What is p number and f number

what is p number and f number

F-NUMBERS / F?No . in welding! what is its means?

42 rows · Feb 17,  · When a base metal with a UNS number Designation is assigned a P-Number, then a base metal listed in a different ASME material specification with the same UNS number shall be considered that P-Number. The table below is a guide and is for instructive purposes only. Anyone specifying materials or requirements should refer directly to the ASME. Nov 09,  · This number is used to group similar Base Metals, allowing qualification of an entire selection versus qualification of just one. These base metals are grouped by material and assigned P Numbers based on what material they are. For example, the P Number 1 is assigned to Carbon Manganese or Low Carbon Steel base rkslogadoboj.com:

Alloy Selection. Stainless Steel. Structural Welding. Ferrous metals whar have specified impact test requirements have been assigned Group Numbers within P-Numbers. These assignments have been based on comparable base metal characteristics, such as:.

Composition Weldability Brazeability Mechanical Properties Indiscriminant substitution of materials in a set of P-Numbers or Group Numbers may lead to problems or potentially failures.

Engineering assessment is necessary prior to a change in materials. The table below is a guide and is for instructive purposes only. Anyone specifying materials or requirements should refer directly to the ASME Boiler and Pressure Vessel Code to specify materials, P-Numbers, procedures, or other requirements and not rely on the table below. These assignments have been based on comparable base metal characteristics, such as: Composition Weldability Brazeability Mechanical Properties Indiscriminant substitution of materials in a set of P-Numbers or Group Numbers may lead to problems or potentially failures.

Base Metal Typical or Example. Carbon Manganese Steels four Group Numbers. One and a quarter Chromium, half Molybdenum two Group Numbers. Two and a quarter Chromium, one Molybdenum.

Chromium, Molybdenum, Vanadium five Group Numbers. Ferritic Stainless Steels Grade High Chromium Stainless Steel.

High Chromium, Molybdenum Stainless Steel. What is court of tax appeals high strength low alloy steels six Group Numbers. Various high strength low alloy steels ten Group Numbers. High Aluminum content and series. Aluminum series - Aluminum series — Aluminum whqt - Nickel, Copper - Monel Nickel, Chromium, Iron - Inconel.


P Numbers. Powered by C-spec WeldOffice®. Apr 13,  · Single precision Floating Point numbers are bit. That means that 2,,, is the largest number can be stored in 32 bits. (remember: 1 because of the sign bit) The smallest number that can be stored is the negative of the largest number, that is -2,,, Double precision. Double precision Floating Point numbers are bit. That means that 9,,,,,, is the largest number Author: Steven Curtis. P can either mean Primary or Personal. The notion that it means Phone is arguably* wrong for two reasons: 1) the familiar format already signals that it's a phone number, and 2) H (for Home), W (Work) and F (Fax), and any other designators you might wish to list are also phone numbers.

In optics , the f-number of an optical system such as a camera lens is the ratio of the system's focal length to the diameter of the entrance pupil "clear aperture ". The f-number is the reciprocal of the relative aperture the aperture diameter divided by focal length. Most lenses have an adjustable diaphragm , which changes the size of the aperture stop and thus the entrance pupil size. This allows the practitioner to vary the f-number, according to needs. It should be appreciated that the entrance pupil diameter is not necessarily equal to the aperture stop diameter, because of the magnifying effect of lens elements in front of the aperture.

Ignoring differences in light transmission efficiency, a lens with a greater f-number projects darker images. The brightness of the projected image illuminance relative to the brightness of the scene in the lens's field of view luminance decreases with the square of the f-number.

To obtain the same photographic exposure , the exposure time must be reduced by a factor of four. But compared to the mm lens, the mm lens projects an image of each object twice as high and twice as wide, covering four times the area, and so both lenses produce the same illuminance at the focal plane when imaging a scene of a given luminance.

A T-stop is an f-number adjusted to account for light transmission efficiency. The word stop is sometimes confusing due to its multiple meanings. A stop can be a physical object: an opaque part of an optical system that blocks certain rays. The aperture stop is the aperture setting that limits the brightness of the image by restricting the input pupil size, while a field stop is a stop intended to cut out light that would be outside the desired field of view and might cause flare or other problems if not stopped.

In photography, stops are also a unit used to quantify ratios of light or exposure, with each added stop meaning a factor of two, and each subtracted stop meaning a factor of one-half. The one-stop unit is also known as the EV exposure value unit. On a camera, the aperture setting is traditionally adjusted in discrete steps, known as f-stops.

