{"id":15362,"date":"2025-07-06T19:45:39","date_gmt":"2025-07-06T17:45:39","guid":{"rendered":"https:\/\/www.telescoop.nl\/?post_type=product&#038;p=15362"},"modified":"2026-08-25T15:09:45","modified_gmt":"2026-08-25T13:09:45","slug":"zwo-ir-blocking-filter-d21","status":"publish","type":"product","link":"https:\/\/www.telescoop.nl\/en\/zwo-ir-blocking-filter-d21\/","title":{"rendered":"ZWO IR-blocking filter D21"},"content":{"rendered":"<h2 class=\"wp-block-heading has-text-align-center\"><strong>ZWO IR-blocking filter D21: sharpness and sensor protection for refractors<\/strong><\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">This interference filter blocks infrared light while protecting the sensor of your ZWO ASI camera from dust and moisture. This is important with refractors: infrared focuses at a different point than visible light, which leads to blurred star edges without a filter. With this IR blocker, your images remain sharp and your colors pure.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Do you use a reflector telescope? Then the cheaper ZWO clear glass filter D21 is sufficient as sensor protection, because reflectors do not have an IR focus shift.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Features<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n\n<li>90% transmission in the visible spectrum<\/li>\n\n\n<li>Prevents blurring due to IR focus shift in refractors<\/li>\n\n\n<li>Protects the sensor from dust, moisture, and scratches<\/li>\n\n\n<li>Multicoating against reflections and halos<\/li>\n\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">Compatibility<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Compatible with ZWO ASI cameras featuring a D21 window and M42 connection. Mount the filter as the first element on the camera or in the filter wheel.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Specifications<\/h3>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td><strong>Format<\/strong><\/td><td>D21 (M42 x 0.75)<\/td><\/tr><tr><td><strong>Filter type<\/strong><\/td><td>IR-blocking interference filter<\/td><\/tr><tr><td><strong>Transmission<\/strong><\/td><td>90% in the visible spectrum<\/td><\/tr><tr><td><strong>Coating<\/strong><\/td><td>multicoating, anti-reflection<\/td><\/tr><tr><td><strong>Glass thickness<\/strong><\/td><td>2 mm<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">The D21-format refractor filter of <a href=\"https:\/\/www.telescoop.nl\/en\/brands\/zwo\/\">ZWO<\/a>. For the larger window, there is the D25 version.<\/p>","protected":false},"excerpt":{"rendered":"<p>IR-blocking filter in D21 format (M42) with 90% visible light transmission. Protects the sensor and prevents focus shift caused by infrared light in refracting telescopes.<\/p>","protected":false},"featured_media":21118,"comment_status":"open","ping_status":"closed","template":"","meta":{"_acf_changed":false},"product_brand":[123],"product_cat":[3136,588,56],"product_tag":[],"class_list":["post-15362","product","type-product","status-publish","has-post-thumbnail","product_brand-zwo","product_cat-correctiefilters-uv-ir-cut","product_cat-filters","product_cat-telescoop-accessoires","product_shipping_class-licht","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":15365,"url":"https:\/\/www.telescoop.nl\/en\/zwo-ir-blocking-filter-d25\/","url_meta":{"origin":15362,"position":0},"title":"ZWO IR-blocking filter D25","author":"","date":"06-07-2025","format":false,"excerpt":"IR-blocking filter in D25 format (M42) with 90% visible light transmission. Protects the sensor and prevents focus shift caused by infrared light in refracting telescopes.","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"ZWO IR-Sperrfilter D25","src":"https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Blocking-filters-IR-ASI-D25.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Blocking-filters-IR-ASI-D25.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Blocking-filters-IR-ASI-D25.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Blocking-filters-IR-ASI-D25.jpg?resize=700%2C400&ssl=1 2x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Blocking-filters-IR-ASI-D25.jpg?resize=1050%2C600&ssl=1 3x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Blocking-filters-IR-ASI-D25.jpg?resize=1400%2C800&ssl=1 4x"},"classes":[]},{"id":15337,"url":"https:\/\/www.telescoop.nl\/en\/zwo-helderglasfilter-d21\/","url_meta":{"origin":15362,"position":1},"title":"ZWO Clear Glass Filter D21","author":"","date":"05-07-2025","format":false,"excerpt":"Helderglasfilter D21 met 95% transmissie en M42-schroefdraad. Beschermt de sensor van je ZWO ASI-camera tegen stof en vocht zonder invloed op het beeld.","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"ZWO Klarglasfilter D21","src":"https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Filters-Helderglasfilter-ASI-D21.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Filters-Helderglasfilter-ASI-D21.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Filters-Helderglasfilter-ASI-D21.