Putting all the stars on a fixed sphere would make the parallax effects less visible, as the stars in a given portion of the sky would now all move together at the same apparent velocity – but there would still
these methods may be used to establish discrimination thresholds. The advantage of measuring thresholds is that there is mature and well-validated theory — the theory of signal detection[3]— that enables inferences about the perceptual representation of the stimuli in a manner insulated from effects...
Parallax Error • When using an optical instrument —both the image and cross hairs can be focused- if either is imprecisely focused, the cross hairs will appear to move with respect to the object focused, if one moves one's head horizontally in front of the eyepiece. ...