{"id":23541,"date":"2021-09-16T00:00:00","date_gmt":"2021-09-16T00:00:00","guid":{"rendered":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/?post_type=purple_issue&p=23541"},"modified":"2021-10-22T11:46:50","modified_gmt":"2021-10-22T11:46:50","slug":"first-light-explore-scientific-bt-100-sf-giant-binocular","status":"publish","type":"post","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/2021\/09\/16\/first-light-explore-scientific-bt-100-sf-giant-binocular\/","title":{"rendered":"First Light: Explore Scientific BT-100 SF Giant Binocular"},"content":{"rendered":"\n

A super-sized set of binoculars for views with greater clarity and contrast<\/h4>\n\n

WORDS: STEVE TONKIN<\/strong><\/p>\n\n

<\/div>
\n

VITAL STATS<\/strong><\/p>\n\n\n\n

\u2022 Price \u00a31,445.20<\/span><\/p>\n\n\n\n

\u2022 Optics Fully multi-coated (Enhanced Multilayer Deposition)<\/span><\/p>\n\n\n\n

\u2022 Aperture 100mm<\/span><\/p>\n\n\n\n

\u2022 Focal length 550mm, f\/5.5<\/span><\/p>\n\n\n\n

\u2022 Eyepieces & magnification 20mm, 28x<\/span><\/p>\n\n\n\n

\u2022 Angular field of view 2.3\u00b0<\/span><\/p>\n\n\n\n

\u2022 Focusing Individual focus<\/span><\/p>\n\n\n\n

\u2022 Eye relief 15mm<\/span><\/p>\n\n\n\n

\u2022 Interpupillary distance 54\u201376mm<\/span><\/p>\n\n\n\n

\u2022 Weight 6.8kg<\/span><\/p>\n\n\n\n

\u2022 Supplier Telescope House<\/span><\/p>\n\n\n\n

\u2022 Tel 01342 837098<\/span><\/p>\n\n\n\n

\u2022 www.telescopehouse.com<\/span><\/a><\/p>\n<\/div><\/section>\n\n

\"\"<\/figure><\/div>\n\n

Nothing quite matches the pleasure of scanning a clear, dark sky with big binoculars, so Explore Scientific\u2019s new 100 SF Giant Binocular \u2013 part of its Binocular Telescope (BT) series \u2013 looks like an attractive option, in theory.But how does it fare in practice?<\/span><\/p>\n\n

The binoculars come protected in a foam-lined box, which includes the 20mm, 62\u00b0, Argon-purged eyepieces. After you\u2019ve secured them into their focusers, you can focus the eyepieces individually with self-centring compression rings. They have fold-down eyecups and just enough eye relief to allow you to see the entire field of view if you wear spectacles. You adjust the interpupillary distance (IPD) \u2013 the distance between the pupils of your eyes \u2013 with levers on the eyepiece holders. These move smoothly and are sufficiently stiff to make it unlikely that you\u2019ll alter the IPD when you\u2019re focusing or changing eyepieces. The helical focusers rotate smoothly, making it easy to get a pin-sharp view.<\/p>\n\n

For this review the binoculars were mounted on a Universal Astronomics T-Mount (with a load capacity of 13.5kg), which was an ideal platform. There are no trunnions (cylindrical protrusions used as a pivot point) on the BT-100 binoculars for a yoke-type mount. If that\u2019s your preferred option you\u2019ll need a mount with a mounting plate suitable for larger binoculars like those in the BT series, such as Explore Scientific\u2019s U-Mount with tripod. The BT-100\u2019s base can also be attached to camera or video tripods, but you will need a very substantial tripod head to do so.<\/p>\n\n

Two become one<\/strong><\/h4>\n\n

At first light, the binoculars were producing double images. Fortunately, the BT-100 is designed to be collimated by the user. By using a lens spanner to rotate the eccentric rings around the objective lenses and, after a bit of refinement on the star Polaris, we found that the images had merged acceptably. You can\u2019t adjust the eccentrics while you\u2019re at the <\/span>eyepiece end though, so in-the-field collimation is really a two-person task.<\/p>\n\n

