First light for my WO RedCat 51

After a couple of weeks of trial and error with rails and counterweights, I took my William Optics RedCat 250/51 mm telescope out for some first light images with the Sony a7iii. Conditions were typical under the Austin light dome, with occasional thin high clouds that ate about half my images. I was also photo-bombed by a train of satellites running through Orion. Mounting the telescope and camera, finding and framing my first target went smooth as can be. I then made a rookie mistake and balanced my rig spot on for the driven RA axis. I spent most of an hour trying to find the source of the tracking errors, before sliding my counterweight over to consistently take up the gear backlash. By then the Pleiades’s were loosing contrast and I switched to Orion.

I was getting cold so I set up to shoot a quick sequence of 30 second exposures at ISO 6400. The full frame image is vignetted and a bit dimmer in the corners, but stars look good and sharp across the image without noticeable color aberrations. The image below, taken from my home under a Bortle class 6 light dome, compares very favourably to a similar image I took in Terlingua, a Bortle class 1 dark sky site, with a Nikkor 300mm ED lens.

First light with a Williams Optics RedCat 250/51mm telescope and Sony a7iii. 28 minutes total of 56 30" exposures at ISO 1600. Bortle Class 6 light dome with fair transparency. Stacked in Nebulosity, with cropping and exposure adjustment in Photoshop.

Many of my exposures showed a train of satellites right through Orion, possibly the SpaceX Starlink satellite constellation. A crop of a typical frame is shown below.

Equipment List

My imaging setup is shown below:

  • Williams Optics RedCat 51 telescope with saddle handle bar
  • WO 48mm to Sony E-mount adapter
  • Sony a7 iii full frame mirrorless camera with I/R remote
  • Davis & Sanford C88 tripod
  • Sky-Watcher Star Adventurer Equatorial Wedge Base
  • Vixen Polarie Star Tracker mount with polar scope
  • Vixen Polarie Multi Mounting Block
  • Sky-Watcher Star Adventurer Dec Bracket with optional SVBONY Dovetail Clamp
  • Sky-Watcher Star Adventurer Counterweight Kit
  • ScopeStuff one pound end counterweight with 6mm threads
  • Optional lithium rechargeable battery with two outputs and mini-USB and USB-C cables for mount and camera
  • Optional intervalometer with micro-USB connection for Sony a7 iii for exposures > 30 sec

Unprocessed image crops

The following crops from a sample 6000x4000 pixel full frame image are unprocessed other than the conversion from RAW to JPEG formatting and cropping:

Center sample image

Upper Left sample image

Upper Right sample image

Lower Left sample image

Lower Right sample image

Content created: 2019-12-23




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