Wednesday, December 1, 2004, 8:42:38 AM, Jens wrote: JB> Thanks for the comments on this lens. What is coma? JB> It would be nice to see a couple of shots posted. JB> Really nice would be comaparisons with the Pentax 16-45mm :-)
Unfortunately, I don't own neither the 16-45 nor the IstD, I tested this lens on another brand ;-) I guess I am keeping the Spotmatic just to be "eligible" for PDML <vbg> (no, it's one of the best cameras as well) Coma is, in layman terms, when especially light sources have a comet-like tail longer the further they are from center of the frame. Imagine sun in the middle circled by several comets, whose tails are pointing outside the solar system, and that's coma ;-) This aberration is most visible on light sources and areas of high contrast, but results in overal weakening of details nevertheless. For a nice primer on aberrations, look at http://www.panix.com/~zone/photo/czlens.htm (at the end of the article). It is quite possible that I am seeing results of another aberration or several combined, maybe it's more astigmatism than coma. I am just a dabbler in things this technical. But the result is that objects like thin branches have a lateraly displaced and smeared "ghosting", displaced in direction outwards from the center of frame. One problem of trying out a lens on digital cameras is that the camera or the raw converter applies some sharpening which may improve some things and obscure others. So the results also depend on camera or raw converter (for example, some Canon cameras apply sharpening even to RAW files, without user control!). But if I tested it with sharpening turned off in the raw converter, it would be too much soft because of the demosaicing, in my opinion. And in real world pictures from digital we sharpen them usually. Anyway, I will post some crops from it soon, probably next week. Or I can email you a converted jpeg from the raw file, if you want. It would be few megs though. Good light! fra
