{"id":33784,"date":"2025-11-14T16:12:58","date_gmt":"2025-11-14T15:12:58","guid":{"rendered":"https:\/\/www.telescoop.nl\/?post_type=product&#038;p=33784"},"modified":"2026-03-04T17:13:02","modified_gmt":"2026-03-04T16:13:02","slug":"william-optics-91-540-refractor-apo-space-gray-ota","status":"publish","type":"product","link":"https:\/\/staging.telescoop.nl\/en\/william-optics-91-540-refractor-apo-space-gray-ota\/","title":{"rendered":"William Optics 91\/540 Refractor APO Space Gray OTA"},"content":{"rendered":"<h3 class=\"wp-block-heading\">Compact power, razor-sharp images<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The <strong>William Optics AP 91\/540 FluoroStar<\/strong> shows stars as dots.It <strong>triplet of FPL-53 and lanthanum glass<\/strong> delivers sharp images and pure colors.Double stars are clearly visible separately.Jupiter and Saturn reveal fine details as if you were close by.<\/p>\n\n\n\n<figure class=\"wp-block-gallery has-nested-images columns-default is-cropped wp-block-gallery-1 is-layout-flex wp-block-gallery-is-layout-flex\">\n<figure class=\"wp-block-image aligncenter size-large\"><img decoding=\"async\" data-id=\"33785\" src=\"https:\/\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-AP-91-540-Apochromatische-refractor-Space-Gray-OTA-1.jpg\" alt=\"William Optics AP 91\/540 frontal view OTA with removable lens cap and Losmandy dovetail\" class=\"wp-image-33785\" title=\"\"><\/figure>\n<\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Lots of light, large field of view<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The <strong>91 mm opening<\/strong> Captures a lot of light for bright deep-sky and planetary observations.With the <strong>Flat6AIII flattener<\/strong> you get a flat image field, even on full-frame cameras.Astrophotography becomes easier and faster, with an even image all the way to the edge.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Accurate focusing, even with heavy equipment<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The <strong>rack-and-pinion focuser<\/strong> works smoothly and precisely.The <strong>1:10 reduction<\/strong> Helps you focus perfectly.The focuser is <strong>rotating<\/strong>, so your camera is always in the right position.The <strong>Bahtinov mask<\/strong> Makes focusing easy even for faint stars.<\/p>\n\n\n\n<figure class=\"wp-block-gallery has-nested-images columns-default is-cropped wp-block-gallery-2 is-layout-flex wp-block-gallery-is-layout-flex\">\n<figure class=\"wp-block-image aligncenter size-large\"><img decoding=\"async\" data-id=\"33786\" src=\"https:\/\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-AP-91-540-Apochromatische-refractor-Space-Gray-OTA-3.jpg\" alt=\"William Optics AP 91\/540 side view OTA with dew cap and focuser collapsed in detail\" class=\"wp-image-33786\" title=\"\"><\/figure>\n<\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Lightweight and travel friendly<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The <strong>retractable dew cap<\/strong> Makes the tube compact for transportation.With <strong>4.16 kg<\/strong> take it with you easily when traveling.The telescope has a sturdy handle and Vixen\/Skywatcher accessory shoe.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Ideal for astrophotography and planets<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Perfect for detailed shots of planets, nebulae and galaxies.Suitable for advanced and compact observatories.<\/p>\n\n\n\n<h1 class=\"wp-block-heading\"><strong>Specifications<\/strong><\/h1>\n\n\n\n<h3 class=\"wp-block-heading\">Optics<\/h3>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Feature<\/th><th>Description<\/th><\/tr><\/thead><tbody><tr><td>Type<\/td><td>Refractor<\/td><\/tr><tr><td>Design<\/td><td>Apochromat<\/td><\/tr><tr><td>Aperture (mm)<\/td><td>91<\/td><\/tr><tr><td>Focal length (mm)<\/td><td>540<\/td><\/tr><tr><td>Focal Ratio (f\/)<\/td><td>5,9<\/td><\/tr><tr><td>Resolution<\/td><td>1,52\u2033<\/td><\/tr><tr><td>Limit value (mag)<\/td><td>12,3<\/td><\/tr><tr><td>Light output<\/td><td>170<\/td><\/tr><tr><td>Max. useful magnification<\/td><td>182\u00d7<\/td><\/tr><tr><td>Lens