WARNING SOLAR FILTERS

Here's the place for any sights you wish to remark on

Moderators: Guy Fennimore, joe, Brian

David Frydman
Posts: 5366
Joined: Mon Jan 18, 2010 9:25 am
Contact:

WARNING SOLAR FILTERS

Post by David Frydman »

I have just ordered some used binoculars from a reliable shop.
He also had a 94mm dark filter for viewing the Sun to clip on front of a telescope. It is old and has been in the shop several years and alarmingly is of a well known make but not a specialist solar make.
I asked him if he has a T.V. in the shop with infra red remote. YES. He went upstairs and tried the remote through the filter and the T.V. instantly went on and off. I said could it be bouncing of the walls of the shop. NO as it doesn't turn T.V. on bouncing directly off walls.
I told him to chuck it, but he is sending it to me free of charge to test.
So all you users of dark front mounted telescope solar filters try the T.V. test to make sure.
This is not a conclusive test but if the T.V. works through the filter with an infra red remote something is wrong.

Regards, David
Ender Of Days
Posts: 201
Joined: Fri Oct 10, 2008 9:00 pm
Location: north sheffield
Contact:

Post by Ender Of Days »

Reminds me of a spotting scope I got back in the mid 90's,it came with both Lunar and Solar filters (both screwed into the rear of the eyepiece),
The lunar filter soon found its way down the back of a set of heavy drawers (prob still there :? )
I did use the Solar filter quite a bit,but only for a few seconds at a time,it was only when I started observing sunspots over 5 mins at a time did I realise how weird my eye felt afterwards,it actualy felt warm :shock:

My eyes still work just as well today as back then,but it does make me wonder just how "good" that filter was,

JJ..
aint no speed limit where im comin from ..
lets hit the highway doing 69


ETX 125
Meade Series 4000 box set
David Frydman
Posts: 5366
Joined: Mon Jan 18, 2010 9:25 am
Contact:

Post by David Frydman »

Dear JJ, From what you say it was unsafe, but did not luckily do you damge. It probably ttransmitted infra red and possibly near blue and or UV.

The problem with rear Sun filters is they shattered suddenly, possibly putting shards of glass in the observers eye or blinding the observer with direct sunlight of enormous intensity.

That is why solar filters must come from the most reputable sources.

I have been told that at a Turkish eclipse the solar viewers given out or sold were unsafe.

I THINK that welders glass shade 14 and possibly shade 13 tilted are safe.
This is a whole area where eye safety is paramount.
We do our best to ensure this where we can. It was only because of my previous involvement with this subject that I thought to ask the salesman to do the T.V. test. I was amazed the purpose built filter is probably unsafe.

Regards, David
mike a feist
Posts: 3303
Joined: Sun May 11, 2008 6:11 pm
Location: Portslade, Sussex Lat 50deg 51min Long 0deg 13mins West
Contact:

Post by mike a feist »

During the "school playground eclipse" of 1954 I used (as was at the time considered ok apparently) two pieces of smoked glass, face to face and separated by a cardboard strip around the edges so that they did not touch each other or your fingers!!! Now this would be considered extremely unwise of course!!!!!maf
David Frydman
Posts: 5366
Joined: Mon Jan 18, 2010 9:25 am
Contact:

Post by David Frydman »

Mike,
That might have been not too bad.
Black and white film fully black was considered O.K. but NOT colour film.

The use of welders glaa 14 and tilted slightly 13 is of course for unaided eye use only. Should be welders glass.

Best regards, David

Welders glass not to be used with optical aid.
brian livesey
Posts: 5625
Joined: Mon Jan 09, 2006 11:05 am
Location: Lancashire
Contact:

Post by brian livesey »

I have a No.13 welder's glass. I tried switching the telly on by pointing the remote control through the glass, but the telly stayed off.
When using the glass on the Sun, I always tilt it for extra protection. It must be said that a welder's glass should never be used in conjunction with binoculars or a telescope.
brian
David Frydman
Posts: 5366
Joined: Mon Jan 18, 2010 9:25 am
Contact:

Post by David Frydman »

TEST OF SUSOECT FILTER.

