Friday, 25 October 2013

Binoculars, The BCRS buyers guide


When shopping for binoculars it pays to know what your looking for and what the specifications mean.
You'll notice that binoculars have numbers such as 7x25 or 10x50 proudly printed on them. These numbers are the magnification and objective lens ratings and are obviously important, but there is so much more to consider.....

Magnification

The first number is the magnification, how much the binocular will magnify what you're looking at. It's very easy to get carried away and think bigger is better, but high magnification binoculars can be hard to hold on target and have a smaller field of view, the higher the magnification the greater the effect of handshake. Another consideration is weight, the higher the magnification, the greater the weight, the more your arms ache! 7x and 8x binoculars can be used by most people for long periods with out causing much trouble, where as anything above 10x WILL make your arms ache! 7x to 10x binoculars will be perfect for viewing Ison, and will also be good for general use.

Objective Lens or Apeture

The object lens is the bigger lens at the front of the binoculars. The rating is the size of the lens in mm, so for example a 10x50 will have a 50mm diameter lens. The object lens is an important consideration, as it will determine how much light can enter the binoculars. The more light, the brighter and clearer the image, which is especially important for night time viewing.

Exit Pupil

This is rarely given when buying binoculars, but is important none the less. Exit pupil is the amount of light which leaves the binoculars at the rear, which is the light you see! To magnify the image the light coming into the binoculars is spread which makes it dimmer. This is not usually a problem in daylight, but at night viewing dim objects you can struggle. The exit pupil is the objective lens size divided by the magnification, the higher the answer the better!
For example to work out the exit pupil of 10x50 binoculars: 50/10 =5 
If we compare that to 8x50 binoculars 50/8 = 6.25
The 8x50 binoculars will there for give a brighter image than the 10x50 even though they have the same objective lens size.

Field of view

This may be written as "field", "angle" or as a number of degrees. Most binoculars in the UK will be marked with field and have the specification below which will be something like "70m at 1000m". This means that if you were viewing a wall that was 1000 metres away, you would be able to see 70 metres of it. A larger field of view makes it easier to locate objects and to keep it in view. The benefit for comet viewing is of course being able to fit the tail in! 


Lens Coating

Most binoculars nowadays have coated lenses. Look at the objective lens and you will probably notice the lens is red, blue, green or yellow. The idea of this coating is to prevent the light from scattering which can make the image darker, in reality we have found these coatings to make very little difference when using the binoculars for astronomy. The one exception is "Ruby coated" lenses, which should be AVOIDED at all costs! I have seen these advertised as "night vision" but nothing could be further from the truth! Ruby coating actually reduces the amount of light that enters the binoculars, the opposite of what you want for night viewing!


Prisms

There are two types of binoculars which you will come across, Porro prism and Roof prism. There is not much between them when it comes to use, but there is when it comes to price. Roof prism binoculars are more expensive than Porro prism. If we had the choice of two binoculars one Porro and one Roof, both costing £100, we would rather our money went on the lenses than the prism, so we would buy the Porro's.
Its quite easy to tell the difference, look at the picture, notice the Porro's have a "step" where as the Roof binoculars are "straight"

Where to buy

The best place to buy binoculars is from astronomy shops or camera shops. Here you can get a good feel of the size and weight, which can vary dramatically between models. The advice from a good shop is also invaluable. You might have seen cheap unbranded Chinese binoculars on market stalls, and ebay but these are usually very low quality and best avoided if possible. If you are on a tight budget try second hand shops, car boot sales or even army surplus stores, but always test them well!  Even the best bins can be rendered useless if they've been dropped! Outdoor/camping shops can also throw up a bargain especially this time of year! Online optic specialist's often sell binoculars much cheaper than the high street shops, but of course you cant pick them up and make sure they fit you well.

Brands

We're not going to recommend any brands over another, but do recommend buying branded to ensure good quality. There are many manufacturers and this short list only contains a few to give you a idea of what's out there. You'll probably notice the big camera manufacturers on the list, with binoculars just like cameras, its all about the lens, and if anyone knows lenses, it's a company that makes cameras!
Top of the price range look for: Steiner, Nikon, Cannon, Celestron, Pentax, Leupold, Praktica, Lecia, Swaroski 
Bottom of the price range: Bushnell, Tasco, Minolta, Vivtar and Jason

We can not express enough that the "bottom of the price range" list is means exactly that, it is in no way to say they are lower quality, in fact my favorite binoculars are Bushnell! 
Expect to pay around £25 for a small pair of budget binoculars up to several hundred at the other end of the scale.

Conclusion

The ideal pair of binoculars will be between 7x and 10x magnification and have a objective lens of between 35 and 50mm. Binoculars which are larger will be heavy and awkward to use and may even require a tripod! Avoid astronomical binoculars they are far to large for comet watching, and useless for everyday use.
Compact binoculars usually have a 25mm or smaller objective lens and should also be avoided if your budget will allow.  If you have to go for compact, get a lower magnification to increase the exit pupil rating.

Chose a pair of binoculars that you can use not just for astronomy, but for bird and wild life watching. You might discover that you're just not in to comets, so a pair of £300 celestial binoculars would be a bad purchase! Avoid any red coating on the lenses especially ruby coating. Lastly the weight, we can not express enough how important this is! A heavy pair of binoculars can be really uncomfortable to use and at the end of the day, if your not enjoying it whats the point.............

2 comments:

  1. Jacob said, wow! lots of informations about binoculars and I think these all are very valuable informations especially those who want to buy binoculars and have lack of knowledge about this issue. So if someone read this blog then he or she will be able to know so many things about binoculars. Thanks for sharing this blog.

    ReplyDelete