There is also an absolute limit of quality increase: the aperture in millimeters multiplied by 2. As a rule, the further growth of the increases will not allow the addition of new details in the picture. The image will grow in size, but at the same time will 'Zamylivatsya. "Telescope with the largest aperture among models: Orion XT4.5 and StarBlast, equipped 41/2-dyuymovym primary mirror, and Scientifics Astroscan, the aperture which is 41 / 8 inches. Refractors among the best when buying a telescope optics has a model of Orion Observer 70mm. She has all the characteristics of 70-mm achromatic lens: sharp, high contrast and pronounced chromatic aberration that is a false color with the optics of the three refractors Meade. They are characterized by total or significant astigmatism spherical aberration of eyepieces of telescopes.
Particularly strong astigmatism has an optical scheme NGC-70. We were pleasantly surprised by the current quality eyepieces. Two high quality Plossl eyepiece includes a complete set of telescopes Orion XT4.5, Astroscan, Meade NG-70 and NGC-70. However, even lower-quality eyepieces, which are equipped with almost all other models are sufficiently large relative aperture. Only two models – reflectors mark Bushnell and Celestron – showed increased much less than that promised by the manufacturers. Both of these telescopes use low-quality 3-fold Barlow lens and a mediocre 4 mm eyepieces to gain ostensibly to 525h. However, it seems that in fact the maximum net increase in each telescope is about 150X, and despite the fact that an increase of 4 mm eyepiece without the Barlow lens 175h! Recording offered by manufacturers, together with telescopes were also markedly higher quality than before.
Best viewfinder 6h26, direct images supplied Orion XT4.5. Other models are equipped with Orion finder with laser point, and the set includes telescope Astroscan sight. Recording with a laser dot sight and work fine, provided that the target remains fairly yarkoy.Ostalnye telescopes equipped with optical finders 5h24 with a single lens as the eyepiece. The aperture in eyepiece viewfinder is not such as it is a fairly common practice, and the increase provided by this lens, only slightly exceeds the capabilities of the unaided eye. Good viewfinders are equipped with bracket with two rings and six mounting screws. However, due to the limited field of view of approximately 41 / 2 , weak optics and an inverted image such searchers, we believe, are not suitable for entry-level.