Eyepiece size question

[gustavo_sanchez]

Why the high power eyepieces always come in 1.25" size and the low power eyepieces can come in 2"? Is there any, for example, 4mm FL 2" eyepiece?

[John]

The only real advantage with 2" eyepieces is that the field of view can be wider because of the larger barrel diameter. For focal lengths less than around 16mm there is no advantage to using the 2" format so you will find very few, if any, manufacturers do them.

So there would be no point (and no sales !) in a 4mm eyepiece in the 2" format.

The Tele Vue Ethos SX 3.7mm comes with a 2" barrel adaptor for convenience but even that is a 1.25" eyepiece underneath.