wilfredo Posted January 2, 2008 Share #1 Posted January 2, 2008 Advertisement (gone after registration) I've never had a Back Focus problem and I don't know what it looks like. Can someone post a picture demonstrating this problem? I often read about this issue here on the forum. Thanks, Wilfredo Benitez-Rivera Photography Quote Link to post Share on other sites More sharing options...
Advertisement Posted January 2, 2008 Posted January 2, 2008 Hi wilfredo, Take a look here Back Focus Problem. I'm sure you'll find what you were looking for!
Shootist Posted January 3, 2008 Share #2 Posted January 3, 2008 Wilfredo I don't have a image at hand but backfous is easy to see if you have it. It is when you focus on something and some other thing behind what you thought/knew you were focusing on is in better/more focus. Like if you take a head shot of someone, straight on, and you focus on there eye/s and there ears are in better focus. That means the lens/camera is actually focusing on a point behind what you focused on. Same goes for frontfocus. IE focus on there eye/s and the tip of there nose is crystal clear while the eye/s are slightly blurry Quote Link to post Share on other sites More sharing options...
glenerrolrd Posted January 3, 2008 Share #3 Posted January 3, 2008 See attached chart. This is close to perfect focus...leading figure 8 and trailing figure 8 are both inside DOF. Backfocus would show the trailing figure 8s sharp and the leading one out of the DOF. Backfocus can be caused by either the camera or the lens. Many of the ASPH lenses also exhibit "focus shift" which is gradual backfocus as you stop down. The reason this is such an issue ..is that the apparent DOF using the M8 is much tighter than with prior film Ms. Basically you can just see it more clearly. 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! Quote 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/41704-back-focus-problem/?do=findComment&comment=441269'>More sharing options...
Bill W Posted January 3, 2008 Share #4 Posted January 3, 2008 Roger, Your depth of field chart is very easy to understand, is there an on-line version we could print and use. I am sure others would appreciate is as well. Quote Link to post Share on other sites More sharing options...
arthury Posted January 3, 2008 Share #5 Posted January 3, 2008 Roger, That's a nice focus chart. Where did you get this one? Where can I get one? Quote Link to post Share on other sites More sharing options...
ho_co Posted January 3, 2008 Share #6 Posted January 3, 2008 Not to intrude, but that's the chart Leica used in final evaluation of Roger's lenses after focus calibration. He gave an extensive rundown of that process in another thread. See also Nikon D70 Focus Chart, where Tim Jackson presents a downloadable chart as well as some photos showing what backfocus looks like. The Leica chart has the benefit that you can walk up to it and don't need to turn the camera to vertical. "What does backfocus look like?" It looks as if you goofed. Example: I made some snapshots outdoors in bright sun with the M8 and 75 Summilux of several performers on stage from about 30 feet. When I looked at the images, the performers were all out of focus, but the stage curtains about 10 feet behind them were sharp. The way I could tell it was backfocus was that the results were consistent over an entire afternoon's pictures with that lens, even though I changed lenses, distance and viewpoint a number of times. When I saw the same consistency in pictures I shot with the 75 on a Bulgarian holiday, it became undeniable. Lens is currently at Leica for adjustment. --HC Quote Link to post Share on other sites More sharing options...
sagarwal Posted January 3, 2008 Share #7 Posted January 3, 2008 Advertisement (gone after registration) An example of backfocus with a Noctilux at f/4. I had focused (or thought I had) on the number 7, but 3 and 4 look to be in much better focus. 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! Quote 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/41704-back-focus-problem/?do=findComment&comment=441284'>More sharing options...
wilfredo Posted January 3, 2008 Author Share #8 Posted January 3, 2008 This is very helpful. If the issue ever comes up for me I will be able to identify it. Hopefully it won't. Cheers, Wilfredo Benitez-Rivera Photography Quote Link to post Share on other sites More sharing options...
Catatac Posted January 3, 2008 Share #9 Posted January 3, 2008 Hi Wilfredo Here is an example of back focus for you. Its with the Lux 50/1.4. I focused on the person's nose but as you can see it is his shirt and ears which are sharply in focus. Managed to fix via the infinity/Alen key method thankfully. Quote Link to post Share on other sites More sharing options...
Albert4321 Posted January 3, 2008 Share #10 Posted January 3, 2008 okay, it may be a crazy unrelated question: How could one tell if it is back focus or focus shift? With the 35lux or 50lux, the image can be pin sharp wide open and back focus (focus shift) when shops down. Quote Link to post Share on other sites More sharing options...
Shootist Posted January 3, 2008 Share #11 Posted January 3, 2008 okay, it may be a crazy unrelated question: How could one tell if it is back focus or focus shift? With the 35lux or 50lux, the image can be pin sharp wide open and back focus (focus shift) when shops down. Yes but that only shows up with some lenses. Other lenses have more DOF to cover the focus shift and even with some of the 35 Lux's this isn't a problem. With my 50 Lux I do have focus shift but the point of focus never is out the DOF range. It doesn't move forward to much and mainly moves back as I stop down. So If I want front and back to be equal I have to front focus a little when stopping down Quote Link to post Share on other sites More sharing options...
ho_co Posted January 3, 2008 Share #12 Posted January 3, 2008 okay, it may be a crazy unrelated question: How could one tell if it is back focus or focus shift?With the 35lux or 50lux, the image can be pin sharp wide open and back focus (focus shift) when shops down. Albert-- The terms overlap. Focus shift can cause backfocus. If your lens is in focus wide open but exhibits focus shift on stopping down, that focus shift causes backfocus. So in this case, backfocus is a sign of the focus shift. Focus shift is a property of lens design. Backfocus is a characteristic of an image, and may be related to focus shift, to rangefinder inaccuracy, or to photographer error. Very good question, and your second sentence states accurately that a lens may focus properly wide open but then (due to focus shift) exhibit backfocus on stopping down. --HC Quote Link to post Share on other sites More sharing options...
thpeters Posted January 3, 2008 Share #13 Posted January 3, 2008 Here is an example of back focus for you. Its with the Lux 50/1.4. I focused on the person's nose but as you can see it is his shirt and ears which are sharply in focus. Managed to fix via the infinity/Alen key method thankfully. Hi Catatac, Many times there is a slightly head movement with a low shutter time....I have that same effect with my Summilux 50 mm. Maybe you can provide us with more details about this picture. I bet it is a low shutter time. Theo Quote Link to post Share on other sites More sharing options...
