Re: Foveon-like full colour sensor with IR channel

Discussion in 'Digital Photography' started by Kevin McMurtrie, Jan 10, 2011.

  1. In article <>,
    Alfred Molon <> wrote:

    > Apparently IR penetrates through haze, which is why IR images are more
    > sharp/contrasty if I understood things properly.
    >
    > So, suppose somebody launches a camera with a stacked layers sensor
    > (RGB) with an additional layer for IR. Such a camera should achieve
    > better results in hazy conditions, if the IR channel is used to
    > reconstruct the structure data. Just a thought...


    IR penetrates haze because it doesn't diffract as much as visible light.
    That same property would prevent a lens from focusing IR and visible
    light at the same time. It would require a cumbersome setup, like a
    dichroic mirror sending IR to a separate sensor that moves to focus
    itself and software to correlate the two sensors. Even then there may
    be other problems, like aperture misalignment or vignetting.
    --
    I will not see posts or email from Google because I must filter them as spam
    Kevin McMurtrie, Jan 10, 2011
    #1
    1. Advertising

  2. Kevin McMurtrie

    Martin Brown Guest

    On 10/01/2011 14:14, Alfred Molon wrote:
    > In article<>, bugbear
    > says...
    >> Yes - since you've increased the range of frequencies
    >> the camera is handling, the lens would (in principle)
    >> need redesigning!

    >
    > Tell me then how people are able to take IR photos by simply screwing an
    > IR filter on the camera...


    To first order you just have to alter the focus.

    You also have to adjust the focus slightly for IR when you put the
    filter on as compared to visual light. Modern TTL autofocus cameras will
    focus OK on the IR image but most digicam CCD sensors have a hot-mirror
    near IR blocking filter to avoid contaminating the image.

    CCDs are actually very sensitive to near IR so if you have a sensor
    without a hot mirror filter and photograph for instance a star field
    containing a strong near IR source it will be out of focus when all the
    normal stars are sharp. Amateur astronomers see this fairly often.

    Many lenses intended to be used for IR have a mark on the focus ring
    from the days when you focussed in the visible and then put the filter
    on (and used film that had to be handled in total darkness since the
    light trap on film canisters doesn't work too well at IR wavelengths).

    Unexposed developed slide film with organic dyes making black is a
    reasonable cheap near IR filter (which is why it is unsafe as a filter
    for looking at the sun - the visual light level is comfortable, but the
    IR and associated heat load still gets through).

    If you try it and persevere for about half a minute you will regain
    approximate colour vision through the black filter but with foliage on
    trees and grass looking much lighter than you would expect.

    Regards,
    Martin Brown
    Martin Brown, Jan 10, 2011
    #2
    1. Advertising

  3. Kevin McMurtrie

    Whisky-dave Guest

    On Jan 10, 2:14 pm, Alfred Molon <> wrote:
    > In article <>, bugbear
    > says...
    >
    > > Yes - since you've increased the range of frequencies
    > > the camera is handling, the lens would (in principle)
    > > need redesigning!

    >
    > Tell me then how people are able to take IR photos by simply screwing an
    > IR filter on the camera...


    I don't think they do. When I've done IR I've adjusted the focus
    slightly there's a littel red indicator mark
    on the lens but this was in the days of film.
    With things at a distance the IR shift doesn't matter that much but
    for closeup work it would.
    I'm not sure what YOU mean by infra red filter either.
    Such a filter would either let through IR or not let it through.

    > --
    >
    > Alfred Molon
    > ------------------------------
    > Olympus E-series DSLRs and micro 4/3 forum athttp://tech.groups.yahoo.com/group/MyOlympus/http://myolympus.org/photo sharing site
    Whisky-dave, Jan 10, 2011
    #3
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. George Preddy

    How much does a Foveon sensor cost?

    George Preddy, Nov 24, 2003, in forum: Digital Photography
    Replies:
    63
    Views:
    1,556
    Guest
    Dec 3, 2003
  2. Alfred Molon

    New Foveon-like full colour sensor from Fujifilm

    Alfred Molon, Mar 25, 2006, in forum: Digital Photography
    Replies:
    19
    Views:
    645
    W (winhag)
    Mar 26, 2006
  3. Usenet Account

    Re: Canon 75MP DSLR and triple-layer full-colour sensor

    Usenet Account, Jul 25, 2013, in forum: Digital Photography
    Replies:
    0
    Views:
    168
    Usenet Account
    Jul 25, 2013
  4. RichA
    Replies:
    0
    Views:
    173
    RichA
    Jul 25, 2013
  5. nospam

    Re: Full colour sensor research

    nospam, Apr 13, 2014, in forum: Digital Photography
    Replies:
    4
    Views:
    89
    Paul Ciszek
    Apr 19, 2014
Loading...

Share This Page