Some false colour is inevitable in a 100mm, f\/5.5 achromatic lenses, so we tested them on Vega (Alpha (a) Lyrae). Although it was difficult to detect \u2018on-axis\u2019 chromatic aberration \u2013 an effect usually seen as coloured rings around brighter objects \u2013 at the centre of the field of view, some false colour did become apparent \u2018off axis\u2019, further away from the centre of the field of view.<\/p>\n\n

Jupiter and Saturn were shining brightly, low in the southern sky, during the test period and both showed the effects of atmospheric dispersion. It\u2019s possible to counteract this, to some extent, by finding the spot in the bottom half of the field of view where the atmosphere partially corrects chromatic aberration.<\/p>\n\n

At this \u2018sweet spot\u2019, Jupiter\u2019s equatorial belts became visible, and it was possible to discern dark space between Saturn\u2019s rings and the planetary disc. A number of faint points of light near Saturn were later revealed as the moons Titan, Tethys, Dione and Rhea after cross-referencing them in a planetarium app.<\/p>\n\n

\"\"<\/figure><\/div>\n\n

Reflections and contrasts<\/strong><\/h4>\n\n

When Jupiter was a degree or so below the field of view, it was sometimes possible to see a horizontal flash of light that was probably a reflection of a prism edge. It appeared impossible to induce any spurious reflections from objects that were either within or immediately outside the field of view, however.<\/span><\/p>\n\n

The next target was Albireo (Beta (\u03b2) Cygni), which displayed two sharp components with the gold and sapphire colour contrast; the rendition was good.<\/p>\n\n

The 1.25-inch eyepieces on the BT-100 are threaded for filters. After inserting a UHC (ultra-high contrast) filter in one, the binoculars revealed the structure in the Dumbbell Nebula. And after panning over to the Ring Nebula, it was possible to \u2018blink\u2019 it, making field stars fade and re-emerge by swapping between the filtered and unfiltered eyepieces.<\/p>\n\n

The strength of the BT-100 binoculars is viewing clusters and galaxies. M31 overflows the field of view and M81 and M82 fit easily within it. It was also a joy to identify open clusters in the northern Milky Way.<\/p>\n\n

This is a well-implemented achromatic set of binoculars that will appeal to observers who want a capable, large-aperture instrument without the extra expense of a premium apochromatic design.<\/p>\n\n

\n\n

Reflection reducers<\/h4>\n\n
\"\"<\/figure><\/div>\n\n

Look into the objective lenses of the BT-100 binoculars and two things immediately become apparent. The first is how transparent they appear \u2013a consequence of Explore Scientific\u2019s proprietary Enhanced Multilayer Deposition (EMD) antireflective coatings. These use the optical phenomenon of destructive interference to reduce reflection. Light that is not reflected from a transparent surface must be transmitted through that surface, resulting in brighter images.<\/p>\n\n

This transparency allows you to notice the second thing: two rings on the inside of the objective tubes. These are light baffles and their job is to intercept any light reflected off the inside wall of the tubes so that it can\u2019t reach the prisms and eyepieces where it could cause ghost images or image degradation. They are positioned so that they don\u2019t intercept light directly from the objective lenses, so the imageforming light is all transmitted. The result is a bright, high-contrast image in the eyepiece, enabling you to make out subtle detail and detect fainter objects \u2013a desirable trait in any optical device.<\/p>\n\n

<\/div>
\n

KIT TO ADD<\/strong><\/h4>\n\n\n\n

1. <\/strong>Explore Scientific U-Mount with tripod for giant binoculars<\/p>\n\n\n\n

2. <\/strong>Fotomate VT-680-222R extraheavy-duty professional two-way tripod<\/p>\n\n\n\n

3. <\/strong>Explore Scientific 1.25-inch UHC nebula filter<\/p>\n<\/div><\/section>\n\n

ALL PICTURES: @THESHED_PHOTOSTUDIO<\/p>\n","protected":false},"excerpt":{"rendered":"

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