Wide+field+camera

=__Overview__=

The Wide Field Camera is installed in the Run-off Roof Observatory. Outline requirements are listed below.
 * The wide field camera will be used for supernovae searches to support the 20 inch telescope in the dome and for public outreach remote access.
 * The telescope and mounted in equitorial mode to allow for longer exposures without field rotation.
 * Wide Field Camera Autoguiding
 * Wide Field Camera Autofocus
 * The telescope is a composite instrument with a focal length of 407mm according to ACP (That makes it around F1.6 with the nominal 250mm objective)
 * The observatory will be a simple Run-off Roof Observatory fully automatic with Observatory Auxiliary Control.
 * The observatory will link into the exsiting Observatory control room and weather station
 * The telescope services from the main control room will be a 240V mains supply, Ethernet link and a cable for linking into the weather station
 * ACP will be used to schedule observations

See Run-off Roof Observatory documentation for documents and drawings relating to the telescope and run-off roof observatory.

See also the newly installed (October 2010) Wide field camera flat field light box

=__Telescope and mount__=

The telescope is a very short focal length instrument and is ideally suited to wide field imaging. The only issue being that the CCD camera must require very small pixels to get a usable image scale on sky.

The telescope is mounted on a Meade LX200 GPS mount that originally housed a 16 inch RC. It has undergone modifications (April 2010) to mount it in equitorial mode, install axis limits and modify the central cable connector inside the fork to allow additional cables to run through. This will prevent 'wind up' and snagging of cables that originally where going to be 'dragged' around the mount.

Some details of internal mount wiring is here: Meade Mount RCX400



Images shown below are of the telescope on its concrete wedge in the dome in June 2010. The telescope is now nearly ready for observations after extensive modifications to the observatory run off roof control system. The only thing that will change over the next few months will be the focuser and CCD camera. The camera installed for testing and early observations is the Starlight Xpress MX716.

Magnetic reed switches (in white) can be seen on theAzimuth and Altitude axis. There are 2 axis limits for Altitude (upper and lower) and 1 x parked switch. The Azimuth axis has 1 parked switch and 1 axis limit switch. The telescope can slew +/- 180 degrees from its parked position of 180 degrees Azimuth (i.e. cannot track/slew through North). The roof will close if any axis limit is activated. The roof will close if 'both' parked switches are activated.

Status of the parked and axis limit switches can be seen using the Observatory Auxiliary Control application.



=__Mount modifications__=

The mount required some modifications due to the instrument mounted in it and also to allow for cables to pass through the azimuth bearing rather than be 'dragged' around the mount.

The image below shows the Azimuth central boss being 'opened up' to allow for additional cables to be routed through the central bearing.



The original idea was to have the telescope AltAz mounted. The thinking behind this was that exposure lengths would be very short for the type of work it would be doing. But, if there was a requirement to do longer exposures or mosiacs for education etc, then equitorial would be a bettre option. All we had to do was make a concrete wedge. Additional images of making the wedge can be seen under Run-off Roof Observatory Construction



Other modifications include magnetic switches for 'Park' and 'Ultimate limit' position. These are wired back to the control panels and USB inputs.

The 'Park' switches on Altitude and Azimuth will close the roof when both are made, and open the roof when either one is not made and the weather is ok. =__CCD Camera__=

The CCD finaly selected and now installed is the ATIK 320E []


 * Sensor Type || CCD - Sony ICX274 (datasheet) ||
 * Horizontal Resolution || 1620 pixels ||
 * Vertical Resolution || 1220 pixels ||
 * Pixel Size || 4.40µM x 4.40 µM ||
 * ADC || 16 bit ||
 * Readout Noise || 3 e- ||
 * Interface || USB 2.0 High Speed ||
 * Power || 12v DC 0.8A ||
 * Maximum Exposure Length || Unlimited ||
 * Minimum Exposure Length || 1/1000 s ||
 * Guide Port || ST-4 compatible ||
 * Cooling || Thermoelectric set point with max ΔT=-25°C ||
 * Backfocus Distance || 12mm ||
 * Thread on front of camera || T-Thread (M42x0.75) ||
 * Dimensions || 110mm diameter, 53mm deep ||
 * Weight || approx. 350 gr ||

Other CCD options considered were:-

CCD may be a SXV-MX8C [] Small (3 micron) pixels will be required to achive the required resolution (2 arc/sec/pix) This will provide approx 1 degree field (based on test results with the MX7

The Opticstar Opticstar DS-335C ICE []

These cameras were not selected for different reasons. Colour was deemed unecessary and the Opticstar was going to be difficult to mount.

A test image against the CCD calculator is below. M51 was the target and was only 20 seconds with the MX716

The image below shows the rear of the telescope. The focuser and CCD camera (MX716) has now been replaced with a an Atik 320e (October 2010). The focuser has one limit switch to prevent overtravel of the focuser in either direction. Minimal movement is required only duetothe fast optical system. Focus is very fine and difficult to achive by hand. The motor may be controlled via the Observatory Auxiliary Control application. Image below has been left for archive only.



The images below show the newly installed (October 2010) Atik 320e. The focuser is a Bespoke unit made from 'bits and bobs'. The depth of focus of the telescope is TINY!

Limit switches have been installed to prevent over run. A model aircraft servo is used with a belt drive for focus. The focus is controlled from the Observatory Auxiliary Control screen.





Below is our first 'Calibrated' image of 10 x 60 sec of NGC 7331 with the new Atik 320e camera. The light box seems to work quite well. Some tweeks are still needed, but the image is not bad. Quite a large field of view. Stephan's Quintet can be seen lower right. The camera gives 3 arc/sec/pix resolution and around 1 degree field of view. Focal length 300mm at F1.2.