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Posted: Fri Apr 27, 2012 10:13 am
hi all,i watched a programme last evening about solar storms,very interesting too.A few of the people on the programme were looking at the sun for sunspots,using what seemed to be a 'square' dark coloured piece of plastic.they were handheld,and around i'd guess 3 inches by 3 inches square.any idea what these 'pieces' of dark coloured plastic were.
Posted: Fri Apr 27, 2012 1:17 pm
You have to be really careful here.
There is solar viewing material similar to that sold in eclipse viewers.
These solar viewers have a nominal shelf life of five years, but must be inspected for pinholes.
There were some dreadful plastic so called solar filters, which I had measured professionally and they let through about 30% of infra red. It was a major undertaking to get the seller to stop selling these and a few years later he sold them again. They were advertised in the best astro journals. Users were getting hot eyes even though the eye itself is not meant to have pain receptors I think.
The seller refused to accept how dangerous they were.
Periodically one gets persons like this trying to make money from their crazy schemes.
I use large welders glass 13 and 14 glass filters which may be O.K. for decades but I don't know if they have a shelf life.
The 14 is for bright sunshine and the 13 for a lower Sun in Britain tilting as necessary to get an optimum density.
The resolution with the welders glasses is much higher than with eclipse glasses which cannot be readily tilted and diffuse the images of sunspots.
I found the transit of Venus very easy with unaided eyes, welders 13 tilted and distance specs.
The eclipse viewers were more difficult.
I also saw the Mercurty transit with filtered exactly 3x opera glasses at 12 arcseconds, making a 36 arcsecond resolution.
With 20/20 or 6/6 vision an observer should just see dark round sunspots at 40 arcseconds with ideal filtration.
Some persons with exceptional sight regularly see 20 arcseconds sunspots and I think this can be bettered in certain cases.
So I would not seek out 3 inch square plastic filters and any filters you buy must come from an impeccable source.
Welders glass 14 and maybe 13 are O.K. and try to get the larger size.
They must have the kite mark or similar with the standard etched on the glass and the welders number also etched on the glass.
Some have these stamped but should be protected with Sellotape or similar as these numbers rub off.
I sellotape all the glass edges to stop cuts.
Posted: Fri Apr 27, 2012 1:24 pm
I bought a few eclipse viewers from the BAA a couple of years ago. £1.75 each and they are quite handy as a grab and go option. I used them to look at the last partial solar eclipse. They are just a piece of card with a strip of solar film in.
The link to the relevant part of the BAA shop is here: http://www.britastro.org/sales2006/inde ... larviewers
Hope that helps,
Posted: Sat Apr 28, 2012 9:08 am
Regarding the sharp edges around welding glasses, as David mentioned. A neater solution to cellotaping the edges is to rub them down with a carborundum stone.
I did this with my No.13 glass ( No.14s seem hard to get in the UK ).
Posted: Sat Apr 28, 2012 2:12 pm
HI All,thanks very much for your help and advice.Much appreciated.
Some very interesting points there,i shall do a bit more digging on the net,
all the best,
Posted: Sun Apr 29, 2012 7:07 am
The whole business of safe ways to look at the Sun is no doubt going to be at the fore again as the Transit of Venus will soon be upon us. From the southcoast here we are likely get less than an hour and then only if one can find a really good horizon and of course as the Sun rises in the NE there is no chance of a sea-horizon. Clouds and/or horizontal murk will no doubt cause worry....or obscuration.
As to what to use to see it, with such a "narrow window", and requiring to be at rather out of the way locaton, transport will be essential, and the following, from the simplest to the most complex might be a good range..... (1) a correct-grade (13 or 14) piece of welders glass (2) 10X25 Binomite white-light Coronado binoculars and (3) PST on a tripod. maf
Posted: Sun Apr 29, 2012 9:35 am
The problem is that there may be low elevation haze or cloud and although a shade 13 welders glass is likely to be sufficient, although a really transparent sky might warrant a shade 14, then with poor transparency the view through a welders 13 or eclipse glass may be too dim.
Then there will be the great temptation to view the transit of Venus with no filtration at all or sunglasses.
It is likely some eye damage will result from this event, if not in the U.K. then elsewhere. There always is.
Being so early though it may be less than usual.
Hopefully it will be reasonably clear and people will be able to use correct and safe equipment.
Today and the last 24 hours lots of rain very windy and no Sun.
But we do need water.
Posted: Sun Apr 29, 2012 5:05 pm
Rain here this Sunday morning but after lunch there was a break with some large blue patches which enabled a period of observation of the crescent Venus in the Minox and a 10x30 mono handheld....but soon lost again. maf
Posted: Sun Apr 29, 2012 6:53 pm
I got some of the solid squarre filters back around the 1999 solar eclipse,
They were too dark to get sharp focused solar images when I used them,
I've used one recently as I made a filter holder for my ETX,
But will still buy something like filter film,although I'd love to get the solid one for the scope but at around £100 maybe I'll go with the film
Posted: Sun Apr 29, 2012 7:42 pm
As a minimum try to work the infra red T.V. remote through your square filter or anything else you try.
If you can change the T.V. channels or any other T.V. feature through any so called solar filter I would not use it.
What was your source of the thick plastic 'filter'? Is it marked with a name?
I hope it was not one the ones originating from the Nottinghamshire seller of plastic offcuts purporting to be solar filters.
Posted: Sun Apr 29, 2012 11:21 pm
They were from a place in Norwich,Norfolk called "Solar Products Nch,I saw their advert in Astronmomy Now,
Still got one un touched,and at least 3 in cardboard holders,
The remote won't work through the filter,
I suspect it may have been a company set up just for the Solar Eclipse,
I don't use them visualy anymore,