Help Needed- Zoom question of digicam,videocam and binocular

[maisatomai]

Hi,

I live near to a stadium(500m) and love to watch the soccer match there. I used to use a bino 10X70 to watch it but recently i came across a videocam 30X. I was thinking if the 30X from the videocam can be compared to the 10X of my binocular(if it is compareable), then the videocam should be able to zoom 20X more than my binocular. Then how does the 30X compared to the 12X digicam which i thinking to buy. Thanks- Mr Blur

Question summarized. Who will win?
1)10X70 Bino

2)30X Camcorder

3)12X ultrazoom Digicam

[Tom LaPrise]

The "10x" figure for the binoculars is magnification, not zoom ratio. The "30x" for the videocamera and "12x" of the digital camera are zoom ratios-- the longest focal length comared to the shortest focal length--not magnifications.

In 35mm photography, 50mm is usually accepted as being close to normal eyesight, in terms of (lack of) magnification. Your 10x binoculars would have a focal length equivalent of around 500mm--quite a telephoto lens.

It gets less simple with the videocam and the digital camera. A zoom range of 5-60mm is "12x," but so is 10-120mm, 3-36mm, etc. While these ranges are all "12x," the magnification they give are all different. Most (if not all) digital cameras give their focal length as "35mm equivalent," so you could use the 35mm equivalent at the telephoto end to get an idea of your reach with the camera and camcorder.

For example, my Minolta DiMage Z1 has a 10x zoom; the 35mm equivalent focal lengths at the wide angle and tele ends are 38mm and 380mm (and 380/38=10, which is where the "10x" comes from). The binocular-equivalent reach, you might say, at the tele end is 380mm/50mm or about 7.6x.

[maisatomai]

Hi Mr LaPrise,

Thanks for your answer. So can I say that the 30X zoom of the camcorder is more powerful than the 10X of my binocular? Thanks in advance

[VTphotog]

Tom is correct that binoculars and telescopes use a magnification factor. This is due to the optics being optimized for human eyes. Magnification is derived by dividing the focal length of the eyepiece into the focal length of the objective lens. You can also find the 'exit pupil' of your binoculars or scope, knowing the objective diameter and magnification. Exit pupil is simply the size of the cone of light leavng the instrument. If it is too small, the glass will be dim and not too useful in low light. Human eye pupil diameter ranges up to about 5-6mm in dim light. Your 10x70 binoculars will have an exit pupil of 7mm.

With cameras, the usually accepted standard for '1x' is, as Tom mentions, 50mm in 35mm camera terms. This givesfield of view that most people accept as normal. As far as magnification is concerned, I find that approcimately 100mm is more nearly '1x'. You can determine this for yourself if you have a camera with a viewfinder and a zoom lens. Keeping both eyes open, adjust zoom until the view in both eyes is the same as if the camera wasn't there, then read the 35mm equivalent focal length.

brian

[Tom LaPrise]

Not necessarily. The "30x zoom" of the camcorder could possibly have a maximum focal length less than that of the focal length of the binocular. "30x" for the camcorder is the ratio of longest to shortest focal length (not the magnification), and "10x" for the binocular is the magnification. If the camcorder's zoom starts at a very wide angle, then 30 times that could be less than what you get with the binocular.

The camcorder should have the zoom range (probably in 35mm-equivalent) printed on it somewhere, usually either on the part surrounding the lens glass (looking right at the lens) or on the body of the camcorder near the lens. Use the maximum focal length to judge how "powerful" the camcorder's zoom is compared to the binocular.

maisatomai wrote:

Hi Mr LaPrise,

Thanks for your answer. So can I say that the 30X zoom of the camcorder is more powerful than the 10X of my binocular? Thanks in advance

[maisatomai]

Below are just my BEGINNER opinion:

The focal length for a 26X canon camcorderis 35.3~917.8. So i guess the focal length for a 30X canon camcorder should be 35.3~1000+. It is simply amazing that a binocular which cost over $1000 would lose to a budget camcorder which cost less than $300. I checked with the shop today and they told me that a telephoto which can zoom that far would cost around 20k. Amazing!!!

[jacks]

No, it's not amazing at all.
The lens on the video camera makes a tiny, tiny image which would be useless to the human eye or to a larger camera sensor. The actual focal length of that lens is probably more like 3-90mm which is a relatively small lens (the physical size would be even smaller due to some fancy optics). The tiny sensor the lens projects onto gives the same field of view as a 30-900mm lens would if it were projecting onto 35mm film. Clearly a 900mm lens is going to be a LOT bigger than a 90mm one (1000 times bigger, all other things being equal). The image through such a lens would contain far, far more information than that through the video camera lens which is one reason why video camera stills don't look anything like photos from a half decent camera.
Sigma make a 300-800mm zoom and it sells for a few thousand dollars. A 30-800 would be far bigger, more expensive, optically poorer and totally less practical than a two lens solution so no one makes one.
I doubt binoculars need to make an image as large as 35mm film, but then you also need two lenses.