Archived posting to the Leica Users Group, 2005/02/12
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Ben, Erwin's book has a decent discussion on MTF charts. Simply put, the 10 to 20 cycle lines demonstrate the ability to show coarse to moderate detail. 30 and 40 cycle lines demonstrate the ability to resolve fine to extremely fine detail. You usually see M and S lines shown separately. Out of focus images will look smoother if both M and S lines are relatively close to each other. The second part is the distance from the center point of the lens. In a decently centered lens the point at 0 should be close to 100 percent transmission. As you go out to about 22mm (the diagonal of a 35mm frame from the middle point) a great lens will stay above 60 percent contrast. However, many lenses considered quite good go to near 0 contrast in the extreme corners wide open. So in general, higher is better, flatter is better, and non divided is better. If a lens wide open delivers over 60% contrast in the corners you will have truly wonderful performance. As noted in a previous discussion, flare, and out of focus rendering are not found in an MTF chart. I hope this helps. Don dorysrus@mindspring.com -----Original Message----- From: lug-bounces+dorysrus=mindspring.com@leica-users.org [mailto:lug-bounces+dorysrus=mindspring.com@leica-users.org] On Behalf Of Benjamin Marks Sent: Saturday, February 12, 2005 4:51 PM To: lug@leica-users.org Subject: [Leica] MTF Data Anyone know of a good primmer on-line (or care to explain) how to read an MTF graph? This was spurred by looking at the MTF graphs on Leica's web-site for the 2/35 and 1.4/35 lenses and going "hunh" . . . Not that MTF graphs are the be-all and end-all, but I've been sauntering through my photographic life for the last 20 years without knowing what they mean. (not much of a theory-head when it comes to optics). So, here's the softball question: what kind of numbers (or what kind of curves) make a lens "better" in MTF land? What about the 1.4/35's graph indicates that it is such a winner? bemusedly, Ben Marks benjamin marks at verizon dot net _______________________________________________ Leica Users Group. See http://leica-users.org/mailman/listinfo/lug for more information