On Fri, 06 Jan 2012 08:36:31 -0600, "steveu" <steveu@n_o_s_p_a_m.coppice.org> wrote: [Snipped by Lyons]>> >>Hi Rune, >> it seems like the Norwegian education system is run >>by idiots, but I bet it's still not as bad as the >>self-destructive lunatics in America. Here in the >>states we have a government organization called the >>Equal Employment Opportunity Commission (EEOC), >>an outrageously crazy organization that has far too much >>influence over American business. Those harebrained >>EEOC fools have issued a "letter" warning American >>businesses that it might someday be illegal for a >>business to require that job applicants have a high >>school diploma!! I'm not making this up. >> >>(Why are white cultures so suicidal????) > >What a strangely racist thing to say. Ask any middle aged Indian or Chinese >about their education system and will get just as many sad stories about >how their education system has been wrecked. > >SteveHi Steve, Well, ... I don't know if that's true or not. I have no one to ask. But I can tell ya' this: I've been teaching a DSP class for 13 years now. Thirteen years ago a class would consist of 8 white guys and one Indian or Chinese. Last year my typical class consisted of 8 Indian or Chinese and one white guy. See Ya', [-Rick-]
Internet access during exams
Started by ●January 5, 2012
Reply by ●January 7, 20122012-01-07
Reply by ●January 8, 20122012-01-08
>On Fri, 06 Jan 2012 08:36:31 -0600, "steveu" ><steveu@n_o_s_p_a_m.coppice.org> wrote: > > [Snipped by Lyons] >>> >>>Hi Rune, >>> it seems like the Norwegian education system is run >>>by idiots, but I bet it's still not as bad as the >>>self-destructive lunatics in America. Here in the >>>states we have a government organization called the >>>Equal Employment Opportunity Commission (EEOC), >>>an outrageously crazy organization that has far too much >>>influence over American business. Those harebrained >>>EEOC fools have issued a "letter" warning American >>>businesses that it might someday be illegal for a >>>business to require that job applicants have a high >>>school diploma!! I'm not making this up. >>> >>>(Why are white cultures so suicidal????) >> >>What a strangely racist thing to say. Ask any middle aged Indian orChinese>>about their education system and will get just as many sad stories about >>how their education system has been wrecked. >> >>Steve > >Hi Steve, > Well, ... I don't know if that's true or not. >I have no one to ask. > >But I can tell ya' this: I've been teaching a DSP class >for 13 years now. Thirteen years ago a class would consist >of 8 white guys and one Indian or Chinese. >Last year my typical class consisted of 8 Indian or Chinese >and one white guy. > >See Ya', >[-Rick-]What conclusion do you draw from that? I guess it would depend a lot on whether your students were Americans of Asian origin, or Asians who expect to make their futures back in Asia. Steve
Reply by ●January 9, 20122012-01-09
On Jan 7, 4:45�am, Mac Decman <dearman.m...@gmail.com> wrote:> On Fri, 06 Jan 2012 15:14:35 -0500, Jerry Avins <j...@ieee.org> wrote: > >On 1/5/2012 5:40 PM, Rune Allnor wrote: > >> Just a heads-up / warning for the regulars who answer > >> questions and provide other help here: > > >> The Norwegian Ministry of Education is abut to test > >> examinations where students have access to internet: > > >>http://www.aftenposten.no/nyheter/iriks/Skeptiske-til--bruke-Internet... > > >> (Haven't found an English version yet; no doubt some will > >> pop up as soon the international news stations pick up on > >> this lunacy.) > > >> As for now, there is a non-vanishing chance that there > >> might pop up questions from students who need answers > >> not for homework or projects, but for exams. The idea > >> is insane enough to actually spread to other parts of > >> the world, so beware; the answers you give here might > >> be what get your next colleague his or her diploma... > > >I have a small and simple web site on which I have a few recipes and > >self-aggrandizing rants. It is now pretty much in disrepair. You can the > >public stuff athttp://users.rcn.com/jyavins/, but there's a lot you > >can't see.http://users.rcn.com/jyavins/gathering.jpgis one example of > >that. It would be easy for me to post pages of facts and formulas if I > >had an exam that allowed web access. (So how do you like mt vulture > >pictures? One was taken withhttp://users.rcn.com/jyavins/photoadapter.htm.) > > >Jerry > > Hey Jerry, > Have you ever built an adaptor to turn your lenses around to shoot > macro. �I was thinking of making one in our shop one day.- Hide quoted text - > > - Show quoted text -If you do this in an afocal sense, it can work. But if you just try to use a telescope objective this way, you will likely run into a lot of spherical aberation. Clay
