LENTES jaci

    published in the october 97 edition of the "Guia do Amador de Astronomia"

    To all amateur astronomers:

    In the middle of September I returned to Brazil.  In the USA I gave do Mr. Denis di Cicco, at Sky & Telescope, in Cambridge, MA, and to Mr. Steve Peters at Orion Telescope and Binocular Center, em Watsonville, CA, two samples of my new focal-reducers, I named "tele-compactors", "tele-shortners" ou "tele-lessers", or, if you prefer simply "jaci Lenses".

    I have done so as a contribution to the amateur astronomical community.  You may use my invention, if you wish to.

    A historical narrative:

    Paul Valleli, an amateur astronomer from Boston, has published an article in Dec '73, in Sky & Telescope magazine, in wich he called attention upon the fact that when he once inserted a convergent lens in the light cone of an instrument he was able to reduce its focal length.  This way, he enlarged the area of the field photographically yelded by his Celestron, a catadioptric telescope, transforming his f/10 'scope in a "faster"f/5 system ( fl 1000 ).

    In Valleli diagram, FL is the original focal-length; d1 and d2, as indicated, are the distance between the componentes; EFL is the new effective focal length using the "reducer" lenses.

    Valleli enphasized however that in the caso of using his "reducer" in a refractor for example, one should plan to have a new focuser, for the old one may never reach focus, particularly in a kind of refractor that carries small-travel focusers.

    As you probably know, on the contrary of the famous divergent "Barlow lenses", the "reducers" acts increasing the convergence of the light cone, producing a smaller immage at a smaller focal length.

    Today we can find in the USA the so called "telerreducers" ( from Celestron ), tele-compressors ( from Meade ) and "wide field viewers" ( from Lumicon ), which are only employed in catadioptric telescopes: Schmidt Cassegrains, Maksutovs and Mak-Cass.  The reducers I designed do not depend on telescope types, whatever they may be, for they are related only to star diagonals or to the eyepieces.

     Existem hoje no comércio americano "tele-redutores", "tele-compressores" ou "rich-field viewers" desenhados especificamente para instrumentos catadióptricos, como os Schmidt-Cassegrain, os Matsukov e os Mak-Cass.

    My focal-reducers work like this:

    Model 1 is threaded to the tube of all standard star diagonals like those from Adorama and Orion, for Cassegrains, Schmidt-Cassegrains, Maksutovs and refractors.

    Model 2 is threaded to almost any type of eyepieces, just like a filter.  It is obviously to be used in all kinds of telescopes, from reflectors to refractors and catadioptrics.

    Model 3 is a complement to models 1 and 2.  It was made for 0,965" ( japanese ) eyepieces.  I just showed its prototype to Mr. Di Cicco and Mr. Peters.

    In model #1 the lenses nearly touch the diagonal prism.  The conception of my focal-reducers differs from all the existing ones because in all three models we have a virtual image of the object, the sky for instance, surrounded by a black circle of the eyepiece diaphragm.  There is no vignetting, no image degradation.  In the future my reducers may, perhaps, be also used attached to modern CCD cameras.

    Before going to USA in August '97, I bought the lenses to be used in my focal-reducers from Edmund Scientific, because there are no manufacturers of the small objective lenses with the optical specifications I needed.  The specifications are: dia:25.00mm/EFL:150.00/BFL:146.10/glass type:BK7-SF5/stock # coated A32,494.

    In the model #3 I used 27mmD lenses with EFL 110mm because I have no other objectives.

    With just one jaci-lenses you may transform an "old" and cheap eyepiece ( Ramsden, Kellner, modified achromat, ortho and Pössl ) into "modern" and expensive rich-field ones!

    I believe that I have developed a very simple and yet revolutionary kind of focal-reducers that works with all types of telescopes.  Now it is up to you making and using them, as I said before.  By the way, Orion is testing my invention with no compromise in fabricating them.

    Best regards.  I hope to hear from you soon.

    Mario jaci - Chairman of Clube de Astronomia do Rio de Janeiro

    you can reach me at astronomia@astronomia-carj.com.br

    rua Carlos de Carvalho, n.84 apt.720

    Rio de Janeiro - BRASIL - 20230-180

    tel/fax: 0055.21.2202811