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Telescope with etched mirrors
Posted: Mon Mar 25, 2019 3:00 pm
by tafig
I'm the Coordinator of the Polisch Solar Observation Section. For my observations I use a 114 x 900 telescope with etched mirrors. Such equipment transmits about 0.8 to 1.4 beams of sunlight. I'm inserting an OIII filter into the eyepiece. The question is this.
Does this filter adequately protect against infrared radiation? I have not found any answer to this and I use this equipment for visual observation of the Sun. Greetings.
Re: Telescope with etched mirrors
Posted: Mon Mar 25, 2019 7:04 pm
by marktownley
Greetings Tafig! By etched do you mean the coating has been removed from the mirror?
Re: Telescope with etched mirrors
Posted: Mon Mar 25, 2019 7:11 pm
by tafig
Hello! Exactly
Re: Telescope with etched mirrors
Posted: Thu Mar 28, 2019 3:10 pm
by skyhawk
tafig wrote: ↑Mon Mar 25, 2019 7:11 pmHello! Exactly
The comment Hello ! exactly sounds rather a RUDE comment and not needed
I hope I am wrong but it sounds dangerous what you are doing, I certainly would not want to be the one to use it
Re: Telescope with etched mirrors
Posted: Thu Mar 28, 2019 3:13 pm
by skyhawk
Such equipment transmits about 0.8 to 1.4 beams of sunlight
What does this mean ??????????
Re: Telescope with etched mirrors
Posted: Thu Mar 28, 2019 5:06 pm
by marktownley
I think using with a uv/ir cut filter is not a bad idea.
Re: Telescope with etched mirrors
Posted: Thu Mar 28, 2019 5:57 pm
by bart1805
If both mirrors are etched about 4% of 4% enters your eye. OIII normally does not block above 1000nm. I would follow Mark's suggestion.
Re: Telescope with etched mirrors
Posted: Thu Mar 28, 2019 6:19 pm
by marktownley
skyhawk wrote: ↑Thu Mar 28, 2019 3:10 pm
tafig wrote: ↑Mon Mar 25, 2019 7:11 pmHello! Exactly
I hope I am wrong but it sounds dangerous what you are doing, I certainly would not want to be the one to use it
It's perfectly safe, there are quite a few people who have done it now. The uncoated mirror reflects a similar amount of light as a solar wedge transmits (assuming only the primary is uncoated). Therefore additional ND filtration is required to bring things down to a safe visual level, if imaging is the only consideration the more light the better as exposures will be shorter.
Re: Telescope with etched mirrors
Posted: Thu Mar 28, 2019 7:07 pm
by tafig
During the solar eclipse. O III filter in the eyepiece
- Zaćmienie Słońca.jpg (167.95 KiB) Viewed 4556 times
Re: Telescope with etched mirrors
Posted: Thu Mar 28, 2019 7:17 pm
by christian viladrich
OIII filters are not all the same. Photographic OIII filters give more protection than visual OIII filters. Still they usually block up to 1100-1200 nm.
Here is the example of the Astronomik CCD OIII :
So, as said before, it is better to associate the OIII with a neutral density filter, and if possible to an IR filter (KG3 or equivalent), in order to have blockage beyond 1100 nm. A good IR filter is the Beloptik IR filter.