In article ,
canopus56 wrote:

Finally, your pickup on the gravitational lensing was one that I
enjoyed -
using natural events - the chance positioning of large galaxies as a
"telescope".
I guess using a 200,000 light year diameter galaxy qualifies as the
largest "lens" ever used!

That "lens" is much larger than the galaxy itself! It works through the
gravity from the galaxy which bends the light rays - and the gravity from
the galaxy extends well beyond the physical size of the galaxy itself,
making the effective size of the "lens" perhaps a few million light years
large!

And, in contrast to glass lenses, a gravitational lens is completely
achromatic! I strongly doubt a gravitational lens could be used well
as a telescope though, because it probably suffers from several other
horrible aberrations....





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