h�bbd``b`��@�� Ľ$��A\�K:��nLG@��Cq&FG���4�?��7� �� What Telescope Magnification Really Means. Those two variables are dependent on a, B an A, which vary with the location of the secondary mirror. h�b```f``2d`a``;� Ȁ �@1�H6`I4R�8 �I�Q�J��B��>�r�]��,n�x����fE�R���巪�u�k�f���5��D��&���5�w#�kV&��cv��!� ���5�5w;��Ȼ&�Tt40� �����dt40)A�����@!0�� fe;��@*;@J�H����O� ��m�R � �`�p^Ɗ�'�:qh��]��b�ι�!���5��o��4�'oA��^ �d`�|��` ��zW Telescope Formulas, Common Telescope ... have become woven into the fabric of amateur astronomy. For example, in a 12.5" F/12.5 Classical Cassegrain, Kp = -1 for the primary and Ks = -4.00 for the secondary. Other terms that need to be defined for future use: With that introduction, here are the important equations for designing the dimensions of a Cassegrain telescope. Physics - Formulas - Telescope Magnification: A common question when purchasing a telescope is what "power" it is. All that is left is to determine the shape of the primary and secondary mirrors. To get started, we just need two numbers: 1. For a Cassegrain this means that the secondary mirror must be large enough to allow the entire primary mirror to be "seen" from the parts of the focal plane that we wish to fully illuminate. Telescope Magnification Formula. Telescope Equations Magnification of the Telescope Theory Size and Distance in the Sky. The magnification of any telescope is controlled by the eyepiece being used and can be calculated by dividing the focal length of the telescope by the focal length of the eyepiece. The f-ratio of the primary can be just about anything but above F6 the total effective f-ratio becomes too high. This gives f-ratio (f#) and plate scale The final focal length is fpm where m = magnification produced by the secondary. -If you are figuring a Cassegrain secondary using star testing, increasing the correction of the secondary will decrease the correction of the system. So, moving the secondary toward the primary should slightly increase the correction of a Dall-Kirkham system in the system. . It was also obtained from ATM Vol 1, A general formula for the shape of a cross section of a mirror's surface is given as a reference by: Basically, the parameter K determines the type of shape a concave or convex mirror has. endstream endobj 179 0 obj <> endobj 180 0 obj <> endobj 181 0 obj <>stream fp is the primary focal length. After you choose a magnification, ... You should be able to now calculate the necessary dimensions for your Cassegrain telescope from the above example. For example, if we know the location of the focal plane and we put our eye there at its center, we should see the reflection of the primary mirror centered in the secondary mirror. Common sense seems to indicate that, for the 12.5" F/12.5 Cass, with an F/4.2 primary and a secondary magnification of 12.5/4.2 = 3, moving the secondary 0.01" toward the primary should move the focal plane back 0.01" * 3 = 0.03". Cassegrain telescopes are laid out in a kind of juggling act to get the telescope to work well, seduce the problems making the optics and give a telescope that is comfortable to use - all at the same time. For an example, a 14.25" F/21 Cassegrain is: Here is a page that describes the different ways of defining this asphereic shape, eccentricity, Conic Constant and so forth. While magnification is really not as important as field of view of aperture, to determine the power of a telescope, simply divide the eyepiece diameter to the telescope focal length: (This assumes it is large enough to be moved and still intercept all of the light from the primary). How Much Power is Enough? They can be manipulated as needed to solve for various quantities. If the fully illuminated field is larger, say 0.5" in diameter, then we should be able to move our eye off the optical axis by 0.25" from the center of the field and still see the entire primary mirror in the secondary mirror, though it will no longer be centered in the secondary. There are several important factors to consider with telescope magnification: magnification, true field, apparent field, exit pupil, and resolution. The primary is a parabola, so we know how to test that. A quick numerical calculation using the mirror spacings for my 12.5" classical Cassegrain indicate that if it were a Dall-Kirkham, then moving the secondary toward the primary would require a slightly less corrected primary. So how to figure the mirrors? 201 0 obj <>stream The things that make an R-C difficult are the typically fast focal ratio of the primary that is often used to gain a relatively fast telescope and the significant correction that must be applied to the secondary mirror as a result. 186), hence these systems are known as Maksutov-Cassegrain telescopes (MCT). 178 0 obj <> endobj This means that for Foucault testing, we simply multiply the ideal Foucault knife edge positions for a parabola by 1.04167, and that gives us the ideal knife edge positions for the hyperbolic primary mirror (or concave test plate for the secondary mirror with the appropriate multiplier to the parabola values). The sensitivity to changes in these quantities increases as the magnification rises. The correction of a Cassegrain optical system with an aspheric secondary mirror (classical, R-C) is dependent on the primary-secondary distance. So where does the extra sensitivity come from? In order to design a Cassegrain, we need to calculate it according to the type of Cassegrain we wish to make. Full-aperture meniscus corrector can be also used in various arrangements, including two-mirror systems, as described in Maksutov's extensive writings between 1941 and 1946. Physics - Formulas - Telescope Magnification: A common question when purchasing a telescope is what "power" it is. Formulas you can use to figure out how your telescope will perform, how best to use it and how to compare telescopes. To determine power, divide the focal length of the telescope (in mm) by the focal length of the eyepiece (in mm). The eyepiece has a field of view of 52°, so the field of view for the telescope at this magnification will be 52 ÷ 30 = 1.7°. The following is a selection that involves telescope magnification. This is done with the two formulas below. 1", asphereic shape, eccentricity, Conic Constant and so forth. Nowadays, it is most often used in the Cassegrain configuration FIG. %%EOF There are even some files for OSLO-LT (usable in the EDU version as the EDU version is an upgrade and it reads files from earlier versions) that show examples of finding the necessary Conic Constants and other such necessary specifications for the secondary. Magnification of a telescope is actually a relationship between two independent optical systems: the telescope itself and the eyepiece you are using. m = 1 for flat. A telecompressor lens and long-focal-length eyepiece give 14x magnification. As for the magnification, its sign according to our convention is positive if the image made by the secondary has the same orientation as the object for the secondary.

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