2" and 1.25" eyepieces, what's the difference and best?

[jon1000]

Just a quick question, my telescope will accept 1.25" & 2" ep's, what's the difference (other than the size), what's the benefits of the 2" ep's and which are the best? I'm only asking because my telescope come with only 1.25" but I'm wondering about why they would include them and not 2" ones.

Thank you.

[umadog]

It's simple, really. The amount of sky you can see through the eyepiece (the so called true field of view) is equal to the eyepiece field stop diameter divided by the telescope focal length multiplied by 57.3

The eyepiece field stop is the metal that defines the edge of the field of view when you look through the eyepiece. If you look at the non-eye end of the eyepiece, you're looking at the field stop. So the bigger the field stop, the bigger the true field of view. That means that 2" eyepieces give you a larger true field of view: you'll see more sky because they have bigger field stop diameters.

The down-side to this is that more glass is needed so the ocular will weigh more and cost more.

[brantuk]

Hi Jon - the supplied eyepieces tend to be the cheaper kind that are just good enough to get you going with the scope and provide acceptable views. They tend to be smaller and lesser quality than others.

This is because eyepiece choice is a very personal thing - what suits one eye may not suit another. 2" eyepieces tend to offer more lens elements, wider views, and lower magnifications depending on what scope you are using them with.

Neither size is "the best" - that's all down to what brand, and eyepiece type you choose, and what quality level you go for. There are some excellent 1.25" and 2" ep's on the market. You need to try a few to see what suits you

[sunshine185]

If, for instance you wanted to view Jupiter, then a 2" ep would be a waste of time, a 1.25" ep is fine for this a Jupiter would be in the middle of the fov so the "extra sky" of the 2" ep would be wasted. On the other hand, if you wanted to view the plaeides, then a low power 2" ep with its wide field of view will give you lots "more sky" in the eyepiece.

[jon1000]

If, for instance you wanted to view Jupiter, then a 2" ep would be a waste of time, a 1.25" ep is fine for this a Jupiter would be in the middle of the fov so the "extra sky" of the 2" ep would be wasted. On the other hand, if you wanted to view the plaeides, then a low power 2" ep with its wide field of view will give you lots "more sky" in the eyepiece.

So andromeda would be best viewed with a 2" ep or will the magnification not be enough?

[jon1000]

Thanks for your help everyone

[John]

So andromeda would be best viewed with a 2" ep or will the magnification not be enough?

You need a big field of view, rather than magnification, to view the Andromeda Galaxy (M31). The 2" eyepiece format gives you that.

[hemihaggis]

You need a big field of view, rather than magnification, to view the Andromeda Galaxy (M31). The 2" eyepiece format gives you that.[/quote

John is right , but you would also need a good dark sky to see all of m31 ,it is huge !! most small and medium sized scopes from urban areas in UK will only show the central core , I find in a small/medium scope a decent 25-32mm ep works just fine something like a tmb or a bst explorer