New Telescope and First Light on the Pleiades

I trust everyone had a Merry Christmas and looking toward the new year.  After 2016's horrible weather conditions I'm praying for some better sky conditions this year.

Wifey got me a new 4" APO for Christmas.  For those of you who have no idea what an APO is, here are the basics:

APO = Apochromat, which means a lens that has better correction of chromatic and spherical aberration than the much more common achromat lenses.  OK, still a bit too scientific.  It boils down to a lens that produces sharp, crisp images with very little color aberrations. In telescope jargon, when someone talks about an APO they are referring to a refractor telecope that contains an APO lens combination. These are quality instruments and typically cost a lot more than the simple achromat versions.

William Optics GT102 f/6.9 APO

So my new addition is a William Optics GT102, a 102mm (4") APO scope.  I added the iOptron telescope mount to make this a complete, portable astrophotography-ready telescopic. 

iOptron iEQ30

Unlike a reflector telescope which reflects light off a large mirror (like my EdgeHD11) a refractor focuses light much like a very large telephoto lens does on a camera.  There are many pros and cons between a reflector and refractor, but typically, the refractor produces much cleaner, sharper images, with a bit more contrast than the SCT like my Edge since it doesn't have any obstruction in the light path like the SCT does due to the secondary mirror.

Now this new scope has a 4" objective lens. My EdgeHD-11 has an 11" mirror. The Edge will collect about 7.5x more light, but is also huge and bulky. It will outperform the APO on planets, the moon and small deep space objects like galaxies and small nebulae, as it's long focal length, combined with the extra light gathering, allows some high magnification factors. The APO is much smaller, light weight, and portable. It's shorter focal length and clear optical path produces nice wide angle views of the night sky.

It took a few days to get everything working correctly, and I still do not have all my software working with the new mount yet, but I was able to take a couple of images to test out the capabilities of the new scope and the mount. 

The following image show the Pleiades star cluster taken with my Canon50D attached to the GT102 with telecompressor and field flattener. This reduces the focal ratio to a fast f/5.5.  The image is a combination of ten, 1 minute exposures, stacked and processed in PixInsight.  Not bad for a quick test run. And the really big deal is that this image was taken without active guiding - just the mount running the RA axis!  The star images do show some trailing in RA, which may be due to periodic error (which I can correct for once I get the system shaken out).

Pleiades star cluster (Dec 29, 2016)
William Optics GT102; Canon50D
10x60sec ISO1600

I haven't imaged with my QHY10 astro camera yet.  I've also ordered some additional equipment to allow me to mount the GT102 on my CGEM mount, that holds the Edge. 

I've had some people asking about why you stack multiple images in astrophotography.  Well, that is a complicated discussion, so I'll save that one for a later blog.  But to demonstrate in a simple way why this technique is critically important in capturing deep space objects, I have uploaded the following additional images of the Pleiades as a demonstration.

The first image is a single frame from my camera; a 60sec exposure at ISO 1600. Since it is captured via my astro software, it is not yet debayered (the color is not present yet).

Single 60sec exposure - no debayer

 The second image is the debayered version.

Debayered version

The third image shows the result of post-processing with PixInsight to remove background sky light (light pollution effects) and to stretch the image, essentially pulling out the weak signal contained in the image. The stretch is the real magic in the post-processing.

Single 60sec exposure - post processed

This image is actually pretty good, but it has a lot of image noise caused by the camera's heat, the sensor electronic noise, etc. So the technique of stacking multiple images is used to reduce this 'noise'. Again, a discussion of how this works is left to a future blog. But, you can see that the stacking of just ten images really reduces the noise in the image, which allows me to stretch the image even more, bringing out more of the faint details. I usually stack 30-40 images minimum, but this was just a quick test of the new equipment.

The WO GT102 produces excellent images, and I am excited about what I should be able to produce with this new scope in the future.