piblondin Posted December 31, 2012 Share #1 Posted December 31, 2012 Advertisement (gone after registration) I've noticed that the Summilux ASPH FLE is really good on my M8 at f/1.4. Sometimes it appears to back focus, but I attribute that to user error. There's also more purple fringing than I would expect, but that may just be an issue with my post-processing and RAW imported. However, what I don't fully understand is what seems to be the focus shift I'm experiencing at mid-distances, say 10-25 feet when I stop the lens down to f/2.8 to f/4. I find it almost impossible to get one of these shots in focus. For example, see the shot here, where the wall behind the girl appears to be in focus but the girl does not. https://dl.dropbox.com/u/35075545/backfocus.jpg I do shoot a lot at f/1.4, but I also need to shoot at slower apertures when I know that the subject will be moving or I need to capture multiple subjects with a larger DOF. So, I tried a simple focus test with a tape measure. I attempting to focus on the closest 4 in 44. See my tests: https://dl.dropbox.com/u/35075545/f1.4.jpg and https://dl.dropbox.com/u/35075545/f4.0.jpg There definitely appears to be some shift, but it seems like 44 is still in focus at f/4.0, albeit at the front of the DOF. This test was done at a distance of about one meter. Could it be that at greater distances, the targeted focal point ends up outside the DOF? Is the problem my lens? My M8? Me? Any thoughts on this would be much appreciated. Thank you! Link to post Share on other sites More sharing options...
Advertisement Posted December 31, 2012 Posted December 31, 2012 Hi piblondin, Take a look here Help: Trying to Solve 35mm f/1.4 ASPH FLE Focus Issue. I'm sure you'll find what you were looking for!
Erik Gunst Lund Posted December 31, 2012 Share #2 Posted December 31, 2012 Most fast glass has CA wide open, this is one of them. Looks like field curvature and a little bit of focus shift... On rangefinder lenses it's a compromise where to optimize the focus plane for field curvature and focus shift... Looks like it just needs a calibration... but Many more shots would be needed to be sure... Link to post Share on other sites More sharing options...
piblondin Posted December 31, 2012 Author Share #3 Posted December 31, 2012 Hi Erik, Thank you for your response. You're suggesting that the lens might need calibration? Thanks! Link to post Share on other sites More sharing options...
Erik Gunst Lund Posted December 31, 2012 Share #4 Posted December 31, 2012 I would shoot some more test images with full control of the camera on a tripod to see where optimum plane of focus is and how the DOF is at different apertures form 1.4 to 8.0 half stops. To get to know the lens better... Then decide what to do... Could also be the camera is off... Link to post Share on other sites More sharing options...
01af Posted December 31, 2012 Share #5 Posted December 31, 2012 In comparison to the immediate predecessor, i. e. the Summilux-M 35 mm Asph without floating elements, the current model with floating elements has the focus shift significantly reduced but not entirely eliminated. There still is some focus shift ... but it shouldn't be bad enough to spoil any pictures. By the way, it doesn't make any sense to shoot focus-shift test pictures hand-held. Do use a tripod! And test at various distances. Link to post Share on other sites More sharing options...
lct Posted December 31, 2012 Share #6 Posted December 31, 2012 The girl's boots look sharp. At what aperture did you shoot her? Link to post Share on other sites More sharing options...
jankap Posted December 31, 2012 Share #7 Posted December 31, 2012 Advertisement (gone after registration) The depth of field at 13 feet (4 m) is one foot in front and one and a halve foot in the back. But where lies the focus point? The photo of the girl: if the focus is on the wall, you only have one foot from the wall to eyes of the girl. The boots are further away and possibly are on a distance covered by the full DOF (2.5 feet). You should not forget too, that a sensor in behave of DOF is more critical than film. Further is the DOF on the lens barrel an estimated amount only. DOF is an agreement, not a fixed definition. Jan PS I bought a pre FLE yesterday Link to post Share on other sites More sharing options...
Erik Gunst Lund Posted December 31, 2012 Share #8 Posted December 31, 2012 The field curvature is quite obvious also in the two test shots. Link to post Share on other sites More sharing options...
TomB_tx Posted December 31, 2012 Share #9 Posted December 31, 2012 When you look critically with a scale as in your test shots you find some focus shift in almost all reasonably fast lenses. All versions of the Summicron 50 I've tested (haven't tried the unobtanium version) show some shift, although most people never notice it. I have the Voigtlander Nokton 35 f1.4 "classic" lens because of its small size and speed. I really like it at 1.4 and 2.0, but you have to compensate focus quite a bit as it stops down, or indeed you get nice in-focus backgrounds. Compared to it your lens is great! But my point is that if you know how your lens shifts as you stop down you can adjust the focus to compensate. (Of course, I've compensated the wrong way a few times when learning how... on a lens with both front focus and focus shift.) Some lenses, like the Zeiss Biogon 35 2.0 advertise that they have "almost no" focus shift - so it is a design choice how much to correct this "physics" issue. Link to post Share on other sites More sharing options...
lct Posted December 31, 2012 Share #10 Posted December 31, 2012 First tests i've done with the FLE don't show significant focus shift so far. Not sure that the OP's problem is there. Link to post Share on other sites More sharing options...
piblondin Posted December 31, 2012 Author Share #11 Posted December 31, 2012 To clarify, I attempted to focus on the girl, not on the wall. Aperture was set at f/2.8, I believe. This is the sort of shot that I never miss with my 40mm and 50mm lenses, and yet I totally missed focus here. Why would her boots be in focus but not her body? Shouldn't the plane of focus be flat not curved, if I'm holding the lens barrel parallel to the ground and perpendicular to the subject? Thanks for your replies and apologies for my naiveté. Link to post Share on other sites More sharing options...
01af Posted December 31, 2012 Share #12 Posted December 31, 2012 Why would her boots be in focus but not her body? Shouldn't the plane of focus be flat not curved ...? Yes it should, but it isn't ... just like lenses should be distortion-free, vignetting-free, and free of focus shift and chromatic aberrations but, alas, aren't. Link to post Share on other sites More sharing options...
lct Posted December 31, 2012 Share #13 Posted December 31, 2012 I would shoot a still subject at same distance and different apertures to be sure, with a tripod naturally. Link to post Share on other sites More sharing options...
ho_co Posted January 1, 2013 Share #14 Posted January 1, 2013 Note also that the camera was apparently aimed downward a bit in the picture of the girl and the wall, judging from the diverging verticals. That can partially explain the focus differential between the boots and the face. Link to post Share on other sites More sharing options...
jankap Posted January 2, 2013 Share #15 Posted January 2, 2013 The boots of the girl only seem to be sharp, I think. Sharp are the yellow structure, the white wall and the fire label. Not the bag and not the trousers. I think, it is a back focus problem, what reason it may have. By the way, out of the center line of the lens the DOF will be larger. The front and back planes of the DOF are curved. The plane of the exact focus is flat, the one perpendicular to the center line. Jan Link to post Share on other sites More sharing options...
01af Posted January 2, 2013 Share #16 Posted January 2, 2013 The front and back planes of the DOF are curved. The plane of the exact focus is flat ... Not true. Link to post Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.