Diff types of lens hoods?

Discussion in 'Beyond the Basics' started by prodigy2k7, Jul 30, 2008.

  1. prodigy2k7

    prodigy2k7 No longer a newbie, moving up!

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  2. reg

    reg TPF Noob!

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    Flower hood - wide angle lenses to prevent vignetting.
     
  3. nynfortoo

    nynfortoo TPF Noob!

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    It isn't just for wide-angles.

    My understanding is that a petal hood is designed specifically for each lens to block out as much non-image-forming light as possible without getting in the way.

    The shorter parts of the hood relate to the corners of the sensor.

    Technically, a petal hood can have longer sections (relating to the top, left, bottom and right of the sensor) whereas a circular hood has to cater to the lowest denominator (the corners) when it comes to blocking light..

    Petal hoods, I guess, are just more efficient. And they look better, too.
     
    Last edited: Jul 31, 2008
  4. JerryPH

    JerryPH No longer a newbie, moving up!

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    Huh?? Not even close. Vignetting is a result of lens design.

    It is to prevent sun or extraneous light from entering the lens and cause lens flare. ;)

    A petal hood is more a visual look, they are less effective than a hood that is evenly wide all around. Personally, I may like the look of the petal hood better, but it cannot protect the lens as effectively as a hood that is the same all around.

    I don't even know why petal hoods are being made, to be honest... lol.
     
  5. tron

    tron TPF Noob!

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    cause noobs think form outdoes function :lol:
     
  6. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    Petal hoods are definitely a function of design, and not of fashion.

    A perfectly round lens hood blocks light evenly on all 4 sides of the image. That's great if the image frame has the same angle of view vertically and horizontally like a square. Anyone out there got a square format 35mm SLR or DSLR? Nope, they are all rectangles. Petal hoods are designed for the most efficient light blocking taking into account that one dimension of the image has a significantly wider or narrower angle of view.

    Take a zoom lens that'll go wide, fill in the cut-out sections of it's petal hood with electrical tape, set the lens to it's shortest focal length, and it will probably vignette where the petal hood has been filled in.

    Vignetting can be caused by all sorts of things. If you put a lens hood designed for a long focal length on a short focal length lens it will vignette.
     
  7. Garbz

    Garbz No longer a newbie, moving up!

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    Jerry did you ever try that putting the square through the circle in the matching the shapes game when you were a toddler ;)

    From the point of view of the lens if you unwrap a pedal hood onto the sensor plane you end up with a square. The pedal shapes allow the circular hood to be made longer without vignetting into the corners of the frame.

    /EDIT: That sounded somewhat insulting sorry not meant like that at all.
     
  8. Bifurcator

    Bifurcator TPF Noob!

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    I thought it was a good illustration of what might happen to a conical shape (a round hood) if it were sliced through by the squareness of a trapezoidal projection (or "trapagon" if I'm getting my shape names right - I suspect that's not as precise as t could be. I wanna say octahedral but that would only be half right. :D).

    Posts 2, 3, 6 and 7 win!!! Sorry, no prizes - and you still have to pay your taxes.
     
    Last edited: Jul 31, 2008
  9. Moglex

    Moglex TPF Noob!

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    I think you mean a section of cone sliced by a rectangular section linear taper horn.

    Not sure where the 'octahedral' (even if only half right) come into play.
     
  10. dEARlEADER

    dEARlEADER TPF Noob!

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    ouch.... Jerry.... I've never seen you miss before....lol....
     
  11. prodigy2k7

    prodigy2k7 No longer a newbie, moving up!

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    Ha, jerry quick edit your thread nobody will ever notice :S

    THANKS EVERYONE! For once I easily understood the answer to one of my questions. HA!
     
  12. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    Petal hoods do a better job than round hoods that go all the way around. Check with your lens manufacturer if you don't believe me. Don't think of a petal hood as a round hood with parts missing. Think of it as a round hood with parts added. The only hood better than a petal hood is a rectangular hood, as seen on some medium format cameras and video cameras. Unfortunately rectangular hoods don't slide nicely around the lens for easy, compact storage. A petal hood is a compromise between the effectiveness of a rectangular hood and the ease of storage of a round hood.

    Possibly where the confusion is occurring is that petal hoods often come with zoom lenses, and obviously zoom lens hoods have to make compromises to work effectively with the entire range of focal lengths available.
     

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