TonyField Posted November 18, 2014 Share #121 Â Posted November 18, 2014 Advertisement (gone after registration) ***Yawn***. I've watching this thread descend into a argument between techies. Do you guys actually take photos or do you get off on analysing technical specifications and reading textbooks on advanced optics? And believe it or not some of you wonder why there aren't more women on this forum. Â As it turns out, I personally know more women than men who are technically very astute in photography. They apply the technical knowledge well when the need arises. This is true of people I know in digital photography as well as in the good old days of darkroom work. Link to post Share on other sites More sharing options...
Advertisement Posted November 18, 2014 Posted November 18, 2014 Hi TonyField, Take a look here New article on overgaard.dk - "Leica 75mm Summilux-M f/1.4". I'm sure you'll find what you were looking for!
pico Posted November 18, 2014 Share #122 Â Posted November 18, 2014 CoC is a calculation variable and not a characteristic of lens, sensor or film. Â We can use a small CoC to calculate but the physics of real life may not follow. Link to post Share on other sites More sharing options...
CheshireCat Posted November 18, 2014 Share #123  Posted November 18, 2014 CoC is a calculation variable and not a characteristic of lens, sensor or film. We can use a small CoC to calculate but the physics of real life may not follow.  CoC is a calculation variable used to model a characteristic of lenses. As any mathematical model, it is an approximation of physics. But if the approximation error is controlled, the model is good enough to support a lot of interesting and useful theories.  If the the physics of real life does not follow, then the model is wrong.  However, although the CoC model is very simplistic, it has been working fine for quite a few years. Link to post Share on other sites More sharing options...
pop Posted November 18, 2014 Share #124 Â Posted November 18, 2014 However, although the CoC model is very simplistic, it has been working fine for quite a few years. Â ... when used for the purpose and within the constraints for which it was invented. Link to post Share on other sites More sharing options...
CheshireCat Posted November 18, 2014 Share #125 Â Posted November 18, 2014 ... when used for the purpose and within the constraints for which it was invented. Â Tautological, but certainly true. Link to post Share on other sites More sharing options...
pop Posted November 18, 2014 Share #126  Posted November 18, 2014 Tautological  Not when you look at some of the arguments used within this thread. Link to post Share on other sites More sharing options...
CheshireCat Posted November 19, 2014 Share #127 Â Posted November 19, 2014 Advertisement (gone after registration) Not when you look at some of the arguments used within this thread. Â If you do not agree with some of the arguments, then please speak your mind, and point out any inconsistency. Clearly. What is wrong, Philipp ? Link to post Share on other sites More sharing options...
01af Posted November 19, 2014 Share #128  Posted November 19, 2014 CoC is a calculation variable ... Cir·cle of Con·fu·sion [n] — A group of photographers desperately trying to understand –> Depth-of-Field.  Seriously ... the circle of confusion—or more precisely, its diameter—is not just a calculation variable. It's a physical entity that can be seen and measured. Probably you're confusing the circle of confusion with the maximum allowed diameter of the circle of confusion which is used for depth-of-field calculations and is often falsely called just 'circle of confusion' for short ... after all, everybody knows what's meant, right? Link to post Share on other sites More sharing options...
pop Posted November 19, 2014 Share #129  Posted November 19, 2014 Cir·cle of Con·fu·sion [n] — A group of photographers desperately trying to understand –> Depth-of-Field.  See what happens when photographers are out of their depths? Link to post Share on other sites More sharing options...
pop Posted November 19, 2014 Share #130 Â Posted November 19, 2014 If you do not agree with some of the arguments, then please speak your mind, and point out any inconsistency. Â It's not about agreement, particularly since I have joined the discussion myself. Â However: Â The concept of depth of field and its one prominent measure, the CoC, is a pragmatic approach to the question of how to select an appropriate aperture such that everything which needs to be sharp in a picture will be reasonably sharp when viewed under a rather limited set of circumstances. The CoC or, rather, the disc shown in place of a point in an image is, of course, an artifact of any lens based imaging device. Â The reasoning behind the idea of the depth of field is straightforward. I rather think that in most cases the DoF for any given lens is calculated for an abstract imaging device of the given focal length and not for any particulars of a specific lens. Â The whole concept centers on this single artifact. It holds for a reasonable set of magnification factors and viewing distances. Â Pardon for repeating the obvious; I need some kind of consensus before proceeding to the limitations, which now follow: Â - The concept of the DoF, based on the CoC, does not take into account any other kinds of imaging artifacts which may be present at the same time. Obviously, the blurred part of the image is not only described in terms of the CoC alone as we would never have any discussions about Bokeh. - The concept does not take into account any other kinds of artifacts introduced by other steps in the processing chain, such as oscillations of the enlarger columns, aberrations of the enlarger's lens and so on which may impose limits on the magnification scale. - The concept may become inapplicable for larger scales of magnification if they reveal other artifacts, such as aberrations of the imaging device or quantization noise. Â By "applicable" I understand that you can use the underlying formulas with confidence that the final picture after magnification and when viewed from a "reasonable" distance is reasonably sharp. Â The presence of and possibly interaction with other artifacts, introduced in any step of the processing chain at all, might render the DoF calculation less than useful. Â The quantization device and process in conjunction with the CoC have certainly been discussed within this thread. As the quantization interacts with the visual appearance of the CoC, the concept of the DoF can only be used for large factors of magnification with some caveats. Link to post Share on other sites More sharing options...
