I constructed my first telescope out of a 100mm diameter, two-element authorities surplus lens of 500mm focal size within the early 1970s. Whereas I used to be immensely pleased with my four-inch, f/5 refractor, its photos of the Moon and brilliant planets have been surrounded by a vivid purple halo. Thus I had my introduction to the bane of straightforward lens-based devices: chromatic aberration. I shortly realized easy compound lens composed of a sandwich of two forms of glass with opposing dispersive (prismatic colour-making) qualities solely goes a restricted solution to cancelling out this annoying inherent defect of refractors. In reality, using crown and flint forms of glass to style a so-called ‘achromatic’ lens able to bringing two wavelengths of the color spectrum (often purple and blue) to focus dates again to the British inventor Chester Moore Corridor, in round 1730. Nevertheless, for an achromat of sometimes encountered sizes to have a suitable degree of color correction, an optician must make the instrument’s focal size at the least twelve instances the diameter (or aperture) of the lens, which instantly explains the lengthy tubes of classical refractors.
Within the intervening years, opticians have developed so-called ‘apochromatic’ (or ‘apo’) refractors, sometimes composed of a three-glass component sandwich able to bringing three colors of the seen spectrum (sometimes purple, inexperienced and blue) to a typical focus. Such exquisitely crafted devices from high-end producers equivalent to Takahashi and Astro-Physics use unique glasses, floor and polished to complicated geometries, to create compact refractors that present basically excellent imagery for visible and photographic use, however they often command an eye-watering worth. Nevertheless, comparatively current optical analysis has led to the mass manufacturing of extra-low-dispersion (‘ED’) glass varieties able to curbing the tendency of a lens to separate white gentle right into a spectrum to such an extent that brief focal-ratio refractors with glorious color correction can now be produced from a two-element lens, generally known as a doublet. Calcium fluoride (CaF2), which happens naturally because the mineral fluorite, makes a superior ED lens component, however it’s a considerably fragile materials to grind and polish, plus it’s thermally unstable (that means that it’s form adjustments barely with temperature). An ED glass manufactured by Ohara in Japan, often called S-FPL-53 (generally written FPL53), has very related optical traits to fluorite, however it’s cheaper, far simpler to shine and is extra secure, each chemically and thermally. Ohara additionally produces S-FPL-51, which is an ED glass that’s cheaper than FPL53 and even simpler to work with. With the proper prescription of lens geometry and mating glass component, FPL51 is able to producing a superb ED refractor, however the selection of FPL53 glass wherever attainable provides the optical designer far higher freedom to provide a doublet with a efficiency deserving of the title ‘apo’. Such is the on-paper prescription of the TS-Optics PhotoLine 60mm, f/6 FPL53 that I evaluation right here. First impressions When a 17 × 21 × 31 centimetre transport field arrived at my door from Telescope-Service (TS) in Germany, I initially thought that I’d been despatched the unsuitable product: may a package deal this small actually comprise a 60mm, f/6 refractor? It seems that it could actually, for as soon as it’s divested of packaging, the instrument is simply 23 centimetres lengthy from the entrance lens cap to the rear of its 2-to-1.25-inch eyepiece adapter when each its dewshield and focuser drawtube are totally retracted. Being so small, the TS PhotoLine 60mm, f/6 forgoes tube rings and a dovetail bar in favour of a reversible, hinged split-ring collar with an L-shaped foot possessing two ¼–20 and one central three/8ths-inch photo-tripod connections. Straight out of the field, the instrument ideas the scales at simply 1.52 kilograms.
The target, which has a full aperture of 60mm, is totally multi-coated with the unblemished deep inexperienced hue that one involves anticipate of a top quality lens nowadays. The rear collar of the sliding dewshield, superb focusing knob, two-inch eyepiece-locking collar on the finish of the focuser and the drawtube lock knob are all anodised in a placing purple that contrasts with the in any other case wholly black and white livery. (For the extra conservative amongst you, TS-Optics present a model of this instrument in a black and white end with a gold-coloured superb focus knob.) Contained in the optical tube, which has an efficient matte black coating, there’s a single baffle about two centimetres behind the doublet. The remaining suppression of scattered inside gentle is supplied by the 14.2 centimetre-long focuser drawtube that has an inside diameter of 50.8mm (two inches) and a finely milled end with a matte black coating, a mixture that’s significantly efficient. The 118mm-long helically-cut brass rack has no discernible backlash in opposition to the pinion, and one full rotation of the 1:9:three ratio superb focusing wheel advances the drawtube 2.25mm over a complete journey of 75mm. The drawtube’s engraved millimetre scale is beneficial for reproducing approximate visible and photographic foci (extra on imaging later). The focuser doesn’t rotate with respect to the tube, however ought to the focusing knobs not lie in a handy place for you, then slackening a knurled knob on the hinged split-ring collar lets you rotate all the optical tube relative to the L-shaped foot. The drawtube is lockable as soon as exact focus is discovered. Two-inch push-fit diagonals and equipment are secured by a non-marring brass compression ring through three clamping bolts at 120-degree intervals.
