I spent a bit more time with the Cave 6" on epsilon lyrae last night, this time giving the 'scope time to come down to ambient temperature and let the tube currents die down fully. I found the results interesting.

16mm Orthostar (75x): a clean split on both components, with black space visible in between. (On epsilon lyrae 1 I did have to wait for instants of good seeing to see the black line dividing the two components; on 2, I could hold the black space most of the time.)

25mm Pro-Optic Plossl (48x): an occasional hint of maybe some black space between the components of 2, but on 1, I was never able to get a convincing view of any separation (though it was elongated). I found that I had to be very careful of where I put my eye -- there was a "sweet spot" where I had to be, and moving even slightly in any direction caused the star images to smear out. I'd never noticed this effect so strongly before with this eyepiece (and it's my most-used eyepiece, so this mostly shows that I don't do a lot of fine detail work with it).

The Pro-Optic Plossl is basically the most cheap and generic eyepiece imaginable (despite the fact that it's my favorite deep-sky eyepiece), so I decided to see what a good Plossl would do. I happened to have a 17mm Tele-Vue Plossl on loan, which seemed like the perfect test since I could compare it to what I'd already seen in the 16mm Orthoscopic.

17mm Tele-Vue Plossl (70x): really no better than the 25mm Pro-Optic. Black space was visible, on instants of good seeing, between the components of EL2; I could never discern any separation between the components of 1.

This was the most convincing demonstration I'd seen so far of the differences between different eyepiece designs, and I came out convinced that Plossls, even brand-name ones, are not good eyepieces for fine detail. Is my experience a fluke, or does this agree with other people's experiences?

And another question: it seems quite consistent that I find epsilon lyrae 2 easier to split than epsilon lyrae 1. I thought their separation was about the same? Monday night, I wrote it off to tube currents (the flattening of the diffraction pattern was in the same direction as the orientation of EL1, but not EL2); but Tuesday night, there were no tube currents interfering, yet EL1 was still more difficult. It occurred to me that there might actually be a directional difference in the resolution of my retina, so I tried moving my head 90 degrees, so that the EL2 components became "side by side" while EL1 was "one above the other". This did seem to make a difference -- now I could no longer see the black space between the EL2 components, but I still couldn't quite split EL1 with either of the Plossls.