Archived posting to the Leica Users Group, 1998/05/30
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Erwin Puts wrote: > > You wrote > > >I just got the MTF diagrams from Leica for the new R-50 f1.4 > >& the 180 f2.8 apo lenses. I also have the BAS charts for > >most previous Leica glass; thus, we can get at some > >comparisons. > > > I have stated it before and got screaming protests. Still this is my view: > 1. BAS test results are worthless in themselves and can not be compared to > any other testresult. > 2. BAS results are NOT (repeat NOT) MTF measurements and/or evalutions. > BAS uses a projection method: a fine transparant testchart with the usual > blocks of lines (horizontally and vertically) is projected on a wall. Then > a CCD video camera with 430000 pixels takes a shot at 80x enlargement. > This result is fed into a computer where an unknown softwareprogram > analyses the data. How and what is analysed is not known. > 3. Even if BAS were a MTF measurement: one can not compare two MTF graphs > if the method and paramaters are not identical. As every manufacturer uses > a different program and different parameter,s any comparison is impossible > or a very dangerous undertaking. Some conclusions might be made if more is > known about the several MTF measurement programs. I do know the ones from > Zeiss and Leica quite well and so could compare the results and get some > very cautious conclusions. I would not dare to do so with Canon graphs. > 4.Even if the graphs are comparable then the actual results might differ > quite well, as any one has its own set of interpreatations. As example. The > 10lp/mm for the Zeiss Planar G 2/50 is situated lower on the curve than the > Summicron-M 2/50, So the Summicron should have higher contrast at full > aperture? Ask PopPHoto or Chasseurs d"Image! > 5. Comparisons of lenses based on some graphs, how tempting it might be, is > a minefield. Be aware of this fact: it might be the only true conclusion > from my extended research into lens comparisons. > > Erwin Erwin, I fully agree with you on this. It seems to be human nature to want to distill things down into a simple binary factor but it just cannot be done. Best for those of us less well equiped to use the lens in question and decide if the results are what we want. There is nothing wrong with reading reports but we should never let them make our final decisions. IMO of course! Dennis - -- Experience is a tough teacher. It gives the test before the lesson. - -unknown