Archived posting to the Leica Users Group, 2008/04/20
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Hi Len. Thanks for sharing your conclusions. Clearly you have made considerable efforts. There are quite a few different points for consideration amongst all of this. Optical principles, sensor characteristics, test methodology and parameters, assessment criteria and method etc etc. I'll stop now before Dr Ted gets cranky ;-) As a practical matter you need to be satisfied with what works for you. Everything else is theory. Cheers Geoff http://www.pbase.com/hoppyman/e http://gallery.leica-users.org/v/gh/ -----Original Message----- Subject: Re: [Leica] Noctilux DOF Film vs M8 My comparison of DOF between film and M8 were all taken at the same distance and wide open. On the Noctilux I made the comparisons at f1.0, f2.0 and f4.0. I only tested the Noctilux for focus shift because wide open it had nearly no DOF before the target. I have known about the focus shift in the Noctilux for a long time, ever since I made the first resolution test using the USAF test target and the resolution was much better at f1.0 then it was at f2.0. Moving the focus point of the lens improved the resolution tremendously even though now the rangerfinder said I was not in focus anymore. The DOF measured on a film camera vs the M8 at the same distance at the same lens opening certainly does change. There are a couple of reasons for this besides rangefinder alignment. First, I have to blow up the photo in order to make a determination what is in focus and what is not. This is especially difficult for me, especially with the Noctilux wide open, because the detail is soft to start. It is much easier to test the 50mm Summilux Asph because the detail is so much sharper wide open. My Summilux is fine. But because the M8 gives me a sharper photo, the DOF appears to be about 1 inch wider on the M8. It's easier for me to determine. Don't forget my data is made on my determination on what is sharp or not. Leica and even Erwin has sophisticated instruments to make this measurement. With that said why did Leica release lenses where the focus point fell so close to the front of the DOF. This is really a mystery since they knew there was a back focus shift with this lens. The only thing I can think of is that this is a manufacturing fault at the plant that produced the lens. In this case not even a Leica factory. When I aligned my M8 rangefinder I made sure it was in focus at f1.0 and f2.0 and at f4.0. Leica could probably done the same thing with the lens. I believe there is some reason why Leica has not optimized the near focus rangefinder alignment on the M8 to match the film camera performance. I think it's a compromise to compensate for some differences in the characteristic of the sensor. Cheers, Len On Apr 20, 2008, at 6:17 PM, Geoff Hopkinson wrote: > Len it IS a very interesting issue for M8 users and subject to > quite a lot > of discussion in the Leica forum, some more objective than others! > When you > mention focus shift and back focus, firstly are you talking about > each lens > shot wide open or the sharpest plane moving as you change the > aperture? > That is two separate things, I think. > LFI reports Leica's position as that the focus shift when stopping > down a > little has always been there (with fast lenses) but is more > detectable with > the M8 due to several factors. Purportedly, only the 50 asph and > the 75AA > that shares its design are immune. > What apertures are you testing all of those lenses at? You are > testing I > think, at 8 feet? The comparison could only be valid at the same > aperture. > I have heard about the infinity point adjusting in the M8 body, but > the > shimming is new to me. The DoF of each lens cannot change at the same > aperture and focus distance surely. Certainly you could shift the > focus > point with either method. What works in practice may have > theoretical or > actual disadvantages I would think? > No question but that I am noticing missing focus with the 50 asph > using it > close-up stopped down to f4 or so. I did the same on my M7. I think > that it > is operator error. The 1.25 magnifier seems to help. > Cheers > Geoff > http://www.pbase.com/hoppyman/e > http://gallery.leica-users.org/v/gh/ > > -----Original Message----- > Subject: [Leica] Noctilux DOF Film vs M8 > > This is a very interesting issue. I don't know if anybody has > mentioned what happens to the depth of field of the Noctilux, or any > other lens, in a Leica film camera versus the M8 digital camera. It > seems that nobody complains about the focus on a film body but all > kinds of complaints on the M8, especially the Noctilux, Summilux Asph > and the 75mm Summilux. Is there a difference? Yup, there sure is. I > tested 16 leica lenses for depth of field at a distance of 8 feet. I > tested 13 of the lenses with film using a .85 MP and compared the > results to those taken with an M8 and a 1.25 Leica magnifier. > > In every case the DOF shifts away from the camera with the M8. In > other words the lens appears to back focus. The worse lens for this > shift is the Noctilux. But even on a film camera it is barely in > focus. The typical back focus shift of any 50mm Leica lens is about 4 > to 5 inches at 8 feet with the M8. The backward shift of the Noctilux > is between 8 and 9 inches. This puts the focused point of the > rangefinder outside the depth of field of the lens. The other thing I > noticed is the DOF is better centered on the older LTM lenses then on > the newer lenses. I don't know if this is a quality control problem > now or if the focus point test has changed. I tested 7 LTM lenses, > the Xenon, Summarit, Summitar, Summicron Coll, 50 Elmar RS, 90 Elmar > and 135 Hektor. The focus point nicely stayed within the DOF on both > cameras. Of the M lenses the best is the 1st 50mm Summicron rigid > version followed by the current 50mm Summicron. > > I verified my results with a second M8. The MP body is one year old > and purchased new. I also sent my Noctilux and 75mm Summilux to DAG > for focus adjustment even though the lens is still in warranty. I'm > also shooting more with film these days. > > Len > > > > _______________________________________________ > 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 _______________________________________________ Leica Users Group. See http://leica-users.org/mailman/listinfo/lug for more information