Long spells of dull weather between these rare clear nights but it looks like an all-night session tonight. I thought I'd have a bash at M33 the Triangulum galaxy, named because it is in constellation called Triangulum. It is a face-on spiral with low surface brightness.
This means one needs some really long exposures to capture it in full glory. I am using my Canon DSLR at prime focus on a 6" achromatic refractor. A feature of refractor telescopes is that red, green and blue light comes to focus at different points from the lens. This means if you focus on green then you may see blue, red or violet fringes around bright stars. An Achromatic refractor goes some was to reducing this effect, known as chromatic aberration by introducing two lenses (doublet). Also the choice of glass, e.g. crown and flint with differing refractive index. More recently a new type of refractor has been introduced called an apochromatic that has the newest and highest quality of glass yet known. It may also be a triplet lens (three lenses in combination).
Also on the agenda tonight is M45 or the Pleiades and also known as The Seven Sisters. As mentioned before this cluster is a good test of eyesight. Typically 5-7 stars can be seen by
the average naked eye. There are in fact at least 500 stars in this cluster. The aim in photographing this cluster is to capture some of the nebulosity that still surrounds some of the stars as they awake from their cocoon. Again long exposure is required but this leads to saturation on the main stars. Here is my best attempt so far but still leaves a level or more to aim for.
