High Falls, Pigeon River

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Maybe it is clear from my question that I don't know much about lenses, both on binoculars and super-zoom cameras, for example I don't know how can I compare the light that enters a binocular with a camera.

Binoculars are identified by two numbers (eg. 8x42) where 8 is the magnification and 42 is diameter of the objective lens, the one in the front of binocular, the bigger it is, it will allow more light and results in better image. I also know the basics of the lenses on cameras, bigger sensors and bigger aperture means brighter image.

But since I haven't got a super-zoom camera, nor a binocular, I have no idea why people pay for binoculars when they can get a super-zoom camera like Panasonic Lumix DMC-FZ70 for lower price and much higher zoom?

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I've purchased 16x60 binoculars for less than $100 USD. They provide about the same magnification as the longest focal length of the DMC-FZ70 that costs $400 USD. The light gathering ability of the two large 60mm objective lenses are enough that when I use them for astronomical viewing under dark skies I lose my 'night vision' and have to wait for my eyes to adjust to the darkness after removing them from my eyes. –  Michael Clark Oct 23 '13 at 8:04

4 Answers 4

up vote 6 down vote accepted

There are both similarities and differences in terms of the optics between binoculars and using the longer focal lengths of a Superzoom camera to view distant objects.

First, let's look at the similarities:

  • Focal Length. Both the binoculars and the camera use optics to enlarge distant objects. If a binocular has a magnification factor of 10x, that would equate to roughly a 500mm focal length (35mm FF comparison), since a 50mm lens on a FF camera yields about the same image size in the viewfinder as the unaided eye would see.
  • Entrance Pupil. Both the binoculars and the camera would normally have larger entrance pupils that the opening of the iris in the human eye, which ranges from about 2-3mm in bright light to 5-7mm in the dark. This allows them to gather more light being reflected by the distant objects which allows the magnified image to be brighter than it would be if a smaller entrance pupil were used. Even here the binoculars start to pull away a little as a 10x50 set of binoculars have an entrance pupil of 50mm (times two - one for each eye), which is quite a bit larger than the entrance pupil of a typical superzoom camera at 500mm focal length (35mm/FF equivalent).

Now, let's look at some of the optical differences:

  • Angle of View/Field of View (FoV). The image in the camera's viewfinder, and also in the resulting photo, at longer focal lengths is restricted to a very narrow FoV. Again using 35mm FF equivalents, a 500mm lens yields a FoV of around 5°. At 1,000 yards a 5° FoV translates to around 260 feet. In other words, you could see two objects that are both 3,000 feet away in the same FoV if they were no wider than 260 feet apart. In comparison, a typical set of 10x50 wide angle binoculars such as the Orion UltraView has an FoV of 341 feet at 1,000 yards.
  • Full Image Circle. The camera truncates the image circle of a lens to a (usually) rectangle. The maximum FoV is only possible along the diagonal of the frame. Binoculars allow you to see the full circle of the FoV and thus the maximum FoV in all directions. Even if a camera and binoculars have the same FoV, the binoculars allow you to see 1.7 times the area at the same distance because a camera with a 3:2 ratio only displays about 59% of an image circle with the same diameter as the diagonal of the rectangular image sensor.
  • Image Brightness. The exit pupil of a decent pair of 10x50 binoculars is around 5mm. This allows them to be used in fairly low light, including astronomical viewing, without amplification. They allow you to directly view the subject optically. Most Superzoom cameras, on the other hand, use an electronic viewfinder. While this allows the image to be amplified, it also introduces problems of limited resolution introduced by the resolution of the EVF and electronic noise that would make the experience of using them for astronomical or other low light viewing much less satisfying.
  • Stereo Vision. Binoculars allow both eyes to see slightly different angles of the same objects that allow use of depth perception. Other than specialized 3D cameras, most cameras are monocular.

Some of the non-optical differences:

  • Batteries. All digital cameras need a source of electricity. Usually this is supplied by a battery that needs to be constantly recharged or replaced. Most binoculars don't. You can store them for months, years, or even decades and they are ready when you need them. You can also use them non-stop forever without worrying about the batteries going dead because they don't have any batteries to go dead!
  • Environmental Factors. Most binoculars are made to withstand fairly robust weather conditions and other environmental factors such as dirt/dust/sand and extreme temperatures much more severe than even the hardiest professional grade camera bodies.
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Camera optics and binocular optics are inherently different things. The x multiplier on a super zoom is effectively meaningless as it depends on what the shorter focal length is. A 2mm to 10mm lens is a 5x zoom, but it isn't particularly impressive. A 200mm to 1000mm lens on the other hand is also only a 5x zoom, but would be one crazy amount of zoom.

