by Dave Rowe.
The following images show the Slevogt camera in an unfinished state. Cosmetically, the camera will get a full outer treatment including several coats of paint, the aluminum parts will be anodized and the outer truss structure will get light baffling and a shoud of some kind and, of course, the mirrors will be silvered. Non-the-less, the images do convey the spirit of construction and the test and fabrication methods. Click on any of the images to get a larger view. I hope you enjoy this little tour, in pictures, of the Slevogt camera.
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| This is the primary and secondary mirror mount structure for the Slevogt. The truss elements are Invar rods, 5/16" in diameter, the use of which greatly reduces the variation in focal plane position due to temperature. The Invar rods are held in place, top and bottom, by set screws. This truss arrangement is exceptionally strong, allowing the telescope to be rotated in all directions without causing a measurable collimation shift. The 3/8" thick aluminum ring at the top holds the secondary spider (hard to see in the photo), which in turn holds the secondary mirror cell. This cell uses three screws and three stiff springs to allow secondary collimation. The wooden ring at the bottom slips into the octagonal wooden tube shown in the next image. The primary mirror cell (at the bottom, not visible) also uses three screws and three stiff springs for collimation. In addition, the entire cage assembly can be adjusted with respect to the tube by the use of three more springs and screws. Both the primary and secondary mirrors are RTV'ed to their respective cells. |
 | This is the full view of the Slevogt camera. The black truss structure and end ring hold the corrector plate at the right distance from the primary. The truss tubes are made from 0.75" diameter, thin-walled aluminum tubing. Either a shroud will be used over the truss structure, or a tube will be fabricated inside the truss to prevent unwanted light from hitting the film plane. At the moment, the octogonal wooden tube is in a bit of a mess because it was salvaged from another project. Four bolts fasten the truss assembly to the octogonal tube assembly for easy transportation and set up. |
 | This image shows the assembled Slevogt being tested by a 10" Newtonian telescope (dimly, in the background). The Newtonian is pointed back at the Slevogt, collimated and focused. A HeNe laser, seen in the foreground, is focused onto an 8 micron pinhole located at the infinity focal position of the Slevogt. Thus, light is collimated by the Slevogt into parrallel rays and is then focused back to a point (we hope) by the Newtonian. In this way, null testing of the optical system can be accomplished, in the garage, without the use of a distant point source. The usual tests are performed on the optics, namely, inspection of the in-focus and extra-focal images, knife edge testing, and Ronchi testing. In addition, the rear plate of the Slevogt with two sets of three collimation screws can be seen. |
 | This image better shows the two telescopes back to back for testing. The Slevogt is sitting on a large work bench and the Newtonian is sitting on a table saw. Various books and magazines are used underneath the telescope to adjust the vertical location of optical axes. |
 | This image shows the little area in the garage where the mirrors and corrector were ground and polished. The ceiling in this area was lined with 4 mil plastic sheet and then sheeting was dropped from the ceiling to the floor, like a make-shift shower stall. In the background, shelves can be seen with various ATM materials including a plaster and tile tool and various laps. The lap on the round grinding stand is for corrector polishing. |
 | This image shows the vacuum pan used to deflect the corrector into a fourth-order curve. In use, the lip is coated with vacuum grease, the pan, valve and a clear tube (not shown) are filled with water and the corrector plate is carefully placed on top of the pan lip. The pan is then partially evacuated using lung power while the central deflection of the plate is monitored by a spherometer (see next image). The corrector plate surface, under deformation, in then ground and polished into a very long radius sphere. |
 | This image shows the spherometer, sitting on a 10" calibration flat, used to measure the deflection of the corrector plate when under partial vacuum. The dial indicator is moved amongst various large and small spherometers in the various phases of making the primary and secondary mirrors. The 1/2" thick aluminum plate shown in this image was rough cut from salvaged material. On the underside of this plate are three 1/4" ball bearings on a 9.25" diameter circle. The indicator currently reads 100 microinches convex. In the background is an unfinished CB CCD camera in a machined aluminum housing. Wires and vacuum lines protrude for testing. |
 | Another love of mine is woodworking. Shown are two of the many boxes that I have made. Rare wood burls are combined with solid, figured hardwood sides for a nice look. A box like these will eventually hold the medium format camera back, film, focusing devices, and accessories needed in the field for astrophotography. |
Thanks for taking a look.