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Focal length refers to the distance from a point within a lens to the film plane when the lens is focused on infinity. For a 50mm lens, this point (rear nodal point) is 50mm away from the film plane if the lens is focused on infinity.
An image on the ground glass of a view camera is focused by racking the lens board towards or away from the glass, but the principle is the same. The rear nodal point of a 250mm lens will be that distance from the glass when focused on very distant objects.
It is virtually impossible to physically measure the focal length if that's what you're trying to do, since the rear nodal point is contained within the rear optic. If you're trying to calculate it, that's a subject beyond me, and perhaps the Photography category also. In that case, you might want to try asking somewhere over in the Physics category.
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∙ 15y ago
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What kind of PS digital camera can you get with a wider view than the standard shorter focal length so you can take shots in tighter spaces?
Your going to have to do some research and look at the focal length on cameras. The smaller the number the wider the angle. You want a camera with a small focal length.
What is focal length of a door peephole's lens and is it concave or convex?
The lens in a door peephole is a convex lens with a very short focal length, giving it a wide field of view. If it were on a camera, it would be called a "Fisheye lens".
What does the 18-200 camera lens digits stand for?
18 mm is the wide angle focal length and 200 mm is the telephoto limit of the zoom. for more info searching on focal length and field of view will give you lots of info.
What is the meaning of focal length in camera?
The focal length of a camera's lens refers to the the magnification or telephoto power of the lens and is expressed in the millimeters of the lens, like 100mm, 300mm, etc. www.goldprints.com
What will decreasing a telescope's eyepiece focal length?
The magnification of the telescope image is(focal length of the objective) divided by (focal length of the eyepiece).The focal length of the objective is fixed.Decreasing the focal length of the eyepiece increases the magnification of the image.(But it also makes the image dimmer.)
Does the field of view narrow when focal length increase?
yes
What is a wide angle focal length lens?
On a digital SLR camera, anything less than about 32 mm (50 mm for a 35 mm film camera). The focal length of a wide angle lens varies depending on the size of the negative or digital sensor. Most camera manuals for smaller cameras will give you an idea for that camera, often in 35 mm equivalents, so use the 50 mm standard for those.
What does mm mean for a digital camera?
MM refers to the focal length of the lens. In the old, old days of Paul Rudolph's original Tessar lens, "focal length" meant the distance between the middle of the lens and the "focal point" - the point at which all the rays of light coming out of the lens converge on one spot. That lens was first introduced in 1902, and since then we've learned that different focal lengths of lenses have different angles of view...so now, if a lens has an angle of view equal to that of a 50mm lens, we call the lens a "50mm" regardless of the actual length of the lens.
What is the X in digital camera zooms?
The lens of a digital camera has a certain focal length, expressed in mm. For example, a 50mm lens has a field of view that approximates what we see with our eyes looking straight ahead. A 25mm wide-angle lens has a field of view that approximates what we see with our eyes when we turn our head from side to side. The shorter the focal length of a lens, the wider the field of view. The longer the focal length of a lens, e.g. 300mm, the narrower the field of view. Of course, a narrow field of view is equivalent to zooming in to a far object, like when we look into binoculars. A lens can either have a fixed focal length, e.g. 25mm, 50mm, 300mm, etc. or can have a range of focal lengths, e.g. 25mm - 100mm, 50mm - 300mm, etc. A lens that has a range of focal lengths is called a zoom lens. The zoom factor of the lens is calculated by dividing the maximum focal length by the minimum focal length. That zoom factor is the "X" you are referring to. For example: 1. A 25mm - 100mm lens is a 100/25 = 4x zoom lens. 2. A 50mm - 300mm lens is a 300/50 = 6x zoom lens. 3. A 50mm - 200mm lens is also a 200/50 = 4x zoom lens. 4. A 100mm - 400mm lens is also a 400/100 = 4x zoom lens. So knowing the zoom factor of a lens alone does not tell you what its minimum and maximum focal lengths are. Both examples 1, 3 and 4 above are 4x zoom lenses, but example 1 has a minimum focal length that is a wide-angle and allows us to take wide landscape shots or include all our classmates in one shot. Example 4 has a maximum focal length that is a long telephoto and allows us to bring far object near.
What it means 18mm - 200 mm in photo lens?
This describes the focal length range of the lens. It means that the lens can be set between 18mm (a wide angle which takes in a larger field of view) and 200mm (a telephoto, which creates a narrower field of view). ******* Note: the above is certainly true for 35mm format, but focal length is relative to the format. For 4x5 cameras, the equivalent "normal" focal length is around 200mm.
Would the ocular unit increase or decrease as magnification increases?
Field of view will decrease as the aperture remain same but things become larger and so we can see smaller area after magnification
What are diverging and converging lenses?
Lenses enable individuals to view objects. A Converging lens has a positive focal length, which facilitates the convergence of the exiting rays. While, diverging lenses have a negative focal length, which facilitates the divergence of the exiting rays.
