Just what causes that white cross?

[Jimtheslim]

Against my better judgement, I returned home from work at 1am and decided to get the scope out rather than get some sleep before getting up early. I gave my scope about 20 minutes to cool before having a look at Jupiter. In my Meade 12.4 plossl there was a massively noticeable white cross through the disc of the planet, stretching out to the edges of the field of view. I have had hints of this before, but otherwise liked this eyepiece for Jupiter. When I switched to the Celestron X-cel 8mm it was gone, however seeing wasn't great so the view was pretty poor overall in both eyepieces. I was just wondering what causes this cross of light in the plossl eyepiece, whether it was the seeing or the eyepiece design/construction itself?

[John]

Sounds like it could be diffraction spikes from the 4 vanes supporting your secondary mirror. They cause a cross effect when viewing bright objects.

Not sure why they should be more obvious in one eyepiece than another though ?

[CraigT82]

I'm guessing the extra magnification of the 8mm Xcel is dimming the cross so that it's not noticeable?

[YKSE]

A possibility is reflection from stray light through your eye. Try to cover your head and eyepeice with something, see if it disappear.

[Jimtheslim]

I thought it might be the vanes, however it's not been anywhere near as noticeable before, even with the same eyepiece. Hey ho, lets hope seeing improves soon!