Switch to English Language Passer en langue franšaise Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 74,536   Posts: 1,646,048   Online: 890
      
Results 1 to 5 of 5
  1. #1
    zydeholic's Avatar
    Join Date
    Apr 2009
    Shooter
    Medium Format
    Posts
    33

    Different color, different focusing depth

    I've been hearing about how different frequencies of light will focus at different focal lengths. This is why lenses have coatings, to bend them back to the same plane.

    I've heard this happens with pinhole, but no way to rebend the light. Just wondering if the resulting images might be of different sizes too, i.e. the red image might be just a little higher and wider than the green image, etc.

    Just thinking that I might be able to retweak things in photoshop by changing the height and width of the resulting image for each color channel. I know, off-the-wall question.

  2. #2

    Join Date
    Apr 2008
    Location
    Los Angeles, CA
    Shooter
    Multi Format
    Posts
    8,006
    Images
    4
    With a pinhole, it is really a non consideration, IMO. If you want the most sharp and technically sound picture, use a lens. If you must, you can throw whatever wavelength you want into the "ideal" hole diameter equation in order to favor any one color over another. The standard is 550nM (green-yellow), as it is pretty much in the middle of the visible spectrum.
    Last edited by 2F/2F; 04-23-2009 at 04:41 AM. Click to view previous post history.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

    - Rob Tyner (1944 - 1991)

  3. #3
    zydeholic's Avatar
    Join Date
    Apr 2009
    Shooter
    Medium Format
    Posts
    33
    I was thinking more about correcting color abberations over sharpening, but bottom line, my gadgety mind was wanting something to chew on.

  4. #4
    Ole
    Ole is offline
    Ole's Avatar
    Join Date
    Sep 2002
    Location
    Bergen, Norway
    Shooter
    Large Format
    Posts
    9,282
    Blog Entries
    1
    Images
    31
    Quote Originally Posted by zydeholic View Post
    I've been hearing about how different frequencies of light will focus at different focal lengths. This is why lenses have coatings, to bend them back to the same plane...
    No, that's not why lenses have coatings. But it is why lenses have more than one element.

    A pinhole has no chromatic aberration, but it can still show a little bit of colour fringing due to the differences in diffraction of different wavelengths. The only way to get rid of this is to use a monochromatic filter.
    -- Ole Tjugen, Luddite Elitist
    Norway

  5. #5

    Join Date
    Mar 2005
    Shooter
    ULarge Format
    Posts
    875
    Images
    24
    Ole is on top of the question. If you are really concerned about the different wavelengths, use a cut off filter. Allow only one wave length to enter the pin hole. I remember there was an article several years ago in Phototechniques where a high school student compared shaprness of photographs taken with an old, uncorrected (non-APO) lens with no filter and with a cut off filter. The ones with the cut off filter were sharper. I suppose the same would work with a pin hole. But, the filter will affect the distribution of tones, which may or may not be desirable.



 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  Ś   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin