ฟิลเตอร์ส่องดวงอาทิตย์ Thousand Oaks ID 4.25" (108mm) แบบ Glass 2+ #4250

• กระจกคุณภาพสูงที่คัดด้วยมือ เคลือบสาร Thousand Oaks Optical's Solar II Plus coating จึงมีความคงทนมากที่สุดรุ่นนึงในตลาด 
• สวมเข้ากับขอบของหน้ากล้องอย่างแน่นพอดี (เสริมด้วย felt lining ที่รวมอยู่ในชุด) เพื่อป้องกันการหลุดของฟิล์เตอร์ กรองแสงดวงอาทิตย์ที่จะเข้าสู่หน้ากล้องได้ 99.999%
• ขอบนอกทำด้วยอลูมิเนียมที่เบาทนทานและแข็งแรง ขอบในเสริมวัสดุที่ช่วยให้การสวมใส่แน่นกระชับ (friction fit) เพื่อเพิ่มผิวสัมผัสกับขอบกล้องดูดาว ป้องกันอุบัติเหตุที่อาจทำให้ฟิลเตอร์หลุดโดยง่าย
• ส่งผ่านแสงเพียง 1/1000 ของ 1% (Optical Density 5) เหมาะสำหรับใช้สังเกตด้วยตาและการถ่ายภาพ
• ขนาดขอบใน = 4.25" (ใช้ได้กับกล้องที่มีขอบนอกระหว่าง 4.00" ถึง 4.25" โดยใช้ felt lining เสริมขอบในของฟิลเตอร์ 3-6 ตำแหน่ง)
• ถ้าใช้งานอย่างระมัดระวัง ฟิลเตอร์ Thousand Oaks Optical รุ่นนี้สามารถอยู่ได้ไม่ต่ำกว่า 20 ปี และอาจนานชั่วชีวิตคน
• แบรนเนมคุณภาพจาก USA; รับประกัน 2 ปี

ข้อควรระวัง:

1. วิธีเลือกฟิลเตอร์ที่พอดีกับหน้ากล้องสามารถทำได้โดยการวัดที่ขอบนอกของหน้ากล้อง (OD)โดยตรงและเทียบกับขนาดขอบใน (ID) ของฟิลเตอร์ (OD ของขอบกล้องดูดาวมักจะใหญ่กว่าหน้าเลนส์หรือกระจกของกล้องดูดาวเป็นปกติ เช่นกล้องดูดาวขนาด 8" อาจมีขอบกล้องที่ 9.25" เป็นต้น) ขนาดฟิลเตอร์ควรมี ID ที่พอดีหรือมากกว่าขอบกล้องดูดาวไม่เกิน 0.25"  ดูวีดีโอหรือรูปประกอบได้จากด้านล่าง

2.ไม่ควรมองดวงอาทิตย์โดยไม่ผ่านฟิลเตอร์แม้เพียงเวลาเสี่ยววินาที เพราะอาจทำให้กระทบการมองเห็นอย่างถาวร

Who said you have to be in the dark to do astronomy? Turning your telescope to the Sun is fun and educational. Watch the march of giant sunspots, the clouds of glowing vapor in the photosphere, and solar "granulation" detail. But be sure to protect your precious vision with a safe Thousand Oaks solar filter! Looking at the Sun without one, even for an instant, can permanently damage your eyes.

Superior to Mylar
These full-aperture optical glass telescope filters deliver superb views of the Sun, without risk to your eyes. While more expensive than Mylar filters, Thousand Oaks glass solar filters provide better contrast, a more natural yellow-orange color instead of blue, and their glass and aluminum construction is much more durable. They're ideal for photographing the Sun too!

The glass elements are machine-polished and triple-coated with an advanced nickel-chromium stainless steel alloy for a scratch-resistant surface. The filter passes only a fraction of the incoming light, rejecting harmful ultraviolet and infrared radiation.

Each Thousand Oaks filter is mounted in an aluminum cell that slide-fits over the front of your telescope. Size shown in the chart below is the ideal diameter of front of telescope; filter will fit diameters up to 1/4" smaller with foam tape liner supplied.

CAUTION: Never look at the Sun, even for an instant, without a protective solar filter. Doing so can permanently damage your eyes.