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Filters-Helderglasfilter-ASI-D21.jpg?resize=700%2C400&ssl=1 2x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Filters-Helderglasfilter-ASI-D21.jpg?resize=1050%2C600&ssl=1 3x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Filters-Helderglasfilter-ASI-D21.jpg?resize=1400%2C800&ssl=1 4x"},"classes":[]},{"id":15341,"url":"https:\/\/www.telescoop.nl\/en\/zwo-helderglasfilter-d25\/","url_meta":{"origin":15362,"position":2},"title":"ZWO Clear Glass Filter D25","author":"","date":"05-07-2025","format":false,"excerpt":"D25 clear glass filter with 95% transmission and M42 thread. Protects the sensor of your ZWO ASI camera from dust and moisture without affecting the image.","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"ZWO Klarglasfilter D25","src":"https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Filters-Helderglasfilter-ASI-D25.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Filters-Helderglasfilter-ASI-D25.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Filters-Helderglasfilter-ASI-D25.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Filters-Helderglasfilter-ASI-D25.jpg?resize=700%2C400&ssl=1 2x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Filters-Helderglasfilter-ASI-D25.jpg?resize=1050%2C600&ssl=1 3x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Filters-Helderglasfilter-ASI-D25.jpg?resize=1400%2C800&ssl=1 4x"},"classes":[]},{"id":14833,"url":"https:\/\/www.telescoop.nl\/en\/zwo-blocking-filters-uv-ir-125\/","url_meta":{"origin":15362,"position":3},"title":"ZWO Blocking Filters UV\/IR 1.25\u2033","author":"","date":"23-06-2025","format":false,"excerpt":"UV\/IR-cut filter 1.25 inch: lets only visible light pass through for sharper stars and pure colors with color cameras without a built-in IR-cut filter.","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/06\/ZWO-Blocking-filters-UV-IR-1-25-.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/06\/ZWO-Blocking-filters-UV-IR-1-25-.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/06\/ZWO-Blocking-filters-UV-IR-1-25-.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/06\/ZWO-Blocking-filters-UV-IR-1-25-.jpg?resize=700%2C400&ssl=1 2x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/06\/ZWO-Blocking-filters-UV-IR-1-25-.jpg?resize=1050%2C600&ssl=1 3x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/06\/ZWO-Blocking-filters-UV-IR-1-25-.jpg?resize=1400%2C800&ssl=1 4x"},"classes":[]},{"id":25245,"url":"https:\/\/www.telescoop.nl\/en\/omegon-blocking-filter-infraroodfilter-125\/","url_meta":{"origin":15362,"position":4},"title":"Omegon Blocking Filter Infrared Filter 1.25\u2033","author":"","date":"07-08-2025","format":false,"excerpt":"\u00a0 Omegon Blocking Filter Infrared Filter 1.25\" - blocks unwanted IR radiation in photography and visual observation, for sharper images and better color correction.","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"Omegon Blocking Filter Infraroodfilter 1,25\"","src":"https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/08\/Omegon-Blocking-filters-Infrared-band-elimination-filter.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/08\/Omegon-Blocking-filters-Infrared-band-elimination-filter.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/08\/Omegon-Blocking-filters-Infrared-band-elimination-filter.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/08\/Omegon-Blocking-filters-Infrared-band-elimination-filter.jpg?resize=700%2C400&ssl=1 2x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/08\/Omegon-Blocking-filters-Infrared-band-elimination-filter.jpg?resize=1050%2C600&ssl=1 3x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/08\/Omegon-Blocking-filters-Infrared-band-elimination-filter.jpg?resize=1400%2C800&ssl=1 4x"},"classes":[]},{"id":15074,"url":"https:\/\/www.telescoop.nl\/en\/zwo-asi432mm-mono\/","url_meta":{"origin":15362,"position":5},"title":"ZWO ASI432MM Mono","author":"","date":"04-07-2025","format":false,"excerpt":"Monochrome camera with Sony IMX432 global shutter sensor: 9 micrometer pixels, 97,000 electron full well, 120 fps, and glow-free. The specialist for solar and lunar photography.","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"ZWO ASI432MM Mono","src":"https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Camera-ASI-432-MM-Mono.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Camera-ASI-432-MM-Mono.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Camera-ASI-432-MM-Mono.jpg?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Camera-ASI-432-MM-Mono.jpg?resize=700%2C400&ssl=1 2x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Camera-ASI-432-MM-Mono.jpg?resize=1050%2C600&ssl=1 3x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2025\/07\/ZWO-Camera-ASI-432-MM-Mono.jpg?resize=1400%2C800&ssl=1 4x"},"classes":[]}],"_links":{"self":[{"href":"https:\/\/www.telescoop.nl\/en\/wp-json\/wp\/v2\/product\/15362","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.telescoop.nl\/en\/wp-json\/wp\/v2\/product"}],"about":[{"href":"https:\/\/www.telescoop.nl\/en\/wp-json\/wp\/v2\/types\/product"}],"replies":[{"embeddable":true,"href":"https:\/\/www.telescoop.nl\/en\/wp-json\/wp\/v2\/comments?post=15362"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.telescoop.nl\/en\/wp-json\/wp\/v2\/media\/21118"}],"wp:attachment":[{"href":"https:\/\/www.telescoop.nl\/en\/wp-json\/wp\/v2\/media?parent=15362"}],"wp:term":[{"taxonomy":"product_brand","embeddable":true,"href":"https:\/\/www.telescoop.nl\/en\/wp-json\/wp\/v2\/product_brand?post=15362"},{"taxonomy":"product_cat","embeddable":true,"href":"https:\/\/www.telescoop.nl\/en\/wp-json\/wp\/v2\/product_cat?post=15362"},{"taxonomy":"product_tag","embeddable":true,"href":"https:\/\/www.telescoop.nl\/en\/wp-json\/wp\/v2\/product_tag?post=15362"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}