Reply by ●January 9, 20122012-01-09
On 1/9/2012 10:07 AM, Clay wrote:> On Jan 7, 4:45 am, Mac Decman<dearman.m...@gmail.com> wrote: >> On Fri, 06 Jan 2012 15:14:35 -0500, Jerry Avins<j...@ieee.org> wrote: >>> On 1/5/2012 5:40 PM, Rune Allnor wrote: >>>> Just a heads-up / warning for the regulars who answer >>>> questions and provide other help here: >> >>>> The Norwegian Ministry of Education is abut to test >>>> examinations where students have access to internet: >> >>>> http://www.aftenposten.no/nyheter/iriks/Skeptiske-til--bruke-Internet... >> >>>> (Haven't found an English version yet; no doubt some will >>>> pop up as soon the international news stations pick up on >>>> this lunacy.) >> >>>> As for now, there is a non-vanishing chance that there >>>> might pop up questions from students who need answers >>>> not for homework or projects, but for exams. The idea >>>> is insane enough to actually spread to other parts of >>>> the world, so beware; the answers you give here might >>>> be what get your next colleague his or her diploma... >> >>> I have a small and simple web site on which I have a few recipes and >>> self-aggrandizing rants. It is now pretty much in disrepair. You can the >>> public stuff athttp://users.rcn.com/jyavins/, but there's a lot you >>> can't see.http://users.rcn.com/jyavins/gathering.jpgis one example of >>> that. It would be easy for me to post pages of facts and formulas if I >>> had an exam that allowed web access. (So how do you like mt vulture >>> pictures? One was taken withhttp://users.rcn.com/jyavins/photoadapter.htm.) >> >>> Jerry >> >> Hey Jerry, >> Have you ever built an adaptor to turn your lenses around to shoot >> macro. I was thinking of making one in our shop one day.- Hide quoted text - >> >> - Show quoted text - > > If you do this in an afocal sense, it can work. But if you just try to > use a telescope objective this way, you will likely run into a lot of > spherical aberation.It's a rather thick doublet, about f/3, obviously not part of a telescope. I had used it to make an acceptable collimated light source, then reworked it to make the close-up attachment. Speed is not a criterion for the slide copier, but color fringing would be. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●January 9, 20122012-01-09
On Jan 9, 11:56�am, Jerry Avins <j...@ieee.org> wrote:> On 1/9/2012 10:07 AM, Clay wrote: > > > > > > > On Jan 7, 4:45 am, Mac Decman<dearman.m...@gmail.com> �wrote: > >> On Fri, 06 Jan 2012 15:14:35 -0500, Jerry Avins<j...@ieee.org> �wrote: > >>> On 1/5/2012 5:40 PM, Rune Allnor wrote: > >>>> Just a heads-up / warning for the regulars who answer > >>>> questions and provide other help here: > > >>>> The Norwegian Ministry of Education is abut to test > >>>> examinations where students have access to internet: > > >>>>http://www.aftenposten.no/nyheter/iriks/Skeptiske-til--bruke-Internet... > > >>>> (Haven't found an English version yet; no doubt some will > >>>> pop up as soon the international news stations pick up on > >>>> this lunacy.) > > >>>> As for now, there is a non-vanishing chance that there > >>>> might pop up questions from students who need answers > >>>> not for homework or projects, but for exams. The idea > >>>> is insane enough to actually spread to other parts of > >>>> the world, so beware; the answers you give here might > >>>> be what get your next colleague his or her diploma... > > >>> I have a small and simple web site on which I have a few recipes and > >>> self-aggrandizing rants. It is now pretty much in disrepair. You can the > >>> public stuff athttp://users.rcn.com/jyavins/, but there's a lot you > >>> can't see.http://users.rcn.com/jyavins/gathering.jpgisone example of > >>> that. It would be easy for me to post pages of facts and formulas if I > >>> had an exam that allowed web access. (So how do you like mt vulture > >>> pictures? One was taken withhttp://users.rcn.com/jyavins/photoadapter.htm.) > > >>> Jerry > > >> Hey Jerry, > >> Have you ever built an adaptor to turn your lenses around to shoot > >> macro. �I was thinking of making one in our shop one day.