The suspect filter has been sent to me free of charge to test.
It is not as bad as I first thought.
Firstly, although it is in a well known binocular and scope maker's box from the cheaper end of optical suppliers, there is no name on the filter. So I will not name the maker's box.
Secondly, it is not a glass filter as i at first was led to believe but a mylar type silver filter. The mount fits over a 93mm tube and the 'mylar' is 65mm clear aperure. It might be for an 80mm scope.

The manager of the shop easily turned his cheap T.V. set on and off.
For me it is more difficult. It may be that the infra red waveband is broader in his cheaper set or the wavelength different to my good makes remote control.

The mount seems to be aluminium. The unit is well made and could be professional or a skilled amateur.
There is minor scratching and possibly the tiniest pinhole but I avoided using that part of the filter. I think the mylar itself is transmitting a smallish amount of infra red.
My remote needs new batteries. On previous tests I could change the T.V. at about 15 feet, now ten feet.
Through the mylar I had to average 2/3 feet to turn T.V. on or off.
If a square rule is involved this implies perhaps half a per cent transmission at the wavelength of my remote. If it is more linear then a higher percentage.

The shop manager says the filter predates him and has been in the shop several or more years.

To properly test this filter I would have to send it to a prper laboratory able to produce a curve of transmission against wavelength from UV to infra red over a large part of the Sun's spectrum.
I did this in the past but the costs are far to great.
CONCLUSION.

I am not satisfied the filter is made by the maker in whose box it resides, so I will not name the maker.

The mylar could have deteriorated with time.

I would definitely not use it if it transmits even half a percent at my remote's wavelngth and probably more of the shop's T.V.remote.

It is not nearly as bad as a plastic filter I reviewed several years ago.

I will briefly look at Sun with unaided eye through it. It shows the filament of an incandescent bulb about as bright as a solar filter should.
I will definitely not use it on a scope.
I will replace my remote's batteries with fresh ones and try again.

And all you users of solar filters do the T.V. test, perhaps on several different old and new T.V.s
If the T.V. turns on or off or the T.V. indicating light responds through the filter don't use the filter.

Hope this test is of some use.
I think that the eye does not have pain receptors yet several people have reorted their eyes feeling warm on using certain filters. This canot be good and if you feel that any filter is suspect do't use it and mark it as suspect or destroy it.
And at least test any solar filter or eclipse glass or anything intended for direct solar viewing with the simple T.V. test

Regards, David
Brian
Posts: 3751
Joined: Fri Dec 03, 2004 9:58 pm
Location: Wellingborough
Contact:

Post by Brian »

Dear David.

Thank you for the "heads-up" regarding "mylar" solar filters. I immediately tested my Baader Astrosolar Filter ND=5 - now some 7 years old - with my Sky-box handset.

I found the results depended on just how well I could stop reflections from the rear surface of the film bouncing around the room. By just holding the filter between the handset and the box, the handset worked as normal. When I "sealed" the gap by wrapping a towel around the filter body and handset, so that the only path for the handset signal out was through the film, the handset ceased to operate the box. I even approached the box to within a foot or so, and still it did not respond to the handset.

From this simple experiment I'm happy that the Baader Astrosolar Film works as advertised. Baader claim that UV radiation is fully absorbed by the film, IR radiation is reflected - but they don't go so far as to claim that NO IR is transmitted. I've not found any data on the IR-transmission of the film. For that reason I've always used the film in conjunction with an IR-cut filter for visual observation and imaging using my 4 inch refractor.

I will though admit to using the film with binoculars from time to time, so no IR-cut filter in that case.

Regards,
Brian
52.3N 0.6W
Wellingborough UK.

254mm LX90 on Superwedge, WO ZS66SD, Helios 102mm f5 on EQ1, Hunter 11x80, Pentax 10x50
ASI120MC Toucam Pros 740k/840k/900nc mono, Pentax K110D
Ro-Ro roof shed
Cliff
Posts: 6670
Joined: Sat Dec 11, 2004 8:18 pm
Location: Manchester
Contact:

Post by Cliff »

