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The viewing provisions of an eyepiece are expressed in two methods. Firstly, the circle of sunshine that’s offered in the event you maintain an eyepiece as much as the attention is known as the obvious area. It is a perform of eyepiece design.
The second is what is known as the true area. That is the world of precise sky that’s offered to the viewer when the eyepiece is utilized in a telescope. This true area is well calculable by dividing the obvious area by the ensuing magnification that it produces on the telescope.
As you enhance the obvious area of an eyepiece, so the window on the true sky additionally will increase, which is why these eyepieces of very massive obvious fields have gotten more and more fashionable – together with the vary of which this reviewed eyepiece is a brand new member.
APM’s line-up of extreme-wide-angle eyepieces (typically referred to as hyperwide) is spectacular, however till not too long ago a teammate has been lacking. Following delayed manufacturing and keen anticipation (by not a number of, myself included!) the HDC XWA 7mm, 100-degree X-treme has lastly made its debut. I snapped it up as quickly as the primary tranche of deliveries turned obtainable and was eager to find how properly it complemented the opposite focal lengths within the vary.
The lacking hyperlink
Providing obvious fields of 100 to 110 levels, APM’s line-up of extraordinarily wide-field eyepieces has hitherto comprised focal lengths of three.5, 5, 9, 13 and 20mm. At first look, this vary may appear complete, however because the focal lengths of eyepieces turn out to be shorter, the distinction within the magnifications between them turns into proportionately bigger.
Take into account a telescope of two,000mm focal size. Whereas a 20mm eyepiece will present a magnification of 100×, the 13mm will yield 154×, offering a step up of simply 54×. Nearer the highermagnification eyepieces, the 9mm offers 222×, but the 5mm will increase this to 400× –a distinction now of 178× (3 times the decrease magnifications hole). Such a divide might, by prevailing seeing circumstances, span the house between an influence that could possibly be pushed a bit extra, and the following that the seeing circumstances wouldn’t help.
So, the introduction of this 7mm eyepiece has crammed a sorely wanted emptiness within the APM XWA vary and, as far as my very own wants are involved, meets a vital optimum place the place additional magnification is often thwarted by common seeing circumstances.
Like different eyepieces on this vary, this isn’t a small eyepiece. With a size of 157mm and girth of 58mm, the nine-element eyepiece weighs in at 414g. But it’s far lighter than a few of the largest I’ve seen, however with adequate mass to maybe require compensating adjustment of a small telescope on its mount.
The barrel (which has a conical design to accommodate binoviewer use) is kitted out with a rubberised grip and a fold-down eye guard that shields its 13mm eye reduction. This, plus an eye fixed lens totally 30mm in diameter, signifies that regardless of the eyepiece’s comparatively brief focal size, there is no such thing as a eyeball-grazing ‘pinhole’ discomfort right here. As a bonus, the rubber eye guard is detachable to reveal an M44.5 × 0.75 male thread for cameras.
Regardless of its dimension, the eyepiece sports activities a 1.25-inch becoming, but in addition consists of an adaptor for deployment on a two-inch focuser – with each nosepieces threaded for filters. As befits an eyepiece containing 9 glass components (in six teams), the entire optics are edge-blackened and totally multicoated.
The focal size designation is clearly inscribed, however (and I make a common heartfelt criticism of all eyepiece producers right here) not notably seen at nighttime, which by advantage of its goal is once you want it. Why are eyepiece focal lengths not luminous, fluorescent, signified by raised dots, converse their focal lengths when dealt with or no matter? Both the producers are lacking one thing apparent or I’m. If somebody takes up certainly one of these concepts, please don’t overlook my fee!
It is a fantastically constructed eyepiece, which hits the candy spot of yielding a respectably excessive magnification with out pushing additional than the circumstances would usually allow
An astronomical guinea pig
For the needs of this evaluation, I used two telescopes. The primary is my mainstay 356mm, f/10 Meade ACF. However used at f/10, most eyepieces must be unchallenged and carry out properly, so I accompanied my evaluation with a small, rich-field 114mm, f/4 Newtonian, which is totally unfair in the wrong way.
Preferring to evaluate gear on objects that I’m aware of (deviations from the norm are extra simply detected), I selected the Andromeda Galaxy (M31) as my preliminary guinea pig. I started my evaluation utilizing the small Newtonian. The irony that there was most likely extra glass contained in the eyepiece than within the telescope was not misplaced on me. This telescope has solely a 1.25-inch focuser, however this was no downside for the eyepiece because it took solely a second to unscrew its two-inch adaptor.
The view was huge. On a telescope of solely 450mm focal size, the ensuing magnification for a 7mm eyepiece is already simply 64×. However with an obvious area of 100 levels, the true area delivered by this eyepiece was 1.6 levels, which is ready to embody greater than three Moons edge to edge!
The brilliant core of the galaxy was apparent, with the fainter outer ellipse properly seen too. As with all hyper-wide-angle eyepieces, what was additionally delivered was context. The big area permits surrounding stars to be included with the article underneath statement, and it’s this facet that provides such eyepieces their wow energy. To see this basic galaxy along with a sprinkling of ‘foreground’ stars gave this commonplace goal added depth.
