With larger apertures, too much heat ends up in the narrow H-alpha filter at the rear without a pre-filter. With the DayStar ERF E-120N100 for the aperture, you prepare your telescope for H-alpha observations of the Sun.<\/p>\n\n\n\n
The filter blocks ultraviolet and infrared light and allows the red light through, where the H-alpha filter works. It is part of our sun filters and pre-filters<\/a>. If you would rather view the Sun without the individual components in H-alpha, please check our complete solar telescopes<\/a>.<\/p>\n\n\n\n Which ERF you need depends on the aperture and the outer diameter of your telescope. Measure the outer diameter of your tube or dovetail and compare that with the stated size of the mount first. An ERF itself is not a solar filter to use for viewing. Use it only in conjunction with a suitable H-alpha filter and never look at the sun without the full filter setup.<\/p>\n\n\n\n Other sizes are, for example the ERF E-130N100<\/a> and the ERF E-110N75<\/a>.<\/p>","protected":false},"excerpt":{"rendered":" Energy rejection pre-filter E-120N100 from DayStar that protects your H-alpha filter and telescope from the heat, UV and infrared of the sun.<\/p>","protected":false},"featured_media":113155,"comment_status":"open","ping_status":"closed","template":"","meta":{"_acf_changed":false},"product_brand":[3282],"product_cat":[56,3178],"product_tag":[],"class_list":["post-113158","product","type-product","status-publish","has-post-thumbnail","product_brand-daystar","product_cat-telescoop-accessoires","product_cat-zonnefilters","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":113157,"url":"https:\/\/www.telescoop.nl\/en\/erf-voorfilter-e-120n80-voor-h-alpha-zonnewaarneming-daystar\/","url_meta":{"origin":113158,"position":0},"title":"ERF-prefilter E-120N80 for H-alpha solar monitoring | DayStar","author":"Info telescoop","date":"09-10-2026","format":false,"excerpt":"DayStar's E-120N80 pre-filter for H-alpha solar observation, which prevents heat, UV and infrared from entering your telescope before it opens.","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2026\/10\/12827_1.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2026\/10\/12827_1.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2026\/10\/12827_1.jpg?resize=525%2C300&ssl=1 1.5x"},"classes":[]},{"id":113161,"url":"https:\/\/www.telescoop.nl\/en\/erf-voorfilter-e-150n100-voor-h-alpha-zonnewaarneming-daystar\/","url_meta":{"origin":113158,"position":1},"title":"ERF-prefilter E-150N100 for H-alpha solar monitoring | DayStar","author":"Info telescoop","date":"09-10-2026","format":false,"excerpt":"DayStar pre-filter in size E-150N100 that blocks UV and infrared outside your telescope, as the first step of an H-alpha setup.","rel":"","context":"Similar post","block_context":{"text":"Similar post","link":""},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2026\/10\/12827_1.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2026\/10\/12827_1.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.telescoop.nl\/wp-content\/uploads\/2026\/10\/12827_1.jpg?resize=525%2C300&ssl=1 1.5x"},"classes":[]},{"id":113166,"url":"https:\/\/www.telescoop.nl\/en\/erf-voorfilter-e-325f90-voor-h-alpha-zonnewaarneming-daystar\/","url_meta":{"origin":113158,"position":2},"title":"ERF pre-filter E-325F90 for H-alpha solar monitoring | DayStar","author":"Info telescoop","date":"09-10-2026","format":false,"excerpt":"DayStar ERF pre-filter 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