Catatac Posted January 3, 2008 Share #14 Posted January 3, 2008 Many times there is a slightly head movement with a low shutter time....I have that same effect with my Summilux 50 mm. Maybe you can provide us with more details about this picture. I bet it is a low shutter time. Theo Unfortunately not. The shot was taken at 1/1500. It was one of many that exhibited a back focus issue on my Lux (I did the ruler test as well). After adjustment, my Lux has been tack sharp (touch wood !) with exceptions such as the one you noted above. Quote Link to post Share on other sites More sharing options...
wwulfsohn Posted January 4, 2008 Share #15 Posted January 4, 2008 Once you diagnose that you have a back focus issue with a lens, is there anything you can do to adjust it away? Quote Link to post Share on other sites More sharing options...
ho_co Posted January 4, 2008 Share #16 Posted January 4, 2008 Once you diagnose that you have a back focus issue with a lens, is there anything you can do to adjust it away? William-- We've learned a lot about Leica lens design since the M8 came out, so your question doesn't allow a simple answer. First, yes, you can adjust it away if it's a fault, i.e. a misadjusted lens or a misadjusted rangefinder. You'll get other takes on this, but when I discover such a problem, I let Leica take care of it. Second, no, because many Leica lenses are designed to shift focus as they are stopped down, and it's possible that this may present a problem for you. For example, one reason the 75/1.4 was discontinued is that it has an extreme focus shift as it stops down. My 75 Summilux backfocuses slightly wide open, despite the fact that according to E Puts the focus should always be exact wide open. Since mine is already backfocusing at full aperture, backfocus becomes very noticeable at apertures around f/2.8 to f/5.6. When I focus by the rangefinder at about 30', the image is actually focused at about 40', and my intended subject is quite unsharp. The 75 Summilux and the 35 Summilux ASPH are designed to exhibit focus shift, but actual focus is supposed to remain within the depth of field. Some people say their 75's have been adjusted by Solms to slightly front-focus wide open so that the lens's intentional focus shift doesn't cause so great a backfocus as it's stopped down. In other words, you might discover that in some cases a given lens is backfocusing, and that may simply be the way the lens is designed. In other cases, the lens may be designed to show focus shift, and because it is improperly mounted, that focus shift is exaggerated and the backfocusing is egregious. There is also the possibility that the rangefinder in a person's camera is out of adjustment; that could also cause backfocus with all lenses, and can and should be adjusted by Leica. That's a completely different issue from having a lens with backfocus problem. A couple issues back, LFI carried an excellent article on the topic of back focus, focus shift and the sensitivity of the M8 to such matters. There have also been a number of threads here where we gradually figured out what was up before the LFI article. --HC Quote Link to post Share on other sites More sharing options...
thpeters Posted January 4, 2008 Share #17 Posted January 4, 2008 Unfortunately not. The shot was taken at 1/1500. It was one of many that exhibited a back focus issue on my Lux (I did the ruler test as well). After adjustment, my Lux has been tack sharp (touch wood !) with exceptions such as the one you noted above. Ok, but what was the ISO settings that time?. higher then 640? it is an inside shot right? Theo Quote Link to post Share on other sites More sharing options...
Shootist Posted January 4, 2008 Share #18 Posted January 4, 2008 Unfortunately not. The shot was taken at 1/1500. It was one of many that exhibited a back focus issue on my Lux (I did the ruler test as well). After adjustment, my Lux has been tack sharp (touch wood !) with exceptions such as the one you noted above. Ok, but what was the ISO settings that time?. higher then 640? it is an inside shot right? Theo ISO has nothing to do with focus. Whether the shot was taken at ISO 160 or 2500 does not matter. Back or front focus is camera/lens dependent and ISO will have no affect on focusing. What would make you think any differently. Quote Link to post Share on other sites More sharing options...
Perspectics Posted January 4, 2008 Share #19 Posted January 4, 2008 Hi Wilfredo Here is an example of back focus for you. Its with the Lux 50/1.4. I focused on the person's nose but as you can see it is his shirt and ears which are sharply in focus. Managed to fix via the infinity/Alen key method thankfully. Whats the "infinity/Alen key method"? Quote Link to post Share on other sites More sharing options...
Shootist Posted January 4, 2008 Share #20 Posted January 4, 2008 Whats the "infinity/Alen key method"? That is YOU adjust the wheel that the lens cam hit to make sure that at the infinity stop on the lens the images line up in the view/rangefinder at something that is really at infinity, like a star or the moon (A star is better). Trying to do this withanything else, like a pole or building that YOU THINK is far enough to be at infinty can give you false results. You use a 2mm allen key to turn the wheel mounting point which is off center of the wheel (or is it the wheel is off center to the center of that adjustment point?) to make the adjustment. There are a few threads on this subject and a simple search will turn them up. Quote Link to post Share on other sites More sharing options...
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