I have no informations on squid's visual acuity, but Hughes (1977) reported that the cuttlefish has a very high visual acuity, which is better than that of the cat (!!!) (cited in a paper by Schaeffel et al., 1999)...
Like many other aquatic and non-aquativ invertebrates, cephalopods are also sensitive to the polarization of light 'cos the microvilli within their retina have a special horizontal/vertical arrangement (e. g. see Shashar et al., 1996; Shashar et al., 2000 etc.).... My eyes are not very sensitive to polarized light , so regarding polarization of light the ceph-eyes are better than my human eyes...
Sorry, that's not quite an answer to your "black spot"-squid-question...
I don't know about all cephs, but some of them have the veins feeding the eye from behind, rather than inside. The human eye has a hole where the veins feed through the back then spread out across the retina. This creates the blind spot. Cephs don't have that.
That said, all eyes are "functional" to their specific purpose. The human eye is very generalized, able to see in a wide range of conditions. Other eyes in other creatures are equally specialized to their environment. None is "better". Just specialized to their purpose.
Moreover, the mammalian lens is flexible. Cephalopods have a rigid lens that has developed a clever compromise; it changes optical characteristics (diffraction angle) near the edges, to help with focusing. And the animal grows rapidly, keeping all of this properly aligned. But the lens must move forward and back to focus.
In general, cephalopods are much more sensitive to low light, as well as being able to see three of the six kinds of polarized light. (So far as I know, only the mantis shrimp sees all six.) On low light vision, I have seen references that described a cat as ten times the human sensitivity (ability to see in the dark) and at least one species of octopus as 200 times. This was not a deep sea species.
Most octopuses and squid seem to be colorblind, but we have discovered at least one species of octopus and a few squid which are not.
It has been parked while I handle other concerns, unfortunately. Big deadline coming Friday; after that, we'll see.
Worth noting -- in mammals, the eyes form as extensions of the brain. In cephalopods, they form as extensions (inward) of skin tissue.
And the optic gland is wired to the eye in both octopuses and squid -- and gets signals from day length that control the animal's maturity and lifespan.
Another trivia bit: Humans have rods and cones -- and we recently (2006) discovered a third type of sensor cell, that works a bit like the octopus's optic gland: These retinal ganglion cells send the brain signals on the length of the day. Each eye has about 2,000 of them, and they bypass the retina's circuits and go right to the brain.