Archived posting to the Leica Users Group, 2008/04/20
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]On Apr 20, 2008, at 4:34 PM, Geoff Hopkinson wrote: > 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. With a rangefinder camera what you see and what you capture are independent. Yet one should predict the other. If not, you have a problem. Interesting that the costly Noctilux, used at its limits, is the most likely scenario where you may find such a problem, an expensive one. So it pays to fix it, done... now back to taking photos. Steve > > > > 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 > > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information best, Steve "I never wanted to be famous" http://www.blurb.com/bookstore/detail/186890