52
Why is glass still the norm for amateur telescopes?
(lemmy.world)
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
this post was submitted on 01 Jun 2025
52 points (98.1% liked)
Ask Science
10847 readers
1 users here now
Ask a science question, get a science answer.
Community Rules
Rule 1: Be respectful and inclusive.
Treat others with respect, and maintain a positive atmosphere.
Rule 2: No harassment, hate speech, bigotry, or trolling.
Avoid any form of harassment, hate speech, bigotry, or offensive behavior.
Rule 3: Engage in constructive discussions.
Contribute to meaningful and constructive discussions that enhance scientific understanding.
Rule 4: No AI-generated answers.
Strictly prohibit the use of AI-generated answers. Providing answers generated by AI systems is not allowed and may result in a ban.
Rule 5: Follow guidelines and moderators' instructions.
Adhere to community guidelines and comply with instructions given by moderators.
Rule 6: Use appropriate language and tone.
Communicate using suitable language and maintain a professional and respectful tone.
Rule 7: Report violations.
Report any violations of the community rules to the moderators for appropriate action.
Rule 8: Foster a continuous learning environment.
Encourage a continuous learning environment where members can share knowledge and engage in scientific discussions.
Rule 9: Source required for answers.
Provide credible sources for answers. Failure to include a source may result in the removal of the answer to ensure information reliability.
By adhering to these rules, we create a welcoming and informative environment where science-related questions receive accurate and credible answers. Thank you for your cooperation in making the Ask Science community a valuable resource for scientific knowledge.
We retain the discretion to modify the rules as we deem necessary.
founded 2 years ago
MODERATORS
Googling says thermal expansion. It's 8x worse.
This is exactly why. Some numbers:
Most amateur telescopes are used shortly after dusk when the temperature is changing more rapidly than deep in the night when the temperature might be more stable. Also, the coatings are not as resistant to more dramatic expansion cycles (remember that you need those mirrors to stay very smooth). Given the high price and low volume of the goods, it doesn't make sense to cheap out on a critical component like this and give yourself a bad reputation among a very small but dedicated community.
Low thermal expansion glasses/ceramics can have coefficients of thermal expansion of 0 (+/- tolerance). For example, SCHOTT ZERODUR can be 0 +/- 0.02 * 10^-6 per degree C.
(amateur)
Also, I can make thermals irrelevant easily with a small heating element and PID loop running on a $0.50 microcontroller. Many people run such elements already to avoid issues with moisture.
Which is more complexity.
You haven't really presented any compelling reasons to use poly.
Whats the advantage that outweighs the negatives?
The OP said cost. A 16" glass mirror is $1400. Adding $20 of microcontrollers, heaters and sensors to a $100 plastic mirror could be extremely interesting.
There is also a weight savings which makes the rest of the design easier.