TELESCOPES

15

EYEPIECES -
BARLOWS
EYE RELIEF
TYPES

Cont'd.

Whenever extra glass is put between the image and the eyepiece, some of the light is reflected, so a Barlow does dull an image slightly and there is more glass to look through which may decrease the resolution of the image ever so slightly.

Some Barlows cannot be used for anything more than splitting double stars. These are the ones which come with small refractors. If a standard F/12 refractor were to use a 2x Barlow, this would make it a F/24 focal ratio. This would have a extremely narrow field of view making it almost

TELESCOPE LINKS:

Basics

Mounts

Light Gathering Power

impossible to use. If using a Barlow at these high

magnifications

you need

Closer Look At Refractors

a large amount of patience! Try starting with a low magnification first then build up. Using a 2x Barlow will half the light being double magnification.

Closer Look At Reflectors

Dimensions

Balancing

Eye Relief

How close your eye has to be to the eyepiece is determined by how much eye relief it has. Generally the longer the focal length of the eyepiece the better the relief. Some eyepieces are so bad and unsuited to a telescope that it seems you must put your eye right inside the eyepiece just to see all the field of view. Eye relief can be improved by manufacturers by changing the optics in the eyepiece usaully by adding more lenses. Of course this makes the eyepiece more expensive and owners of telescope can use a Barlow instead.

Cleaning

Tips

Astrophotography

Build your own telescope

Build your own telescope
for schools

Binoculars

Types of Eyepieces

There are many different designs for eyepieces, some old and some new. The standard 1" eyepieces which come with most telescopes are 2 glass

focal length

element Huygens. You can tell usually by a 'H' next to the

of the eyepiece.

For wide field, low magnification, Kellner eyepieces which have multiple elements are popular and affordable around $90.

For the planets and Moon the ever increasing popularity of the Plossl is the best choice. These eyepieces have good colour correction, wide fields of view and long eye relief. They cost around $120.

If you wish to pay more than $120 for a better quality eyepiece, with even wider fields of view and better colour correction then there is a vast choice of different types available which can cost up to $700ea! The views given by these eyepieces are awesome.

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TELESCOPES

15

EYEPIECES - BARLOWS EYE RELIEF TYPES

Eye Relief

Types of Eyepieces

END OF EYEPIECES

EYEPIECES -
BARLOWS
EYE RELIEF
TYPES