Each " stop " is marked with its corresponding f-number, and represents a halving of the light intensity from the previous stop. Each element in the sequence is one stop lower than the element to its left, and one stop higher than the element to its right.

The values of the ratios are rounded off to these particular conventional numbers, to make them easier to remember and write down. The sequence above is obtained by approximating the following exact geometric sequence:. In the same way as one f-stop corresponds to a factor of two in light intensity, shutter speeds are arranged so that each setting differs in duration by a factor of approximately two from its neighbour. Opening up a lens by one stop allows twice as much light to fall on the film in a given period of time.

Therefore, to have the same exposure at this larger aperture as at the previous aperture, the shutter would be opened for half as long i. The film will respond equally to these equal amounts of light, since it has the property of reciprocity. This is less true for extremely long or short exposures, where we have reciprocity failure.

Aperture, shutter speed, and film sensitivity are linked: for constant scene brightness, doubling the aperture area one stop , halving the shutter speed doubling the time open , or using a film twice as sensitive, has the same effect on the exposed image. For all practical purposes extreme accuracy is not required mechanical shutter speeds were notoriously inaccurate as wear and lubrication varied, with no effect on exposure.

It is not significant that aperture areas and shutter speeds do not vary by a factor of precisely two. Photographers sometimes express other exposure ratios in terms of 'stops'.

Ignoring the f-number markings, the f-stops make a logarithmic scale of exposure intensity. Given this interpretation, one can then think of taking a half-step along this scale, to make an exposure difference of "half a stop".

Most twentieth-century cameras had a continuously variable aperture, using an iris diaphragm , with each full stop marked. Click-stopped aperture came into common use in the s; the aperture scale usually had a click stop at every whole and half stop.

On modern cameras, especially when aperture is set on the camera body, f-number is often divided more finely than steps of one stop. Half-stop steps are used on some cameras. Usually the full stops are marked, and the intermediate positions are clicked.

The next few f-stops in this sequence are:. As in the earlier DIN and ASA film-speed standards, the ISO speed is defined only in one-third stop increments, and shutter speeds of digital cameras are commonly on the same scale in reciprocal seconds.

A portion of the ISO range is the sequence. An H-stop for hole, by convention written with capital letter H is an f-number equivalent for effective exposure based on the area covered by the holes in the diffusion discs or sieve aperture found in Rodenstock Imagon lenses.

A T-stop for transmission stops, by convention written with capital letter T is an f-number adjusted to account for light transmission efficiency transmittance.

A particular lens' T-stop, T , is given by dividing the f-number by the square root of the transmittance of that lens:. Some reviews of lenses do measure the t-stop or transmission rate in their benchmarks. Cinema camera lenses are typically calibrated in T-stops instead of f-numbers. The f-number may then be adjusted downwards for situations with lower light. Selecting a lower f-number is "opening up" the lens. Selecting a higher f-number is "closing" or "stopping down" the lens.

Depth of field increases with f-number, as illustrated in the image here. This means that photographs taken with a low f-number large aperture will tend to have subjects at one distance in focus, with the rest of the image nearer and farther elements out of focus. This is frequently used for nature photography and portraiture because background blur the aesthetic quality known as ' bokeh ' can be aesthetically pleasing and puts the viewer's focus on the main subject in the foreground.

The depth of field of an image produced at a given f-number is dependent on other parameters as well, including the focal length , the subject distance, and the format of the film or sensor used to capture the image. Depth of field can be described as depending on just angle of view, subject distance, and entrance pupil diameter as in von Rohr's method.

As a result, smaller formats will have a deeper field than larger formats at the same f-number for the same distance of focus and same angle of view since a smaller format requires a shorter focal length wider angle lens to produce the same angle of view, and depth of field increases with shorter focal lengths.

Therefore, reduced—depth-of-field effects will require smaller f-numbers and thus potentially more difficult or complex optics when using small-format cameras than when using larger-format cameras. Beyond focus, image sharpness is related to f-number through two different optical effects: aberration , due to imperfect lens design, and diffraction which is due to the wave nature of light. The larger number of elements in modern lenses allow the designer to compensate for aberrations, allowing the lens to give better pictures at lower f-numbers.

