Sigma 2.8/18-50 DC first impressions
Hi, As I promised, I will write some first impressions of this lens. Later, when time permits, I might post few crops from the sample I tried. Keep in mind that this is preliminary, based on just quick'n'dirty evaluation of just few test photographs. Real "review" would be based on using the lens to actually photograph some more real world subjects than a backyard scene from the balcony of the photographic shop (although the scene was varied nicely in contrast and detail). Long end - good overall, low vignetting, slight coma in the outer zones. Contrast is good. Overall, the lens is very respectable at 50mm and 2.8 aperture. Best performance is at f/8, but even at f/4 you would be hard pressed to find faults and 5.6 is almost indistinguishable from f/8. I couldn't see any big chromatic aberration which was a plus. Wide end - quite visible coma in 2/3 and outer zones of the reduced frame plus overall veil make the image soft at full aperture (although not nearly as much as Sigma's previous 1.8/20mm lens was at 1.8). Coma is decreased somewhat at f/4, and virtually gone by 5.6. Veiling is virtually gone by f/4. No big visible chromatic aberration! Vignetting is severe at 2.8, slight but still somewhat noticeable at f/4 and virtually gone by 5.6. Overall, wide open the performance is just acceptable (but I have seen worse). Once stopped to f/4 it gets much better, with 5.6 and 8 being both very good. Finer details of the lens (tonality, boke', et cetera) would require having it for much longer. I am still somewhat at a loss about the wide end wide open pictures. Some of them looked good, and some looked bad. Will have to try it more. For the money, it doesn't seem as a bad lens at all, with good wide open performance for portraits but questionable wide open 18mm end. The inevitable comparison would be to 16-40 Pentax. Which I don't have ;-). The 1 stop gain is real (unlike some older Sigma lenses like the EX 1.8/20mm which had true T/stop around 2.2-2.3 and were unusable until 2.80), and usable at the long end, but at the wide end, for good performance you have to stop down to f/4 anyway... Frantisek
RE: Sigma 2.8/18-50 DC first impressions
Thanks for the comments on this lens. What is coma? It would be nice to see a couple of shots posted. Really nice would be comaparisons with the Pentax 16-45mm :-) Jens Bladt mailto:[EMAIL PROTECTED] http://hjem.get2net.dk/bladt -Oprindelig meddelelse- Fra: Frantisek [mailto:[EMAIL PROTECTED] Sendt: 28. november 2004 23:44 Til: PDML Emne: Sigma 2.8/18-50 DC first impressions Hi, As I promised, I will write some first impressions of this lens. Later, when time permits, I might post few crops from the sample I tried. Keep in mind that this is preliminary, based on just quick'n'dirty evaluation of just few test photographs. Real "review" would be based on using the lens to actually photograph some more real world subjects than a backyard scene from the balcony of the photographic shop (although the scene was varied nicely in contrast and detail). Long end - good overall, low vignetting, slight coma in the outer zones. Contrast is good. Overall, the lens is very respectable at 50mm and 2.8 aperture. Best performance is at f/8, but even at f/4 you would be hard pressed to find faults and 5.6 is almost indistinguishable from f/8. I couldn't see any big chromatic aberration which was a plus. Wide end - quite visible coma in 2/3 and outer zones of the reduced frame plus overall veil make the image soft at full aperture (although not nearly as much as Sigma's previous 1.8/20mm lens was at 1.8). Coma is decreased somewhat at f/4, and virtually gone by 5.6. Veiling is virtually gone by f/4. No big visible chromatic aberration! Vignetting is severe at 2.8, slight but still somewhat noticeable at f/4 and virtually gone by 5.6. Overall, wide open the performance is just acceptable (but I have seen worse). Once stopped to f/4 it gets much better, with 5.6 and 8 being both very good. Finer details of the lens (tonality, boke', et cetera) would require having it for much longer. I am still somewhat at a loss about the wide end wide open pictures. Some of them looked good, and some looked bad. Will have to try it more. For the money, it doesn't seem as a bad lens at all, with good wide open performance for portraits but questionable wide open 18mm end. The inevitable comparison would be to 16-40 Pentax. Which I don't have ;-). The 1 stop gain is real (unlike some older Sigma lenses like the EX 1.8/20mm which had true T/stop around 2.2-2.3 and were unusable until 2.80), and usable at the long end, but at the wide end, for good performance you have to stop down to f/4 anyway... Frantisek
Re: Sigma 2.8/18-50 DC first impressions
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 (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
