Eye relief VS fov. FIght !

[John]

With plossls and orthoscopics, as Gaz says, the eye relief is generally around 70%-75% of the focal length of the eyepiece. Hence the short focal length ones are rather "tight" when it comes to how close you need to get your eye to them.

With such designs, a barlow lens can help with this because it actually extends the eye relief somewhat, as well as amplifying the magnification. Not so useful with a longer focal length eyepiece of this design though because they already have reasonabl eye relief and extending it further often means that you need to position and hold your eye somewhere above the eyepiece / eye cup top, which can prove far from relaxing as well as permitting stray light to get onto the top lens of the eyepiece.