Whereas the machining and end of the tube, lens cell and focuser are all first fee and the instrument feels reassuringly sturdy in hand, I’ve just a few niggles with the design. The tip of the prolonged dewshield lies simply 50mm in entrance of the target, which is barely satisfactory. Given that there’s nonetheless 50mm of tube behind the retracted dewshield, why not make it 50mm longer to make sure a full 100mm of dew safety and an efficient gentle defend for daytime use? I feel that Telescope-Service additionally missed a possibility to make the L-shaped mounting foot’s cross-section suitable with the Vixen-style dovetail block used on the overwhelming majority of small telescope mounts; TS expects you to buy a Vixen-compatible dovetail rail for an additional €24.89. Moreover, whereas there are two domed-head Allen mounting bolts on both facet of the focuser, a finderscope mounting shoe is a €24 add-on. I recognize that margins are tight nowadays, however a Vixen dovetail mounting rail and a finderscope mounting shoe ought to be normal gear for a telescope of this calibre. Visible impressions For the reason that PhotoLine 60mm, f/6 has a drawtube focusing vary of 75mm, then nearly each two- and 1.25-inch (50.eight and 31.75mm) push-fit star diagonal and eyepiece mixture ought to allow you to achieve focus at infinity – each eyepiece at my disposal suitable with this instrument actually did. Given the focal size of 360mm and the focal ratio, mature observers with totally dilated pupils of round 5mm could be suggested to not use eyepieces with a focal size longer than 30mm in the event that they want to accommodate the total exit pupil. On the magnification of 12× delivered by such an eyepiece, even 1.25-inch oculars will ship true fields of view nicely in extra of 4 levels; two-inch eyepieces provides you with fields in extra of six levels for monocular-like views. On the higher magnification vary, one ought to be aware that that is only a 60mm aperture telescope, so eyepieces with focal lengths shorter than about 3mm (or the Barlowed equal) are to be averted. For my high-power exams I used a three.2mm focal size TMB Optical Planetary II eyepiece delivering 113× magnification along with a TeleVue 1.25-inch mirror diagonal. Used on this configuration through the daytime, tiny but intense specular reflections seen in distant beads of dew revealed that the evaluation instrument was completely collimated with a vanishingly small quantity of under-correction. Defocusing the instrument just a few waves intra-focally revealed symmetrical diffraction rings with a faint purple tinge, whereas the diffraction rings seen the identical distance extra-focally displayed a central reddish hue and greenish-blue periphery. Nevertheless, at focus, even on extraordinarily brilliant examples of water droplet ‘synthetic stars’ in daylight, the color correction of the evaluation mannequin TS PhotoLine 60mm, f/6 was undoubtedly spectacular. For these observers desiring to additionally use the instrument as a daytime spotter-scope for nature research or sporting occasions, I may deal with topics simply 7.5 metres away whereas utilizing the TeleVue 1.25-inch diagonal and a 10mm Plössl eyepiece at 36×. Nevertheless, for normal terrestrial use, an Amici prism star diagonal for delivering a totally erect picture, plus a top quality zoom eyepiece, could be good investments.
Turned to the night-time sky, the TS-Optics PhotoLine 60mm, f/6 FPL53 apo excels at lunar observations. On a night of reasonably good seeing on the finish of civil twilight on Monday 2 December, the six-day-old waxing lunar crescent offered a wealth of element within the three.2mm TMB eyepiece at 113× magnification. My observing notes relate that within the Moon’s northern polar area, the horn-shaped crescent tapered to a jagged level with three close by excessive lunar peaks past the terminator catching the rays of daylight, wanting like tiny islands in a jet-black sea separated from an isthmus of land. Heading south alongside the dawn line on the lunar floor, 95-kilometre-wide impression crater Posidonius, on the north-eastern fringe of Mare Serenitatis, was replete intimately, specifically displaying the virtually semi-circular concentric rim of the inside lava-flooded crater, in addition to the central craterlet Posidonius A and hints of the primary crater’s intensive rille system. In Mare Serenitatis itself, wrinkle ridges parallel to its jap shore have been equally nicely seen. Additional south, 40-kilometre-wide Plinius prominently marked the boundary of Mare Tranquillitatis and I lingered some time on the southern fringe of this lunar sea, close to the well-known touchdown web site of Apollo 11. The spotlight of this explicit lunar tour was the distinguished and equally sized trio of craters Theophilus, Cyrillus and Catharina, to the west of Mare Nectaris within the Moon’s southern hemisphere. One-hundred-kilometre-wide Theophilus intrudes into Cyrillus, the previous clearly displaying its huge, terraced rim and central triple peak. One thing that I had in all probability seen earlier than at this waxing lunar section however not likely appreciated was the hourglass-like ‘waist’ separating craters Cyrillus and Catharina that was wreathed in shadow on the night time of two December. At magnifications starting from 33× to 113×, I positioned the lunar crescent simply outdoors the sting of the sphere of view and couldn’t detect any spurious glows from scattered gentle in any orientation. Photographic impressions Given its comparatively brief f/6 focal ratio, this instrument will present indicators of area curvature with each cropped and full-frame DSLRs, or large-format CCD/CMOS units. This isn’t a fault of the TS PhotoLine 60mm f/6 FPL-53 apo per se, since all quick refractors with out some type of field-flattening accent will show stars as brief streaks within the corners of the body, whereas these stars within the centre of view are completely spherical and sharp. Luckily, Telescope-Service provides an non-compulsory flattener and area corrector often called the TSFlat60. Simply 95mm lengthy and including 237 grams to the mass of the telescope, the TSFlat60 has a male M54×zero.75 thread on the telescope facet that screws securely into the focuser’s drawtube as soon as the two-inch eyepiece locking collar is unthreaded. On the digital camera facet of the TSFlat60 there’s a regular male M48×zero.75 photograph thread, so all you want is the T-mount bayonet adaptor acceptable to your DSLR digital camera physique to mechanically set up the optimum again focus of 55mm from the male M48 thread.
