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Thread: Difference Between 9 and 7 Diaphragm Blades

  1. #1

    Default Difference Between 9 and 7 Diaphragm Blades

    hi...i just wonder wht is the mening stand for betwwen 9 and 7 blades???
    is it really a issue to get lens???
    and which one is better?in term of wht???

    thx in advance..

  2. #2

    Default Re: Difference Between 9 and 7 Diaphragm Blades

    9 blades are usually more expensive. Most of the high end end lens such those with constant aperture ie f/2.8... 9 blades diaphragm makes more beautiful bokeh for ur pics while 7 blades wont give u smooth, natural n beautiful bokeh as when only 7 blades to make the aperture diaphragm, is less round den the 9 blades, therefore, affects the incoming light.

  3. #3

    Default Re: Difference Between 9 and 7 Diaphragm Blades

    You can read more about bokeh and diaphragm blade relationship here

    http://www.kenrockwell.com/tech/bokeh.htm
    Meow!

  4. #4

    Default Re: Difference Between 9 and 7 Diaphragm Blades

    Quote Originally Posted by ominblue View Post
    9 blades are usually more expensive. Most of the high end end lens such those with constant aperture ie f/2.8... 9 blades diaphragm makes more beautiful bokeh for ur pics while 7 blades wont give u smooth, natural n beautiful bokeh as when only 7 blades to make the aperture diaphragm, is less round den the 9 blades, therefore, affects the incoming light.
    i giv an example....the sigma 28-70mm F2.8 EX DG is better than Tamron AF28-75mm F/2.8 XR Di LD Aspherical (IF) is because the sigma one got 9 blades.....right???

    One more thing???how is the lens construction effect the lens....
    i dont understand the meaning of like 14 groups 16 elements....

    can advise me...thx so much..

    again...how to verify the Sigma and Tamron lens to knw whetehr is FX or not???
    Last edited by Mrkcw; 3rd October 2008 at 01:51 AM.

  5. #5
    Member lennyl's Avatar
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    Default Re: Difference Between 9 and 7 Diaphragm Blades

    My 2 cents, from personal observation. Feel free to correct me.

    1. Number of aperture blades is not very significant - the shape of the aperture is much more important for bokeh. Incidentally my more expensive lenses has 8 blades.

    2. Number of aperture blades affect the number of points in the star when you shoot point light source at small apertures. The formula is : for even # of blades, # points = # blades. For odd # of blades, # points = 2 * # of blades. I don't know why. I'm sure the physics is available somewhere if you google.

    3. # of elements and groups - rather than type everything in, I found a page for you : http://www.earthboundlight.com/photo...nd-groups.html

    Comparing # of blades and # of elements / groups will not tell you which lens is better.

  6. #6

    Default Re: Difference Between 9 and 7 Diaphragm Blades

    Quote Originally Posted by Mrkcw View Post
    i giv an example....the sigma 28-70mm F2.8 EX DG is better than Tamron AF28-75mm F/2.8 XR Di LD Aspherical (IF) is because the sigma one got 9 blades.....right???

    One more thing???how is the lens construction effect the lens....
    i dont understand the meaning of like 14 groups 16 elements....

    can advise me...thx so much..

    again...how to verify the Sigma and Tamron lens to knw whetehr is FX or not???
    You cannot make that assumption. There are alot more other factors that determine whether a lens is better.
    Meow!

  7. #7
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    Default Re: Difference Between 9 and 7 Diaphragm Blades

    Quote Originally Posted by ominblue View Post
    9 blades are usually more expensive. Most of the high end end lens such those with constant aperture ie f/2.8... 9 blades diaphragm makes more beautiful bokeh for ur pics while 7 blades wont give u smooth, natural n beautiful bokeh as when only 7 blades to make the aperture diaphragm, is less round den the 9 blades, therefore, affects the incoming light.
    Rubbish. Don't mislead. The smoothness of the bokeh is dependent on the shape of the aperture opening, especially when stopped down. When the aperture is held wide open, it is a moot point anyway, as most, if not all openings, are round.

    There are aperture openings that are round even with 7, 8, or 9 blades. Take the Canon 24-70. It has 8 aperture blades, but the bokeh you get is pretty much magical.


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    Default Re: Difference Between 9 and 7 Diaphragm Blades

    Quote Originally Posted by GavinTing View Post
    You cannot make that assumption. There are alot more other factors that determine whether a lens is better.
    agreed. There are an INCREDIBLE amount of factors that affect lens performance, so you can't just analyse 2 lens like that.

    I suggest just going out and shooting rather than fretting about specs!

  9. #9

    Default Re: Difference Between 9 and 7 Diaphragm Blades

    Quote Originally Posted by calebk View Post
    Rubbish. Don't mislead. The smoothness of the bokeh is dependent on the shape of the aperture opening, especially when stopped down. When the aperture is held wide open, it is a moot point anyway, as most, if not all openings, are round.

    There are aperture openings that are round even with 7, 8, or 9 blades. Take the Canon 24-70. It has 8 aperture blades, but the bokeh you get is pretty much magical.

    wht is the meaning of when stopped down...sometime heard tht this lens or tht lens is not so good when stopped down......thx...

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    Default Re: Difference Between 9 and 7 Diaphragm Blades

    Quote Originally Posted by Mrkcw View Post
    wht is the meaning of when stopped down...sometime heard tht this lens or tht lens is not so good when stopped down......thx...
    Stopped down means to stop down the aperture from its widest opening.

  11. #11

    Default Re: Difference Between 9 and 7 Diaphragm Blades

    Quote Originally Posted by lennyl View Post
    My 2 cents, from personal observation. Feel free to correct me.

    2. Number of aperture blades affect the number of points in the star when you shoot point light source at small apertures. The formula is : for even # of blades, # points = # blades. For odd # of blades, # points = 2 * # of blades. I don't know why. I'm sure the physics is available somewhere if you google.
    I think this is because fall-off happens to both sides of the blade. In case of even numbers, they overlap, as there's a symmetric blade facing any given blade. So we just count 2*n as n.

    TS, bokeh is affected by many other factors than merely the number of aperture blades. Perfect bokeh has a lot to do with lens construction. Having said that, EVERYTHING ELSE being equal, larger number of aperture blades are generally better but only as a determining factor for aperture shape.

  12. #12
    Moderator Octarine's Avatar
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    Default Re: Difference Between 9 and 7 Diaphragm Blades

    Quote Originally Posted by Mrkcw View Post
    wht is the meaning of when stopped down...sometime heard tht this lens or tht lens is not so good when stopped down......thx...
    Means: closing the aperture (higher f-number).
    See this: http://www.clubsnap.com/forums/showthread.php?t=309544 - page 6, it's highlighted in red. Might also be helpful to read the other chapters.
    Each setting, also aperture, has effects and limits. What is good in one situation might not be good in a different one. There is no "one setting fits all purposes."

    In addition, "I heard of ..." is not a reliable source of information. Many people hear a lot of things but only a few really know. Get the facts instead of rumours.
    Last edited by Octarine; 3rd October 2008 at 01:45 PM.

  13. #13
    Member lennyl's Avatar
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    Default Re: Difference Between 9 and 7 Diaphragm Blades

    Quote Originally Posted by Mrkcw View Post
    wht is the meaning of when stopped down...sometime heard tht this lens or tht lens is not so good when stopped down......thx...
    caleb answered the 1st part of your question. And incidentally, many lenses are soft when wide open, but sharp when stopped down, not the other way around.

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