The SV215 zoom eyepiece is designed to provide the good balance of contrast, comfortable eye relief, and resolution for the critical planetary observer, particularly those with ultra-premium short focal length refractors. Parfocal Design: SV215 zoom eyepiece maintains focus throughout the zoom. You don't have to refocus when you magnify. Click /Stops: Improve the customer's hand feel of variable times adjustment operation. Smooth zoom action with click-stops at 3, 4, 5, 6,7 and 8mm for quick changes to precise preset magnifications. Apparent Field of View: 56°：The field of view will not change with the change of focal length, the process of doubling to give customers a fixed point to pull into the visual enjoyment. Eye Relief: 10mm: The transformation ratio customers do not need to adjust the distance of eye relief, so as to adapt to the observation environment again and improve the observation comfort. Features --Dielectric coatings provides 99% reflectivity --M28.5x0.6 filter thread can connect with 1.25in filter directly --Built-in brass ring to prevent the accessories barrel from being scratched --Machined and anodized aluminum housing make the SV188P dielectric diagonal durable and uniform. Compatible with Telescope.1.SV188P 1.25in dielectric diagonal compatible with any 1.25in refractor telescope . 2.SV188P can not connect with the SCT telescope directly, the additional adapter is required if you want to connect SV188P with the SCT telescope. 3.SV188P does not fit for reflector telescope. Specifications: Size: 1.25in. Coatings: Dielectric. Reflectivity: 99%. Thread: 28.5*0.6. Material: Aluminum Alloy. Screw: M4 Set Screw. Net Weight: 125g / 4.41oz. Package Includes: 1 x 1.25in 90 Deg Dielectric Mirror Diagonal, 1x M4 Screws,1x Dust proof plug,1x Dust proof cover. SVBONY SV135-This is definitely a must for beginners to start a good eyepiece collection.with this eyepiece, you can enjoy planetary astronomy .As a beginner; SV135 is good for starter astronomer!