Binoculars on the other hand are not focal devices, they project a field of light that your eye focuses. The focal length of the eye is around 17mm so if you have a 20x pair of binoculars, it means that the effective focal length is around 340mm.

The other thing that is a factor is the size of the image or light field that needs to be projected. For a point and shoot, the sensor is small compared to the eye, so it is easier to make a projection that fills that space. For binoculars, they need to fill any space the eye may look and since the eye moves around, it ends up being a pretty decent size area that needs to be covered.

The optical problems are also different since one doesn't project an image at a given depth while the other does.

Additionally, the optical quality makes a difference in terms of distortion and such. You can get high zoom binoculars pretty cheap, but a good pair that will have clearer, brighter images with a wider field of view are more expensive due to the more complex optics required.

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I doubt the projection size argument. The image circle projected by binoculars is equal to their exit pupil size, which reaches 7 mm (DMC-FZ70 sensor diameter) on only the largest binoculars. Through EVF, a super-zoom camera projects the image similarly for the whole eye to see. –  Imre Oct 22 '13 at 18:28
@Imre - the reason I got rid of my previous answer is because technically binoculars don't make an image circle. I had to do some additional reading on binocular optics to figure that out though. The EVF may project the image for the whole eye, but that wasn't accomplished optically. The sensor itself is still small, but I suppose you are right that everything has to be seen through the rear eyepieces, which may have smaller openings. –  AJ Henderson Oct 22 '13 at 18:53
The 17mm focal length of the human eye is in regard to FoV, not magnification. Viewed through a typical camera you need a 35mm equivalent focal length of around 40-50mm to see the subject at the same size as you would with the unaided eye. A 20X pair of binoculars will give roughly the same amount of magnification as a 1,000mm lens on a FF camera with a 100% viewfinder. –  Michael Clark Oct 22 '13 at 19:22
Unlike the image that is recorded by a camera, the light projected by a camera's viewfinder is also a field of light meant to be focused by the eye looking into it. That is one among several reasons why DoF preview is only approximate. –  Michael Clark Oct 22 '13 at 21:21

First, you'll have to consider what the main uses of binoculars are:

  • marine
  • military/hunting
  • astronomical
  • theatre

In these settings (except theatre, where binoculars tend to be smaller and cheaper), there are several important disadvantages for super-zoom cameras when compared to binoculars:

  • they're generally not as weather resistant nor rugged as binoculars generally are
  • dependent of power - usage over a few hours would require drain battery of any super-zoom, while binoculars are good for however many months you need
  • the EVF performs much worse in low-light than strictly optical binoculars
  • slower usage (initialization time upon turn-on, screen lag)
  • lack of range scale often found in marine binoculars (allows you to estimate distance from an object with known height)
  • the monoscopic image (projected to only one eye) is suitable only for short-term viewing, not longer observation

People who have used both binoculars and tele lens, seem to be wondering the other way around - why are cheap binoculars so much better than an expensive lens :)

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The big advantage of superzoom cameras is that you get a big zoom lens at a reasonable price.

The downside is that the optical quality is often not that good. A superzoom lens may offer

say 28mm wide angle to 1000mm zoom. 50mm is what the eye sees so 1000mm = 20 x magnification

(i.e. objects will appear 20x nearer). Binocular optical quality can often be better than the

quality of a powerful superzoom lens which sometimes means a powerful zoom lens may produce

'soft' images which lack sharpness. However you may get better results by selecting 600 or 700 mm

which is still a very good magnification factor. In this game you really do get what you pay for!

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This answer is based on the premise that 50mm is what the eye sees, which is only a convenient number, also based on many assumptions. The eye is far more complex than any camera, and so we cannot relate a focal length to 'what the eye sees' and how the images are displayed affects the magnification of the image and so it is not possible to assign a zoom factor to the images. For binoculars, however, it is possible, since the eye is viewing the image projected by its lenses directly. –  damned truths May 13 at 11:59

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