Transferring the eyepiece to the bigger instrument, the Meade’s 3.5 metres of focal size resulted in a magnification of 508×. That is on the increased finish of this telescope’s usability underneath regular circumstances. But with this eyepiece, it nonetheless nonetheless delivered a real area of 12 arcminutes. The bigger aperture, after all, delivered a core of Andromeda that was brighter, however what impressed me most was the impression on gentle air pollution {that a} wide-field eyepiece achieves.
Keep in mind that it has all the time been a helpful ploy to extend magnification with the intention to improve distinction – the background gentle air pollution is unfold extra thinly and consequently darkened. However doing so with typical eyepieces additionally reduces the scale of the true area. With the 7mm, 100-degree eyepiece, I used to be in a position to get pleasure from its enhanced distinction of a darkened sky with out the impression of a diminished area dimension. My view of Andromeda demonstrated this precept astoundingly properly.
Certainly, I subsequently discovered that (when utilizing the small Newtonian), I may see extra of the Andromeda Galaxy within the 7mm than I may by a 40mm eyepiece!
Beating the drift of demise
After all, the undisputed grasp of our latesummer sky this yr was Jupiter, having come to opposition in mid-August. The planet’s presence provided quite a lot of teases for this new eyepiece.
Starting with the small Newtonian, I rigorously centred Jupiter and located that even at solely 64×, various element in Jupiter’s belts could possibly be discerned. To the east of its disc, all 4 Galilean moons have been strung out like beads on a necklace – and of their orbital sequence. This pleasing line-up, 8.5 arcminutes in extent, could possibly be loved in its majesty as a result of they swam in a area about ten occasions as massive. Once more, context of the system’s environment enhanced the view. And, after all, this largess signifies that if used on a telescope that has no sidereal drive, a goal may be stored in view with minimal effort.
I tracked the planet slowly in the direction of the periphery of the sphere, in what I wish to time period the ‘drift of demise’, to find how close to to the sting I may get the planet earlier than its picture high quality began to emphasize.
Commendably, the picture remained tack sharp till Jupiter was inside about 15 per cent of the sphere cease. Contemplating the demanding f/4 focal ratio, with out use of a coma corrector, I used to be impressed – and it carried out considerably higher than related eyepieces on the identical check. I additionally famous that there was no ghosting or inside reflection, regardless of inserting Jupiter simply inside and simply outdoors of the sphere.
Staying with the Jovian system, I then deployed the 7mm eyepiece on the 356mm, f/10 Meade. I used to be not anticipating an excessive amount of because the seeing circumstances have been removed from superior. The truth is, what the climate companies nowadays select to name clear nights are more and more blighted by a excessive haze that fuels gentle air pollution. But the thinning of background sky illumination that the eyepiece achieves offered wonderful distinction that yielded Jovian element that might in any other case have been washed out.
There have been colors, however not on account of chromatic aberration, which is totally absent on this eyepiece. Element in Jupiter’s belts was properly depicted in ruddy-browns and blue-greys. Very pleasing.
Even at 508×, the true area of 12 arcseconds that the eyepiece delivered meant that regardless of the comparatively excessive magnification, I may nonetheless embody each planet and Galilean moons with room to spare. It was as if I have been hitching a experience on a Voyager spacecraft whereas approaching on a fly-by.
Once more, I walked Jupiter by the drift of demise. The planet sailed by the barrier of the sphere cease and not using a backward look – as clear and undistorted because it was when useless centre. There was not even a glimmer of chromatic aberration because it handed by. After all, within the 356mm, the Galilean moons have been clearly discs – and that’s the manner they remained as they left the sphere, one after the opposite, in Jupiter’s wake.
Fantastically constructed
The satan in me slewed the 356mm to repeat this check on close by Saturn, decrease and to the west of Jupiter. The diminished altitude was pretty detrimental to the standard of the picture, however a finely depicted Cassini Division provided itself as element to be scrutinised. Its curving pencil line barely flinched as I pressured it by the sting of the eyepiece area.
It is a fantastically constructed eyepiece, which for me hits the candy spot of yielding a respectably excessive magnification (on my 356mm) with out pushing additional than the circumstances would usually allow. Glare and inside reflection countermeasures, along with its expansive area, end in nice high quality, highcontrast viewing. Pulling targets nearer with enhanced distinction is a job this eyepiece excels at. I’ve loved my time with the eyepiece throughout this evaluation and totally anticipate that to proceed.
Sadly, the Moon was decidedly shy through the evaluation interval, being round when it was cloudy and never when it was clear. Nonetheless, my calculations point out that used on the 356mm, I ought to have the ability to view your complete Imbrium basin space, encompassing the lunar Apennines, Copernicus, Aristarchus and Plato, all at 508×. I can’t wait.
At a look
Focal size: 7mm
Obvious area: 100 levels
Weight: 414g
Size, diameter: 157mm, 58mm
Optical building: 9 components in six teams – all FMC Waterproof to IPX5 normal
Worth: €193.28 excluding VAT (teleskop-express.de)
Worth: £230 together with VAT (astroshop.eu)
Worth: €269 together with VAT (apm-telescopes.de)
Steve Ringwood is an everyday contributor to Astronomy Now.
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