Design<\/td><td>Triplet<\/td><\/tr><tr><td>Tube weight (kg)<\/td><td>4,16<\/td><\/tr><tr><td>Tube diameter (mm)<\/td><td>100<\/td><\/tr><tr><td>Tube length (mm)<\/td><td>510<\/td><\/tr><tr><td>Transport length (mm)<\/td><td>441<\/td><\/tr><tr><td>Coating<\/td><td>STM<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Focuser<\/h3>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Feature<\/th><th>Description<\/th><\/tr><\/thead><tbody><tr><td>Design<\/td><td>Rack-and-pinion<\/td><\/tr><tr><td>Ocular connection<\/td><td>2\u2033<\/td><\/tr><tr><td>Connection (camera side)<\/td><td>T2<\/td><\/tr><tr><td>Reduction<\/td><td>1:10 finesse<\/td><\/tr><tr><td>Rotatable<\/td><td>Yes<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Mount<\/h3>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Feature<\/th><th>Description<\/th><\/tr><\/thead><tbody><tr><td>Design<\/td><td>OTA<\/td><\/tr><tr><td>Type of mount<\/td><td>Without<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Included accessories<\/h3>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Section<\/th><th>Description<\/th><\/tr><\/thead><tbody><tr><td>Divergent optics<\/td><td>No<\/td><\/tr><tr><td>Dovetail<\/td><td>Losmandy-Style<\/td><\/tr><tr><td>Handle<\/td><td>Yes<\/td><\/tr><tr><td>Focusing aid<\/td><td>Bahtinov mask<\/td><\/tr><tr><td>Transport bag<\/td><td>Yes<\/td><\/tr><tr><td>Accessory shoe<\/td><td>Vixen\/Skywatcher Level<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">General<\/h3>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Feature<\/th><th>Description<\/th><\/tr><\/thead><tbody><tr><td>Series<\/td><td>FluoroStar<\/td><\/tr><tr><td>Color<\/td><td>Silver<\/td><\/tr><tr><td>Application<\/td><td>Astrophotography, Moon &amp; Planets, Nebulae &amp; galaxies, Sun (with filter)<\/td><\/tr><tr><td>Recommended for<\/td><td>Advanced<\/td><\/tr><tr><td>Observatory use<\/td><td>Yes<\/td><\/tr><\/tbody><\/table><\/figure>","protected":false},"excerpt":{"rendered":"<p>William Optics AP 91\/540 comes with retractable dew cap, Bahtinov focus mask, Losmandy swallowtail, sturdy handle, 1:10 rack-and-pinion focuser and deluxe transport bag - ideal for sharp visual observation and astrophotography. \u00a0<\/p>","protected":false},"featured_media":97298,"comment_status":"open","ping_status":"closed","template":"","meta":{"_acf_changed":false},"product_brand":[643],"product_cat":[51,567],"product_tag":[],"class_list":["post-33784","product","type-product","status-publish","has-post-thumbnail","product_brand-william-optics","product_cat-telescopen","product_cat-refractors","first","instock","taxable","shipping-taxable","purchasable","product-type-simple"],"bundled_by":[],"bundle_stock_status":"instock","bundle_stock_quantity":null,"bundle_virtual":false,"bundle_layout":"","bundle_add_to_cart_form_location":"","bundle_editable_in_cart":false,"bundle_sold_individually_context":"","bundle_item_grouping":"","bundle_min_size":"","bundle_max_size":"","bundle_price":[],"bundled_items":[],"bundle_sell_ids":[],"acf":[],"jetpack_sharing_enabled":true,"jetpack-related-posts":[{"id":34297,"url":"https:\/\/staging.telescoop.nl\/en\/william-optics-flt91-flat6a-iii-special-edition\/","url_meta":{"origin":33784,"position":0},"title":"William Optics FLT91 Flat6A III Special Edition","author":"","date":"17-11-2025","format":false,"excerpt":"William Optics FLT91 Flat6A III comes with custom flattener, 2\" telescope connector, camera adapter and fixed flange distance - designed for full field of view adjustment on the FLT 91 refractor.","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-FLT91-Flat6A-III-Special-Edition.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-FLT91-Flat6A-III-Special-Edition.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-FLT91-Flat6A-III-Special-Edition.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-FLT91-Flat6A-III-Special-Edition.jpg?