28 January 2012

A bit about Binoculars

I don't know much about binoculars, but have been doing a bit of research about them today. I realised that we've aquired 3 sets of binoculars over the years and I didn't know what they were best for. So here's what I've found in my books and the Internet, I hope it's helpful - if only to get you looking for these terms elsewhere on the Internet.


The binoculars on the left are Porro Prism (named after Ignatz Porro) binoculars. The lenses have two prisms which act as mirrors and bend the light, making the binocular tube seem longer. These are cheaper to make and also produce a better stereoscopic image.

The binoculars on the right are Roof Prism binoculars. These cost more due to the higher glass quality and prism complexity. The light path is reflected four times and produces a more compact design.


On the right side of the photo above we can see it says '8x21'. The 8 relates to the magnification, therefore the image is magnified 8 times. The 21 relates to the size of the objective lense - the lense at the end of the binoculars. The binoculars in the first image all have their objective lenses pointing to the left of the photo. The greater the magnification means that any hand movement is also magnified, so with greater magnification there is a need for a tripod or something solid to lean on. The larger the objective lense the bigger, and heavier, the binoculars are likely to be - but a larger objective lense also allows in more light - which is good for star gazing.

You will also notice that the other specification on the image is 126M/1000M. This means that when looking at an object 1000M you will see 126M of that 1000M. Another of my pairs has a specification of 99M/1000M, so I would only see 99M of a view at 1000M, which I take to mean that the magnification is better.


The binocular tubes should be close enough together so that they provide a single circle of vision when you're looking down them. If the view is out of focus, then there is a central focusing wheel, which can be seen in the photos above.
Because our eyes can focus differently, some binoculars will have individual focusing wheels on either one or both of the tubes at the end closer to the eye. This allows you to set up the binoculars beforehand so that you can use just the central wheel when actually using them.
Another important point is the weight of the binoculars. The heavier they are, the more your hands will move, making the point you are trying to view very diffcult to focus on. It's important to keep your elbows close into your body to keep the binoculars as steady as possible.
If wearing binoculars around your neck try to keep them around the cheat area so that the don't swing around too much or become an uncomfortable pain around the neck!

Which for what now?

My astronomy book says that the maximum diameter of a fully dark adapted pupil is around 7mm. Therefore a pair of binoculars of 7x50 would give an optimum exit pupil, as 7x50 specification worked out as 50/7 = 7.14.

Birdwatching / Wildlife observation
My bird book says that there is no one binocular that is the best choice for birdwatching. Therefore it's important that you go for a binocular that you are happy with. It would seem that a magnification between 8x and 10x is popular; with 8x allowing a closer focusing. Remember that the larger the objective lense the brighter the image, therefore a larger objective lense between 42mm-50mm may be necessary if observing in poor light conditions, dusk for instance.

The Complete Illustrated Encyclopedia of British and European Birds. ISBN 978-1-84786-225-9.
An Introduction to Practical Astronomy. ISBN 1-85627-647-3.

27 January 2012

A cool Geocache near Bath

So, Lucy and myself had spent the day helping out the National Trust ranger cut back some hedging and cutting steps into a steep slope for 6 hours, but even though we were tired, couldn't resist logging a cache!

It's one that Lucy had found and we were quite intrigued that the statement on the cache page that the cache was in plain sight, not hidden or camoflagued in any way! So loading up the cache coordinates on the GPS, off we trundled.

It was starting to get dark and we thought we might be pushing our luck, but Lucy spotted the cache with the help of the photos posted on the cache instructions. As it said, it's really not comoflagued or hidden, just literally 'stuck' up in a tree.
But how to get it down? We saw that there was some fishing line, two lengths of it, running from the cache. We followed these to seperated trees and immediately saw what we needed to do.
 With the lines undone, Lucy gave it a bit of a prod as the weight of the cache didn't seem to be enough to bring the container down.
 Here's Lucy collecting the container!
Definitely a worthwhile cache. We've not seen one like this before and found it really interesting. It's worth noting that the trees that had the nails in were trees that had previously come down - probably due to weather.

29 February

Vladimir on the Geocaching Europe Facebook group posted a link to the most recent Groundspeak Geocaching blog.

It says that "Everyone who logs a “Found it” or “Attended” this February 29 will receive the Leap Day Souvenir on their profile."

This year that day is a Wednesday, the sun is due to rise at 06:47 and set around set around 17:40, that gives nearly 11 hours of daylight to get out caching and bag yourself the profile souvenir! Unless you're night caching that is, in which case check your torch batteries and get caching!

For full details: http://blog.geocaching.com/2012/01/grounspeak-weekly-newsletter-january-18-2012/

Here are some more cool cache photos:

Our canine cacher Cazzie managed to find this one when we couldn't!