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Post deleted by robertj

Discussion in 'Help Team' started by robertj, Sep 22, 2003.

  1. TimF

    TimF With as stony a stare as ever Lord Reith could hav

    Re: Focal length/28 is 28

    Sometimes Robert I reckon you think too much for your own good. A distant object looks smaller than a closer one (and lets say these are two identical objects for arguments sake) not because our eyes have lenses, but simply because it is further away from our position. It matters not a jot whether you focus your eyes upon the close object or the distant one. The distant object still appears smaller.

    Tim BSRIPN
    [​IMG]
     
  2. robertj

    robertj Well-Known Member

     
  3. huwevans

    huwevans Not Really Here

    Re: Focal length/28 is 28

    the 28mm f/2.8 PC Super Angulon-R, which is a rebadged Schneider effort

    Well it would be - 'Super Angulon' is a Schneider design and registered trade mark, so all Super Angulons are Schneider lenses, unless perhaps some were manufactured under license by other optical works.

    Huw Evans.

    www.huwevans.freeuk.com
     
  4. Benchista

    Benchista Which Tyler

    Re: Focal length/28 is 28

    The only SA I own is a 90mm...... which should identify what it's for pretty easily.

    Nick BSRIPN
    I am a camera.
     
  5. jonlee

    jonlee Well-Known Member

    Re: Focal length/28 is 28

    Robert,
    You are blinding us with science. I'm not quite sure if we can answer your questions apart from Huw who is our technical expert.
    Reading your threads, I'm not sure if you are concern with photography, geometry, physics, or philosophy. Whatever it is, we just take pictures. You are going far too deep into the science of the lens.
    Jon
     
  6. Benchista

    Benchista Which Tyler

    Re: Focal length/28 is 28

    Surely there's room for everyone whatever their interests?
    Mind you, Roberts, don't be surprised if you don't get too many answers!/img/wwwthreads/wink.gif

    Nick BSRIPN
    I am a camera.
     
  7. TimF

    TimF With as stony a stare as ever Lord Reith could hav

    Re: Focal length/28 is 28

    Surely there's room for everyone whatever their interests?

    I would certainly hope so - unless they're like that annoying twerp of a few weeks ago.

    Jon, my opinion, for what its worth is that Robert's interest in philosophy is the driving force here. Much of what he has written in this thread is way beyond my comprehension! Come down to the level of us "mere mortals" Robert, and I'm sure we can enjoy each other's company here. /img/wwwthreads/smile.gif

    Tim BSRIPN
    [​IMG]
     
  8. TimF

    TimF With as stony a stare as ever Lord Reith could hav

    Re: Focal length/28 is 28

    I hope I'm not a bother

    Not at all. /img/wwwthreads/smile.gif

    Tim BSRIPN
    [​IMG]
     
  9. Larry Shone

    Larry Shone Well-Known Member

    and at the other end of the scale...

    ...we have so called telephotos. Now many lenses ae called telephotos, even zoom lemses(the zoom telephoto-80-200,75-300 etc) yet they are not true telephoto in design.
    A telephoto lens is one that is quite simple in construction.The old 300 and 400mm presets were classic telephoto design. A lens at one end, the aperture mechanism and another lens at t' other end!A basic telescope is a telephoto design, and with telephotos the lenses are quite long, pretty close to the marked focal length(a 300mm is roughly 300mm long). This is due to the simplistic design, the 'telephoto' design. Modern 300s and 400(excluding the big end f2.8 jobbies,not sure about those) are much smaller and have more in common with the retro design of wideangles, that is the optical centre is not the same as the physical centre.

    I don't do people!
     
  10. TimF

    TimF With as stony a stare as ever Lord Reith could hav

    Re: and at the other end of the scale...

    Ah, now there you're incorrect Larry. Kingslake (in his A History of the Photographic Lens) defines a Telephoto as a type of photographic objective consisting of a positive front component and a negative rear component, such that the focal length is greater than the total length from the front vertex to the image plane. The ratio of the total length to the focal length is known as the telephoto ratio.

    A telescope - and the old lenses you refer to are in fact simple long-focus lenses.

    Tim BSRIPN
    [​IMG]
     
  11. Larry Shone

    Larry Shone Well-Known Member

    Re: and at the other end of the scale...

    actually i wasnt far out, i meant that in telephoto design its the other way round to w/a lenses, in that the perceived focal length is greater than the physical length. With extreme w/angles their actual physical length is much greater than the focal length.
    And the word telescope means to fold light, which comes from the old folding brass jobs.Most telescopes arent actually 'telescopes' at all!(Tho some, mine included, incorporate prisms in the design, to reduce size)
    (Tho you could say a mirror lens is a telescope in that the light path is definitely folded in such a lens!

    I don't do people!
     
  12. TimF

    TimF With as stony a stare as ever Lord Reith could hav

    Re: and at the other end of the scale...

    in telephoto design its the other way round to w/a lenses, in that the perceived focal length is greater than the physical length. With extreme w/angles their actual physical length is much greater than the focal length.

    That's true. Another way of saying retrofocus is reverse telephoto.

    Tim BSRIPN
    [​IMG]
     
  13. Larry Shone

    Larry Shone Well-Known Member

    Re: and at the other end of the scale...

    Another way of saying retrofocus is reverse telephoto.


    oh, you mean that old favourite Otohpelet!/img/wwwthreads/wink.gif

    I don't do people!
     
  14. 0

    0 Guest

    Re: and at the other end of the scale...

    > And the word telescope means to fold light

    No it doesn't! It means to see far, from tele, meaning far or distant, and skopeein, to see. Fold light, indeed!

    Steve
     
  15. 0

    0 Guest

    Re: Focal length/28 is 28

    > Can you look at the world without your eyes?

    Do you sleep with you eyes open, Robert? If you don't, how do you see your dreams? And how's your sense of touch?/img/wwwthreads/smile.gif

    Steve
     
  16. robertj

    robertj Well-Known Member

     
  17. TimF

    TimF With as stony a stare as ever Lord Reith could hav

    Re: Focal length/28 is 28

    The real image is one in real world of 3D objects and the perceived image is one in our retina (a 2D image) interpreted by our brain

    If that were the case, how would you know the "real world" is 3D if your brain is interpreting only in 2D?. We know the reality to be 3 dimensions (of height, width and depth) because our brain can interpret fully the information the eyes pass to it. It is precisely because we have two eyes, each of which sees a slightly different view to the other that we are able to perceieve that reality.

    Tim BSRIPN
    [​IMG]
     
  18. 0

    0 Guest

    Re: Focal length/28 is 28

    And of course the "real world" is only your real world. Everyone applies their own filters on what they see - that's what makes photographs interesting. Compare two eye-witness accounts of an RTA./img/wwwthreads/wink.gif

    Steve
     
  19. gordonblue

    gordonblue Well-Known Member

  20. Larry Shone

    Larry Shone Well-Known Member

    2 eyes make 3D!

    i only see thru one eye so can only really see in 2D, which is why i tend to bump into things a lot and when drawing can never manage to get the picture in the middle!

    [​IMG]
     

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