siriusdogstar
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any light sourced behind an aperture refracts on the way through; i.e. the aperture itself introduces CA which is added to lens CA, thus light behind holes punched in foil (even by laser-cutting the hole) will not work for measuring lens CA.
star brightness is affected by atmosphere; we want a specific light-value. stars emit specular light; we want to use full-spectrum white light.
inexpensive, commonly available equipment, and a specific setup, is required to give commonly reproduceable results. here's my list; the "specifics" still need to be worked out:
a specific target with specific reflectance is necessary, i.e. the specific target is printed on a specific brand and version and size of photo paper at a specific size using a specific brand/version ink, at a specific dpi.
lens and target are oriented exactly perpendicular to line-of-sight, set a specific distance(s?) apart; specific distance(s?) is dependent on lens focal length.
in an otherwise dark room with non-reflective walls, floor, and ceiling, front-light the target from a standard position (specific x, y, and z) and distance with a specific brand/version of halogen bulb mounted in a specific socket in a pecific orientation; adjust brightness using rheostat to produce a standard EV as measured at the camera. (all this is perhaps the most difficult to set up)
photos are taken at various aperture/shutter speed according to measured EV using a camera with properly calibrated shutter speed, and set to a specific iso.
specific portions of images are examined for CA at a specific magnification, chosen to permit usage of most folks cameras, thereby eliminating differences in pixel density and sensor size.
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