purpose of spider vane ?

MooEy · Post by **MooEy** » Mon Sep 13, 2004 7:54 pm

has to do with on-axis and off-axis. if one were to connect the fast newt scope directly to a camera and take a shot of a star field. one will notice that at the middle of the photo, the stars will be nice and sharp. but as u move away from the center of the photo and towards the edge, stars will star to turn into little seagulls.

most optics are design for maximum performance on-axis. in a newt, coma starts to come in when u goes off the axis. in a high power eyepiece, u are looking at the very center of the "image circle", when u use a low power eyepiece, u get to see the edges of the "image circle", thus u see coma at edges of a low power eyepiece.

~MooEy~

Kamikazer · Post by **Kamikazer** » Mon Sep 13, 2004 9:13 pm

so good optics and excellent eyepieces for wide field viewing is the only way to reduce coma without using coma correctors?

btw do diffraction spikes affect extended light sources?

Post by **weixing** » Mon Sep 13, 2004 9:37 pm

Hi,

so good optics and excellent eyepieces for wide field viewing is the only way to reduce coma without using coma correctors?

From my experience, it does help.

btw do diffraction spikes affect extended light sources?

It only affect bright stars... most DSO are not affected at all.

Check below website if you are interested in getting more information about coma: http://www.opticalmechanics.com/about_coma.htm

Have a nice day.