M51, Whirlpool Galaxy 04-15-17

This object is not a new one to me, or to any visitors to this site. If you have a telescope then you have probably looked at this galaxy colliding with another creating a spectacular view in images. This galaxy and it’s dance partner are roughly 23.16 million light years away in the constellation Canes Venatici. The larger galaxy is Messier 51, also known as the Whirlpool Galaxy, while the smaller galaxy it is colliding with is cataloged as NGC 5195. Discovered on October 13, 1773 by Charles Messier.

I recently purchased a used Celestron 8″ Schmitt-Cassegrain Telescope (SCT). This is a whole new beast to me in the world of astronomy since I’ve only ever used Newtonian Reflectors as my viewing and imaging source in the past. This, however, was my very first time imaging with this telescope although I’ve had it for over a month at this point.

This telescope has a focal length of 2300mm (Newtonian was 750mm), so I get a more magnified view of objects. The downside of this telescope is that it’s a bit “slower” than the Newtonian. The Newtonian had an aperture of F/5, meaning it allowed more light making objects appear brighter in a shorter amount of exposure time. The Celestron SCT I purchased has an aperture of F/10, so images need a much longer exposure to collect photons from deep space images. This telescope is typically used for planetary and lunar imaging as the magnification allows a much better view of these objects for visual and imaging purposes.

Considering all that, and the fact that I am using a low magnification guidescope, and that I attempted 5 minute images with a magnification of 86x compared to the 28x magnification I was getting with the DSLR and the Newtonian. I would have to say I am quite pleased with the final results of my first imaging session with the new-to-me telescope. Maybe a bit more tweaking needed for the polar alignment and I will have rounder stars, as you can see with the 5 minute exposures they are a little oblong.

M51, Whirlpool Galaxy in Ursa Major

M51, Whirlpool Galaxy in Canes Venatici (Schmitt-Cassegrain) April 2017

For a comparison, here is the image taken a few years back with the same camera, but connected to the faster, less magnified, Newtonian.

M51, Whirlpool Galaxy in Ursa Major (Newtonian)

M51, Whirlpool Galaxy in Canes Venatici (Newtonian) March 2014

Quite the reduction in field of view with the SCT, but the object being imaged is much larger. Both images were taken with a full spectrum modified Canon 350D, both were a combination of 5 minute images. The SCT was a combination of 10 images at 5 minutes a piece, and the Newtonian was 21 images at 5 minutes a piece. Both shot at ISO 800. Both images contained a set of dark images, but the Newtonian also made use of flat frames, which I did not do for the SCT image.

All in all, I’m extremely happy with the results of this new-to-me telescope, and I really look forward to more clear nights for imaging some of those small objects I never really attempted with my Newtonian telescope. I did purchase a focal reducer for the SCT which would essential turn my F/10 SCT into an F/6.3, but with that aperture reduction comes a reduction in magnification. If I remember correctly, adding the focal reducer would essential drop the 2300mm focal length to somewhere around 1200mm, which is still more magnification than I was getting with the Newtonian, and roughly the same aperture.

Equipment:
Celestron Celestar 8″ Schmitt-Cassegrain Telescope
CG-5 Mount
Canon 350D Full Spectrum Modification
Lin_Guider on Linux Ubuntu for autoguiding
Deep Sky Stacker for image stacking
Photoshop for post processing the stacked image