<b>SVBONY Bahtinov mask has become the preferred method of focusing a telescope, either visually or when imaging with a CCD camera, DSLR or webcam.</b><br> <b>Please be assured that these focusing masks will work excellently for both reflectors and refractors with whatever focal length. </b><br><br> <b>Note: you need to measure your telescope tube size and choose the right size of the mask.</b><br><br> <b>How to use SVBONY Bahtinov Focus-Mask?</b><br> Step 1:Place the SVBONY Bahtinov Focus-Mask over the end of your telescope, then locate a bright star near your target, take a 3-5 second picture and view the diffraction spikes. <br> Step 2:Change your focus, take another picture and again, view your diffraction spikes. Is the center spike moving further from center? Then change the direction your focusing and try another picture. <br> Step 3:Watch the direction the spikes are moving and when the center spike passes the middle of the other two spikes, change direction and fine tune your tuning knobs until the center spike is in the middle. Your now in perfect focus.<br><br> <b>Come with well protected 3 screws</b><br> The masks grip the telescope tube gently but firmly with three metal posts which have non-scratching silicon sleeves to protect you valued telescope surface.<br><br> <b>Solid design</b><br> Premium grade of aluminum, valued for fall resistance.Don't worry about it being damaged.<br><br> <b>Very thin and lightweight</b><br> A thin bahtinov mask can help you achieve the purpose of focusing, and the light weight will not break the balance of your telescope.<br><br><br> <b>Features:</b><br> Masks now feature 3 holes which can be attached with 3 screws to prevent the mask from falling all the way to the ground<br> Perfect focusing for your CCD, DSLR or Webcam in seconds<br> Aluminium alloy material thickness: 1 mm<br> Weight: 31g<br><br> <b>Package Include: </b><br> 1 X Bahtinov Mask <br> 3 X Screw Kit