###### diameter of the entrance pupil

- The f/ number is calculated as focal length/diameter of the entrance pupil. (largeformatphotography.info)
- 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. (wikipedia.org)
- The f-number N or f# is given by: N = f D {\displaystyle N={\frac {f}{D}}\ } where f {\displaystyle f} is the focal length, and D {\displaystyle D} is the diameter of the entrance pupil (effective aperture). (wikipedia.org)
- The f-number ("relative aperture"), N, is defined by N = f/EN, where f is the focal length and EN is the diameter of the entrance pupil. (wikipedia.org)
- Instead, the angular aperture of a lens (or an imaging mirror) is expressed by the f-number, written f/ or N, which is defined as the ratio of the focal length f to the diameter of the entrance pupil D: N = f D . {\displaystyle N={\frac {f}{D}}.} This ratio is related to the image-space numerical aperture when the lens is focused at infinity. (wikipedia.org)

###### lens's focal

- When the object is not distant from the lens, however, the image is no longer formed in the lens's focal plane, and the f-number no longer accurately describes the light-gathering ability of the lens or the image-side numerical aperture. (wikipedia.org)
- The simplest way to make a lens telecentric is to put the aperture stop at one of the lens's focal points. (wikipedia.org)

###### Lens Focal Length

- The advantages of a longer tube lens focal length becomes apparent when comparing systems having a focal length range between 160 and 250 millimeters. (microscopyu.com)
- The Focal Length slider is utilized to adjust the tube lens focal length to a new value, which either increases or decreases the Infinity Space between the objective and the tube lens. (microscopyu.com)

###### ratio

- Or do they go to 2.8, 1.9 etc and have a greater aperture to focal length ratio? (largeformatphotography.info)
- They are easiest to produce by moving your head from side to side while viewing a star centered in the field of a wide angle eyepiece or in a small focal ratio objective. (handprint.com)
- The eyepiece exit pupil diameter is found by dividing the eyepiece focal length by the telescope focal ratio. (astronomics.com)
- It was of the Ritchey-Chrétien type with an effective entrance pupil of 60 cm, a focal length ratio of 15 and a resulting focal length of 900 cm. (wikipedia.org)
- It is also known as the focal ratio, f-ratio, or f-stop. (wikipedia.org)
- For a telescope, the diameter of the exit pupil can be calculated by dividing the focal length of the eyepiece by the focal ratio (f-number) of the telescope. (wikipedia.org)
- Those parameters are: Magnification - The ratio of the focal length of the eyepiece divided into the focal length of the objective gives the linear magnifying power of telescopes. (wikipedia.org)
- The format size ratio (relative to the 35-mm film format) is known as the field of view crop factor, crop factor, lens factor, focal length conversion factor, focal length multiplier or lens multiplier. (wikipedia.org)

###### eyepiece

- To take full advantage of a scope's light-gathering capacity, the diameter of an eyepiece exit pupil should be no larger than the 7mm diameter of your eye's dark-adapted pupil, so that all of the light collected by the telescope enters your eye. (astronomics.com)
- The location of the exit pupil thus determines the eye relief of an eyepiece. (wikipedia.org)
- Good eyepiece designs produce an exit pupil of diameter approximating the eye's apparent pupil diameter, and located about 20 mm away from the last surface of the eyepiece for the viewer's comfort. (wikipedia.org)
- The emergent light at the eyepiece then fills the eye's pupil, meaning no loss of brightness at night due to using such binoculars (assuming perfect transmission). (wikipedia.org)
- The exit pupil can be visualized by focusing the instrument on a bright, nondescript field, and holding a white card up to the eyepiece. (wikipedia.org)
- By moving the card closer to or further away from the eyepiece, the disc of light will be minimized when the card is at the exit pupil, and the bright disc then shows the diameter of the pupil. (wikipedia.org)
- A clear vial of milky fluid can also be used to visualize the light rays, which appear as an hourglass shape converging and diverging as they exit the eyepiece, with the smallest cross-section (the waist of the hourglass shape) representing the exit pupil. (wikipedia.org)
- In general terms, larger objective lens diameters, due to their ability to gather larger amounts of light, provide a larger exit pupil and hence provide a brighter image at the eyepiece. (wikipedia.org)

###### magnification

- Tubes of various lengths can be stacked, decreasing lens-to-subject distance and increasing magnification. (wikipedia.org)
- Exit pupil Transmittance Pupil magnification Greivenkamp, John E. (2004). (wikipedia.org)
- In that case, the exit pupil can be easily calculated as the diameter of the objective lens divided by the magnification. (wikipedia.org)

###### Nodal Point

- Wouldn't it be great if everyone entered their values for their NPP / Nodal Point / Entrance Pupil for lens and camera combinations. (panotools.org)
- Wouldn't it be great if everyone entered their values for their Nodal Point / Entrance Pupil for lens and camera combinations. (panotools.org)
- Panoramic photographers often incorrectly refer to the entrance pupil as a nodal point, which is a different concept. (wikipedia.org)

