{"product_id":"explore-scientific-2-inch-variable-polarizing-filter","title":"Explore Scientific 2-inch Variable Polarizing Filter with Continuously Adjustable Brightness","description":"\u003ch2\u003eProduct Overview\u003c\/h2\u003e\u003cp\u003eThe Explore Scientific 2-inch Variable Polarizing Filter, item 310250, is a two-element polarising filter that lets you set image brightness continuously rather than in fixed steps. Explore Scientific publishes a light transmission range of 40 per cent down to 1 per cent, adjusted simply by rotating the two halves of the housing against one another. The cell is black anodised aluminium with a 2-inch filter thread on both the inside and the outside, and the optical elements are described as highly parallel optical glass. A dust cover is supplied. Explore Scientific positions it as a universally applicable filter for lunar, planetary and solar observing, particularly behind a Herschel wedge or on large apertures where brightness needs to come down to a comfortable level.\u003c\/p\u003e\u003ch2\u003eWho It's For\u003c\/h2\u003e\u003cp\u003eThis is the filter for the observer who is tired of swapping fixed densities. Brightness at the eyepiece is a moving target: the Moon changes by several magnitudes between a thin crescent and full, a 12-inch reflector delivers far more light than a 4-inch refractor at the same magnification, and the eyepiece you reach for at the end of the session may be four times faster than the one you started with. A fixed neutral density filter is chosen for one of those situations and is wrong for the others. Here you leave the filter in place and turn the ring until the view looks right, then keep turning as conditions change.\u003c\/p\u003e\u003cp\u003eIt also earns its place with anyone doing white-light solar work behind a Herschel wedge. A wedge dumps the great majority of the solar energy out of the back, but what reaches the eyepiece is still bright, and because a wedge outputs strongly polarised light, a polarising filter behind it is the accepted way to trim the remaining brightness smoothly to a comfortable working level.\u003c\/p\u003e\u003ch2\u003eKey Features \u0026amp; Design\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eContinuously variable transmission from a published 40 per cent down to 1 per cent\u003c\/li\u003e\n\u003cli\u003eAdjustment by rotating the two halves of the housing, so brightness can be set at the eyepiece without unthreading anything\u003c\/li\u003e\n\u003cli\u003eStandard 2-inch filter thread on both the inside and the outside of the cell, so it can be sandwiched between accessories or carry a second filter\u003c\/li\u003e\n\u003cli\u003eBlack anodised aluminium housing, which suppresses internal reflections as well as resisting handling wear\u003c\/li\u003e\n\u003cli\u003eHighly parallel optical glass elements, so the filter does not introduce wedge error into the converging beam\u003c\/li\u003e\n\u003cli\u003eWell suited to Herschel wedge solar work, where the output is already polarised\u003c\/li\u003e\n\u003cli\u003eDust cover included\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eFilter Design\u003c\/h2\u003e\u003cp\u003eThe filter is a pair of linear polarisers mounted in the two rotating halves of the cell. Starlight and reflected sunlight arriving at the telescope are effectively unpolarised, so the first element passes only the component aligned with its own axis, which is why the maximum transmission is around 40 per cent rather than anything close to 100. The second element then acts on light that is already polarised, and the fraction it passes follows the square of the cosine of the angle between the two axes. With the axes parallel you are at maximum transmission; as you rotate towards 90 degrees the transmission falls away steeply, reaching the published 1 per cent at the crossed position. The practical consequence is that the adjustment is not linear across the rotation. Most of the useful range sits in a fairly narrow band of rotation near the crossed end, so a small movement there makes a large difference to brightness. It is worth knowing that both elements are neutral in intent rather than coloured, so the view darkens without taking on the green cast that older single-element moon filters were known for, although a slight warming is normal with polarising material.\u003c\/p\u003e\u003ch2\u003eRecommended Uses\u003c\/h2\u003e\u003cul\u003e\n\u003cli\u003eLunar observing across all phases, where the required attenuation changes night to night\u003c\/li\u003e\n\u003cli\u003ePlanetary work on bright targets such as Venus, and on Jupiter in a large aperture\u003c\/li\u003e\n\u003cli\u003eWhite-light solar observing behind a Herschel wedge, to trim the residual brightness smoothly\u003c\/li\u003e\n\u003cli\u003eAny large-aperture telescope where the Moon is uncomfortable to look at even through a fixed density filter\u003c\/li\u003e\n\u003cli\u003ePublic observing sessions where the same telescope has to suit many pairs of eyes in a short time\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch2\u003eCompatibility and Accessory Notes\u003c\/h2\u003e\u003cp\u003eThe cell carries the standard 2-inch filter thread and screws into the barrel of most 2-inch eyepieces, and into many 2-inch star diagonals and adapters. Because the thread is doubled, inside and outside, you can also mount it between two components of a 2-inch train or thread another 2-inch filter onto it. Note that access matters here: you have to be able to reach the cell to rotate it, so mounting it deep inside a diagonal where your fingers cannot get to it defeats the purpose. Most observers thread it onto the eyepiece barrel or the front of the diagonal for that reason. This is the 2-inch version and will not fit 1.25-inch eyepieces. If you want to confirm it will work in a particular diagonal or focuser arrangement, contact our team in Bolton with the models and we will check it for you.\u003c\/p\u003e\u003ch2\u003eGood to Know Before You Order\u003c\/h2\u003e\u003cp\u003eExplore Scientific publishes no shipping weight for this item, so we are confirming it on our own scales before the listing goes live. That is why it is currently unpublished. Contact us and we will give you a shipping figure for your address. On safety, be clear about what the solar reference means: this filter is used behind a Herschel wedge or another certified solar filter that has already removed the dangerous energy. A polarising filter at the eyepiece is never itself a solar filter and must not be used to view the Sun on its own. Also note that a 2-inch filter cell adds physical length and a little weight to the eyepiece end, which can matter on a delicately balanced mount, and that the adjustment being non-linear takes a session or two to get a feel for. What is included is the filter and a dust cover; eyepieces, diagonals and wedges are separate.\u003c\/p\u003e\u003ch2\u003eFrequently Asked Questions\u003c\/h2\u003e\u003cp\u003e\u003cstrong\u003eHow dark can it actually go?\u003c\/strong\u003e Explore Scientific publishes a range of 40 per cent down to 1 per cent transmission. At the dark end that is a reduction of about four magnitudes, which is more than enough for a full Moon in a large aperture.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhy is the maximum only 40 per cent?\u003c\/strong\u003e Because a single linear polariser can only pass the component of unpolarised light aligned with its axis, so about half is lost before the second element does anything. That is inherent to how polarisers work, not a shortcoming of this filter.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eCan I use it with a Herschel wedge?\u003c\/strong\u003e Yes, and that is one of its intended uses. The wedge does the safety work and the polariser trims the remaining brightness. Never point a telescope at the Sun without a purpose-made solar device fitted correctly.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill it fit 1.25-inch eyepieces?\u003c\/strong\u003e No. This is the 2-inch version. Ask us if you need the smaller size instead.\u003c\/p\u003e\u003ch2\u003eBottom Line\u003c\/h2\u003e\u003cp\u003eIf you observe the Moon and planets regularly and own more than one eyepiece, a variable polariser replaces a drawer full of fixed densities and gives you exactly the brightness you want at any moment. The dual 2-inch threading and anodised aluminium cell make it easy to work into an existing train. Contact our team in Bolton if you would like help deciding where in your optical train to fit it.\u003c\/p\u003e","brand":"Explore Scientific","offers":[{"title":"Default Title","offer_id":53958592036975,"sku":"310250","price":200.95,"currency_code":"CAD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0686\/0049\/6239\/files\/310250_1.jpg?v=1785960605","url":"https:\/\/ontariotelescope.com\/products\/explore-scientific-2-inch-variable-polarizing-filter","provider":"Ontario Telescope and Accessories","version":"1.0","type":"link"}