BST Explorer 5 mm or 25 mm ?

[Catweazel]

I had a similar experience with a 6mm Radian and TMB clone on Jupiter. I think it is a large eye lens out in the cold with a warm eye pushed up against it. I likened it to looking through a steamed up window at a light source. I put it down to this as it did not do it all the time, only now and again and I have never noticed it with the smaller eye lens on plossls.

That sounds a reasonable explaination, they certainly are large eyed and it was very cold last night, so perhaps the eyepiece needed to cool down from being indoors & in the case. I will certainly give it another go.