binoc advice

I'm looking for some not too expensive but decent binocs for astro
viewing. But here's the problem. I've used two 7mm exit pupil binocs:
11x80 from a reputable company, and Omcon 7x50, both made in Japan. In
both, bright stars and planets are asymmetrical and spiked (usually
one big spike in one direction), even at best focus. This problem is
not so bad on dimmer planets/stars. I returned the 11x80s. The Omcons
are much better of the two, but still unacceptably bad.

I was told it could be the binocs or my eyes. I'm nearsighted and
need glasses for distance. My optometrist says I have some
astigmatism, but I don't know how much. When I look thru the 7x50s
with glasses on, this problem seems only a bit better, but not much.
The 'blob' shape of the star flips 90* as I pass through focus. The
orientation of the spikes seems to turn with my head as I rotate my
head while leaving the binocs level. And images don't 'snap' into
focus...it's more like a zone of modiocre focus.

On my 7x50s, I tried using black tape to step down the aperture to
only about half an inch, and bright stars become much much sharper.
Also, I have 20x50 and 10x25 binocs (both have 2.5mm exit pupil...and
both are cheap), and through them, bright stars and planets are
reasonably sharp.

Based upon all this, is it the fault of my eyes, or the binocs?

Worrying that it's my eyes, I'm thinking about 16x70, 20x60,
20x70, or 20x80 binocs since they'll have a relatively small exit
pupil. Anyone know if any of these are any good: (I'm skeptical about
the optical quality of Chinese made binocs, but maybe it's unfounded):

http://www.oshmans.com/product/index...oductId=534455

http://www.adorama.com/PRO1670R.html

-'National Geographic' 20x70s

http://cgi.icq.ebay.com/ws/eBayISAPI...tegory=28 180

Orion 20x70 Little Giants look perfect for me, but they are a bit
expensive. But if I knew they'd give me good on-axis resolution, I
might get them. My main concern is on-axis sharpness, I'm less picky
about edge of field sharpness.