Solar Scope idea ...

ZeroID (Brent) · #1 20-12-2011, 10:55 AM

With the upcoming Venus transit in June and just the general cloud issues I was looking into building a solar scope as another viewing option.
I've got an 4" f12 mirror from a old newt that the silvering has been mostly gone and wondered if using it as a low reflective surface ( silver all gone ) how it would work either as a projector setup or whatever.

Anyone ever played with this setup or am I re-inventing the wheel badly ?

I have plenty of other lenses and the old 60mm Refractor which could become a 'sacrificial' projector scope. If it melts it ain't a big loss so to speak.
Come to think of it I have another wee scope that could be a guinea pig with no loss incurred.

Add it to the project list .. could be fun

cheers
Brent

GrahamL · #2 20-12-2011, 08:32 PM

There are quite a few posts floating around online about this .

Important to remember BOTH the primary and secondarys coatings are completely removed.

gbeal · #3 20-12-2011, 08:45 PM

I reckon it's a good idea, and like Graham suggested, have the secondary uncounted as well.
You still may need an ND filter, but it will be less than if they were coated.
Gary

Merlin66 (Ken) · #4 21-12-2011, 04:32 AM

Yes, It works.
Stripthe coatings from the drimary and secondary mirrors; you may have to paint the rear of the secondary to prevent ghost images...
You'll definately need a ND3 at the focuser.

ZeroID (Brent) · #5 21-12-2011, 09:50 AM

Thanks for the warnings guys. I had thought about the secondary but not about the filter. I have some optical flats that can become a secondary, the bonus of being a collector of oddball bits.
Very cagey about frying my eyeballs, may go with a webcam test first or a bit of projection viewing.

Yogie-One (Paul) · #6 01-01-2012, 05:14 PM

Hi all, I also would remove the silvering from Primary and Secondary. I have also had this plan in mind for a 3-inch I had. I would sugest using non direct ways of testing. Why fry a video, when a piece of paper across the eye piece would tell how hot it gets, then projection viewing.

Y/O (YogieOne)

ZeroID (Brent) · #7 09-01-2012, 10:14 PM

Sun was shining today. most unusual, clouds had gaps in them.
Setup my wee 60/700 refractor with a cheap binoc EP and .965 diag and pointed it at the sun. What the heck if it all fries.
Waved a piece of paper in front of the EP and had an image. A wee tweak with the focusser and I could see sunspots !! Who knew it was so easy !!
I switched the paper for a piece of frosted plastic screen from an old LCD screen I'd pulled to bits and had a projection screen image of about 150mm with sunspots as clear as a bell.
I've been dead scared to point anything at the sun but it worked better than I expected by far. Roll on the Venus Transit in June, I'm ready !!
And I have something to play with whenever the sun comes out to play, probably about April or May ...

new toy ...

Poita (Peter) · #8 10-01-2012, 02:38 AM

For such a small refractor, get a piece of solar film for the front. It will cost almost nothing and be far less fry-ey.

bojan · #9 10-01-2012, 06:38 AM

During my student days, I was using Herschel prism for Sun observing (it was made by Zeiss) see some info here:
http://www.cloudynights.com/item.php?item_id=109
Due to it's construction (total reflection of light + polarisation), it was possible to adjust the amount of light (white - there was no filtering) that reaches the eye.
However, today Baader Planetarium foil filter is much more practical, inherently safer and way cheaper solution.

ZeroID (Brent) · #10 10-01-2012, 08:18 AM

Cheers Peter & Bojan,
I've spotted Solar film on local trademe, only about $15 for a piece more than big enough to work.
I guess I've just been a bit over cautious about the safety aspect of solar viewing. I've only got one 'good' eye these days and also wasn't sure about the heat effects on a scopes internals. The wee 60/700 was a no loss test that was more successful than I'd imagined. I even set it up on the old GEM mount and was able to track it by slowly turning the drive shaft.
Just another astro-option to play with. Don't think I'll ever spend the large $$$ for a solar scope with all the fancy doodahs but I'll spend a few $$ for film and some sort of screen mounting system for future experiments.
It's just another star .. right ?