mmradman Posted November 19, 2014 Share #131  Posted November 19, 2014 See what happens when photographers are out of their depths?  Talking of accuracy is it photographers as in people who photograph or people who own cameras and discuss photography relates issues on the internet. Reading thread would be beneficial if technical points were illustrated with sample images illustrating particular point(s), Ken Rockwell does it  Back to Summilux 75mm, it is lens capable of wonderful images, all internet pundits already said so. Link to post Share on other sites More sharing options...
pico Posted November 19, 2014 Share #132 Â Posted November 19, 2014 Interesting approaches here. Â Speaking of CoC and nudged by my dislike of late APO Leica lenses OOF, I think of the inclusion of an apodization filter is appropriate. Does not such a filter selectively modify the CoC? Link to post Share on other sites More sharing options...
01af Posted November 20, 2014 Share #133 Â Posted November 20, 2014 Does not such a filter selectively modify the CoC? It modifies the circle of confusion but not the diameter thereof. Link to post Share on other sites More sharing options...
TonyField Posted November 20, 2014 Share #134  Posted November 20, 2014 Interesting approaches here. Speaking of CoC and nudged by my dislike of late APO Leica lenses OOF, I think of the inclusion of an apodization filter is appropriate. Does not such a filter selectively modify the CoC? A number of years ago I was playing with "apodiztion filters" on my 6x7 film reflex camera. (Actually, I was trying to get a "glow" like a Zeiss Softar filter using the peripheral of the lens which would emphasize aberations) Using photoshop, I created a square image about 2 inches in diameter. Among other things, I applied a radial gradient and then adjusted the black-to-white image with photoshop "levels" or "curves" to have a middle grey to white transition. I printed this on transparent mylar printing material on my laser jet. After cutting the "print" into circular forms, I taped it to the lens. I tried a few different overall densities and shapes..  Indeed, this did change the bokeh of the out of focus "blobs" and bright/dark transitions. I only shot 20 frames on this silly experiment (2 rolls of 120 was all I was prepared to waste).  I have not tried this on any digital camera - no particular interest in this area Link to post Share on other sites More sharing options...
01af Posted November 20, 2014 Share #135  Posted November 20, 2014 A number of years ago I was playing with "apodization filters" on my 6x7 film reflex camera. (Actually, I was trying to get a "glow" like a Zeiss Softar filter using the peripheral of the lens which would emphasize aberrations). [...] So your home-made filter—and the intended effect thereof—was just the antipode of an apodisation filter. Link to post Share on other sites More sharing options...
Erik Gunst Lund Posted November 20, 2014 Share #136 Â Posted November 20, 2014 ....to have a middle grey to white transition..... Â Just to clearify, I guess you are stating you used a transition from a 'middle' (something like 50 %) gray at the edge that transitioned to transparent in the center? Â Also why not black to transparent? Link to post Share on other sites More sharing options...
jaapv Posted November 20, 2014 Share #137 Â Posted November 20, 2014 Why not a Minolta/Sony STF 135/2.8 lens for these experiments? Link to post Share on other sites More sharing options...
CheshireCat Posted November 20, 2014 Share #138  Posted November 20, 2014 Seriously ... the circle of confusion—or more precisely, its diameter—is not just a calculation variable. It's a physical entity that can be seen and measured.  The CoC is just a simplified model of the complex physical entity it represents. The actual shape may not even be a circle, and the density of the shape may not be uniform for different reasons. For example, if the lens has three blades, the shape is a triangle, and you will have a hard time measuring its diameter.  In any case, the simplified CoC model works as a calculation variable for most purposes. The problem is just in the calculations done with it. The classic DoF formulas do not take sensor element size into account, therefore it is not uncommon to see photographers thinking their lens is broken when they examine their digital photos.  Luckily, some people use formulas to solve problems. If the old formulas don't work any more, they come up with new ones. And so we have new DoF formulas that can help us take sharp digital photos. Link to post Share on other sites More sharing options...
pop Posted November 20, 2014 Share #139 Â Posted November 20, 2014 There are no sharp digital photos. They're all pixelated. Link to post Share on other sites More sharing options...
TonyField Posted November 20, 2014 Share #140  Posted November 20, 2014 So your home-made filter—and the intended effect thereof—was just the antipode of an apodisation filter. Indeed I wanted to opposite That is why I put "apodization filter" in quotes :)  Just to clearify, I guess you are stating you used a transition from a 'middle' (something like 50 %) gray at the edge that transitioned to transparent in the center? Also why not black to transparent? My test filters were made in three styles with gradients dark in the centre and light on the edges, centre light to dark edges, and completely transparent with a some petroleum jelly on dabbed on the surface.  All versions produced different bokeh effects.  Why not a Minolta/Sony STF 135/2.8 lens for these experiments? Nice idea ... however that would be an expensive experiment Link to post Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.