pico Posted February 12, 2012 Share #21 Â Posted February 12, 2012 Advertisement (gone after registration) The human visual system including the visual cortex is an amazing thing. Â For aerial recon we had 9" square (negative to print) stereo images viewed through devices with which you are familiar. The human brain could, with training, tease out enormous detail. . Link to post Share on other sites More sharing options...
Advertisement Posted February 12, 2012 Posted February 12, 2012 Hi pico, Take a look here Definition of Infinity?. I'm sure you'll find what you were looking for!
darylgo Posted February 12, 2012 Share #22  Posted February 12, 2012 2000 times the focal length or about 62 miles for a 50mm lens. Y'all should see the fanatic calculations aerial/mapping/recon people go through for photography. First, all lenses are certified at widest aperture, and no conventional aircraft fly high enough for their long lenses. The Black Bird flies at a publicized ~17 miles altitude, although we know it goes higher, quite possibly to 90,000 feet plus. It literally skips along the atmosphere varying 1000 feed at a time, like a stone skips across water. Talk about focusing issues.  -- Pico - once stationed with the RAF @ Upper Heyford - where we knew this stuff. The U2 was easier to deal with.  That must have been one great ride. For 62 miles to be a multiple of 2000 wouldn't the focal length need to be 62 x 5280 x 12 x 2.54 x 10 /2000 or miles x feet/mile x inche/foot x cm/inch x mm/cm divided by 2000 = 50,000mm? Link to post Share on other sites More sharing options...
tobey bilek Posted February 12, 2012 Share #23 Â Posted February 12, 2012 Infinity is where light rays radiating from the subject are parallel. Â 200 meters,no. 1/2 mi probably ok. I use a star at night. Link to post Share on other sites More sharing options...
lct Posted February 12, 2012 Share #24  Posted February 12, 2012 […] human visual acuity is capable of detecting 0.6-1.0 arc minutes under normal viewing. But, it can improve to as much as 0.13 arc minutes under hyper acuity viewing, such as that utilized in lining up the range finder patch[…] The critical base length formula i was referring to has been used since the sixtees if memory serves. I don't know if visual acuity values have changed since then but it has always worked for me with my 0.68x (M8.2), 0.72x (M4, M4-2), 0.91x (M3) and 1:1 (R-D1) rangefinders. Link to post Share on other sites More sharing options...
Rick Posted February 12, 2012 Share #25 Â Posted February 12, 2012 The critical base length formula i was referring to has been used since the sixtees if memory serves. I don't know if visual acuity values have changed since then but it has always worked for me with my 0.68x (M8.2), 0.72x (M4, M4-2), 0.91x (M3) and 1:1 (R-D1) rangefinders. Â Have to define terms: No idea what you mean by "critical base length formula?" and you need to define "visual acuity." There are several ways to measure the human visual system when it comes to perceived resolution. The range finder system relays on one of our strongest abilities to resolve - vernier alignment. Â We really don't fully understand how the human visual system can resolve beyond the spacial frequency of the size of the cones in the fovea of the retina. But, we can by a substantial amount. Link to post Share on other sites More sharing options...
lct Posted February 12, 2012 Share #26 Â Posted February 12, 2012 Have to define terms: No idea what you mean by "critical base length formula?"...t. It's been discussed in the thread i thought you were referring to. See http://www.l-camera-forum.com/leica-forum/customer-forum/219656-rangefinder-focussing-accuracy-rule-thumb.html. Link to post Share on other sites More sharing options...
lars_bergquist Posted February 12, 2012 Share #27  Posted February 12, 2012 Advertisement (gone after registration) Re: The f x 1000 rule  There's a church tower about 2kms from where I live. I went out and took two pictures of it with my M9. The 50mm Summilux ASPH was set to f:1.7 (1/4000 at ISO80).The first picture is the full frame.  The second picture was focused on a roof ventilator at a distance of about 60m. I show a strong crop. At that distance the index mark was about 3/4mm from the infinity setting.  The third picture was taken at mechanical and rangefinder infinity. The difference between the two settings was visible in the rangefinder as it should be.  So it seems that with modern lens and sensor technology, the textbook rule is too lax. The churchtower is visibly sharper in the third picture than in the second.  More than half a century ago, I went outside one early summer evening and was stunned to see, hanging in the still dark blue sky, a tiny but intensely bright crescent 'moon'. It took me several seconds to grasp that what I was seeing was the evening star – the planet Venus. The first man to 'officially' see that was Galileo Galilei in the early 17th century, and he used a primitive telescope.  What astronomers call 'the seeing' was perfect. The air was very still and clear, and the still slightly illuminated sky lowered the contrast. Still, it was a unique event that has never been repeated.  What we can see depends very much on conditions. But seeing Venus in the sky, two vernier lines and a print at 25cm are three different things and I think that a realistic resolution standard for print viewing is pretty close to 1.0–0.8 minutes of angle.  The old man who saw it with his own eyes 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/172450-definition-of-infinity/?do=findComment&comment=1924502'>More sharing options...
