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It is a teaching tool fully functional, but that was not designed for the application to a telescope.
The photographs are already quite significant and require little additional information.
The body of the spectroscope is obtained from an aluminium square tube 60 x 60 mm and thickness of 2 or 3 mm. On both sides to 90 ° are two holes threaded diameter M42 mm.
Two square lids close the two openings. At the centre of one of the lids is practiced the hole to which is applied a flange within which rotates the shaft diameter of 5 mm, on which are keyed the grating and the knob. (Attention to the direction of the grating lines, which must be parallel to the shaft....).
The optics consist of two recovery camera lenses 24x36, with Pentax type screw mount M42. Both the focal lengths can be changed, being this an interchangeable assembly. Here they are 135 mm. and 50 mm.
Note that both the lenses are mounted with the frontal filter thread toward the grating. For this purpose we used two reverse optical rings M42, easily available in the WEB ( click here for example).
On the collimation lens is applied a turned barrel, on which is mounted the slit. The length of this barrel is such as to maintain the plane of the slit to 42 ~ 44 mm from the lens.
The adjustable slit in the photo was purchased by SurplusShed - USA ( Click Here ).
However, it could also be very convenient a self-made slit, built with two blades of pencil sharpeners, two pieces of razor blade or, even better, realizing the digital slit shown in this page.
The barrel holding an eyepiece is mounted on the the second lens, on the observation side, (1 "1/4 or 2", as is in this illustration). The length of this barrel must be determined so that the diaphragm of the eyepiece is falling to 42 ~ 44 mm from the threaded rear lens. The focal length of the eyepiece is not obliged, but it is advisable to start the observations using a 25 mm.
Special care is required in the adjustment and the alignment of the optical chain, ensuring the slit to be well parallel to the grating lines. Focusings should start putting halfway the collimation lens and then adjusting the eyepiece lens. Then back again to the collimation lens adjustment, and so on.
It is possible to make some interesting photographs of the spectra by fitting a SLR camera (without other lens) directly to the rear lens. It is obvious the importance of a very accurate focusing of the emission or absorption lines, trough the viewfinder. It is also useful avoid over-exposures trying different exposure times.
For a better and easier observation of the solar spectrum, I found sometime useful a small frosted filter in front of the slit, made of a disk of tracing paper or frosted plastic or glass, placed 2 or 3 cm. from the slit. The photograph illustrates an exemplary embodiment of this add-on.
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