scoop
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| posted on 7/6/09 at 08:30 PM |
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Binocular magnification anyone?
Father in law wants some for fathers day. Have been looking on ebay but i dont know what all the numbers mean. I thought i'd better ask?
We live on the coast and he likes watching all the ships (it's his age).
What does, for instance 10 x 21 mean?
Steve.
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tomgregory2000
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| posted on 7/6/09 at 08:32 PM |
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First no. is the magnification, So 10X
Second no. is the lense dia in mm, So 21mm
Edit the mor mag you have the more shaking you get.
The bigger the dia the more light you get in and of course the bigger field of view
Hope this helps
[Edited on 7/6/09 by tomgregory2000]
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mookaloid
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| posted on 7/6/09 at 08:35 PM |
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quote:
Originally posted by tomgregory2000
First no. is the magnification, So 10X
Second no. is the lense dia in mm, So 21mm
Hope this helps
Sorry to Hijack but this has puzzled me too.
I suppose the 10x is easy enough - does the lens diameter change the size of the field of vision?
"That thing you're thinking - it wont be that."
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blakep82
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| posted on 7/6/09 at 08:36 PM |
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aww i like watching the ships, i'm 26 
give him this address
http://www.shipais.com/currentmap.php?map=RiverClyde
it brilliant. i live right next to the clyde, if i see an unusual ship going by, open this up and it tells me all about it live tracking and
everything.
of course its got maps for the whole coastline for britain.
no good on binoculars though...
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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Peteff
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| posted on 7/6/09 at 08:41 PM |
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If you go to the larger sizes you will need something to rest them on as the slightest shake will lose whatever you are looking at. Another option
instead of binoculars is a spotting scope on a tripod.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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Flamez
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| posted on 7/6/09 at 08:42 PM |
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Wikipedia says
Binoculars are usually designed for the specific application for which they are intended. Those different designs create certain optical parameters
(some of which may be listed on the prism cover plate of the binocular). Those parameters are:
Magnification — The ratio of the focal length of the eyepiece divided into the focal length of the objective gives the linear magnifying power of
binoculars (sometimes expressed as "diameters" . A magnification of factor 7, for example, produces an image as if one were 7 times closer
to the object. The amount of magnification depends upon the application the binoculars are designed for. Hand-held binoculars have lower
magnifications so they will be less susceptible to shaking. A larger magnification leads to a smaller field of view.
Objective diameter – The diameter of the objective lens determines how much light can be gathered to form an image. It is usually expressed in
millimeters.
It is customary to categorize binoculars by the magnification × the objective diameter; e.g. 7×50.
Field of view — The field of view of a binocular is determined by its optical design. It is usually notated in a linear value, such as how many feet
(meters) in width will be seen at 1,000 yards (or 1,000 m), or in an angular value of how many degrees can be viewed.
Exit pupil — Binoculars concentrate the light gathered by the objective into a beam, the exit pupil, whose diameter is the objective diameter divided
by the magnifying power. For maximum effective light-gathering and brightest image, the exit pupil should equal the diameter of the fully dilated iris
of the human eye— about 7 mm, reducing with age. If the cone of light streaming out of the binocular is larger than the pupil it is going into, any
light larger than the pupil is wasted in terms of providing information to the eye. In daytime use the human pupil is typically dilated about 3 mm,
which is about the exit pupil of a 7x21 binocular. A much larger 7x50 binocular will produce a cone of light bigger than the pupil it is entering, and
this light will, in the day, be wasted. It is therefore seemingly pointless to carry around a larger instrument.
However, a larger exit pupil makes it easier to put the eye where it can receive the light: anywhere in the large exit pupil cone of light will do.
This ease of placement helps avoid vignetting, which is a darkened or obscured view that occurs when the light path is partially blocked. And, it
means that the image can be quickly found which is important when looking at birds or game animals that move rapidly. A narrow exit pupil binocular
may also be fatiguing because the instrument must be held exactly in place in front of the eyes to provide a useful image. Finally, many people use
their binoculars at dusk, in overcast conditions, and at night, when their pupils are larger. Thus the daytime exit pupil is not a universally
desirable standard. For comfort, ease of use, and flexibility in applications, larger binoculars with larger exit pupils are satisfying choices even
if their capability is not fully used by day.
Eye relief — Eye relief is the distance from the rear eyepiece lens to the exit pupil or eye point[5]. It is the distance the observer must position
his or her eye behind the eyepiece in order to see an unvignetted image. The longer the focal length of the eyepiece, the greater the eye relief.
Binoculars may have eye relief ranging from few millimeters to 2.5 centimeters or more. Eye relief can be particularly important for eyeglass wearers.
The eye of an eyeglass wearer is typically further from the eye piece which necessitates a longer eye relief in order to still see the entire field of
view. Binoculars with short eye relief can also be hard to use in instances where it is difficult to hold them steady.
my build mac1motorsports
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David Jenkins
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| posted on 7/6/09 at 08:47 PM |
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As said above, the first number is the magnification, and the second is the diameter of the front lens. A bigger front lens collects more light and
give a brighter image.
You'll to work out how they will be used - 7 x 50 are ideal for hand-held as you won't see shakes too much. Anything much stronger and
you have to consider mounting them on a camera tripod (gadgets are available to do this).
The biggest gain for your money is the diameter of the beam of light leaving the eyepiece and going into your eye - 'exit pupil' I think
it's called. The bigger this is, the easier it is to get your eye in the right position to get a good image. Cheap bins will have a
small-diameter 'output', which means that the slightest eye movement will give a shading effect.
Had you considered a spotting scope? These do require a tripod, but mine is 30 x 50. There's no way that you can hand-hold it! Great for
watching ships though.
(damn, too slow)
[Edited on 7/6/09 by David Jenkins]
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scoop
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| posted on 7/6/09 at 09:06 PM |
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Wow.What a response.
Thanks all
Steve
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iank
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| posted on 7/6/09 at 09:08 PM |
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Depends what he wants them for, big ones are really quite heavy and awkward, where the small folding ones you can take everywhere.
This might help
http://www.which.co.uk/advice/how-to-choose-binoculars/index.jsp
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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thorpey182
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| posted on 7/6/09 at 09:15 PM |
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I've just bought my mum a pair of 10x50 for my mum (she loves star gazing) got a pretty decent pair for £30. Perfect size for a good field of
view and light enough to be able to hold up & steady withough a tripod.
Light, Strong, Cheap - Choose any two.
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PAULD
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| posted on 7/6/09 at 09:50 PM |
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binoculars
Try Opticron Imagic 8*40 porro prism (they are about £140, very good quality for the money, (thats cheap I'm a birdwatcher and mine were £600))
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BenB
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| posted on 7/6/09 at 10:17 PM |
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Anything about 10X magnification and you're looking for problems with shaking (unless you use a tripod). What's more important is the
second number as the controls the amount of light going into the binoculars.
I've got some 10*50s and they're great for birdwatching (combine it with a 50x scope on a 'pod)...
Other thing to look for is something called eye relief (if he wears glasses). Eye relief is the distance from the eyepiece you can hold your eyes and
still get a good image. Some bins are very sensitive and unless you're exactly the right distance away it all goes yucky...
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dogwood
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| posted on 8/6/09 at 06:55 AM |
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I have to agree with Ben.
I would not go above x10.
Infact I would recomend x8.
Because it'll give you a brighter view,
without too much loss of magnification
JMO
David
FREE THE ROADSTER ONE…!!
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