###### entrance pupil size

- Most lenses have an adjustable diaphragm, which changes the size of the aperture stop and thus the entrance pupil size. (wikipedia.org)
- Research has shown that its maximum baseline is confined to the main lens entrance pupil size which proves to be small compared to stereoscopic setups. (wikipedia.org)

###### illuminance

- It is equal to retinal illuminance produced by a surface whose luminance is one nit when the apparent area of the entrance pupil of the eye is 1 square millimeter. (wikipedia.org)
- But compared to the 100 mm lens, the 200 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. (wikipedia.org)
- Or it can be compared for a fixed focal-plane illuminance, corresponding to a fixed f-number, in which case P is proportional to pixel area, independent of sensor area. (wikipedia.org)

###### eye's

- Your eye's ability to dilate declines with increasing age (to a dark-adapted pupil of about 5mm by age 50 or so). (astronomics.com)
- Since the eye's pupil varies in diameter with viewing conditions, the ideal exit pupil diameter depends on the application. (wikipedia.org)
- In daylight, when the eye's pupil is only 4 mm in diameter, over half the light will be blocked by the iris and will not reach the retina. (wikipedia.org)

###### aperture stop

- Thus it is also called a stop (an aperture stop, if it limits the brightness of light reaching the focal plane, or a field stop or flare stop for other uses of diaphragms in lenses). (absoluteastronomy.com)
- 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. (wikipedia.org)
- 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. (wikipedia.org)
- In an optical system, the entrance pupil is the optical image of the physical aperture stop, as 'seen' through the front of the lens system. (wikipedia.org)
- The exit pupil is the image of the aperture stop in the optics that follow it. (wikipedia.org)

###### objective

- When the tutorial initializes, the Focal Length slider is set to a value of 200 millimeters and the objective exit Pupil Diameter equals 17 millimeters. (microscopyu.com)
- Instead, the f-number f=L/D of the telescope is typically written on the scope, as well as the objective diameter D and focal length L. The individual eyepieces have their focal lengths written on them as well. (wikipedia.org)
- The basic scheme is that the primary light-gathering element the objective (1) (the convex lens or concave mirror used to gather the incoming light), focuses that light from the distant object (4) to a focal plane where it forms a real image (5). (wikipedia.org)

###### camera's

- He also developed a method of computing depth of field from a camera's entrance pupil location and diameter, without reference to focal length and f-number (see his 1904 and 1906 books). (wikipedia.org)
- The geometric location of the entrance pupil is the vertex of the camera's angle of view and consequently its center of perspective, perspective point, view point, projection centre or no-parallax point. (wikipedia.org)

###### telescope

- An astronomical telescope requires a large pupil because it is designed to be used for looking at dim objects at night, while a microscope will require a much smaller pupil since the object will be brightly illuminated. (wikipedia.org)

###### lenses

- A negative value means the entrance pupil is before the lens base, such is the case with many telephoto lenses. (panotools.org)
- Telecentric lenses tend to be larger, heavier, and more expensive than normal lenses of similar focal length and f-number. (wikipedia.org)

###### dark-adapted

- A set of 7×50 binoculars has an exit pupil just over 7.1 mm, which corresponds to the average pupil size of a youthful dark-adapted human eye in circumstances with no extraneous light. (wikipedia.org)

###### telecentric

- An entrance pupil at infinity makes the lens object-space telecentric. (wikipedia.org)
- If both pupils are at infinity, the lens is double telecentric (or bi-telecentric). (wikipedia.org)

###### microscope

- At constant focal length, variations in the Pupil Diameter slider produce much larger changes in θ , which affects the image quality seen in the microscope. (microscopyu.com)

###### image

- As the focal length of the tube lens is increased, the distance to the intermediate image plane also increases, which results in a longer overall tube length. (microscopyu.com)
- The corresponding image of the aperture as seen through the back of the lens system is called the exit pupil. (wikipedia.org)
- The entrance pupil is usually a virtual image: it lies behind the first optical surface of the system. (wikipedia.org)
- The pupil constricts in order to prevent strongly diverging light rays hitting the periphery of the cornea and the lens from entering the eye and creating a blurred image. (wikipedia.org)
- The entrance pupil of the eye is the image of the anatomical pupil as seen through the cornea. (wikipedia.org)
- By definition the "standard plenoptic camera" has microlenses placed one focal length away from the image plane of a sensor. (wikipedia.org)
- Because the image sensors in many digital cameras is smaller than the 24 mm × 36 mm image area of full-frame 35-mm cameras, a lens of a given focal length will give a narrower field of view on such cameras. (wikipedia.org)

###### size

- The iris is a thin, circular structure in the eye, responsible for controlling the diameter and size of the pupils and thus the amount of light reaching the retina. (absoluteastronomy.com)
- It is meant as a method for correcting photometric measurements of luminance values impinging on the human eye by scaling them by the effective pupil size. (wikipedia.org)
- In photography, the size of the entrance pupil (rather than the size of the physical aperture itself) is used to calibrate the opening and closing of the diaphragm aperture. (wikipedia.org)
- The accommodation reflex (or accommodation-convergence reflex) is a reflex action of the eye, in response to focusing on a near object, then looking at distant object (and vice versa), comprising coordinated changes in vergence, lens shape and pupil size (accommodation). (wikipedia.org)
- To use an optical instrument, the entrance pupil of the viewer's eye must be aligned with and be of similar size to the instrument's exit pupil. (wikipedia.org)
- The maximum pupil size of a human eye is typically 5-9 mm for individuals below 25 years old, and decreases slowly with age as shown as an approximate guide in the table below. (wikipedia.org)

