![]() ![]() If you’re already sure you’ve got perfect vision and have determined it’s definitely not your eyes. ![]() If the problem is indeed your eyes, the solution might be as simple as wearing glasses when using lower magnifications or just ignoring the issue. At higher magnifications, astigmatism in your eyeball becomes less of a problem – as opposed to astigmatism from the telescope, which becomes more of a problem at higher magnifications. If the orientation of astigmatism changes as you move, it’s not your telescope – you may just have very mild astigmatism in your eyes that hasn’t been noticed by a doctor. First, if you have any doubts, rotate your head/eyes and look through the eyepiece. It can be caused by any of the following in a Newtonian reflector:įinding the cause of regular astigmatism is pretty much a process of elimination. The center of the field of view shows equally astigmatic stars as the edge, and stars look like ovals when out of focus that change orientation if you are inside versus outside the focal plane. Stars will look like crosses (not to be confused with the diffraction spikes in a Newtonian reflector) and at high magnifications become fuzzy and hard to focus at all. The more complicated and harder of the two to solve is regular astigmatism at the focal plane, which is an issue that primarily affects Newtonian reflectors. It’s caused by light focusing differently on different axes, so one “side” focuses ahead or behind the other.Īstigmatism can manifest itself in two ways at the telescope. Visibility: In-focus stars look like crosses out-of-focus stars look oval and rotate 90 degrees depending on which side of the focal plane you’re onĪffects: All telescope designs, but usually reflectorsĪstigmatism is an optical aberration you might already have heard of, as it’s a common defect in our eyeballs – indeed, roughly a third of the population suffers from it. ![]() Regardless, aberrations are annoying, and any telescope user wants to figure out what they are and how to eliminate them. Others are visible as defects in focus either with an eyepiece or camera. Some optical aberrations can be seen during a star test, which is a process in which a bright star is examined out of focus at high magnification and the diffraction rings are examined. Each inherently has its own aberrations essentially by default, which we’ll talk about in a bit. There are essentially two methods of focusing light in any format: by refraction through lenses and by reflection from the surfaces of mirrors. The key to good telescope performance is compromising on what optical aberrations can be tolerated and making their effects negligible whenever possible. Particularly with eyepieces, it is basically inevitable that any telescope will have aberrations at the focal plane in some fashion, and they will always exist. All telescopes – and indeed, most optical devices – work by collecting light at the objective lens or primary mirror, and then converging these light rays into a spot called the focal plane. ![]()
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