Hello!! It's Joseph

Some ATMers on CN are planning to make fast sub-f/4 Newtonians to hyperbolic. Eg   Chantepierre  8 inch f3.5 he is aiming 203mm f/3.5,  cc -1.32,  fl: 720+/-4mm Tommm planning on a 8 inch f3.7 with cc -1.305 Same time they are waiting Ed Jones to calculate for them the expected conic constant, ie cc At first sight, it seems they are using some unknown formula Later on, it's found they are actually referring to this earlier post: Hyperbolic primary w baader coma corrector   from Ed Jones Mike provides a very useful chart to pair with Rosin corrector in this other post Refiguring a 10 in parabolic newton  to hyperbolic  Davidc135 in this post :  The primary's hyperboloid figure must provide  to balance the known under-correction of the Baader MPCC  III , which will be equal to; 0.81 x (4/f#)^4 So, at f4 the conic of an 8'' primary needs to be around -1.29 to produce 0.81 waves but at f3 the 0.81 becomes 2.56 waves SA and the req...

spec: Primary mirror: 200 mm, coated 197mm, 1.9 kg， glass thickness 27mm mirror with cell: 2.8 kg primary mirror: focal ratio: f/4 mirror to inner wall 13.5 mm mirror face to back of tube : 50 mm secondary: 63mm nom. (minor axis). Minimum required is 54 mm tube 230 mm outer OTA: 8.5 kg, including lock rings and dovetail, length 730mm nom. as 100% illumination is around 9.3mm, this configuration is mainly for visual. of course won't stop you to go  for astrophoto, with appropriate sizing of secondary, eg 73mm(minor axis)    The mirror has some minor polishing marks at 70% radius, at r =14 cm, width 1 cm i guess those are left behind from figuring it to parabola Slight hill at centre, radius 5 cm coating is a bit opaque, guess it is over 20 years ago. 80 to 85% reflectivity Focuser: JMI 2 inch, with motorfocus , jmi2 secondary holder:   collimation: not easy, but do-able first make alignment by visual, then use the laser collimator. btw it's a test of laser colli...

 In 2009   Anthony Wesley and Phil Miles, and Christopher Go independently discovered the impact. Anthony used his homemade newtonian telescope to observe the moment of impact on Jupiter Anthony's equipment: 14.5" mirror f/8 Focal length: 1.8m Queensland, Australia Interview   10 questions Archive Cloudynights   CN2

From cosmoquest In a Newtonian telescope, a parabolic mirror is usually used, since that surface focuses light from infinity to a nearly perfect on-axis image. Some telescope manufacturers (and a few amateurs) substitute longer f/ratio spherical mirrors, since they may sometimes be easier for some people to figure and test rapidly. However, if the f/ratio isn't long enough, the performance (especially at high power and for planetary viewing) may suffer. One way to rate telescope mirrors is by seeing how much their surfaces deviate from a perfect parabolic shape. One common rule of thumb states that the telescope's optics must not produce a wavefront error of more than 1/4 wave in order to prevent optical degradation. This requirement is sometimes extended somewhat to require that the mirror's surface must not deviate from a "perfect" paraboloid surface by more than an eighth wave (approximately 2.71 millionths of an inch) in order for the mirror ...