Archived posting to the Leica Users Group, 1998/11/23
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]At 21:13 22/11/98 +0100, Erwin wrote : > >On the fotodo question. They do not produce their own MTF's but hire a Hasselblad facility for it. The straight results from the machine are as usual completely reworked to become meaningless. > >Erwin > ############ Erwin, I've just seen MTF tests published by Photodo and made by Per Nordlung at Victor Hasselblad AB with an Ealing equipment (BTW Chasseur d'images uses an Ealing Eros 200, and you ?). When comparing their results with those of CI, I think that their method is quite accurate. You write :"The straight results from the machine are as usual completely reworked to become meaningless". They write : "MTF is measured 0, 3, 6, 9, 12, 15, 18, and 21 mm from the image center (on axis), at 10, 20 and 40 lp/mm, in two different directions (sagital and tangential). That is all together 48 measurements at each focal length and each f-stop. Rather than listing all these numbers we calculate a weighted average number for each f-stop of all lenses and each focal length of zoom lenses. The center of the image is more important than the edges, and 10 lp/mm is more important than 20 and 40". That's a fair statement of the methodology we can discuss about.For instance : why 10 and not 20 or 40 lp/mm ? What are the weighting parameters ? But we can't gun down in two shakes the work they publish as you do. Moreover the graphics (without weighting parameters)are like the Leica's ones... Dominique Pellissier