YSK: Never use old threaded solar filters that screw into…
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YSK: Never use old threaded solar filters that screw into telescope eyepieces
**Why YSK: There's a surprisingly large number of dangerous threaded SUN filters littered throughout the basements and closets of the world.**
If you have an older telescope, especially one from before the 1990's, check whether it came with small threaded filters that screw directly into the eyepiece. They often came with two of them. One was marked **MOON** and the other was marked **SUN**. The Moon one works great to reduce the glare of a full Moon.
It's the **SUN** filters that are so dangerous. These are the Lawn Darts of the astronomy hobby, if the Lawn Darts had sharpened hypodermic needles at the front.
The original concept was this: Your telescope captures the sunlight and focuses it on the dark SUN filter that is screwed into the eyepiece at the back of the telescope. You place your **delicate eye** up to the eyepiece, only a few inches from the **searingly hot SUN filter**.
As long as the glass didn't crack, you were fine. Unfortunately... they cracked a lot. Like, a whole lot. Sometimes they even shattered. This would instantly expose your retina to the full blinding light of a 3 or 4 inch magnifying glass, instantly causing solar retinopathy and likely blindness.
If you have one of these SUN filters, it is recommended that you **smash & trash** them so that nobody can ever accidently try them out.
I tested an old threaded solar filter while recording it with a camera. It reached 326 degrees Fahrenheit and in less than 12 seconds after installation, the filter cracked from the heat buildup and suddenly allowed bright sunlight through.
**\*\*\* If curious, the demonstration is at the start of this video:** ** https://youtu.be/rtyLH5fBaJE ** https://youtu.be/rtyLH5fBaJE
**Safe Alternatives:**
1. Solar Eclipse Glasses (by themselves, **NOT in combination** with telescopes, binoculars, or cameras).
2. Front-mounted solar filters specifically designed for your telescope. These stop 99.999% of the light energy before it even has a chance to enter your telescope.
**Summary:**
Solar filters for telescopes should go on the front of the telescope, before the sunlight is concentrated. Never put a solar filter at the eyepiece end. If you have one of these old threaded SUN filters, smash & trash it.
Have a safe and exciting solar eclipse experience!
#education
**Why YSK: There's a surprisingly large number of dangerous threaded SUN filters littered throughout the basements and closets of the world.**
If you have an older telescope, especially one from before the 1990's, check whether it came with small threaded filters that screw directly into the eyepiece. They often came with two of them. One was marked **MOON** and the other was marked **SUN**. The Moon one works great to reduce the glare of a full Moon.
It's the **SUN** filters that are so dangerous. These are the Lawn Darts of the astronomy hobby, if the Lawn Darts had sharpened hypodermic needles at the front.
The original concept was this: Your telescope captures the sunlight and focuses it on the dark SUN filter that is screwed into the eyepiece at the back of the telescope. You place your **delicate eye** up to the eyepiece, only a few inches from the **searingly hot SUN filter**.
As long as the glass didn't crack, you were fine. Unfortunately... they cracked a lot. Like, a whole lot. Sometimes they even shattered. This would instantly expose your retina to the full blinding light of a 3 or 4 inch magnifying glass, instantly causing solar retinopathy and likely blindness.
If you have one of these SUN filters, it is recommended that you **smash & trash** them so that nobody can ever accidently try them out.
I tested an old threaded solar filter while recording it with a camera. It reached 326 degrees Fahrenheit and in less than 12 seconds after installation, the filter cracked from the heat buildup and suddenly allowed bright sunlight through.
**\*\*\* If curious, the demonstration is at the start of this video:** ** https://youtu.be/rtyLH5fBaJE ** https://youtu.be/rtyLH5fBaJE
**Safe Alternatives:**
1. Solar Eclipse Glasses (by themselves, **NOT in combination** with telescopes, binoculars, or cameras).
2. Front-mounted solar filters specifically designed for your telescope. These stop 99.999% of the light energy before it even has a chance to enter your telescope.
**Summary:**
Solar filters for telescopes should go on the front of the telescope, before the sunlight is concentrated. Never put a solar filter at the eyepiece end. If you have one of these old threaded SUN filters, smash & trash it.
Have a safe and exciting solar eclipse experience!
#education
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