I have had cloud, light drizzle and now snow. With many roads impassable due to black ice, your heart sinks as this rubbish just keeps going and going – and then, amazingly a sunny day and a whole clear night, frosty but clear; I can live with that. So I decided to change the telescope over to the 8inch RC ( a reflecting telescope ), with a longer focal length. You get more magnification imaging at a focal ratio of f8, let me explain – focal length is the distance light has to travel after going through a lens or bouncing off a mirror before it comes to focus, focal ratio is a function of lens or mirror focal length in mm divided by its aperture in mm, so for my 8 inch RC with a focal length of 1625mm and an aperture of 8 inches you get 1625mm devided by 203mm equals 8 ( called f8 ). My William Optics megrez 72 on the otherhand has a focal length of 430mm and an aperture of 72mm giving f6. This means that the WO72mm has a wider field of view than the 8inch RC, so a lower f ratio has a wider and brighter field of view than a higher f ratio which has a narrower and darker field of view and for my targets last night I wanted a smaller field of view with more magnification.
I got everything set up and running nicely, guiding all good, plate solving just fine and the planetarium software synchronised with the mount, my first target was M1, the Crab nebula in Taurus, this is a supernova remnant that was first observed by chinese astronomers in 1054AD who called it a “guest star”. I captured 30 x 180 second exposures in all three narrowband filters, Ha, OIII and SII for a total of 4.5 hours exposure. I have a 2 inch manual filter wheel at the moment, so I had to rotate the carousel to the next filter each time a run was finished and it was cold -5°C by the time the SII was used. I couldn’t be without a warm room now, even the cat came in and stayed in for the rest of the night.
Then I changed to the Neodymium filter as I wanted to capture 2 galaxies in Ursa Major, M51 the whirlpool galaxy and to get a closer look at M101 the Pinwheel galaxy, again I used 30 x 180 second exposures. This only gives monochrome ( greyscale ) images, however these greyscale images can be used later – added to a colour ( RGB ) image as a luminance layer to give detail to the image.
In my last post, I mention anti-dew heaters and the anti-dew ring on the end of my ZWO asi 1600mm Pro camera,I got this add on heater because my sensor chamber window would every now and then get condensation building up on the outside of the window ( as the sensor is cooled to -20°C this comes as no surprise ), the inside of the chamber is sealed and has 4 desicant tablets inside and does not get condesation, this is a single image to show the effect this has on the captured frames.
It has since turned cloudy again, but for now – I’m happy.