The Second Half of Life: April 2014

Tuesday, April 15, 2014

2014 imaging plans

Entering a new season of better weather in the Pacific NW, I'm now prepared to try to out-perform last years efforts at imaging deep space objects. For my Celestron C8 SCT (1992 version), I've purchased a new Off-axis guider (OAG) and a new, smaller, more sensitive guide camera with the hope of eliminating many of the guiding issues I've had with a separate 50mm guide scope. The OAG unit is the lastest Celestron version and it appears to be very good quality... much more solidly built than the Orion Deluxe OAG I had previously (and broke!). The new guide camera is a Starlight express "Lodestar" (monochrome), which comes highly recommended by my peers at RCA, with small size and good sensitivity. When I tried to use my SBIG ST-402 camera for OAG, I found that there was too little room left over between the camera and the back of the scope.

I use a reduce/corrector on my C8 to shorten the focal length and flatten the field. This requires that I get about 105mm spacing between the reducer/corrector and the imaging CCD. Fitting the pieces together, I find that, with no additional spacers, the distance comes out nearly perfect (104.5mm). I'm going to need at least one practice session where I determine the right distance to achieve focus with the Lodestar and to determine the optimum adjustment of the pick-off mirror into to the incoming light (keeping it from going to far into the CCD's field). Finding undistorted guide stars is the big concern, but the new camera and the adjustability of the OAG should help.

Due to the fragility of the ST-4 cable used to connect from the camera directly to the mount, I've been advised to instead guide through ASCOM directly from my computer. Though I've played with this a little before, it's going to be a new learning curve. I'll also experiment with guiding via Maxim DL.

If I can't get clean enough guide stars, I may need to consider upgrading my SCT to a new "Celestron EdgeHD 8", to get a flatter field. In the end, will this be the secret to better guiding or will I find that the variables I've eliminated (mirror flop and differential flexure) were never a big part of my problem? If the latter, I may have to consider getting a new mount.

Late May will likely be my first good window of opportunity to use the new setup under good conditions (clear skies, no dew and decent temperatures).

April 14-15 Lunar Eclipse

The first of four dreaded "Blood moons" has passed and my experience was that it wasn't very bloody, except when I imaged it. While I entertained the idea of going to a more remote location to view this eclipse, the weather reports influenced me to stay local. Though those reports weren't great, they weren't that much worse than other places. I ended up watching from my backyard and, while I did see the eclipse begin and enter totality, heavier clouds came in and kept me from seeing the end of it. Though there was visibility, it was poor because here was a thin veil of clouds throughout.

I started out trying to image it using my Nikon D40 with just my 200mm telephoto lens. I ended up switching to using my Nikon D40 mounted to my Orion 80mm refractor. I ended up wishing that I had used only the telescope from the beginning. Because of the conditions, I wasn't able to set the telescope up such that I could track the moon (no polar alignment), so I had to keep it in the field of view manually. None of the images are anything to brag about. My key learning was: Don't even try to image a total eclipse if you don't have clear conditions, and if you do have clear conditions, use a telescope with tracking so that you can use long enough exposure times to get the best quality image.

Visually, I didn't see any red through a lens on the telescope. Only the CCD imaging brought that out. I would be interested to hear what color people saw with the naked eye under clear skies.

Here are some of the images: