Bahtinov Focus Mask for Celestron NexStar 4SE

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Bahtinov focus mask Celestron NexStar 4SE This mask is designed to fit on to the front of your scope and not sit up against the corrector plate. This allows you to use the mask when a dew shield is fitted or not. Masks that sit up aginst the corrector plate can mean you touch the corrector plate when fitting or removing the mask leaving smears on your corrector plate. The new and improved mark 2 mask is now available. After several months of testing by myself and members of my astronomical society as well as feed back from past customers I have made a few changes to these to improve their ease of use and functionality.Being made of tougher and thinner material. The thinner material gives a brighter image at small apertures and make focusing much easier.Also the new overall shape prevents roll away. I have gone from 3 mounting bolts down to 2 as sometimes in the dark the 3rd bolt would sometimes be placed inside the dew shield. This did not affect the focus. With 2 bolts you simply hang the mask on the front of the scope. I also use longer bolts than most other makers as I have found it makes it easier to place the mask and makes it more stable. If you are in doubt then please measure the outside diameter of you telescope tube and let me know what it is. I am an engraver and sign maker with over 30 years of experience who has a lifelong love of astronomy I saw these for sale and thought I could make some improvements. Out of focus **************************** Nearly there *************************** Perfect focus *************************** It will take less than 1 minute to achieve perfect focus with your new mask and will mean you spend more time imaging photons rather than focusing them Above is a f10 mask suitable for Schmidt Cassegrains above my own setup consisting of Celestron C925 and William Optics ED102 Megrez 3mm thick Matt black Toughened Acrylic so no reflective light. Unlike ones made of ordinary Acrylic or Perspex these ones will resist cracking and breaking during normal use. However they are NOT unbreakable so treat them with the same care as you do with your lenses and camera equipment. A little tip for you here, I have nails on the wall of my observatory that I hang my masks on through one of the slots, when it is not in use In fact during a destruction test I did, I dropped one several time onto my patio from average scope height before it cracked , even then it was repairable and usable it did not shatter. Light weight so you wont upset the balance on your scope. Precision laser cut. M6 removable black plastic bolts to hang the mask over the front of your scope, these are removable for easy storage of your mask after focusing. My masks differ in several ways from any others that I have seen anywhere for sale. Most are cut to a round shape, mine are cut in a hexagon with an extended square corner. A round shape can roll away when you put in down and stand it up against something, a square one won't. Mine are held in place by two M6 bolts which are thicker and more durable than M5 ones, nylon bolts which will not mark your scope. I mark one of the top corners with reflective tape this is so you can find it again in the dark. Also like most people I have from time to time forgotten to remove the mask before imaging. The bright reflective corner makes it stand out. Unlike a Hartmann Mask which provides no visual cues on the direction of travel needed for focusing. A Bahtinov mask clearly shows the direction of travel needed to achieve focus. Also, a Hartmann mask doesn't provide the focus precision of a Bahtinov mask. The pattern displayed in a Hartmann just gets slightly more in focus, which means the true focus may be off by a significant degree. The Star Sharp Focus Mask shows you exactly where the perfec... read more

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