Just bought some binoculars (20x50) off Amazon, made, inevitably, in China. These:
Comments?
I'm not sure that the lens size and magnification combined give you a larger image. I think that they give you a smaller field of view but much more detail.
Then again I could be wrong as usual.
Cheers
Dave R
My understanding is the 50 will gather more light hence clearer definition and the higher magnification a narrower field of view.
No idea, but this may help
Something is not right!
I just compared an image using my 8 x 24 binocs with my ultra-expensive (not!) Lidl 10 - 30 x 60 zoom binocs. When set to 20x, the image was probably 2.5x the size of the 8 x 24, and when set to 30x it was much bigger than that. When set to 10x it was similar to that of the 8 x 24 binocs - maybe a bit bigger.
I think that's right, angle of view is sometimes given in binocular specifications but it *isn't* anything to do with the second number in the standard AA x BB specification. The first number is (obviously) the magnification, the second is the diameter of (I think) the object lens which is the one at the end away from your eyes. This second number tells you how much light can get into the binoculars and, thus, how good they will be in poor light.
If it is 20x50 I would expect the image to be rather dim (2.5mm exit pupil). Maybe they have misunderstood how to specify these things? 20mm would be a plausible size for the diameter of the lens at the eye end rather than its magnification.
If you compare a specific object - such as a distant church clock - in both, it should be bigger. But the overall field of view won't be any bigger - may even be smaller.
Many decades ago, my brother worked on a ship which went to exotic places. He brought my father some 10x50 binoculars from the far east, which were excellent. Next trip, I asked him to get me some 20x50 which I thought would be better - WRONG!! The field of view is very much reduced, and it's almost impossible without a tripod to hold them steady enough to see anything clearly. There's no chance of finding and following a passing aircraft.
I've still got them, but they don't come out very often.
Certainly with x5 mirrors, there's a noticeable difference between 5 cm. dia. and 12 cm. dia. in terms of 'brightness'. Astronomical telescopes for visible light are better if bigger, as they gather more light.
The larger the lens the bigger the view but conversely the more magnification you use the smaller the field of view. If you cannot focus all over the image, then they are junk.
Brian
I don't think that's right Brian, a large object lens doesn't necessarily provide a wild field of view. A large lens just gets more light in. If you think about wide angle lenses on cameras they aren't necessarily 'fatter' than an ordinary lens. It's the geometry of the binoculars that defines its field of view, not the size of the object lens (i.e. it's the focal lengths of the lenses that gives the field of view).
An F1.4 50mm lens is a lot fatter than an F2.8 50mm lens but you get exactly the same field of view when it's used in a camera.
You may find 20x binoculars quite hard to hold steady enough.
10x50 is usually a better compromise.It also depends a bit on your age and what and how you want to use them for. Binoculars are one of the things where you do get what you pay for.
How much of the objective you can use depends on the magnification and your pupil size. The exit pupil is aperture/magnification.
Dark adapted the young eye under 40 is 7mm so 7x50 is best iff you have a properly dark sky. Otherwise 5mm exit pupil 10x50 is good at night. In daytime your pupil is 2-3mm so 20x50 is OK but will tend to show false colour at the edge of field unless they are good quality.
You should just about be able to see Jupiter as a disk and Saturn as smaller and not quite round with very good quality 20x50's.
Try them on the moon - that will give you something to test against.
8x makes the moon look about 4 degrees across.20x makes the moon look 10 degrees across.
Depending on the age of the Pentax binoculars you may be being misled a bit by the narrower apparent field of view of older eyepieces (typically
40 degrees) compared to modern Plossl eyepieces (typically 50 degrees).I can't believe cheap binoculars would have anything more exotic than that but there are now (expensive) telescope eyepieces with apparent field of view 100 degrees. Some high end binoculars do 60 degrees.
Simplest way is to find something distant that just fills the field of view of the new binoculars and then see how much of the Pentax field it occupies from the same viewpoint.
On 24/01/2021 11:46, Martin Brown wrote: <snip>
a brick wall is good as you can count the courses
Look at a distant object through one half only and line it up with the unbinocularised view from you other eye. Bricks or blocks work well. That way you can count the number of bricks per brick IYSWIM.
But 20 x is too much for handheld IMO.
The Pentax binnies date back to 1980 or earlier. The 20x50 is going back as I can't be sure they are not actually 10 or 12 power; I may get the Bresser
20x50 instead. Thing is, if one buys something that is sold from China by the manufacturer, you're then dealing at arms length with a company that is a long way away. With a more local cmpany, one has a much greater chance of the item being according to spec., even if it is still actually made in China (AFAIK, the German ones are actually made in Germany).And see these:
In 1960 I got a small Japanese telescope as a present, it was 20x25. I could certainly make out Jupiter as a disk and see its major moons.
From my early astronomy days the advice was 7x50 is the biggest lens/magnification that you can comfortably hand hold for some time. I'd be genuinely surprised if 20x50 were really usable.
Secondly there's huge amounts of tat on sale. I've used a variety of cheap and not so cheap binoculars since my youth. One day a friend brought is Leica 8x20 binoculars round to play with. OMG for a small lens small gain pair of binoculars they were stunning. Light and easy to hold and an image quality to die for. Not surprising as they cost £700.
The Amazon linked item is out of stock and no price was shown, how much were they?
£93.75 can you not read....look like they are worth £20...
+1
I always understood that 10x was about the highest magnification that was useful if hand held, otherwise hand-shake made viewing somewhere between difficult and impossible. Any magnification bigger than that needed a monopod, tripod or some other rigid support to be practical. I have a pair of Swift Audbon Mk.II, 8.5x44 (extra wide field, 445 ft at 1000 yds, it says), bought nearly fifty years ago. They are superb.
another thing to bear in mind, especially if you are taking them on a walk, is weight. I have superb pair of Carl Zeiss Jena 10x50 which I mamaged to buy just as the Berlin Wall was falling and I paid a silly price. But they are heavy, espcially in their (real) leather case. Sunsequently I have bought another pair (10x42) to taken on walks.
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