Change to the programme

Please note that we have had to make a change to the programme. Our December speaker has had to rearrange and will now be coming in June 2017. Meanwhile, for December’s meeting, Mr. R. Fleet is coming to talk about video meteor observing.

September’s talk

Stephen Tonkin lectures in Astronomy at Brockenhurst College and is a member of Wessex AS.  His talk was on ‘Binocular Astronomy’, and he has written a whole book on the subject.

As someone who has long known that beginners should always invest in a decent pair of binoculars before ever trying to buy a telescope I was still impressed by the nuggets of information in this talk.

Advantages of using binocular as opposed to mono vision:

  • Statistical summation gives binocular vision a 1.4 x advantage over monocular vision.
  • False stereopsis is the depth effect that you can get when looking at a deep sky object, even though it is so far away
  • You have a blind spot in each eye, but when you are looking at something with both eyes, you won’t necessarily end up seeing something with the same part of each eye.

Useful nuggets:

  • Your thumb joint fits nicely against eye socket, which makes it easier to hold binoculars steady
  • With large binoculars hold one side with both hands and rest the other side on your arm.
  • You can wear a cap and hold a finger from each hand over the front of the cap and that can keep binoculars steady.
  • A monopod with a trigger grip head is actually a very good stable base for heavier binoculars. He recommends Manfrotto.
  • Make a long dew cap for mounted binoculars by wrapping black material round the end of them.
  • Get binoculars where each side has independent focussing. That makes it easier to focus on astronomical objects.  Cap each side while you focus with the other.
  • For best quality in smaller binoculars go for roof prisms, which do not bend the light so much and are easier to focus. The limit in aperture is limited by the distance between our eyes, giving about 55mm.  Porro prisms fold the light path and make it possible to have much larger apertures.  Binoculars with Porro prisms will be heavier and cheap ones can lose collimation easily.

He also told us not to be fooled by sellers’ claims of certain standards, because the standards are not regulated, so if you’re told the optics are fully coated this does not tell us how many coatings the optics have.  The best optics have seven coatings on all surfaces.  You may think that all 10×50 binoculars have an objective glass 50mm in diameter but if you hold a piece of graph paper over the end of the binoculars you may be surprised and find the aperture is smaller.  Shine a torch into the binoculars at 6” distance and the light cylinder that comes through the eyepiece will also tell you how big the aperture is.  Another giveaway that any binoculars will be rubbish is if they have an orange bloom.  This is to remove the red end of the spectrum.  As red light scatters more easily and will show up defects in the focussing it is easier to put the bloom on, thereby reducing the amount of red light reaching the eye.

Mr Tonkin has a website =, where he goes into lots of details regarding binocular specifications.

Celestial line up on the 24th August

Saturn, Mars and Antares all line up on the evening of the 24th August.  The graphic below is for 20:45BST from Abingdon.

3 in a line

The day before Mars will be slightly to the West of the Saturn/Antares line and the day after it will be slightly to the East. Should be a nice photo opportunity and nice naked eye sight.

Clear skies,