Focus Definition and 11 Discussions

FOCUS is a fourth-generation programming language (4GL) computer programming language and development environment that is used to build database queries. Produced by Information Builders Inc., it was originally developed for data handling and analysis on the IBM mainframe. Subsequently versions for minicomputers and such as the VAX and other platforms were implemented. FOCUS was later extended to personal computers and (in 1997) to the World Wide Web: the WebFOCUS product.

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  1. E

    Camera focusing motion: can you solve this math?

    This problem arose in modeling camera focusing movement, such as a control system might do. It assumes a simple (thin) lens, rays close to the optical axis, and monochromatic light. While most camera lenses are not simple, this is a first approximation. Camera lenses project an image of a...
  2. S

    A Focal length and focus point

    First of all, Let me present some of the things I found from research. (considering convex lens) Interpretation 1 => Focal length is the distance from the center of the lens to the point where all rays converge. Interpretation2 => Focal length is the distance from the point of convergence to...
  3. D

    I Explanation for the hyperbolic array of light rays.

    Hello, Recently, a solar power tower plant was founded next to where I work. Since it's the tallest object in the area, it's quite hard to miss it. But apart from that, every morning the reflected light is arranged in a hyperbolic- like way, as you can see in the picture. Does anyone have a...
  4. V

    Optical geometry of smartphone camera.

    I posted the following on a phone forum and got no replies, as expected. It's a bit out-of-the-way and technical. Thought this might be a better place since the question still interests me. I'm using my phone to take photos of assembly procedures on my electronics workbench. However, the focus...
  5. stevendaryl

    Lenses and Pinholes: What Does "In Focus" Mean? - Comments

    stevendaryl submitted a new PF Insights post Lenses and Pinholes: What Does "In Focus" Mean? Continue reading the Original PF Insights Post.
  6. N

    External focus in an optical system

    I feel a bit stuid for asking this. I have an optical system conisting of a laser source, a lens with some focal length F and aperture stop `(with some diamater D), followed by another lens (with another focal length) f and aperture stop d at some distance r from the first aperture stop D. What...
  7. parshyaa

    I Why ellipse has two foci?

    i think there is only one focus of ellipse and we can draw a ellipse with a single focus. please correct my thinking.
  8. G

    Optics - focused vs. defocused image

    Hello, (I am new here, so hopefully this is the right location to ask my question. please let me know if there is more relevant forum) I am trying to understand 2 situations: A) I have an object, lens and a detector. The detector is at the focal plane of the lens. I am reducing the aperture...
  9. R

    Focusing sea waves

    Would it be possible to use diffraction to focus the enrgy of sea waves, on the principle of the zone plate ( but reduced to 2 dimensions? This could be done by an array of wave-opaque objects such as floating breakwaters, particularly along coasts...
  10. T

    Finding focus

    Homework Statement What focus is needed for in order for a diverging lens to produce a magnification of 0.60x on an object located 1.40 meters away? Homework Equations M=hi/ho 1/do + 1/di = 1/f M= -di/do The Attempt at a Solution -di / 1.4 = 0.6 1/1.4 + 1/.84 =1/f -di=0.84 1.42
  11. AdityaDev

    Wave front and convex lens

    If I have a parallel beam of light parallel to x-axis, with the speed of light varying from bottom to top. Let it decrease from bottom to top. (To get such a beam one can pass the beam through a glass slab normal to its surface, whose refractive index increases linearly from bottom to top). Now...