- Hide quoted text - > > >> - Show quoted text - > > > If you do this in an afocal sense, it can work. But if you just try to > > use a telescope objective this way, you will likely run into a lot of > > spherical aberation. > > It's a rather thick doublet, about f/3, obviously not part of a > telescope. I had used it to make an acceptable collimated light source, > then reworked it to make the close-up attachment. Speed is not a > criterion for the slide copier, but color fringing would be. > > Jerry > -- > Engineering is the art of making what you want from things you can get. > �����������������������������������������������������������������������- Hide quoted text - > > - Show quoted text -One of the things that helps alot with collimation is picking a lens (or group) with the right Coddington factor. Essentially spherical aberation is minimized when each lens surface contributes equally to the overall refraction[1]. This is why eyeglass lenses are menisci. Clay [1] this sharing the workload idea comes up often in minimization problems.
Reply by ●January 9, 20122012-01-09
On 1/9/2012 2:14 PM, Clay wrote: ...> One of the things that helps alot with collimation is picking a lens > (or group) with the right Coddington factor. Essentially spherical > aberation is minimized when each lens surface contributes equally to > the overall refraction[1]. This is why eyeglass lenses are menisci. > > Clay > > [1] this sharing the workload idea comes up often in minimization > problems.Unh, Clay, A meniscus lens is positive on one surface and negative on the other, hardly a way to share the overall refraction load. The meniscus becomes optimum because the pupil of the eye is small an the eye moves in its socket. The conditions for optimality have two solutions; the shallow meniscus that is universally used, and a much deeper one that is harder to make and requires more accurate positioning. The design is unrelated (to the extent that anything is) to the aplanatic meniscus used in some microscope objectives. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●January 10, 20122012-01-10
On Jan 9, 3:45�pm, Jerry Avins <j...@ieee.org> wrote:> On 1/9/2012 2:14 PM, Clay wrote: > > � �... > > > One of the things that helps alot with collimation is picking a lens > > (or group) with the right Coddington factor. Essentially spherical > > aberation is minimized when each lens surface contributes equally to > > the overall refraction[1]. This is why eyeglass lenses are menisci. > > > Clay > > > [1] this sharing the workload idea comes up often in minimization > > problems. > > Unh, Clay, > > A meniscus lens is positive on one surface and negative on the other, > hardly a way to share the overall refraction load. The meniscus becomes > optimum because the pupil of the eye is small an the eye moves in its > socket. The conditions for optimality have two solutions; the shallow > meniscus that is universally used, and a much deeper one that is harder > to make and requires more accurate positioning. The design is unrelated > (to the extent that anything is) to the aplanatic meniscus used in some > microscope objectives. > > Jerry > -- > Engineering is the art of making what you want from things you can get. > �����������������������������������������������������������������������Hi Jerry, Actually it does share the load. Think about the case when transforming nearly parallel light to highly convergent light. Try this with a plano convex lens (like the case of the kid burning ants with a magnifying glass although using a plano instead of a double convex lens) where with one orientation only one surface is doing all of the work and in the other orientation both surfaces contribute to the refraction. The book by Meyer-Arendt, Jurgen R., Introduction to Classical and Modern Optics, 2nd Ed, Prentice-Hall, 1984. 3rd Ed, 1989, 4th Ed, actually has quite a bit of detail on Coddington factors and the minimization of spherical aberation. The notion of combining a positive with a negative surface seems counterintuitive, but instead look at how much a light ray is bent by each surface. It is the sharing of the overall bending of the light over all of the surfaces that minimizes the abberation. As you say meniscus lenses come with a price such as when using deep negative surfaces a lot of glass has to be hogged out. But nonetheless retrofocus lens designs (pretty much all superwides and ultrawides are of this type) have extreme coddington factored lens elements in them. One on my ultrawide zooms has 17 elements and only one is aspheric. We see this effect due to the lack of refraction sharing with testing astronomical telescopes since they are designed to only focus at infinity. If you do a "star test" with an artificial star (for example a 50 micron back lighted