In article , Eric Flesch
writes:

On Tue, 25 Oct 11, Phillip Helbig wrote:
writes:
brightish quasar but I find no optical object there, then I must
search for it.

What fraction of quasars are not detectable in the optical at all with
current observations?

By "brightish" I mean quasars brighter than plate limit. My original
quantification (of quasars not seen) of 0.56%, whilst tongue-in-cheek,
is not far off the mark.

So no objects detected in other bands? (If so, then I'm surprised that
almost all have an optical ID.)

Have you contacted the authors of the erroneous data?

Yes, and sometimes I even get a reply. But many of the early
investigators are retired and incommunicado.

Or dead. :-(

1) HE 0435-1223 (this old notation describes a B1950 tile of sky):
a Cyril Hazard quasar -- he rarely published positions for these.

HE is Hamburg-ESO, right?

Ah yes, it isn't a Hazard quasar. So many early quasars beginning
with H are Hazard that I fell into the trap of thinking this one was
too. But this is actually a famous quadruple-image quasar surveyed in
2002. Why they gave it a B1950 monicker beats the heck outta me.

I don't know, but maybe the survey was started, or at least planned,
before J2000 became common, so they decided to stick with a common
system rather than risk conversion errors.