{"id":14979,"date":"2026-05-08T17:05:10","date_gmt":"2026-05-08T15:05:10","guid":{"rendered":"https:\/\/deep-space-astronomy.ch\/?post_type=product&p=14979"},"modified":"2026-05-08T17:05:27","modified_gmt":"2026-05-08T15:05:27","slug":"askar-91f-0-75x-reducer","status":"publish","type":"product","link":"https:\/\/deep-space-astronomy.ch\/en\/product\/askar-91f-0-75x-reducer\/","title":{"rendered":"Askar 91F 0.75\u00d7 Reducer"},"content":{"rendered":"

Askar 91F 0.75\u00d7 Reducer - Full Frame Reducer for Askar 91F<\/h2>\n

Visit Askar 91F 0.75\u00d7 Reducer<\/strong> is a focal reducer specially designed for telescopes. Askar 91F Flat-Field<\/strong>. This accessory transforms the astrograph into a faster, brighter and more versatile system, ideal for wide-field deep-sky astrophotography.<\/p>\n

Thanks to its 0.75\u00d7<\/strong>, it increases the focal ratio from 91F to f\/5<\/strong>, This is combined with advanced field correction to produce fine, uniform stars on all modern Full Frame sensors.<\/p>\n

The wider photographic field and shorter exposure times make this reducer particularly interesting for imaging large nebulae, star clusters and faint deep-sky objects.<\/p>\n

Turn your Askar 91F into a fast f\/5 astrograph<\/h3>\n

Once installed on the Askar 91F, the reducer reduces the native focal length:<\/p>\n

    \n
  • From 609 mm to 455 mm<\/li>\n
  • From f\/6.7 to f\/5<\/li>\n<\/ul>\n

    This reduction brings several important benefits:<\/p>\n

      \n
    • Shorter exposure times<\/li>\n
    • Wider photographic field<\/li>\n
    • Improved light collection<\/li>\n
    • Best efficiency under medium skies<\/li>\n
    • More comfortable imaging of large objects<\/li>\n<\/ul>\n

      The reducer is particularly useful for photography:<\/p>\n

        \n
      • The great nebulae<\/li>\n
      • The rich regions of the Milky Way<\/li>\n
      • Open clusters<\/li>\n
      • Weak objects requiring a lot of signal<\/li>\n
      • Fast-moving or faint celestial objects<\/li>\n<\/ul>\n

        Full Frame integrated field correction<\/h3>\n

        The Askar 91F 0.75\u00d7 Reducer does more than just reduce the focal length. It also incorporates a field correction that effectively limits field curvature and preserves excellent star quality right into the corners.<\/p>\n

        This design guarantees :<\/p>\n

          \n
        • Fine stars in the center of the field<\/li>\n
        • Improved image homogeneity<\/li>\n
        • Excellent Full Frame compatibility<\/li>\n
        • Better use of modern high-resolution sensors<\/li>\n<\/ul>\n

          The supported image circle reaches 44 mm<\/strong>, perfectly suited to full-format 24\u00d736 mm sensors.<\/p>\n

          Optimized triplet optical design<\/h3>\n

          The reducer is based on an optical formula with three lenses<\/strong> specially optimized for the Askar 91F.<\/p>\n

          This design enables :<\/p>\n

            \n
          • Excellent optical correction<\/li>\n
          • Uniform field reduction<\/li>\n
          • Good control of aberrations<\/li>\n
          • Optimum compatibility with Full Frame sensors<\/li>\n<\/ul>\n

            The result is a clean, uniform image across the entire photographic field.<\/p>\n

            Standard backfocus 55 mm<\/h3>\n

            The Askar 91F 0.75\u00d7 Reducer uses a standard backfocus of 55 mm<\/strong> measured from M48 male thread.<\/p>\n

            This distance facilitates integration with most modern astrophotographic equipment:<\/p>\n

              \n
            • Astronomical CMOS cameras<\/li>\n
            • DSLR<\/li>\n
            • Hybrid cameras<\/li>\n
            • Filter wheels<\/li>\n
            • Tilt plates<\/li>\n
            • Standard accessories<\/li>\n<\/ul>\n

              The 91F photographic tube includes :<\/p>\n

                \n
              • M54x0.75 adapter<\/li>\n
              • M48x0.75 adapter<\/li>\n<\/ul>\n

                Installation of the gearbox is fast and particularly simple.<\/p>\n

                2-inch filter compatibility<\/h3>\n

                The reducer incorporates a standard thread M48x0.75<\/strong> compatible with 2-inch astronomical filters.<\/p>\n

                This allows direct installation of :<\/p>\n

                  \n
                • Narrowband filters<\/li>\n
                • Duoband filters<\/li>\n
                • Anti-light pollution filters<\/li>\n
                • UV\/IR Cut filters<\/li>\n
                • LRGB filters<\/li>\n<\/ul>\n