pinhole located hundreds of meters away, you will falsely detect spherical aberation whereas on a real star your optics will be fine. Of course the scope is fine - it was being used incorrectly. Artificial star tests do have their uses and I do use them. Conversely this is why some telescopes work very poorly for imaging nearby subjects. I have a 6 inch Ritchey Chretien telescope which if used to image something as close as 200 meters works very poorly whereas for astronomical objects it works extremely well. I recall in one of the photography forums discussion of Nikon's famed 200-400mm F/4 zoom not being sharp at inifinity. It is pretty sharp there but it is much sharper at 25 to 50 meters. It could have been engineered to be sharp at infinity, but that wasn't its main design purpose. Now with high resolution digital sensors, people are better able to test their optical systems and see their design compromises. Clay
Reply by ●January 10, 20122012-01-10
Clay <clay@claysturner.com> wrote: (snip)> Conversely this is why some telescopes work very poorly for imaging > nearby subjects. I have a 6 inch Ritchey Chretien telescope which if > used to image something as close as 200 meters works very poorly > whereas for astronomical objects it works extremely well.> I recall in one of the photography forums discussion of Nikon's famed > 200-400mm F/4 zoom not being sharp at inifinity. It is pretty sharp > there but it is much sharper at 25 to 50 meters. It could have been > engineered to be sharp at infinity, but that wasn't its main design > purpose. Now with high resolution digital sensors, people are better > able to test their optical systems and see their design compromises.I have wondered how to compare high-resolution digital sensors to ultra-fine grain film. Film, like many analog systems, has a tail on the resolution curve that slowly falls of, where digital has a sharp drop. Well, as sharp as the low-pass filter allows. -- glen
Reply by ●January 10, 20122012-01-10
> > I have wondered how to compare high-resolution digital sensors > to ultra-fine grain film. Film, like many analog systems, has a tail > on the resolution curve that slowly falls of, where digital has a > sharp drop. Well, as sharp as the low-pass filter allows. > > -- glenI recall a great many discussions on what is a fair comparison because it is sort of an apples to oranges thing. For the case of 35mm systems where the image area is 24 by 36mm, it appeared the crossover point was somewhere in the 9 to 12 megapixel range. But now with 24 megapixels and 14 bits per pixel, digital seems to have pulled enough ahead to be deemed the winner on pretty much all metrics. Some of the difficulty stemmed from the debayering (demosaicing) needed for the now classical bayer array sensors. Color films had an inherent resolution limit of around 60 line pairs per mm due to dye bleed. And at that time auto focus systems were pretty much limited to 40 or so line pairs per mm. Now we see sensors resolving over 75 line pairs per mm and now the issue comes down to things like the quality of the lens, did you hold your camera still enough, and is your autofocus tweaked. Some camera bodies allow for lens dependent autofocus fine tuning. I love that feature! When I need to push the limits, I manually focus using a live video mode on the camera with the aperture stopped down to where I'm going to shoot (sidesteps aperture dependent focus shift issues with lenses). So I'm in effect focusing using the actual sensor instead of the autofocus module which gets its light relayed off of a mirror. The lower limit on digital is not quite a hard cutoff since you have noise in the sensor which gives you a kind of dithering. The nikon D2X image quality was likened to be filmlike since they put 12 megapixels in an APS (24 by 16mm) sized sensor and the sensor's noise gave the appearence of grain associated with low ISO films. The D2X sensor works out to be about 176 pixels per mm. The pixel peepers complained alot that they couldn't get sharp images. They were sharper than they had before, but when you look at pixels you must recall you are looking at really tiny airy discs - 10 or 20 microns across! With these high resolution sensors, one finds that going beyond F/11 may result in softer images even if the depth of field is larger due to diffraction resulting from the stopped down lens. Clay
Reply by ●January 10, 20122012-01-10
