eyepiece/focal length

[jim d]

I have a Nexstar6se with a focal length of 1500mm i have eye pieces of 6mm,7.5mm,8mm,13mm,17mm,25mm,32mm and a barlow lens.Can someone explain in laymans terms what these ep will do,which is stronger and are some better than others for veiwing planets,stars,etc...This is all brand new to me.Everybody thanks

[John]

To find the magnification divide the focal length of the scope (1500mm) by the focal length of the eyepiece. Eg: the 13mm eyepiece will give 115x magnification and the 6mm will give 250x.

The barlow lens is probably a x2 in which case it effectively doubles the magnification given by each eyepiece so the 13mm eyepiece + 2x barlow = 230x.

With a 6 inch scope, under the usual viewing conditions we get in the UK 250x is about the maximum useful magnification.

Lots of viewing is done at low to medium magnifications so you could use your 32mm, 25mm and 17mm eyepieces for that.

Magnification is NOT the main purpose of an astro telescope though - light gathering is the key, which is why the aperture (diameter of the main mirror or lens) of the scope is the most important factor.

Hope that helps.

[Capricorn]

Magnification is simply (Scope focal length)/(Eyepiece focal length)

However your scope is f/10: Focal length)/(Diameter)

A 10mm eyepiece will perform the best.

Many opinions on how big a magnification you can go, I tend to go for the conservative side and would say that you might manage 225x (1.5xDiameter in mm) but once in a blue moon.

1.25xDia will be possible more often so that makes 180-190x magnification.

This means the 8mm is your smallest generably usable eyepiece.

You may therefore be able to use the 7.5 occasionally and the 6mm less often. The set does not have a 10mm and a 12mm which would also have been useful.

For locating you will use the 32mm otherwise the field of view could easily be too small.

[Demonperformer]

Hi Jim.

I have the 6SE and have 5, 10 and 14 mm eyepieces for visual work. The 14 & 10 are used 90% of the time, with the 10 probably edging out the 14 marginally.

If you are getting good views with a particular eyepiece, it is worth trying the next most powerful (shorter), but always be willing to go back to the less powerful one rather than struggle to see detail at the higher power.

HTH