By James Vincent
Wednesday 13th October 2021
23 members present and 12 virtually, make 35 in total.
Mike opened the meeting and asked if there were any club notices.
Jim said the clubs 12 and 8 inch Dobson telescopes are available for use and members should contact him if they are interested in borrowing them.
Mike introduced Chris Jones who is giving his talk virtually via zoom called “Large telescopes – a blessing or just a pain in the observatory?”
Chris opened his talk talking about the huge variety of telescopes on offer and started with refractors, he then went on to discuss reflectors and finished with catadioptric giving the pros and cons of each.
He said that one on of the biggest issues in using a telescope is the focal length, fast telescopes have a focal ratio of 5 and below make friendly easy to use telescopes but they do have their problems.
Chris then went on to discuss different types of mount including Equatorial, Fork and Dobson mountings.
The effects of the atmosphere, collimation and age of the observer all have a bearing on the limiting magnitude of a telescope as does the size of the telescopes main optic. Chris presented a graph showing telescopes resolving power and light grasp compared with cost. He said that taking all things into consideration a 10inch reflector is probably the best compromise giving the best optical performance and ease of use for your money.
Housing the telescope could be a big problem if it is very big, Chris spoke about his experiences with a big telescope housed in a dome and how his head got trapped between the eyepiece and the dome, and how he wished the observatory was much bigger!
Chris is a variable star observer and he showed us the light curves of two novas V1678 Her and a very peculiar nova V1505 Cas, carefully explaining what was going on.
The data for the curves were gathered by him using his 18inch NGT Dobsonian telescope.
He then finished of the session by taking questions from the members.
What a very interesting Night we had.