                  This compatibility greatly simplifies the design of the optical train.<\/p>\n

                  High-precision CNC manufacturing<\/h3>\n

                  Like other Askar premium accessories, the 91F 0.75\u00d7 Reducer benefits from precision CNC manufacturing ensuring :<\/p>\n

                    \n
                  • Excellent mechanical rigidity<\/li>\n
                  • Excellent stability<\/li>\n
                  • High durability<\/li>\n
                  • Precise optical alignment<\/li>\n<\/ul>\n

                    The gearbox is supplied with front and rear threaded metal plugs to protect the optical surfaces from dust and moisture during transport and storage.<\/p>\n

                    Robust mechanical connection<\/h3>\n

                    Both ends are threaded M59x1<\/strong>, guaranteeing :<\/p>\n

                      \n
                    • A stable connection<\/li>\n
                    • Limited bending<\/li>\n
                    • Excellent mechanical precision<\/li>\n
                    • Better stability with Full Frame setups<\/li>\n<\/ul>\n

                      This design helps maintain optimum image quality even with advanced imaging configurations.<\/p>\n

                      Summary table of technical specifications<\/h3>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
                      Features<\/th>\nValue<\/th>\n<\/tr>\n
                      Compatibility<\/td>\nAskar 91F Flat-Field<\/td>\n<\/tr>\n
                      Reduction factor<\/td>\n0.75\u00d7<\/td>\n<\/tr>\n
                      Resulting focus<\/td>\n455 mm<\/td>\n<\/tr>\n
                      Resulting focal ratio<\/td>\nf\/5<\/td>\n<\/tr>\n
                      Optical type<\/td>\nTriplet corrector\/reducer<\/td>\n<\/tr>\n
                      Image circle<\/td>\n44 mm Full Frame<\/td>\n<\/tr>\n
                      Backfocus<\/td>\n55 mm from M48 male thread<\/td>\n<\/tr>\n
                      Main thread<\/td>\nM59x1<\/td>\n<\/tr>\n
                      Compatible adapters<\/td>\nM54x0.75 and M48x0.75<\/td>\n<\/tr>\n
                      Filter compatibility<\/td>\nIntegrated 2\u2033 M48 filter thread<\/td>\n<\/tr>\n
                      Weight<\/td>\n0.3 kg<\/td>\n<\/tr>\n
                      Manufacturing<\/td>\nHigh-precision CNC aluminum<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

                      Why choose Askar 91F 0.75\u00d7 Reducer?<\/h3>\n

                      The Askar 91F 0.75\u00d7 Reducer is an excellent complement for astrophotographers wishing to exploit the full potential of their Askar 91F.<\/p>\n

                      By transforming the telescope into a fast astrograph at f\/5 while retaining excellent Full Frame correction, this reducer greatly enhances the instrument's versatility and photographic efficiency.<\/p>\n

                      Its modern optical design, robust mechanics and perfect compatibility with the 91F make it a particularly coherent accessory for deep-sky enthusiasts looking for simplicity and performance.<\/p>","protected":false},"excerpt":{"rendered":"

                      Askar 91F 0.75\u00d7 Reducer \u2013 R\u00e9ducteur Correcteur Full Frame pour Askar 91F Le Askar 91F 0.75\u00d7 Reducer est un r\u00e9ducteur de focale sp\u00e9cialement con\u00e7u pour la lunette Askar 91F Flat-Field. Cet accessoire permet de transformer l\u2019astrographe en un syst\u00e8me plus rapide, plus lumineux et plus polyvalent, id\u00e9al pour l\u2019astrophotographie du ciel profond grand champ. Gr\u00e2ce […]<\/p>\n","protected":false},"featured_media":14980,"comment_status":"open","ping_status":"closed","template":"","meta":[],"product_brand":[382],"product_cat":[650],"product_tag":[],"class_list":{"0":"post-14979","1":"product","2":"type-product","3":"status-publish","4":"has-post-thumbnail","6":"product_brand-askar","7":"product_cat-rducteurs-correcteurs-ap","9":"first","10":"on_supplier","11":"taxable","12":"shipping-taxable","13":"purchasable","14":"product-type-simple"},"_links":{"self":[{"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/product\/14979","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/product"}],"about":[{"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/types\/product"}],"replies":[{"embeddable":true,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/comments?post=14979"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/media\/14980"}],"wp:attachment":[{"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/media?parent=14979"}],"wp:term":[{"taxonomy":"product_brand","embeddable":true,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/product_brand?post=14979"},{"taxonomy":"product_cat","embeddable":true,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/product_cat?post=14979"},{"taxonomy":"product_tag","embeddable":true,"href":"https:\/\/deep-space-astronomy.ch\/en\/wp-json\/wp\/v2\/product_tag?post=14979"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}