Diffraction Patterns with Close Doubles

[chiltonstar]

With close doubles such as Porrima or Epsilon Lyrae, my Mak 127 shows (at times of v.good seeing) a pair of clean disks, but with what looks like several weaker "dots" above and below the axis of the pair.

Experts - is this caused by additive interference of the secondary diffraction rings around each star image, or by eg reflection inside the scope??

Chris

[Merlin66]

I assume you're using pretty high magnifications, so I wouldn't think tube reflections (maybe eyepiece reflections? - this can be quickly verified by obsrving a single star with the same eyepiece) It could be diffraction rings, but usually only one or two at the most are visible and the "stronger" interference images would be btween the star images but just off the axis between them. Test this another eyepiece -see if they are still visible.

[chiltonstar]

A single star with an EP of 6mm (ie x240) gives a ring around the primary disk, but often with sectors missing. The patterns above and below with close doubles are close to the axis and look the same at x200 with another EP.

Chris

[Merlin66]

Then I'd have to say you're seeing the interacting diffraction rings from the stars.

[barkis]

It goes without saying that if you wish to examine diffraction rings, then the seeing has to be perfect, and you know only too well that in the UK that situation rarely exist.

Fragmented rings are usually due to atmospheric disturbances, and probably the likely cause.

Ron.

[FraserClarke]

Sounds like you're seeing the supposition of the two diffraction ring patterns. Another test would be to compare what you see on doubles of slightly different separations; the position of the "spots" should depend on the separation of stars if it the diffraction rings, and not if it is a reflection effect in the optics.