giordano Posted February 12, 2012 Share #28 Â Posted February 12, 2012 So it seems that with modern lens and sensor technology, the textbook rule is too lax. The churchtower is visibly sharper in the third picture than in the second. Â Thank you for the demonstration, Lars. It's always pleasing when the world complies with one's calculations! Link to post Share on other sites More sharing options...
mby Posted February 12, 2012 Share #29  Posted February 12, 2012 n divided by zero, where n is any number? (Just kidding. )   Except zero.  Better take lim (1/x) with x ->0, as n/0 is not defined... Link to post Share on other sites More sharing options...
ravinj Posted February 12, 2012 Author Share #30  Posted February 12, 2012 Re: The f x 1000 rule The third picture was taken at mechanical and rangefinder infinity. The difference between the two settings was visible in the rangefinder as it should be.  The old man who saw it with his own eyes  Lars - thanks for the samples. I would like to know what is the difference between rangefinder and mechanical infinity? Your samples and what I have seen do demonstrate that f x 1000 rule needs to be changed to f x 10,000 at least.  The not so young man coming to grips with the M9 and hoping that Leica would step up and implement a 21st century focusing mechanism that does not rely on perfect vision or anachronisms like magnifiers. Link to post Share on other sites More sharing options...
pico Posted February 12, 2012 Share #31 Â Posted February 12, 2012 That must have been one great ride. For 62 miles to be a multiple of 2000 wouldn't the focal length need to be 62 x 5280 x 12 x 2.54 x 10 /2000 or miles x feet/mile x inche/foot x cm/inch x mm/cm divided by 2000 = 50,000mm? Â I'll trust your math. Â I must add something - there is no record whatsoever of a Blackbird landing in the UK while I was there (up to '68). To the best of my knowledge. Link to post Share on other sites More sharing options...
pgk Posted February 12, 2012 Share #32 Â Posted February 12, 2012 Many years ago I remember being told by an optical lecturer that the 'infinity' mark on many lenses was double the last marked distance (the figure in m or feet) shown on the lens. I never actually bothered to check this out but seem to remember thinking that it was a logical and useful idea if true. It might be worth looking at older Leica lenses to see if this was, at one time, how lenses were actually engraved and if so it may help determine at what point the designer considered the lens to be focused acceptably and effectively at 'infinity'. Link to post Share on other sites More sharing options...
Lindolfi Posted February 12, 2012 Share #33 Â Posted February 12, 2012 Â This is a big error. For example, human visual acuity is capable of detecting 0.6-1.0 arc minutes under normal viewing. But, it can improve to as much as 0.13 arc minutes under hyper acuity viewing, such as that utilized in lining up the range finder patch . I believe his final conclusion is a little off and lenses can be focused with a better precision than what he concluded. Â The human visual system including the visual cortex is an amazing thing. Â Rick, Bert agrees fully, in fact he mentioned the Vernier acuity himself (see here ) Â Ofcourse that high Vernier acuity is only available in good light and with a subject with nice properties for this kind of focussing. Link to post Share on other sites More sharing options...
mjh Posted February 12, 2012 Share #34 Â Posted February 12, 2012 Many years ago I remember being told by an optical lecturer that the 'infinity' mark on many lenses was double the last marked distance (the figure in m or feet) shown on the lens. Why would one mark any other point but real infinity (within mechanical tolerances)? Link to post Share on other sites More sharing options...