On 1/10/2012 10:41 AM, Clay wrote:> On Jan 9, 3:45 pm, Jerry Avins<j...@ieee.org> wrote: >> On 1/9/2012 2:14 PM, Clay wrote: >> >> ... >> >>> One of the things that helps alot with collimation is picking a lens >>> (or group) with the right Coddington factor. Essentially spherical >>> aberation is minimized when each lens surface contributes equally to >>> the overall refraction[1]. This is why eyeglass lenses are menisci. >> >>> Clay >> >>> [1] this sharing the workload idea comes up often in minimization >>> problems. >> >> Unh, Clay, >> >> A meniscus lens is positive on one surface and negative on the other, >> hardly a way to share the overall refraction load. The meniscus becomes >> optimum because the pupil of the eye is small an the eye moves in its >> socket. The conditions for optimality have two solutions; the shallow >> meniscus that is universally used, and a much deeper one that is harder >> to make and requires more accurate positioning. The design is unrelated >> (to the extent that anything is) to the aplanatic meniscus used in some >> microscope objectives. >> >> Jerry >> -- >> Engineering is the art of making what you want from things you can get. >> ����������������������������������������������������������������������� > > Hi Jerry, > > Actually it does share the load. Think about the case when > transforming nearly parallel light to highly convergent light. Try > this with a plano convex lens (like the case of the kid burning ants > with a magnifying glass although using a plano instead of a double > convex lens) where with one orientation only one surface is doing all > of the work and in the other orientation both surfaces contribute to > the refraction. The book by Meyer-Arendt, Jurgen R., Introduction to > Classical and Modern Optics, 2nd Ed, Prentice-Hall, 1984. 3rd Ed, > 1989, 4th Ed, actually has quite a bit of detail on Coddington factors > and the minimization of spherical aberation. > > The notion of combining a positive with a negative surface seems > counterintuitive, but instead look at how much a light ray is bent by > each surface. It is the sharing of the overall bending of the light > over all of the surfaces that minimizes the abberation. > > As you say meniscus lenses come with a price such as when using deep > negative surfaces a lot of glass has to be hogged out. But nonetheless > retrofocus lens designs (pretty much all superwides and ultrawides are > of this type) have extreme coddington factored lens elements in them. > One on my ultrawide zooms has 17 elements and only one is aspheric. > > We see this effect due to the lack of refraction sharing with testing > astronomical telescopes since they are designed to only focus at > infinity. If you do a "star test" with an artificial star (for example > a 50 micron back lighted pinhole located hundreds of meters away, you > will falsely detect spherical aberation whereas on a real star your > optics will be fine. Of course the scope is fine - it was being used > incorrectly. Artificial star tests do have their uses and I do use > them. > > Conversely this is why some telescopes work very poorly for imaging > nearby subjects. I have a 6 inch Ritchey Chretien telescope which if > used to image something as close as 200 meters works very poorly > whereas for astronomical objects it works extremely well. > > I recall in one of the photography forums discussion of Nikon's famed > 200-400mm F/4 zoom not being sharp at inifinity. It is pretty sharp > there but it is much sharper at 25 to 50 meters. It could have been > engineered to be sharp at infinity, but that wasn't its main design > purpose. Now with high resolution digital sensors, people are better > able to test their optical systems and see their design compromises.Hi, Clay. You haven't convinced me yet. I believe still that in a converging spectacle lens, the rear surface is divergent. Maybe I'll undertake a ray tracing to nail that down. In the classic case of a meniscus lens minimizing aberrations the aplanatic meniscus front two elements of a dry high-magnification microscope objective, and in some condensers. Those lenses reduce the divergence of a divergent pencils, but they cannot create convergence while remaining aplanatic. In general, menisci used to form images are used with smallish aperture stops. They sacrifice other desiderata to the interest of wide-angle operation. An early lens of this type (1865!) was the Busch Pantoscop, identical menisci symmetrically disposed around a small stop. (The Hypergon was similar, but not achromatic.) As far as I know, minimizing off-axis astigmatism is the primary benefit of meniscus spectacle lenses. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
