-43 Top Veteran

    842
    Feb 20, 2013
    Wow, pics look awesome! :)
     
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  9. ctc

    ctc Mu-43 Rookie

    20
    Nov 5, 2012
    Denmark, Copenhagen
    Claus Tom Christensen
    Thank you so much tjdean01 :smile:
     
  10. fransglans

    fransglans Mu-43 Top Veteran

    991
    Jun 12, 2012
    Sweden
    gus
    Also got this result from my pl25 last summer. Glad I found some answers here;)
     
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  11. arch stanton

    arch stanton Mu-43 Veteran

    411
    Feb 25, 2012
    London
    Malc
    I love these! Accident or not, keep it up :)
    An ND filter will let you open up the aperture and remove them... but they look great.
    Alternatively you can use low iso and a faster shutter for a couple of stops aperture gain.
     
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