TonyField Posted September 18, 2013 Share #1 Posted September 18, 2013 Advertisement (gone after registration) All high speed lenses suffer from some degree of focus shift when stopping down from maximum aperture. I took some test shots (hand held, I did not have a tripod handy) to see how my 50mm F1.0 Noctilux responded (however the test was otherwise carefully done). The subject of the focusing was an appropriately bent piece of coat hanger which works well as a focus point with the Leica. It was about 3m from the camera. The patio bricks are about 22cm long. Seems to me that I should do a similar test with different focus distances This certainly indicates a shift of focus away from the camera when stopping down. In this case, with a focus point about 3m away, the shift of focus between F1.0 and F4.0 is an estimated 20 cm away from the camera. It would be interesting to see how the 50mm 0.95 newer Noctilux performs. Has anybody done such at test ?? Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/213093-50mm-f1-noctilux-focus-shift/?do=findComment&comment=2424137'>More sharing options...
Advertisement Posted September 18, 2013 Posted September 18, 2013 Hi TonyField, Take a look here 50mm F1 Noctilux focus shift. I'm sure you'll find what you were looking for!
IWC Doppel Posted September 18, 2013 Share #2 Posted September 18, 2013 Im not sure I follow your test, Id recheck using a tape measure held at 45 degrees and focus with a tripod at the middle then see how the focus shifts (The ruler/tape should be angles away from you so the range that can be measured). if its at 45 degrees, divide the measured in distance by 1.4 and youll be accurate enough Link to post Share on other sites More sharing options...
Gerard Posted September 18, 2013 Share #3 Posted September 18, 2013 You should run the test again. Use a tripod. Use an object that has strong typography (like a large cerial packet). And try it with the pack at 1m, then 2m, and so on. You should find that while dof moves from in front of the focal point, to behind the focal point as you stop down, the lens will also be most accurate at one distance. This f-stop/distance can be adjusted by re-shimming the lens if it is critical for you. I had my 75 Summilux shimmed for greatest accuracy at f2 and close focus (as I mainly use it for head shot portraits). Link to post Share on other sites More sharing options...
TonyField Posted September 18, 2013 Author Share #4 Posted September 18, 2013 ...You should run the test again. Use a tripod. Use an object that has strong typography (like a large cerial packet). And try it with the pack at 1m, then 2m, and so on. You should find that while dof moves from in front of the focal point, to behind the focal point as you stop down, the lens will also be most accurate at one distance. Indeed. Ideally the test should have been done with a tripod and should be done at multiple focus distances - but that does not invalidate the test. My only excuse is that I was more interested in the general degree of focus shift. As I indicated in my original post, a tripod and multiple focus distances should be done. I don't think the cereal box would be a good test target. With the bent coat hanger, I can bend it so that it is parallel to the sensor plane - the cereal box would not allow this. In addition, the wire is a better target for the rangefinder mechanism. All of my 50mm lenses focus "perfectly" wide open on the test target. My 50 F1.0, as you can see, is perfectly matched to the focus target (within any ability of mine to align the split/coincident image in the rangefinder). Repeated exposures at F1.0 resulted in only millimeter differences in the critical focus point. As far as I know, Leica sets the lenses for "proper focus" wide open - which is fine for me. I sent my M9 in for sensor replacement (serious banding) - and they also performed an extensive rangefinder readjustment. Before and after sensor replacement, the focus tests were identical for focus precision on my 50mm lenses. My 35mm and 90mm summicrons as well as my 135mm F4 were sent to Allendale for adjustment - that was 5 months ago - and they are still not done ... Link to post Share on other sites More sharing options...
TonyField Posted September 18, 2013 Author Share #5 Posted September 18, 2013 Im not sure I follow your test, Id recheck using a tape measure held at 45 degrees and focus with a tripod at the middle then see how the focus shifts (The ruler/tape should be angles away from you so the range that can be measured). if its at 45 degrees, divide the measured in distance by 1.4 and youll be accurate enough The test is rather simple. The focus target is a wire bent at 30 degrees off of vertical - since I shoot this target from 30 degrees, this ensures the target and the sensor plane are parallel. Since I use 30 degrees for shooting, the correction factor for distance is 0.87. Indeed, I should put a ruler in the test image - making judging focus shift a bit easier. However, the texture of the bricks make it pretty easy to estimate where the point of critical sharpness is. Link to post Share on other sites More sharing options...
Gerard Posted September 18, 2013 Share #6 Posted September 18, 2013 With the cerial box, you angle it at 45 degrees and focus on the edge of one letter in the middle of the logo, like the first 'd' in Shreddies'. It is similar in depth to a human head and gives a good real world understanding of what effect the shift has. Link to post Share on other sites More sharing options...
TonyField Posted September 18, 2013 Author Share #7 Posted September 18, 2013 Advertisement (gone after registration) True Gerard, the box could be used. However, I think the thin wire is a better target for the split/coincidence Leica focus system and the human eye to judge. None the less, any "good target" could be used with success. Link to post Share on other sites More sharing options...
