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An account of peculiar light patterns produced by reflection in a pool under falling rain droplets was recently reported by Molesini and Vannoni (2008 Eur. J. Phys. 29 403-11). The mathematical approach, however, only covered the case of a symmetrical location of a light source and the observer's eyes with respect to the vertical of the falling droplet. Extending such an account to asymmetrical configurations, a general solution for the reflection trails that are observed on the pool surface is presented. (Contains 6 figures.)

The observation of peculiar light patterns produced by reflection from a water surface perturbed by falling droplets is reported. The phenomenon is analysed in some detail, with a simplified model of a surface wave packet. A simple experiment reproducing the phenomenon in the laboratory is presented, also showing evidence of pattern distortions that were not reported before. An account is given in terms of the vector nature of the law of reflection, also referring to the time constant of the eye. (Contains 12 figures.)

The making of microscope devices using inexpensive or recovered materials is demonstrated. Examples of images illustrating the performance of such devices are presented. As a project at the undergraduate level, the task is effective in acquiring familiarity with optical imaging concepts and their practical implementation in the laboratory. (Contains 8 figures and 1 table.)

A holographic process is presented where the object is made of the real image produced by a two-mirror system. Single-step reflection hologram recording is achieved. Details of the process are given, optics concepts are outlined and demonstrative results are presented. (Contains 6 figures and 2 footnotes.)

A phase-shift interferometry experiment is proposed, working on a Twyman-Green optical configuration with additional polarization components. A guideline is provided to modern phase-shift interferometry, using concepts and laboratory equipment at the level of undergraduate optics courses. (Contains 5 figures.)

Early steps tracing back to Galileo's telescope and to the birth of instrumental optics are reported. Particulars of lensmaking technology, basic optics laws, concepts of eye and vision, and issues on instrument trade and service are given. Achievements at the roots of our continuing advances in optical sciences are acknowledged. OCIS codes: 110.6770, 350.1260.

Measuring flats in the horizontal posture with interferometers is analyzed in detail, taking into account the sag produced by gravity. A mathematical expression of the bending is provided for a plate supported at three unevenly spaced locations along the edge. It is shown that the azimuthal terms of the deformation can be recovered from a three-flat measuring procedure, while the pure radial terms can only be estimated. The effectiveness of the iterative algorithm for data processing is also demonstrated. Experimental comparison on a set of three flats in horizontal and upright posture is provided. OCIS codes: 120.0120, 120.3180, 120.3940, 120.4800, 120.6650.

We discuss a simple experiment for detecting small deformations by speckle interferometry. The optical setup uses a laser diode for the source together with a lens to expand the laser beam and a beam splitter dividing the beam and illuminating two scattering surfaces. A low-cost, commercial charge coupled device (CCD) photocamera provides images of the two superimposed speckle fields through the beam splitter. We first take a picture with the system at rest, and then take a second one after a deformation is made in a surface. By simple subtraction of the digital pictures, we obtain a fringe pattern that gives us information about the deformation. [DOI: 10.1119/1.1643375]

A device measuring the optical power of simple lenses by means of moire phenomena is described. The relevant equations are derived, and a working instrument is presented. A power measuring accuracy better than 0.25 [m.sup.-1] in the range of [+ or -]10 [m.sup.-1] is demonstrated. OCIS codes: 080.3630, 120.3930, 120.4120, 120.4570.

Optics of telescope makers Torricelli, Divini, and Campani dating back to the 17th century have been tested interferometrically. It was found that the optical polishing technology had progressed to thorough control over the surface figure and finish, while the nearly paraxial conditions of the aperture remained constant. The instruments that were examined exemplify the knowledge of optics of that time, particularly with respect to the early use of erector units in terrestrial telescopes. OCIS codes: 000.2850, 110.6770, 120.4800, 220.2740, 350.1260.

The statistics of partially developed speckle patterns produced by reflection under coherent illumination can be used to determine the scattering properties of a mirror. The theory of the approach is presented, showing that in proper conditions the standard deviation of the speckle-field distribution expresses the finish grade of the reflecting surface. Interferometric measurements are described, and experiments on selected samples are reported. Key words: Surface scattering, speckle-field statistics, phase-shift interferometry.

The Florentine Istituto e Museo di Storia della Scienza houses two complete telescopes and a single objective lens (reconstructed from several fragments) that can be attributed to Galileo. These optics have been partially dismantled and made available for optical testing with state-of-the-art equipment. The lenses were investigated individually; the focal length and the radii of curvature were measured, and the optical layout of the instruments was worked out. The optical quality of the surfaces and the overall performance of the two complete telescopes have been evaluated interferometrically at a wavelength of 633 nm (with a He-Ne laser source). It was found in particular that the optics of Galileo came close to attaining diffraction-limited operation.

The recent celebration of the discoveries made by Galileo four centuries ago has attracted new attention to the refracting telescope and to its use as an instrument for the observation of the night sky. This has offered the opportunity for addressing in the classroom the basic principles explaining the operation of the telescope. When doing so, a key concept that is faced is magnification. In geometrical optics, the treatment of magnification is generally given in terms of light rays and first order (Gaussian or paraxial) ray tracing. Computer programs are available with which the light path through the lenses and the whole telescope can be simulated.

We discuss the manufacture and use of a prism pair to measure the refractive index of thin liquid films with a spectrometer. The method requires only a drop of liquid and is accurate to ~2 x [10.sup -4]. OCIS codes: 120.0120, 120.3930, 120.4640, 120.6200.

A new optical configuration producing one-step 360 [degrees] rainbow holograms is presented. The method makes use of two concave mirrors in confocal position, with an annular aperture between the two. An experimental demonstration is given. OCIS codes: 090.0090, 090.1970, 090.2870, 090.5640.