Determining the Correct Thousand Oaks Glass Solar Filter for your Telescope

A full-aperture solar filter is designed to fit over the front of a telescope. It allows safe viewing of the Sun by reducing the light by 99.99% and preventing concentrated heat from entering the telescope, which could cause injury to the user or damage to equipment.

If your telescope is not listed on our solar filter reference chart, you can determine the size of filter needed for your scope by taking the following steps:

1. Measure the maximum outside diameter (OD) of the front end of your telescope.

2. The solar filter sizes listed in our catalog and on our website refer to the inner diameter (ID) of the filter's foam-lined metal cell for Thousand Oaks, which slip over the front of the telescope. Choose a filter whose size matches the OD of your telescope's front end, or that is up to 0.25" larger than the front end (for Thousand Oaks Filters only). For a filter that is up to 0.25" larger in diameter than your telescope, apply the supplied adhesive foam tabs as needed to the inside wall of the cell until the cell fits snugly over the front opening. 

Pinholes and Minor Scratches

Pinholes and minor surface scratches are common in solar filters, however, Thousand Oaks Optical's multi-coating technique keeps them to a minimum. A "bright" pinhole may cause "ghosting" due to scattered light. If this is seen during observation, the pinhole(s) should be blocked out. Blocking out any pinholes should be done on inside coated surface. Hold filter 1-2 feet in front of a standard 60-100 watt "soft white" light bulb. Blocking can be done with a fine point felt marker, small drop of paint, typing correction fluid etc. The touch up procedure will not degrade the optical performance. It is not necessary to touch up any small pinholes that do not cause image problems. There is no danger if some small non light scattering pinholes or minor scratches are present. All filters are tested for safety before shipment.

Frequently Asked Questions (FAQs) 

WHICH TYPE IS THE BEST OPTICALLY? The RG film offers the highest resolution with high magnification. The glass is a very close second. Under low to moderate magnification, it's difficult see the difference between RG, Glass or Black Polymer.

WHAT SIZE DO I ORDER? The application guide below lists sizes by clear aperture (filter size) and outer cell wall inside diameter (I.D.) The I.D. of the cell slips over and around the O.D. of the telescope tube or lens holder. Please note that the brands and sizes listed are only a guide. Telescope manufacturers sometimes make changes so we strongly recommend the outside diameter of the tube be measured to be sure the correct part number is chosen. Choose the closest outer cell I.D. size larger than the outside diameter measurement of your instrument. Example: part # 4250 (4 1/4") would fit O.D. measurements from 4" to 4 3/16". Do not choose a size the same as your O.D. since it will be too tight and not allow room for a felt lining. Ample felt is included for custom fitting.

ARE THE FILTERS COMPLETELY SAFE? All of Thousand Oaks Optical Glass 2+, RG-Solar Film & Black Polymer filters are completely safe for unlimited visual use. If handled with care and common sense, all will last a minimum of 20 years to life.

DO THE ALUMINUM CELLS COME WITH THUMB SCREWS? Thumb screws may seem like a good idea, however, our extensive testing found that in most cases it's actually less secure than a felt lining which covers a lot more surface area for a secure friction fit. If the tolerance is within a few thousands of an inch such as with eyepiece holders, it would be fine, but this is rarely the case. Thumb screws can also dent and scratch the tube and put strain on the filter glass. Thumb screws are simply a "one size fits many" manufacturing shortcut and provide a false security.

CAN THE TELESCOPE OPTICS GET HOT OR DAMAGED? No, all the heat and intense light is blocked before it can enter the telescope. Your telescope may get warm from sunlight shining on it, not from the small amount of visible light transmitted through the filter.

WHAT DETAIL IS VISIBLE? Sunspots and surface granulation are the two main features. The only detail that cannot be seen with a standard filter (commonly called white light filter) are prominence and flares which require our highly specialized H-Alpha filter system.

WHY ARE THREADED CAMERA FILTERS ONLY AVAILABLE IN BLACK POLYMER? RG and Glass filters have highly reflective coatings that can cause internal reflections between the filter and camera lens since the filter and lens are in close proximity. This problem is less likely to occur with telescopes, however, mounted telescope filters can be tilted slightly to move any internal reflections off axis and out of view.