Slevogt Camera OTA and OAG

OTA and OAG

The following text and images describe the optical tube assembly (OTA) and off-axis guider (OAG) portions of the Slevogt Camera.

This image shows the new OTA for the Slevogt. The open truss structure has three baffle rings strategically placed to block all undesired sky light. The trusses are 1/2" diameter thin-walled aluminum tubing, intentionally made vary light to reduce the moment of inertia of the OTA and to minimize wind loading on the scope. The white tube is a graphite-epoxy composite with two internal plywood end rings used for mounting the truss and the rear plate. The corrector plate is mounted on the upper end of the truss in a 1/4" rabbit. The secondary spider attachment screws can be seen near the upper end of the tube.

This image shows the rear view of the telescope with the Hassy 12 back and ST-4 in working position. The three nuts on the aluminum plate are for collimating the primary mirror. The OAG is comprised of a helical focuser (closest to the aluminum plate), a rotation stage and the main body, which holds the film back and the autoguider. The ST-4 is mounted in a drawtube which contains the pick-off mirror. This tube can be moved in a radial direction for greater ease in finding a guide star.

This is another view of the rear of the scope showing the OAG without the film back and autoguider. The thumbscrews closest to the aluminum plate are used to lock the helical focuser during an exposure. Nylon inserts are used in the threaded holes to prevent the fine focusing threads from being damaged The other knurled screws have nylon bodies and are used to lock the rotation stage of the OAG.

This close-up view of the camera interface shows the two small custom pieces that were made to replicate in function a Hasselblad camera body. Each piece was carefully shaped so that the back is firmly attached to the OAG when in use. On the far right one can see the two thumbscrews that lock the drawtube in place, and a third screw that prevents drawtube rotation.

This image shows the drawtube and pick-off mirror. The 0.5" minor-axis diagonal has been epoxied to a 46 degree bracket which in turn is screwed and epoxied to the drawtube itself. The drawtube has a wall cutout to allow light from the guidestar to reach the mirror. The bracket is 46 degrees (not 45) to minimize coma as seen by the autoguider. In fabrication, the mirror was carefully aligned using a laser and held in place with masking tape while the epoxy cured. The two thumbscrews secure the ST-4 during exposures, and a milled slot (not shown) prevents the drawtube from rotating in its housing.

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	This image shows the new OTA for the Slevogt. The open truss structure has three baffle rings strategically placed to block all undesired sky light. The trusses are 1/2" diameter thin-walled aluminum tubing, intentionally made vary light to reduce the moment of inertia of the OTA and to minimize wind loading on the scope. The white tube is a graphite-epoxy composite with two internal plywood end rings used for mounting the truss and the rear plate. The corrector plate is mounted on the upper end of the truss in a 1/4" rabbit. The secondary spider attachment screws can be seen near the upper end of the tube.
	This image shows the rear view of the telescope with the Hassy 12 back and ST-4 in working position. The three nuts on the aluminum plate are for collimating the primary mirror. The OAG is comprised of a helical focuser (closest to the aluminum plate), a rotation stage and the main body, which holds the film back and the autoguider. The ST-4 is mounted in a drawtube which contains the pick-off mirror. This tube can be moved in a radial direction for greater ease in finding a guide star.
	This is another view of the rear of the scope showing the OAG without the film back and autoguider. The thumbscrews closest to the aluminum plate are used to lock the helical focuser during an exposure. Nylon inserts are used in the threaded holes to prevent the fine focusing threads from being damaged The other knurled screws have nylon bodies and are used to lock the rotation stage of the OAG.
	This close-up view of the camera interface shows the two small custom pieces that were made to replicate in function a Hasselblad camera body. Each piece was carefully shaped so that the back is firmly attached to the OAG when in use. On the far right one can see the two thumbscrews that lock the drawtube in place, and a third screw that prevents drawtube rotation.
	This image shows the drawtube and pick-off mirror. The 0.5" minor-axis diagonal has been epoxied to a 46 degree bracket which in turn is screwed and epoxied to the drawtube itself. The drawtube has a wall cutout to allow light from the guidestar to reach the mirror. The bracket is 46 degrees (not 45) to minimize coma as seen by the autoguider. In fabrication, the mirror was carefully aligned using a laser and held in place with masking tape while the epoxy cured. The two thumbscrews secure the ST-4 during exposures, and a milled slot (not shown) prevents the drawtube from rotating in its housing.