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I captured these images during a single night from my dining room while the temperature outside was in the teens (F). All images were guided with MetaGuide and off-axis guiding. The seeing was particularly good that night, with fwhm's below 2" in 10 minute sub-exposures. My main planned targets were Horsehead, Rosette, and The Eyes, but I spent some time on M33 and the California nebula as I waited for objects to rise or cross the meridian. The only time I had to go outside was for rotating the OAG to select a pre-planned guidestar, and to take flats with a light box. Since the moon was bright that night, I only took Ha images.
My house is surrounded by trees, so a permanent observatory doesn't make sense. Normally I just image from the south with high trees blocking southern objects, but this setup gives me the flexibility to place the telescope around the house to access different parts of the sky, while controlling from indoors. A key to doing this with a CGE is the new AllStar polar alignment routine, which lets me align even when Polaris isn't visible, as it is here on the north side of the house.
- Horsehead 11x10m, low in south over house
- Rosette Nebula, northern section 9x10m
- California Nebula, section 8x10m, grabbed while waiting for Rosette to cross meridian
- M33 single 10m exposure with 1.5-1.9" fwhm, grabbed before it "set" into tree branches overhead
- The Eyes 15x10m, left imaging unattended from about 1am to 3am. This Ha will be added to LRGB later.
- Optics: Celestron C11 at f/5.7
- Mount: Celestron CGE
- Guiding software: MetaGuide ASCOM
- Camera: Starlight Xpress SXVF-H9
- Filter: Baader 7nm H-alpha filter
- Guiding Camera: Lumenera SKYnyx 2-0M @ 8-20 fps
- Guiding mode: Off-axis guiding with Taurus mini tracker
- Guide Star: Approximately Mags: 5-10
- Image Details: 10m sub-exposures
- 0.85" per pixel
- Raw FWHM: approx 1.5-2.5" depending on altitude
- Image Processing: ImagesPlus, flats, bias, dark subtract. No Photoshop
- Date and Location: Feb. 6, 2009. Hudson Valley, NY.
Dining room observatory, showing CGE outside. Three cables power and control the telescope: A Tripp Lite 36' powered USB cable, a video cable for the video finder, and 12V power. The light box is very helpful for OAG imaging because each change of the OAG angle, for a different object, requires new flats. I built this foam board light box in a couple hours and it has been very effective so far. Since all devices attach through the single USB cable, disconnecting and reconnecting the laptop requires only one plug, and all the USB devices reattach at the same port with no annoying reinstallation.
CGE with power and USB distribution box. The box redistributes power to the devices on the telescope and contains a USB hub to distribute USB. The combination of powered 36' USB cable with the hub works fine. The box also contains two USB2Serial devices to control the CGE itself, via NexRemote, and RoboFocus. I leave it set up in bad weather protected by a TeleGizmos 365 series telescope cover. A Kendrick dew heater prevents dew on the C11 and video finder. I do not use a dew shield to reduce wind buffeting. The trees provide shade from the cold sky to reduce the effect of dew. Note that all devices, including the dew heater, share the same 12V feed from indoors without noticeable interference.
Close up of the modified Mini Taurus OAG, with RoboFocus and Lumenera USB Video camera for guiding with MetaGuide. The angle indicator is critical for dialing in a pre-planned guidestar. The RoboFocus is attached directly to the back of the C11 and allows full 360 degree swing of the OAG and guide camera. Note that there is no spacer on the H9 camera; I shortened the guide port so no spacer would be needed, allowing the guide camera to be closer to the pickoff mirror. This also provides a better f/ratio and less distortion at f/5.7. If I remove the color wheel I will be even closer to the intended f/6.3, and the guide camera has space in the helical focuser to accomodate the inward shift.
Computer screen during acquisition of the Horsehead image. Key applications in use are MetaGuide for guiding, AstroArt for image acquisition with the SXVF-H9 camera and for control of the RoboFocus, and NexRemote for control of the telescope. I use TheSky for selecting guidestars, but without a connection to the telescope. NexRemote connects directly to the CGE through the PC port via a USB2Serial adapter, and MetaGuide guides via ASCOM through a virtual port on NexRemote.
View of the 50mm f/1.4 video finder during the Horsehad acquisition. On the lower left is M42 and on the right are the first two stars in Orion's belt. The finder uses a PC164C video camera. The finder is essential for aligning the telescope from indoors, and very helpful for monitoring sky conditions and the presence of tree branches in the field of view.
Field Of View Indicator (FOVI) in TheSky for selecting guidestar and determining the OAG angle. The target is centered in the main camera rectangle and the ring indicates the area of sky accessible by rotating the OAG. The rectangles show the sizes of the SXVF-H9 and Lumera cameras. Note that with this OAG setup, the main camera can be oriented independent of the OAG angle, so the actual image orientation is N/S. In this case the guidestar is magnitude 10.1, but I was able to guide on it at video rate (8 fps), without stacking, because the star was well focused and the pickoff mirror is close enough to the guide chip that the mirror does not clip off much of the incoming starlight. The use of unstacked video for guidestar centroiding is central to the novel centroiding of MetaGuide. The size and separation of the guide chip must be calibrated, but that only needs to be done once per optical configuration. The angle shown on the guide chip is dialed in directly on the OAG, so that when the object is centered on the main camera, the guide star will appear on the guide chip without hunting. A good alignment of the telescope helps center the object efficiently, and I usually synch on a nearby star.
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