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Celestron® CPC 1100 GPS |
Celestron® Super C8 Plus |
The UCSB physics department has four telescopes for use in sky viewing sessions. One is a Celestron® CPC 1100 GPS, and the other three are Celestron® Super C8 Plus telescopes. These all have a Schmidt-Cassegrain (catadioptric) optical configuration. That is, a primary mirror, at the rear of the telescope, reflects incoming light toward a secondary mirror located at the entrance aperture, which reflects the light through a hole in the primary mirror to the eyepiece assembly, which sits at the focus of the system of two mirrors — the Cassegrain focus. (The eyepiece itself sits at its focal distance behind the Cassegrain focus.) On entering the telescope, light passes through a corrector plate (or corrector lens), which compensates for spherical aberration of the primary mirror.
For the CPC 1100 GPS, the clear aperture is 279 mm and the focal length is 2800 mm, and for the Super C8 telescopes, the clear aperture is 200 mm and the focal length is 2000 mm. For eyepieces, the CPC 1100 GPS has a 25-mm SMA (super modified achromatic) wide-angle lens and a 40-mm Plössl lens. Each of the Super C8 Plus telescopes has a 7-mm orthoscopic lens, a 26-mm Plössl lens and a 36-mm Plössl lens. In addition, there are three 10-mm Plössl lenses, two of which are with the Super C8 Plus telescopes, and one of which is with the CPC 1100 GPS. (These lenses tend to get shuffled around during viewing sesssions.)
All of these eyepieces fit a standard 1-1/4″ mount, and they are all interchangeable between the Super C8 Plus and the CPC 1100 GPS. Each of these telescopes is equipped with a 1-1/4″ mirror star diagonal, which orients the eyepiece perpendicular to the telescope axis, as shown in the photographs above. It also causes the image to be erect along one axis and inverted along the other. That is, with the eyepiece oriented as shown in the photographs above, the image appears right side up, but mirror image from left to right. Similarly, if the star diagonal is rotated so that the eyepiece is horizontal, the image will appear upside down, but correct from left to right.
For wide-angle viewing, we have a Meade 56-mm Super Plössl lens, which has an apparent field of view of 52° and fits a 2″ mount. To accommodate this lens, we have an OPT (Oceanside Photo and Telescope) 2″ mirror diagonal, which fits the rear cell on both the CPC 1100 GPS and the Super C8 Plus. In addition, we have a Celestron reducer/corrector, which shortens the effective focal length of the telescope by 37%, thus increasing the field of view by a factor of 1.6. It fits between the rear cell and visual back (the piece that holds the mirror diagonal).
The orthoscopic lenses have a plano-convex singlet eye lens and a biconvex triplet field lens. The SMA, which is a modified Kellner-type lens, has an achromatic doublet eye lens and a singlet field lens. The Plössl lenses are four-element lenses, having a doublet eye lens and doublet field lens, both achromats. Plössl lenses offer a flatter field of view than the others, and an image that is sharp across the entire field. You can find a useful summary of eyepiece designs and their characteristics on Wikipedia.
The apparent field of view of the 40-mm Plössl eyepiece is probably 46°. As best I can tell, the apparent field of view of all the other eyepieces is close to this, except for that of the SMA, which appears to be 52°. The magnification of a telescope is the ratio of its focal length to that of the eyepiece (M = fo/fe). For example, the CPC 1100 GPS with a 25-mm eyepiece gives a magnification of 2800 mm/25 mm = 112. The field of view is the apparent field of view of the eyepiece divided by the magnification (FOV = FOVapp./M). For the example above, assuming that the lens has an apparent field of view of 52°, the field of view is 52/112 = 0.46°. Assuming an apparent field of view of 46° for all the eyepieces except for the 25-mm SMA, and a 52° apparent field of view for this lens, the available magnifications and corresponding fields of view are:
As noted above, using the corrector/reducer would increase the field of view for any of these lenses by a factor of 1.6. The resulting fields of view are given in the colums labeled “FOVcorr”.
For solar viewing, we have two full-aperture filters for the Super C8 Plus telescopes, and one 3″ filter, also for the Super C8 Plus. (This is an 8″-diameter cover with a 3″ filter set in it.) We also have a solar filter that fits the CPC 1100 GPS.
You can view the manual for the CPC 1100 GPS here, and for the Super C8 Plus here. This version of the manual for the Super C8 Plus is actually not the same as the one that came with the telescopes, but the information it contains should still be useful. A copy of the manual that came with the telescopes is available in room 1630 for anyone who wishes to see it.
Also available is a Celestron Neximage model 93712 solar system imager (CCD camera), for recording images from either the NexStar 11 or a Super C8 Plus. With it is also a reducer lens (Celestron model 94178) to increase its angle of view. This particular camera has been discontinued, and its driver will not work under operating systems later than Windows XP. It will work on machines running newer operating systems, however, with the driver for the Philips SPC900 NC web camera. The capture software (AmCap) that came with the camera should run on newer Windows machines. A laptop computer is available, which has all the appropriate software loaded. Those who wish to use their own laptops can find instructions for installing the software at the following link:
The CD with the capture software is with the camera. Depending on the operating system, other drivers may be available, and the capture software may still be usable.
To arrange for a viewing session:
For safety and security reasons, Broida roof access is limited, and during viewing sessions, there must be at least one official physics department employee (faculty member, postdoc, researcher, staff member or graduate student) present.
If you are a faculty member or graduate student, if you need training in the operation of the telescopes, you must arrange to meet with Louis Grace. If you will need any equipment in the telescope closet, you will need to borrow the key from Louis. (The CPC 1100 GPS is in an enclosure on the roof deck, and has a power strip, extension cord and a small assortment of oculars there.)
If a student group would like to hold a viewing session, a representative from that group must make sure to find someone who is allowed access to the Broida roof (see above) to be present for it. In addition, he must arrange for training in the setup and use of the telescopes by Louis Grace, and for approval for roof access from the group’s faculty advisor. (The person with roof access may take the training, and then supervise the setup and use of the telescopes.) Information about the student group, approvals and training must be recorded on a Broida Roof Access Request Form, which you may download at the link above, or you may obtain from Christine Griffin, in Broida 3019A. Once you have filled in the necessary information and obtained the required signatures, return the form to her. You will then be allowed to borrow the key to the telescope closet (see above).