eye placement in the 120 ed

hi,
Am I the only one that finds that eye placement is pretty important when viewing through the ed 120 or have others found the same as well? When my eye is a little to the side of the view hole the star in view shows some ca and flaring (Airy disc is still clearly visible). When my eye is placed right where it should be then it basically goes away. It is annoying because sometimes it is hard to position the eye just so. In addition I find this more with orange stars (Arcturus) than with others. Another point that may factor in is that when using my 5mm ortho (the one where this happens the most) one can see a few spots over the glass as the UNFOCUSED star illuminates the field. I have tried cleaning the ep to no avail.
Any help would be greatly appreciated.

Itz: In general I find that eye positioning is more dependent on the eyepiece and exit pupil than on the particular telescope. With the 5mm eyepiece and your F/7.5 scope, the exit pupil is 0.67mm, this is a tiny pencil of light Take a look at a 0.7mm diameter lead from a mechanical pencil and then consider that your eye has to take that tiny beam and resolve it.

Anyway, I think eye positioning sensitivity is not about chromatic aberration in your scope but to various issues with the eyepiece and your eye.

At low magnifications/large exit pupils, eye positioning can be an important factor in seeing chromatic aberration in an achromat. This is particularly noticeable during the day or on a bright object like the moon. What happens is that the exit pupil, the beam from the scope, is larger than your eye's pupil, some of the beam enters the eye but some falls around the edges, providing an aperture mask for the telescope. This not only reduces the effective aperture but in so doing increases the effective focal ratio, both these reduce the chromatic aberration. If the eye is well centered then one is looking through the center of objective and the chromatic aberration is noticeably reduced. But if one then looks off axis, then one is looking through an off axis section of the objective and the chromatic aberration can suddenly become very apparent. But this is at low magnifications, say a 4 or 5 mm exit pupil which would be a 30mm eyepiece in your F/7.5 scope

As far as the flaring on yellow stars, this is something with the eye, it's apparent to me in all types of telescopes including Newtonians that have perfect color correction. Exactly why it happens, I asked that question once but the actual mechanism slips my mind...

Jon