The optics of the TSFlat60 are totally multi-coated just like the telescope’s goal lens, whereas all inside surfaces of the sphere flattener are milled and coated matte black to forestall inside reflections. On condition that there isn’t a provision for rotating the telescope’s focuser for framing a shot, the TSFlat60 neatly incorporates a strong 360-degree rotation collar secured by a single knurled lock knob. One other characteristic of the sphere flattener is that it’s designed to protect the f/6 focal ratio (and 360mm focal size) of the TS-Optics PhotoLine 60mm f/6 FPL-53 apo. Moreover, the TSFlat60 can also be designed to ship a totally corrected and illuminated area of view that’s 41mm extensive, therefore cameras with full-frame sensors (43.25mm diagonal) are nearly totally coated. In exams with my full-frame Canon 5D Basic, aggressive picture processing revealed negligible vignetting, whereas plate fixing revealed a real area of view of 5.54 × three.69 levels and a scale of four.57 arcseconds per pixel. On condition that the Canon 5D Mark 1 has eight.2 micron pixels, a mixture of the TS PhotoLine 60mm, f/6 FPL-53 apo plus the TSFlat60 plus a DSLR delivers a real focal size of 370mm, therefore the TSFlat60 is known as a 1.03× area flattener. Nevertheless, the sphere was certainly flat, albeit with negligible pincushion distortion.
Conclusions The TS PhotoLine 60mm, f/6 FPL-53 apo arrives available on the market amid some stiff competitors from the suspiciously related Astro-Tech AT60ED, the Altair 60EDF and the William Optics Zenithstar 61 apo (the Zenithstar’s 61mm, f/5.9 specification possible outcomes from a lens cell with a barely bigger entrance pupil). It’s value noting that the Altair 60EDF additionally contains as normal the 360-degree rotation collar provided with the TSFlat60 however at the same worth, which is a giant plus within the Altair’s favour. All of those telescopes are an ideal match for digital camera monitoring mounts such because the Sky-Watcher Star Adventurer or iOptron SkyGuider Professional. Nevertheless, the truth that one has to purchase a Vixen-style dovetail bar and a finderscope mounting shoe with a view to totally exploit these devices for severe astronomical imaging nearly means that celestial imaging is of secondary significance to the producers – or it may simply be that margins are so tight that these things are thought-about extras. Whichever means you have a look at it, there’s no denying that the TS PhotoLine 60mm, f/6 apo is a less expensive various to sure prime digital camera lenses, and its marriage of well-figured FPL53 and lanthanum glass ensures it delivers a notable photo-visual efficiency, each on land and within the sky. Specs: Telescope: Optical design: FPL53 and lanthanum air-spaced doublet refractor Coating: multi-coated on all air-to-glass surfaces Aperture: 60mm Focal size: 360mm Focal ratio: f/6 Decision: 1.9 arcseconds Weight: 1.52kg Tube size: 230mm (retracted)/355mm (prolonged) Focuser: two-inch rack-and-pinion focuser with 1:9:three discount gearing Drawtube journey: 75mm Producer/Provider: teleskop-express.de Worth: €449
Flattener and area corrector: General size: 95mm Weight: 237g Illuminated and corrected picture area: 41mm Picture scale: 1.03× Connection at telescope facet: M54 × zero.75 thread (male) Connection at digital camera facet: M48 × zero.75 thread (male), size 4mm Working distance: 55mm from the male M48 thread Producer/Provider: teleskop-express.de Worth: €165 The post #astronomy TS-Optics Photoline 60mm, f/6 FPL53 apochromatic refractor – Astronomy Now appeared first on Astronomy Hobby Zone. from https://astronomy-hobby-zone.eshcarmel.org/astronomy-ts-optics-photoline-60mm-f-6-fpl53-apochromatic-refractor-astronomy-now/
0 Comments
Leave a Reply. |
About UsYour source of astronomy supplies at low prices - Astronomy-Hobby-Zone.eshcarmel.org ArchivesNo Archives Categories |