BirdForum is the net's largest birding community dedicated to wild birds and birding, and is absolutely FREE!

Register for an account to take part in lively discussions in the forum, post your pictures in the gallery and more.

Reply to thread

Message: <blockquote data-quote="Holger Merlitz" data-source="post: 3574168" data-attributes="member: 84262">Your example of the spider worm thread is interesting, because it may well be unresolvable in our binocular. A similar case shows up with power lines, which are observed at a distance of several km: We can see them, even though their diameters remain well below the theoretical resolution limit. In this case, we do not receive an image of the power line itself, but rather its diffraction pattern. I have observed that some binoculars are capable of showing these lines at high contrast, as nicely black lines in front of the bright sky background, while others display them as very fine, yet grey lines. Are these differences consequences of different levels of aberration control, or rather rooted in different approaches to stray light control, or do they display different qualities of lens surface smoothness due to polishing, or even a tiny amount of stray light generated inside the glass elements? In the latter case, the coating technology (and hence the transmission value) may be of relevance, and we know that the Habicht is particularly strong in that discipline. For optics used in astronomy, it is common to analyse the wavefront error of the system, which leads to the Strehl number. It essentially tells which fraction of light is shifted away from the primary maximum of the diffraction pattern into secondary (and further) maxima. Now, binocular optics are commonly so bad that they do not even show nice diffraction patterns, because those are blurred by their residual aberrations - few binoculars are actually diffraction limited at full aperture. Hard to say what is going on inside a binocular which happens to show those ultra thin, unresolved threads at a particularly high contrast. The question arises whether those regular black/white patterns used for the test charts do actually test such a feature accurately. Fourier optics is a delicate field, and regular patterns, due to their symmetry, may lead to phenomena that differ from the imaging characteristics of a single, unresolved line. Cheers,Holger</blockquote>

Verification