MarkP Posted September 18, 2013 Share #8 Posted September 18, 2013 or a ruler or tape measure or focus calibration chart... Link to post Share on other sites More sharing options...
IWC Doppel Posted September 19, 2013 Share #9 Posted September 19, 2013 Maybe it's easier to see the focus on the ground with the full images, on my 27" iMaC i am really struggling to gauge sharpness of the ground, hence the reason to suggest a tape measure as it has measurement and something to easily see focus. My 75mm at f1.4 Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/213093-50mm-f1-noctilux-focus-shift/?do=findComment&comment=2424898'>More sharing options...
TonyField Posted September 19, 2013 Author Share #10 Posted September 19, 2013 Yes, the tape measure works well and gives you a metric directly for the degree of focus shift Link to post Share on other sites More sharing options...
TonyField Posted September 19, 2013 Author Share #11 Posted September 19, 2013 Have you done a focus shift test with the 75mm Summilux ?? Link to post Share on other sites More sharing options...
IWC Doppel Posted September 20, 2013 Share #12 Posted September 20, 2013 Have you done a focus shift test with the 75mm Summilux ?? Hi, yes the 75mm Summilux moves a little, it back focusses a little between f1.4-f2.8 then it's fine. Not enough to be a major concern for me, my Pre asph 50mm summilux moved more over the same range Link to post Share on other sites More sharing options...
IWC Doppel Posted September 20, 2013 Share #13 Posted September 20, 2013 At F8, a bit tricky at 1/8th Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/213093-50mm-f1-noctilux-focus-shift/?do=findComment&comment=2425001'>More sharing options...
thighslapper Posted October 27, 2013 Share #14 Posted October 27, 2013 With the M and the evf with focus peaking it is easy to see the focus shift on the 50/0.95..... It is quite noticeable between 0.95 and 1.4 ...... but at smaller apertures there is minimal change above 1.4 ...... at least at 1m, which is where I tried it whilst calibrating the camera. Most interestingly, the 'peaking' nearest point doesn't change that much ..... it's the 'peaking' rear limit behind the original focus point that marches backwards .... and presumably the perfect focus point, but as it is within the DOF it is not so noticeable. I have just readjusted my M's rangefinder to compensate for this .... a compromise point is needed to achieve perfect focus at 0.95 and still keep it ok for the other apertures (and other lenses). Once adjusted and then focussed fixed on a tripod it is very easy with the EVF and peaking to check all your other lenses and make sure you have got it right. It confirmed my 75/2 is front focussing by about 3cm at 1m which is useless ..... it will be going back for remedial treatment I have always had trouble with it ..... but have never been entirely sure why till now..... Focus peaking on the M is a real boon when it comes to things like this and rangefinder calibration in particular Link to post Share on other sites More sharing options...
MarkP Posted October 27, 2013 Share #15 Posted October 27, 2013 Tony, The others are quite right about using a tape measure to check this but it does seem that the ground at the level of the wire is in focus. I think much of what you are seeing here is loss of contrast when shooting wide open which is well known with this lens. Mark Link to post Share on other sites More sharing options...
algrove Posted October 29, 2013 Share #16 Posted October 29, 2013 With the cerial box, you angle it at 45 degrees and focus on the edge of one letter in the middle of the logo, like the first 'd' in Shreddies'. It is similar in depth to a human head and gives a good real world understanding of what effect the shift has. Now I have to tell my wife I am going to the grocery store to buy cereal so that I can calibrate lenses. She knows I am already crazy, but since I have not eaten cereal for 20+ years she will think I am over the top and put me in the loony house. My excuse will be that I need a real world understanding of what effect the shift has on my cereal box. Then she will put me in a straight jacket and deliver me to the looney house! Link to post Share on other sites More sharing options...
MarkP Posted October 31, 2013 Share #17 Posted October 31, 2013 Now I have to tell my wife I am going to the grocery store to buy cereal so that I can calibrate lenses. She knows I am already crazy, but since I have not eaten cereal for 20+ years she will think I am over the top and put me in the loony house. My excuse will be that I need a real world understanding of what effect the shift has on my cereal box. Then she will put me in a straight jacket and deliver me to the looney house! Our wives already know we're crazy Link to post Share on other sites More sharing options...
Gerard Posted October 31, 2013 Share #18 Posted October 31, 2013 Then she will put me in a straight jacket and deliver me to the looney house! They don't have 'looney houses' any more. The authorities will just bung you a bunch of benefits (cash) and hope you manage to look after yourself. Link to post Share on other sites More sharing options...
algrove Posted October 31, 2013 Share #19 Posted October 31, 2013 They don't have 'looney houses' any more. The authorities will just bung you a bunch of benefits (cash) and hope you manage to look after yourself. Sounds even better-more money for gear! Link to post Share on other sites More sharing options...
Gerard Posted October 31, 2013 Share #20 Posted October 31, 2013 I foresee a rush on Shreddies tomorrow. Link to post Share on other sites More sharing options...
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