Rick Posted February 13, 2012 Share #35 Â Posted February 13, 2012 Rick, Bert agrees fully, in fact he mentioned the Vernier acuity himself (see here )Â Ofcourse that high Vernier acuity is only available in good light and with a subject with nice properties for this kind of focussing. Â Didn't see that. I read the first portion with the assumption of 1 arc minute of resolution used in the calculations. I didn't see that it was corrected. It really is amazing to me the way the range finder was designed takes advantage of the strength of our visual system to achieve better than 20/20 focusing ability. Â Cheers Link to post Share on other sites More sharing options...
lars_bergquist Posted February 13, 2012 Share #36  Posted February 13, 2012 Lars - thanks for the samples. I would like to know what is the difference between rangefinder and mechanical infinity? Your samples and what I have seen do demonstrate that f x 1000 rule needs to be changed to f x 10,000 at least. The not so young man coming to grips with the M9 and hoping that Leica would step up and implement a 21st century focusing mechanism that does not rely on perfect vision or anachronisms like magnifiers.  Ideally, they would coincide. But even with 'perfect' adjustment, to the micron level, there will be a limit when the rangefinder cannot discriminate between two slightly different distances. And the same reasoning applies to the lens. What breaks first, the accuracy of the rangefinder, that of the lens, or that of the eye, is anybody's guess.  But remember that the test frames were shot at the aperture detent between 1.4 and 2.0. We do not often shoot landscapes at that aperture.  The old man who saw Venus Link to post Share on other sites More sharing options...
SJP Posted February 13, 2012 Share #37  Posted February 13, 2012 Except zero.  Better take lim (1/x) with x ->0, as n/0 is not defined... No not quite 0/0 can be anything you like, take lim (1-cos(x))/x^2 for x=> 0then lim (1-cos(x))/x^2 ~ lim (1-1+½x^2))/x^2 ~ ½ while still (1-cos(x)) => 0 and x^2 => 0  Analogously lim (1-cos(x))/x goes to zero (½x^2/x)  Some infinites are more infinite than others, some zeros are more zero than others.  Anyway - infinite focus is indeed defined as where the sensor is in the f focal plane i.e. a collimated ray is in focus. That is perfectly allowed by physics, e.g. 1/f = 1/B +1/O, take 1/B = 1/f ("bild" B is at f) then 1/O = 1/f -1/B = 1/f -1/f = 0 and thus object distance O is "infinite".  More importantly while the DoF gives you some margin for error, to be decided at your own convenience or use the "definition" of 30 micron, it does not change the definition of infinite focus above.  Of course you can refocus closer and still keep infinite objects within the CoC/DoF but that is a different matter.  Finally evaluation of sharpness by using "cropped" images may be interesting but really messes up the whole procedure - if you crop then your acceptable DoF changes as the crop process itself changes the CoC value, even if you use the standard 30 micron for a FF image. So if you crop by a factor 10 then the CoC is only 3 micron and any minor misfocus is visible.  Phrased differently: The more you crop the more sensitive you become to subtle differences in focus that are not considered worthwhile for the entire frame. (Basically that is the definition of the CoC "acceptable sharpness" at normal viewing conditions). This is nicely shown in Lars' pictures above. Link to post Share on other sites More sharing options...
pgk Posted February 13, 2012 Share #38 Â Posted February 13, 2012 Why would one mark any other point but real infinity (within mechanical tolerances)? If double the last marked distance was a point indistinguishable from infinity then whether infinity was mechanically 'correct' or at twice this distance is immaterial. This thread is about a definition; this is a possible one (of many). Link to post Share on other sites More sharing options...
mjh Posted February 13, 2012 Share #39 Â Posted February 13, 2012 This thread is about a definition; this is a possible one (of many). There is just one definition and that was given in #23 (http://www.l-camera-forum.com/leica-forum/1973843-post23.html). There are also various rules of thumb. But as far as the marking on the distance scale is concerned, it is supposed to be exact (within tolerances) and to conform to the definition. The light rays from a subject at infinity are parallel and for a lens to be focused at infinity the distance between its rear principal plane and the sensor must be equal to its focal length. The infinity marking signifies where this condition holds. Link to post Share on other sites More sharing options...
darylgo Posted February 13, 2012 Share #40 Â Posted February 13, 2012 When looking at Mtf curves for macro lenses Zeiss gives two or more distances, in the case of the Contax 645 120mm F4 Makro it gives: M1:1, M1:2 and this label: Â Unless otherwise indicated, the performance data refer to large object distances, for which normal photographic lenses are primarily used. Â What distance is Zeiss using? And is this not their (practical) definition of infinity for testing purposes? I would be willing to submit it is a lot less than fx1000 otherwise they would be shooting at a target impossible to construct and need to test on another planet in order to eliminate atmospheric haze. Â 120mm Makro: http://applications.zeiss.com/C12578620052CA69/0/F57F3589D022C8D3C125786800233778/$file/apo-makro-planar4_120mm_e.pdf Link to post Share on other sites More sharing options...
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