----------------------------------- nobody 20 Iun 2018 13:12 ----------------------------------- Exista un nene* care face oculare "double plossl" din obiective de binoclu recuperate si le da cadou incepatorilor pentru ca sunt mai bune decat ocularele "stock" simple care vin cu telescoapele ieftine. Nu am idee care ar fi campul si daca este suficient pentru un ocular de acest gen. Ar trebui sa aiba macar 5 grade pe cer, nu? *) Red Henry @ FB Campul real pe cer depinde si pe ce telescop pui ocularul. Dar omul da explicatii chiar pe FB. Citez: Astronomy last night turned out to be short-lived due to encroaching clouds, but I had time to try some experimental eyepieces I've assembled lately. I rolled the shed away from my 14" telescope and went to work. These are all in 2" barrels, and their approximate focal lengths are marked. They all have quite nice eye relief of about 1 inch. Each one is made from four binocular achromats of between 30mm and 40mm diameter, in the "Double Plossl" design shown in the diagram below. Tonight's comparison target was the great open cluster in Gemini, M35. I started with the 41mm eyepiece, yielding 40X. Sharpness was good but the contrast was only fair, not helped by a high thin layer of clouds which I suspect I was looking through. Star images were good to the edge of the field. But the eyepiece's biggest drawback was an apparent field of view (AFOV) of only about 50° or a bit less, rather narrow by modern standards. Next up was the 40mm eyepiece, giving 40X. Like the first one, this eyepiece has a pair of 35mm achromats for its field lens, but nevertheless its AFOV was quite a bit larger. Star images, as before, were nice at the field ages. But still, contrast was not as good as I wanted. Now for the 38mm eyepiece, yielding 43X... well, sometimes you look through an eyepiece for the first time and say, "Oh my!" This ocular has two 40mm achromats as its field lens, and the AFOV seemed to be 60° or even a little more--quite nice. Contrast was better than for the first two eyepieces, in spite of not much difference in the magnification. Star images were remarkably round at the field edges. With 35mm achromats for the eye lens and 40mm achromats for the field lens, this eyepiece stands out. Next up was the 36mm f.l. eyepiece, giving 46X. Contrast and sharpness across the field were good but did not measure up to the 38mm ocular, and the AFOV was a bit smaller due to the 35mm field lenses. So, the 38mm eyepiece was tonight's clear winner. I put that excellent eyepiece back in the focuser and enjoyed views of M35, then M41, then M47 and M46 east of Sirius, and also the three clusters in Auriga: M37, M36, and M38. The eyepiece held up well, giving pleasing views all around it is a "keeper." At this point serious clouds began covering up the sky, but my mission was accomplished. Now I have that excellent 38mm eyepiece to use in the long run, and some other lenses to disassemble and try in new combinations. Good deal.