Here is a image of the moon collected by the Smartphone Telescope.
A smartphone camera can "look" through the eye piece of a telescope (or microscope) and take an image. I have an inexpensive MEADE 60AZ-AD telescope. Here are some specifications: -Clear aperture (diameter of main lens) is 60 mm -Focal length is 700 mm -Eye piece focal length is 9 mm This provides a magnification of 700/9 or 78x, the ratio of the focal lengths. I cut a small piece of wood so that it would hold my smartphone and drilled a hole in the wood that fit snugly over the eye piece. The smartphone sits on this piece of wood so that the camera lens is centered on the eyepiece (see picture above). I will add a rubber band or two to hold the smartphone to the wood. In order to evaluate how good this digital telescope is, I found a USAF resolution target #1951 at the following website: http://www.photo.net/photo/optics/USAF1951.ps I printed this out on a laser printer at highest resolution and placed it outside. I measured the distance between the telescope and the target to be 27.4 meters (~90 feet). I took an image of the lower target. The set of black bars in the lower target set next to the #1 measured to be exactly 2 cm. The idea behind this resolution target is that the bars get progressively smaller, and the ability to resolve the bars can be measured as a function of spatial frequency (smaller bars mean higher spatial frequency). At some point, a camera viewing the target cannot resolve the bars. Using this concept you can measure the resolution limit of the smartphone telescope. Above is a photograph of the smartphone screen. Notice that the image is reversed as in a mirror image, but still rightside up. The three black bars next to the largest #1 are clearly resolved, as are the bars by the next smaller #1. The resolution degrades from there. Here is the actual image. Notice that the field of view is truncated and black outside the central cirucular region. This is due to a field stop in the telescope. The smallest bars that I can resolve are about 0.05" (this time using the period of one line pair (Each set of three bars covers 2.5 line pairs). From this we can calculate a resolution of 0.05"/1080" or 46 microradians. Astronomers use a unit of arcseconds, which is 1/3600 degrees. In arcseconds, the telescope is resolving ~9.5 arc seconds. (Add link here to a tech note about units of angular measurement). Theory says that the resolving power of telescope is limited by diffraction to 2.44*wavelength/Diameter where the wavelength is visible light (say 550 nm), and the diameter of the telescope is 60 mm. For this system, diffraction limit should be about 22 microradians. So we are getting close, but some improvement is possible. Later I will look into some software to digitize the image and extract more quantitative measurements of the bar contrast versus spatial frequency.
With a solar filter and telescope mount: (1) Measure length of Sun's day by observing movement of sunspots. (2) Measure angular motion of Sun across sky (setting or rising may be easiest as horizon provides fiducial mark) to get length of Earth's day. Remove filter and observe Moon: (3) Observe Moon's angular motion; see how it differs from Sun's angular rate to determine Moon's orbital period. Support with photos of rate of phase change. Observe Galilean moons of Jupiter: (4) Measure orbits of the four moons. I did this one in college with a Celestron 14. I believe the goal is to calculate the gravitational constant itself, which is a huge deal and watershed discovery for Kepler; but I've forgotten the details. |
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