Archived posting to the Leica Users Group, 2005/01/02
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Hi Don, I am intrigued that you find boke unimportant in tele lenses. I use them a lot for wildlife pictures, and find that boke is crucial, simply because the bulk of the frame is often OOF and distracts from the subject if the boke is poor. I find boke to be dependant on several things. The Canon statement that for good boke meridional (sp) and sagital (sp) MTF need to be as close as possible agrees very strongly with my experience (where I have seen the MTF curves). OTOH I have a Canon macro lens which has boke which gets worse as I focus closer, to such an extent it is easily seen in the viewfinder. The sharpest lens I own is a Canon 500mm, its boke is also the best I have seen on any lens. Frank On 2 Jan, 2005, at 14:37, Don Dory wrote: > Frank, > > I concur that calculated MTF's are almost a waste of time for a > consumer. Obviously, for the design engineer, it is a very powerful > tool as the design is massaged to completion > > The center of the image circle is relatively unimportant as all lenses > will do very well assuming no de-centering of elements. That's why > when > looking at an MTF chart I start looking at the area off center; if the > lines start to drop and the T and S lines start to diverge then the > lens > will not be so good. > > You are correct about flare, for that you do need some test shots, or a > really well designed hood. :) I think also that the family history of > the lens line is also important. My recent Leica and Zeiss glass is > mostly flare free in some pretty severe lighting situations, but some > of > my newer Canon and Nikon glass is not so good. I think that the > engineering rules in different design groups have different priorities. > > As to bokeh, as I think a previous poster was largely correct that > bokeh > is a combination of diaphragm blade design, under corrected spherical > aberration, and a modest amount of astigmatism. Especially for modern > aspheric designs I think that the transition to out of focus will be > rapid and somewhat random causing some strange artifacts. Of course, > with a telephoto lens, bokeh becomes largely irrelevant. > > Also, as we move to lenses designed for smaller sensors, controlling > depth of field will become more interesting. > > 0.02 > > 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 Frank Dernie > Sent: Sunday, January 02, 2005 3:52 AM > To: Leica Users Group > Subject: Re: [Leica] Intro > > Don, > The publication of measured MTF would help, calculated does not IME. I > have tested two lenses, one a multi element zoom, another a prime. The > zoom has better (calculated) MTF in the centre of the frame than the > prime, but the prime is clearly superior on photographs. I expect there > is a MUCH greater variability in multi element lenses simply because of > the problem of manufacturing them all the same! > OTOH MTF tells nothing about flare resistance or boke, both more > important than ultimate resolution on the type of photography I do (I > rarely use a tripod and never higher resolution film than Kodachrome > and am now using digital) > Frank > > On 2 Jan, 2005, at 03:53, Don Dory wrote: > >> Jeffery, >> There is, it is called a MTF chart. While every machine is different, >> if a lens is transmitting 60% contrast at the 30 or 40 cycle line out >> 15mm wide open then you have a really good lens. >> >> If every manufacturer would just publish MTF charts for real > production >> lenses then most of the nonsense about my lens is better than your > lens >> houey would stop. >> >> 0.02 >> >> Don >> dorysrus@mindspring.com > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information >