"William Sommerwerck" wrote in message
...
A short wavelength is needed to resolve fine detail. There's nothing
wrong with using a blue laser to read a CD.


I don't think that you will find that is true - at least in my
experience.
Although the physical optics of the optical block - i.e. the lens etc -
may
be common for both formats, there is actually two laser diodes in a DVD
optical block, an IR one for reading CDs, and a visible red for reading
DVDs. In a Blu Ray optical block, there are three laser diodes, IR, vis
red
and blue. Often, there are two sets of optics on these as well, which
manifests to the outside world as two lenses. If one short wave laser
could
be used to read all three formats, the manufacturers would not waste money
and complexity to have a three-diode block.

I stand by what I said. There is nothing at all wrong with using a blue
laser
to read a CD. I did not say that a single optical block for all formats is
desirable -- now, did I?

The //practical// consideration is that shorter-wavelength lasers are set
to
focus closer to the surface of the disk. It's probably simpler to have
multiple blocks, each optimized for the format to be played.


Well, I would have to say that you are going off on one of your word-play
exercises there. I also stand by what I said. I didn't say that you
*couldn't* read a CD or DVD with a blue laser, although I am not
sufficiently versed in the deep nuts and bolts of the technology to know
that for sure. I was actually responding to your contention that there is
"nothing wrong" with using a blue laser. Clearly there is something wrong
with doing so, otherwise in the real commercial world, major manufacturers
like Sony would do it. It's not a case of desirable, or otherwise. It's a
case of cold hard cash.

Arfa