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MAS Frequently Asked Questions

MAS FAQ

MAS Frequently Asked Questions

Frequently Asked Questions about astronomy (see also MAS Beginners page)

This page answers many commonly asked questions about astronomy. If you have a question on a subject any not covered here, please help support this page by using our on-line enquiry form (requires Java Script to be enabled).

Much of the material here has been taken from topics presented at out monthly meetings. If any member has subject they would like to present for 15-20 miniutes as a 'second half' topic, please contact the Meetings Secretary (to contribute directly to this page, please contact the Webmaster

(+) 0001 How do I find a local Astronomical Society ?

(+) 0002 How is Star brightness measured ?

(+) 0003 What are the Constellations ?

(+) 0004 What is the shape of the Earth ?

(+) 0005 What equipment do I need to start astronomy ?

(+) 0007 What telescope should I buy ?

(+) 0008 How much Magnification can I get ?

(+) 0013 What are Equatorial and Alt Az mounts ?

(+) 0100 How do I use my first telescope ?

(+) 0109 What is a finder ?

(+) 0110 What is an eyepiece ?

(+) 0111 What is a Barlow ?

(+) 0112 What is a focal reducer ?

(+) 0114 What are Nebular filters ?

(+) 0116 How do I use Setting Circles ?

(+) 0120 What is collimation ?

(+) 0125 How can I safely observe the Sun ?

(+) 1030 How can I take photos of the stars ?

(+) 1033 How to take photos of the Aurora ? - (Northern Lights)

(+) 1035 How to calculate FOV for prime focus ?

(+) 1036 How do I calculate FOV for Eyepiece projection ?

(-) 1037 How do I use a Raspberry Pi camera for astrophotography ?

Using the Pi camera for astrophotography

The Pi NoIR camera extends it's sensitivity into the near-IR region (700 - 1000nm) region (so it can  act as a CCTV security camera). More to the point, removal of the IR filter increases sensitivity by up to 70% in the deep red hydrogen-alpha (Ha) region (656.3 nanometers).

A Pi Zero + camera board will fit into a 0.1L 'Really Useful box (just) and an old 35mm film canister case used as the eyepiece.

The FOV depends on the focal length of the telescope and if the Pi camera lens is left on (which is equivalent to 'eye piece projection' mode  = see MAS FAQ 1036) or not (which is 'prime focus' mode, see MAS FAQ 1035).

For comparison, a fulkl Moon covers approx 0.5 degrees

Raspberry Pi Cameras (from Elinux.org/Rpi Camera Module) ==================== 5 Mpixel version 1.3 1/4" sensor (3.67 x 2.74 mm ), 65 degree field of view, F2.8 Lens (nice and fast!), Pixels, Count: 2592 x 1944, Size: 1.4 x 1.4 um Lens: f=3.6 mm, f/2.9 Angle of View: 54 x 41 degrees Field of View: 2.0 x 1.33 m at 2 m (in focus, 1m to infinity) Full-frame SLR lens equivalent: 35 mm Max. exposure time (standard drivers) 6s. Max. ISO (standard drivers) 800.

The lens is locked with 3 glue dots in the threads. This can be scraped off allowing manual closer lens focus. For focus at  F cm, unscrew the lens (turn counter-clockwise) by D degrees, where D = 360 * (3.5 cm / F). For example, for 10 cm focus, unscrew lens 360 * (3.5 / 10) = 126 degrees. The closest achievable focus is about 2.5 cm (1"), which requires unscrewing the lens roughly 2 full turns, at which point it's so loose it must be held in place by other means.

8 Mpixel version 2.1 Sony IMX219PQ[7] Color CMOS 8-megapixel Sensor size: 3.674 x 2.760 mm (1/4" format) Pixel Count: 3280 x 2464 (active pixels) 3296 x 2512 (total pixels) Pixel Size: 1.12 x 1.12 um Lens: f=3.04 mm, f/2.0 Angle of View: 62.2 x 48.8 degrees Full-frame SLR lens equivalent: 29 mm Max. exposure time (standard drivers) 10s.
This note last modified: 5th Feb 2017 17:28.

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MAS Frequently Asked Questions