what does this refer to with eyepieces?

[SkywatcherNick]

when looking at discussions with eyepieces what does the degrees mean,  some are 60 degrees some 70 etc, is it a case of higher number more you see or does it relate to view quality. 

Will this figure have an effect on the comfort to your eye when viewing?

[Moonshane]

the key elements to eyepieces are as follows:

focal length - e.g. 10mm or 20mm. the higher the number, the lower the magnification for a given telescope. telescope focal length of scope divided by focal length of eyepiece = magnification

barrel size - 2" or 1.25" generally or for older scopes 0.965". 2" are a lot bigger and heavier generally then the others and provide wider potential fields.

eye relief - the longer the eye relief the further your eye is from the glass when at the focal point. 15mm is often considered a min. if wearing glasses when observing

apparent field of view - this is the 50, 60, 70, 82, 100, 110 etc and if you hold the eyepiece up to your eye then this will be wider for the higher numbers and lower for the lower numbers. the true field of the view (i.e. how much sky you see) is approx apparent field / magnification.

focal ratio = focal length of scope / aperture of scope

exit pupil - is calculated by  focal length of eyepiece / focal ratio of scope. try to avoid an exit pupil of more than 6mm and less than 0.5mm.

hope this helps a bit.

[SkywatcherNick]

thanks for info. So if looking at something like a planet does this mean you would choose a smaller degree number in the apparent field of view as you would just want to concentrate on one object? rather than a star constellation.

[Moonshane]

you don't have to but I personally prefer to. in the main I use 40-50 degree eyepieces for planetary and lunar/double star observing as they seem to me to produce better visual images due to their simple design. many though use 100 degree eyepieces for planets quite happily.

[itmo]

large AFOVs when watching planes is good if you have a non-tracking mount. Less nudging and easier to find stuff. 

[SkywatcherNick]

cheers folks