Using a polariser also makes the viewfinder darker, which makes manual focus much more difficult. I only use manual focus with my sigma 180mm f/3.5 - though to use the AF160FC ringflash I had to use a step down ring from 72mm to 67mm I was concerned about vignetting however even on full frame there isn't a problem with using the step down adapter in conjunction with the adapter rings for the ringflash. The Sigma 180mm f/3.5 [IF] APO EX DG can be a difficult lens to use hand-held with the pentax system in light of the 1/180th synch speed, I don't advise using HSS(high speed synch) with macro lighting because it really kills the power of the flash and for true macro work, HSS is functionally useless because of the reduction in flash power. With macro work in general, maximising DOF is very important and I need all the flash power I can get,incidentally the PENTAX AF160FC is a very powerful flash considering it's competition.
here are a few of my sample images, both were taken with the Sigma 180mm f/3.5 APO [IF] EX DG Macro.
Last edited by Othrelos; 10-12-2010 at 11:07am.
Thanks for the comments, I'll post more flicks as I learn to fly it
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Pentax K20,Pentax K5,,Pentax DA 12-24, Pentax DA 18-55mm,Tamron sp DI 90mm Macro Sigma 70-300mm 1:4-5:6 with macro, ,Sigma 150-500mm 1:5-6.3 APO HSM, Kenko 2X Teleplus MC7, Pentax AF160FC ring flash,Pentax AF 540 FGZ flash, Yongnuo yn460 Flash
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