Dear David
For quite a long time I would only view the Sun using projection.
Then when Mylar came into use and seemed proven to be safe I started observing the Sun with Mylar protection by unaided eye and binoculrs\small telescopes. More recently I have been using Baader Solar filter material.
Tonight I decided to try your TV test.
We have 2 tellies both having IR remote controls.
Interestingly one of the remotes will switch on and off both tellies both whether fired through my Mylar filter or not, the other remote will only switch on or off its own telly, it will not work at all through my Mylar filter.
Best wishes from Cliff
brian livesey
Posts: 5625
Joined: Mon Jan 09, 2006 11:05 am
Location: Lancashire
Contact:

Post by brian livesey »

Solar projection is still a good way to view the Sun in white light. The secret is to make a good quality solar projection box: ensure that the inside is matt black, the screen is as smooth and white as possible and the viewing aperture is not too big to allow in extraneous light.
brian
David Frydman
Posts: 5366
Joined: Mon Jan 18, 2010 9:25 am
Contact:

Post by David Frydman »

Thank you all for your input,
It seems that all Tellys are not the same regarding infra red receivers and all remotes are not the same.
It may be that generic and cheaper T.V.s have wider bandwidths than dedicated controllers, or that they are using different wvelengths or all the above.
But it shows that it is worth trying several different T.Vs and remotes to see if a filter transmits at least some infra red. Of course therecis no indication if the very harmful UV and near blue is being transmitted.

The costs of a lab to test individual filters is far too high, but at least really bad filters can be weeded out as far as infra red is concerned.

ANY SUGGESTIONS for a simple UV test would be welcomed.

All the best,
David
David Frydman
Posts: 5366
Joined: Mon Jan 18, 2010 9:25 am
Contact:

Post by David Frydman »

LIFETIME OF SOLAR FILTERS.

The filter tested does seem to tight and is showing signs of stree, which may account for its passing some infra red. Should say stress.
Apparently mylar filters should be a bit wrinkly.
Welders glass 14 can be used for viewing the Sun with the unaided eyes but is not to be used with binoculars and telescopes.
It is I THINK dyed in the glass and may have a lifetime of decades.
However I think glass filters from the most reputable solar filter makers achieve their properties by coating possibly clear glass. I would think their lifetime would be less than a welders glass, perhaps 20 years at a guess. Anyway they should be checked periodically.
With mylar type filters I would hazard a guess that they deteriorate with age maybe even with careful use. Perhaps their life is measured in years, although with care this could exceed ten years.
The above figures are really guesstimates.

Some older glass filters for use on the back of eyepieces are not only extremely dangerous as they can and do shatter with heat risking eye damage from both shards of glass and full exposure to enormous sunlight.
But they also apparently allow the eye to heat up even when intact. Clearly the glass they are made ofallows heat to pass or they are insufficiently dense.
I had assumed they were in fact made from welders glass of shade 14 or 13, but clearly some or all of them are not.

So one has to be aware in solar observing of safety issues,

I use a PST a lot but not for long periods and I think it is a very safe instrument.
I have in the past tried to get full information from the dedicated solar filters about the transmission curves of their filters without success. Perhaps nowadays this information is available.
But I think that the lifetime of solar filters is not indefinite.

Regards, David
brian livesey
Posts: 5625
Joined: Mon Jan 09, 2006 11:05 am
Location: Lancashire
Contact:

Post by brian livesey »

In the instruction sheets supplied with my LUNT 50mm, Ha, filter and B600 blocker, the kit is guaranteed for a life-time's use.
I'm not expecting to replace any of the components, allowing for accidental damage.
brian
David Frydman
Posts: 5366
Joined: Mon Jan 18, 2010 9:25 am
Contact:

Post by David Frydman »

Dear Brian,
That is reassuring. Are all the components that you mention on your LUNT scope internal or are elements external and liable to weathering?

Do some H alpha filters have external elements liable to weathering?

Regards, David.
David Frydman
Posts: 5366
Joined: Mon Jan 18, 2010 9:25 am
Contact:

Post by David Frydman »

Regarding the 'lifetimes use' guarantee.
Does thsat include leaving the scope outside even in an observatory for sixty years.
I would not consider the PST scope safe if bought by someone of twenty years and left outside for sixty years.
Even Leica who used to give a genuine lifetime guarantee no longer do so.
Most of the top binocular makers limit their warranty to 30 years and there are conditions attached to that.

David.
Post Reply