Just because a binocular will transmit 95% of 630 nm light does not mean the view contains that much light at that point (intensity or saturation). They are actually labeled awkwardly and do not control what they claim to. Do a Google search for contrast and brightness controls for CRT’s. Some of this confusion is learned from the old CRT TV days. I have been guilty of that myself, and still do so occasionally. I think that people may be mixing contrast, as pertains to resolution and MTF with saturation, or level intensity, which is a function of transmission. I think I am going to side with RonH on this one. Just my opinion, that and $1.50 may get you a cup of coffee. If all was limited by visual acuity, why would so many say the Chinese ED’s are sharper than about all they compared them to, surely all of them were not worse than their visual acuity/power. Somewhere on the forum there was a discussion far back that I believe Henry or Kimmo had shown empirical data that supported that notion, but I have been unable to find it, or just not remembering it correctly. I think that the image will show improvement down to about half of the visual acuity (maybe line or point resolution, I have no explanation). Since both terms are for seperation of figures, I deem them to be more applicable to lines pairs test instead of line or point resolution.Īs to the visual acuity, I guess I have a somewhat different impression than you. In general, it is about 85% of the Rayleigh figures. The Dawes Limits were set up by empirical observations of double stars with various size apertures and compiling data of the doubles resolved. From memory, the 1.22 is a constant added to correct for the change from a slit or rectangle to a circular pattern, I do not remember the derivation of the constant. Rayleigh uses two Airy disks, the center of the second star at the end of the Radius of the Airy disk of the first, or two exact size Airy disks separated by their radius. The Rayleigh criterion is set up for splitting double stars or measuring the power in the gap. The following is what I remember (and for me, that is never to be relied upon). It has been quiet some time since I visited Dawes and Rayleigh and I am not going to right now. I don't think I've ever seen exactly the same performance in both. I should also add that the right and left barrels are quite independent. I've come to expect resolution closer to perfect from 30mm binoculars compared to 50mm binoculars, so I hold small binoculars to a higher standard. I would add that small aperture binoculars tend to do better than large ones. I'm not happy to see an expensive binocular do no better than this.Ģ00/D or worse means something is seriously wrong, but even this might not be very visible in most situations if the problem is mostly confined to the outside third of the objective as is often the case with pinching and astigmatism. A star-test will reveal what the problem is. My loose criteria are:ġ30/D or better means you have lucked into an excellent specimen of a good design.ġ40-150/D means probably no problem, but no bragging rights either.ġ60-180/D means something is certainly wrong, but it may be harmless in normal use. A good result raises a nice green flag for axial sharpness and a mediocre or bad result needs to be investigated with a star-test. My experience with measuring the resolution of binoculars closely matches Ron's. In very bright sunlight my pupils constrict to barely more than 2mm when looking through binoculars. It's surprising to me how large my pupils open when looking through a binocular in a heavily shaded area in daylight, around 5mm. This can also be done in low light with a pinhole in aluminum foil covering the lens of a flashlight. Divide that measurement by the magnification of the binocular and the result is the size of you pupil under that particular lighting condition with a binocular in front of your eyes. Adjust the caliper until you see both inside edges of it just barely impinging on the projected disk of your pupil in the binocular. I'll leave it to your ingenuity to fashion some sort of adjustable paper caliper to place in front of the binocular objective. That is actually an image of your eye's pupil (or the exit pupil of the binocular if your eye's pupil is larger than the exit pupil). Focus the binocular at infinity and look at the glitter point at some close distance like 5m. You need a glitter point on a sunny day (tiny reflection of the sun in a small round shiny object). There is also a way to measure the size of your pupils with a binocular in front of your eyes.
0 Comments
Leave a Reply. |