Quote:
Originally Posted by Startrek
Probably the first thing to consider is your budget $$$$
Eye Pieces can range from entry level Plössl type at $50 each to high end premium Televue at +$1000 each
Here’s some basic technical eye piece info below I put together years ago that might be of interest…….,
Telescope Eye Pieces
Various Eye Piece Formulae
Magnification or Power is the amount that a telescope enlarges an object when viewed through an Eye Piece.
A telescopes useful magnification is generally twice its aperture in millimeters ( mm) but this can vary due to many factors like atmospheric turbulence , high cloud , humidity , light pollution and so on …….
Magnification of Telescope = telescope focal length in mm / eye piece focal length in mm
True Field of View of an Eye piece
This is the amount of Sky you can see through an eye piece without being attached to the focuser of a telescope
True Field of View is expressed in degrees
TFV = Apparent field of view / Magnification
Apparent Field of View of an Eye Piece
This is the amount of sky you can see through the Eye Piece when attached to the Telescope.
Apparent Field of View is expressed in degrees
Apparent field of view of an Eye piece = TFV / Eye piece magnification
Telescope focal ratio is a measure of the speed and angle of the light cone from a telescope.
Fast telescopes usually have a focal ratio of f4 to f5 and provide a wider field of view
Slow telescopes usually have a focal ratio of f6 to f10 and provide a narrower field of view
Telescope focal ratio = telescope focal length / telescope aperture
Eye piece exit pupil is the small beam or disc of light ( image ) that leaves the eye piece in order for your eyes to focus on. A young persons pupil dilates to around 7mm but an older person only dilates to around 5mm.
The pupil is like the shutter on a camera. The older you are more difficult it is to maximise the exit pupil out of the eye piece
Eye Piece Exit pupil = eye piece focal length / telescope focal ratio
Eye Piece Field Stop is the edge of the view or black ring you see when viewing through an eye piece which differs from eye piece to eye piece and is measured in millimeters.
Eye Piece Barrel
The Eye piece barrel is the chrome cylindrical section that is inserted into the telescopes focuser to hold it in place.
Eye piece barrels generally come in 1 1/4 “ or 2” barrels. Most telescope focusers are 2” and can accommodate both 1 1/4” ( with a 2” adapter) eye pieces and 2” eye pieces.
Eye Piece Focal Lengths
Eye piece focal lengths ( mm ) usually range from 3mm up to 50mm
3mm to 10mm range are high powered eye pieces for viewing Planets , the Moon and Stars.
10mm to 20mm are medium to high powered eye pieces for viewing Stars , Star clusters , Galaxies and Small nebula and the Moon
20mm to 32mm are medium powered eye pieces for viewing Stars , Star clusters , large galaxies, large nebula and the Moon
32mm to 50mm are low powered eye pieces for viewing Large Star clusters , large Nebula and the Moon.
Filters
Eye piece filters are generally required for Lunar observing and Planetary observing to reduce reflections, glare and enhance colour and detail.
Filters for Light Pollution and Contrast can be used for deep sky objects like planetary nebula and emission nebula to enhance detail.
Clear Skies
Martin
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I want to get them second hand for around 200 each when second hand. Thanks