spider image in Samuel Oschin Schmidt Telescope DSS imagery
Those are almost certainly &quot;ghosts&quot; caused by the internal reflection of light from very bright stars. (That is, the light is reflecting off the insides of the camera, filter, etc.) The pattern is an image of the &quot;entrance pupil&quot; of the telescope, which in practice means the primary mirror + the blockage caused by the secondary mirror and its support structure (hence the four thin dark &quot;arms&quot;).
There's a possibly useful technical discussion in this paper, which among other things shows that the off-center nature of the pattern is due to the bright stars being off-center within the field. (If they're in the center, then the ghost has a symmetric, centered pattern.)
See this question and its answers for the general idea when your entire image is out of focus (i.e., all the stars will look like that). In the case of these DSS images, the ghost reflection images are out of focus because the multiple internal reflections change the total path length of the reflected light, while the rest of the image is focus for light following the expected internal path.
The nature of a wide-field or all-sky survey -- like the DSS -- it that you generally try to image all the accessible sky. This will inevitably include some regions with very bright stars in them, even if you might avoid them for more focused observations (e.g., if you're studying type X objects, you might leave out those which happen to lie very close to a bright star).