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":33729,"url":"https:\/\/staging.telescoop.nl\/en\/william-optics-redcat-91-448-apo-wifd-red-ota\/","url_meta":{"origin":33784,"position":1},"title":"William Optics RedCat 91\/448 APO WIFD Red OTA","author":"","date":"14-11-2025","format":false,"excerpt":"William Optics AP 91\/448 91 comes with a protective nylon carrying case, a Bahtinov mask integrated into the objective cap, M48 and M54 camera adapters and a dovetail rod suitable for Arca-Swiss and Losmandy clamps. \u00a0","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-AP-91-448-91-Apochromatische-refractor-RedCat-WIFD-OTA-4.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-AP-91-448-91-Apochromatische-refractor-RedCat-WIFD-OTA-4.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-AP-91-448-91-Apochromatische-refractor-RedCat-WIFD-OTA-4.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-AP-91-448-91-Apochromatische-refractor-RedCat-WIFD-OTA-4.jpg?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":33717,"url":"https:\/\/staging.telescoop.nl\/en\/william-optics-blackcat-91-448-apo-wifd-ota\/","url_meta":{"origin":33784,"position":2},"title":"William Optics BlackCat 91\/448 APO WIFD OTA","author":"","date":"14-11-2025","format":false,"excerpt":"William Optics AP 91\/448 91 comes with a rotator, tilt lens, M48 and M54 adapters, a versatile dovetail rod, a protective nylon carrying case and a Bahtinov mask integrated into the objective cap for perfect focusing. \u00a0","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-AP-91-448-91-Apochromatische-refractor-BlackCat-WIFD-OTA-11.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-AP-91-448-91-Apochromatische-refractor-BlackCat-WIFD-OTA-11.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-AP-91-448-91-Apochromatische-refractor-BlackCat-WIFD-OTA-11.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-AP-91-448-91-Apochromatische-refractor-BlackCat-WIFD-OTA-11.jpg?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":33684,"url":"https:\/\/staging.telescoop.nl\/en\/william-optics-ap-71-350-71-apochromatische-refractor-redcat-ota\/","url_meta":{"origin":33784,"position":3},"title":"William Optics AP 71\/350 71 Apochromatic refractor RedCat OTA","author":"","date":"14-11-2025","format":false,"excerpt":"William Optics AP 71\/350 71 comes with a protective nylon carrying case, a Vixen\/Arca-Swiss dovetail and a Bahtinov mask integrated into the objective cap - ideal for astrophotographers who want perfect focus and portability. \u00a0","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-AP-71-350-71-Apochromatische-refractor-RedCat-OTA-1.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-AP-71-350-71-Apochromatische-refractor-RedCat-OTA-1.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-AP-71-350-71-Apochromatische-refractor-RedCat-OTA-1.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-AP-71-350-71-Apochromatische-refractor-RedCat-OTA-1.jpg?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":33869,"url":"https:\/\/staging.telescoop.nl\/en\/william-optics-zenithstar-61-360-apo-ii-ota\/","url_meta":{"origin":33784,"position":4},"title":"William Optics ZenithStar 61\/360 APO II OTA","author":"","date":"15-11-2025","format":false,"excerpt":"William Optics AP 61\/360 ZS61 II wordt geleverd met een UniGuide 32mm guidescope, een flattener, buisringen, Arca-Swiss & Vixen-style zwaluwstaart, 2\" naar 1,25\" adapter en een zachte draagtas. \u00a0","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-AP-61-360-ZS61-II-Apochromatische-refractor-ZenithStar-OTA-2-1.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-AP-61-360-ZS61-II-Apochromatische-refractor-ZenithStar-OTA-2-1.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-AP-61-360-ZS61-II-Apochromatische-refractor-ZenithStar-OTA-2-1.jpg?resize=525%2C300&ssl=1 1.5x, 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post","link":""},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-Apochromatische-refractor-AP-108-518-UltraCat-WIFD-10.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-Apochromatische-refractor-AP-108-518-UltraCat-WIFD-10.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-Apochromatische-refractor-AP-108-518-UltraCat-WIFD-10.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/staging.telescoop.nl\/wp-content\/uploads\/2025\/11\/William-Optics-Apochromatische-refractor-AP-108-518-UltraCat-WIFD-10.jpg?resize=700%2C400&ssl=1 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