At small apertures, depth of field and aberrations are improved, but diffraction creates more spreading of the light, causing blur. Light falloff is also sensitive to f-stop. Many wide-angle lenses will show a significant light falloff vignetting at the edges for large apertures. Computing the f-number of the human eye involves computing the physical aperture and focal length of the eye. The pupil can be as large as 6—7 mm wide open, which translates into the maximal physical aperture.

Treating the eye as an ordinary air-filled camera and lens results in a different focal length, thus yielding an incorrect f-number. Toxic substances and poisons like atropine can significantly reduce the range of aperture. Pharmaceutical products such as eye drops may also cause similar side-effects. Tropicamide and phenylephrine are used in medicine as mydriatics to dilate pupils for retinal and lens examination.

These medications take effect in about 30—45 minutes after instillation and last for about 8 hours. Atropine is also used in such a way but its effects can last up to 2 weeks, along with the mydriatic effect; it produces cycloplegia a condition in which the crystalline lens of the eye cannot accommodate to focus near objects.

This effect goes away after 8 hours. Other medications offer the contrary effect. Pilocarpine is a miotic induces miosis ; it can make a pupil as small as 1 mm in diameter depending on the person and their ocular characteristics. Such drops are used in certain glaucoma patients to prevent acute glaucoma attacks. Even though the principles of focal ratio are always the same, the application to which the principle is put can differ.

In photography the focal ratio varies the focal-plane illuminance or optical power per unit area in the image and is used to control variables such as depth of field.

When using an optical telescope in astronomy, there is no depth of field issue, and the brightness of stellar point sources in terms of total optical power not divided by area is a function of absolute aperture area only, independent of focal length.

The focal length controls the field of view of the instrument and the scale of the image that is presented at the focal plane to an eyepiece , film plate, or CCD. The LSST 8. Its short The camera equation, or G , is the ratio of the radiance reaching the camera sensor to the irradiance on the focal plane of the camera lens. The f-number accurately describes the light-gathering ability of a lens only for objects an infinite distance away. In optical design , an alternative is often needed for systems where the object is not far from the lens.

In these cases the working f-number is used. The working f-number N w is given by: [20]. Since the pupil magnification is seldom known it is often assumed to be 1, which is the correct value for all symmetric lenses. In photography this means that as one focuses closer, the lens' effective aperture becomes smaller, making the exposure darker. The working f-number is often described in photography as the f-number corrected for lens extensions by a bellows factor. This is of particular importance in macro photography.

The system of f-numbers for specifying relative apertures evolved in the late nineteenth century, in competition with several other systems of aperture notation. In , Sutton and Dawson defined "apertal ratio" as essentially the reciprocal of the modern f-number. In every lens there is, corresponding to a given apertal ratio that is, the ratio of the diameter of the stop to the focal length , a certain distance of a near object from it, between which and infinity all objects are in equally good focus.

Twenty feet is therefore called the 'focal range' of the lens when this stop is used. The focal range is consequently the distance of the nearest object, which will be in good focus when the ground glass is adjusted for an extremely distant object.

In the same lens, the focal range will depend upon the size of the diaphragm used, while in different lenses having the same apertal ratio the focal ranges will be greater as the focal length of the lens is increased. The terms 'apertal ratio' and 'focal range' have not come into general use, but it is very desirable that they should, in order to prevent ambiguity and circumlocution when treating of the properties of photographic lenses.

The rapidity of a lens depends upon the relation or ratio of the aperture to the equivalent focus. To ascertain this, divide the equivalent focus by the diameter of the actual working aperture of the lens in question; and note down the quotient as the denominator with 1, or unity, for the numerator. Thus to find the ratio of a lens of 2 inches diameter and 6 inches focus, divide the focus by the aperture, or 6 divided by 2 equals 3; i.

Although he did not yet have access to Ernst Abbe 's theory of stops and pupils, [23] which was made widely available by Siegfried Czapski in , [24] Dallmeyer knew that his working aperture was not the same as the physical diameter of the aperture stop:. It must be observed, however, that in order to find the real intensity ratio , the diameter of the actual working aperture must be ascertained.

This is easily accomplished in the case of single lenses, or for double combination lenses used with the full opening, these merely requiring the application of a pair of compasses or rule; but when double or triple-combination lenses are used, with stops inserted between the combinations, it is somewhat more troublesome; for it is obvious that in this case the diameter of the stop employed is not the measure of the actual pencil of light transmitted by the front combination.

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