RASC Hamilton Transit of Venus

Roger Hill Roger.Hill at hiteach.net
Sat May 12 12:08:00 EDT 2012 

What were the issues?  #14 (no less...#12 is NOT dark enough) stops
sufficient ultra-violet, visible and infra-red.  The only danger might
be securely fastening them to the front of a binocular.

Roger

-----Original Message-----
From: astronomers-bounces at hamiltonrasc.ca
[mailto:astronomers-bounces at hamiltonrasc.ca] On Behalf Of Andy Blanchard
Sent: Saturday, May 12, 2012 11:48 AM
To: astronomers at hamiltonrasc.ca
Subject: Re: RASC Hamilton Transit of Venus

London just did whole thing on welders glasses and they are clearly too
dangerous. 

Andy Blanchard
905-465-2031H
905-847-7777B

On 2012-05-12, at 10:34 AM, "Ed Mizzi" <emizzi at cogeco.ca> wrote:

> Roger,
> 
> With the welder's glass, if I secured it to both sides of a pair of
binoculars would that be safe?
> 
> Thanks
> Ed
> 
> 
> On 2012-05-12, at 9:32 AM, Roger Hill wrote:
> 
>> Sorry, Al...I won't be there.  I have my own spot chosen.
>> 
>> In 2004, I saw the Sun rise out of Lake Ontario with a big round 
>> black spot on it.  It was very impressive, and remains one of my 
>> favourite events (and I've seen three total solar eclipses).
>> 
>> I'm going to watch the sun sink down into a lake
>> 
>> The Saltfleet site is very good, and will allow some great 
>> photographs with Venus and tree branches silhouetted against the
setting sun.
>> 
>> One person mentioned solar projection as being safe.  You want to be 
>> careful what sort of telescope and eyepiece you use for this, 
>> particularly the eyepiece.  Make sure that the eyepiece is one that 
>> you don't care about, because the heat build up inside it can ruin 
>> the glues which hold some lenses together.  Apart from that, it is a
safe method.
>> 
>> What is very definitely NOT (and I cannot stress this enough), is the

>> use of eyepiece filters.  You used to find them all the time with 
>> little 60mm refractors sold in the '60's and '70's.  A friend of mine

>> had one, and we'd used it every now and then for a quick glimpse at 
>> the sun.  One time, though, we decided to use it to try our hand at 
>> sketching sunspots. It took less than three minutes to crack. 
>> Fortunately, it did just as Wayne looked away to start sketching and 
>> before I got to have a look.
>> 
>> What you have is 60mm (or more) of sunlight compressed down into a 
>> tiny disk, and then compressed even more by the eyepiece.  All of a 
>> sudden, at the speed of light, all that energy will hit the back of 
>> your eyeball as the filter cracks...you cannot get out of the way 
>> fast enough.  There are no pain receptors in the back of your eye, so

>> it won't be the pain that makes you move out of the way.  There is an

>> excellent chance that the back of your eye will be permanently 
>> burned, and you'll see the transit for the rest of your life, forever
etched in negative.
>> 
>> When I do public courses or classes in Astronomy and we get to solar 
>> observing, I always ask if anyone has one.  I offer to buy it from 
>> them if they'll bring it to the next class.  It has been quite a few 
>> years since I saw one, and I'd really hoped that these nasty pieces 
>> equipment were gone for good.
>> 
>> 
>> Another alternative is #14 welders glass.  This works very well, and 
>> a
>> 2x2 piece of it makes an excellent filter for a finder-scope.  Please

>> make sure that it is secured to the finder, though.  Back in the 
>> '70's, Johnny Carson show had John Davidson as guest on his show.  
>> Davidson was also an amateur astronomers (Carson had a C14), and 
>> mentioned that he'd bought a hydrogen-alpha filter for observing the 
>> sun.  The views were fantastic, but something didn't smell right, and

>> he realized that his hair was smouldering, lit by the finder-scope.  
>> He'd used the projection method to find the Sun (minimize the size of

>> the shadow of the findersope, and then project the image on to a 
>> piece of paper to centre it).  He'd forgotten to put a cap on the
finder-scope.
>> 
>> 
>> Hope this helps,
>> 
>> Roger
>> 
>> 
>> -----Original Message-----
>> From: astronomers-bounces at hamiltonrasc.ca
>> [mailto:astronomers-bounces at hamiltonrasc.ca] On Behalf Of Al Jones
>> Sent: Saturday, May 12, 2012 6:00 AM
>> To: astronomers at hamiltonrasc.ca
>> Subject: Re: RASC Hamilton Transit of Venus
>> 
>> ROGER
>> Thanks for that advice. I did not realize the mylar was a sharper
image.
>> See u at the transit perhaps.
>> AL
>> 
>> On 2012-05-11, at 23:58, "Roger Hill" <Roger.Hill at hiteach.net> wrote:
>> 
>>> Al...
>>> 
>>> Mylar gives a better image.  I've used both, and while I like the 
>>> colour that is produced by InCoNel filters, the image is sharper 
>>> using
>> mylar.
>>> 
>>> Further, since mylar is coated on both sides (the good filters are, 
>>> anyway), if there is a pinhole or a scratch, it's less likely to go 
>>> right through.
>>> 
>>> Lastly, if you drop the mylar filter, it is far more likely to
>> survive.
>>> 
>>> Roger
>>> 
>>> -----Original Message-----
>>> From: astronomers-bounces at hamiltonrasc.ca
>>> [mailto:astronomers-bounces at hamiltonrasc.ca] On Behalf Of Al Jones
>>> Sent: Friday, May 11, 2012 7:41 PM
>>> To: astronomers at hamiltonrasc.ca
>>> Subject: RASC Hamilton Transit of Venus
>>> 
>>> Hi Gary
>>> 
>>> I have a CPC 1100 but no solar filter. I've tried to a get a glass 
>>> one
>> 
>>> from Efston Science but no stock. They said mylar possible but much 
>>> less durable.
>>> 
>>> Suggestions?
>>> 
>>> Thx
>>> 
>>> Al
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