###### astronomical

- The 9 x 63mm SkyMaster DX has a wide 5° field and very bright 7mm exit pupils ideal for serious low power/wide field astronomical viewing. (astronomics.com)

###### optical system

- Reduction in the off-axis diagonal wave flux angle can approach a significant percentage with the longer focal length optical system. (microscopyu.com)
- In optics, the exit pupil is a virtual aperture in an optical system. (wikipedia.org)

###### infinity

- Dramatic enhancement in contrast levels observed with epi-fluorescence illuminators in infinity-corrected systems is attributed to the optical advantage of longer tube lens focal lengths. (microscopyu.com)

###### plane

- The distance of the exit pupil from the sensor plane determines the range of angles of incidence that light will make with the sensor. (wikipedia.org)
- To achieve this, an array of microlenses is placed at the focal plane of the camera main lens. (wikipedia.org)
- Lumsdaine and Georgiev described the design of a type of plenoptic camera in which the microlens array can be positioned before or behind the focal plane of the main lens. (wikipedia.org)

###### corresponds

- This corresponds to a decrease of the pupil and aperture diameters by a factor of 1/ 2 {\displaystyle \scriptstyle {\sqrt {2}}} or about 0.7071, and hence a halving of the area of the pupil. (wikipedia.org)

###### mount length

- To calculate the Entrance pupil distance add the Tripod Mount Length (L1) from the camera and the Entrance Pupil Length (L2) from the lens. (panotools.org)

###### distance

- The second table shows the actual entrance pupil distance which is only dependent on the lens itself. (panotools.org)
- Facing the side of the lens, the distance from the base of the lens to the Entrance Pupil. (panotools.org)
- This is easy to measure and is dependent only on the camera body The second table shows the actual entrance pupil distance which is only dependent on the lens itself. (panotools.org)

###### luminance

- The troland typically refers to the ordinary or photopic troland, which is defined in terms of the photopic luminance: T = L × p {\displaystyle \mathrm {T} =\mathrm {L} \times \mathrm {p} } , where L is the photopic luminance in cd m−2 and p is pupil area in mm2. (wikipedia.org)
- A scotopic troland is also sometimes defined: T ′ = L ′ × p {\displaystyle \mathrm {T'} =\mathrm {L'} \times \mathrm {p} } , where L′ is the scotopic luminance in cd m−2 and p is pupil area in mm2. (wikipedia.org)
- Troland does not directly convert to other units, being a retinal luminance per unit area of a pupil. (wikipedia.org)
- Assuming the corneal luminance L from an extended source, the pupil diameter p and the focal length of the eye F, the retinal luminance is: Lr [lm / m^= pi * L / 4 / (f/#)^2 ~ pi * L * p^2 / 4 / F^2. (wikipedia.org)

###### Tripod

- A panoramic tripod head is a piece of photographic equipment, mounted to a tripod, which allows photographers to shoot a sequence of images around the entrance pupil of a lens that can be used to produce a panorama. (wikipedia.org)

###### typically

- The entrance pupil of the human eye, which is not quite the same as the physical pupil, is typically about 4 mm in diameter. (wikipedia.org)

###### effective

- in simpler terms, the f-number is the focal length divided by the "effective" aperture diameter. (absoluteastronomy.com)

###### produce

- Tube lengths between 200 and 250 millimeters are considered optimal, because longer focal lengths will produce a smaller off-axis angle for diagonal light rays, reducing system artifacts. (microscopyu.com)

###### object

- The 200 mm lens's entrance pupil has four times the area of the 100 mm lens's entrance pupil, and thus collects four times as much light from each object in the lens's field of view. (wikipedia.org)
- He says, "At this point it will be sufficient to note that all these formulae involve quantities relating exclusively to the entrance-pupil and its position with respect to the object-point, whereas the focal length of the transforming system does not enter into them. (wikipedia.org)

###### system

- Longer tube lengths also increase the flexibility of the system with regard to the design of accessory components. (microscopyu.com)
- In addition, moving this slider to longer tube lengths decreases the angle θ between on-axis and off-axis light rays passing through the system. (microscopyu.com)

###### given

- The primary function of the panoramic head is to precisely set the point of rotation about the entrance pupil for a given lens and focal length, eliminating parallax error. (wikipedia.org)

###### smaller

- the eyes adduct, the ciliary muscles contract, and the pupils become smaller. (wikipedia.org)

###### location

- Increasing the focal length of a lens (i.e., zooming in) will usually cause the f-number to increase, and the entrance pupil location to move further back along the optical axis. (wikipedia.org)

###### photography

- According to the Focal Encyclopedia of Photography (1965), "A bibliography of his 571 books and articles was published in Forschungen zur Geschichte der Optik, 1943. (wikipedia.org)

###### increase

- During accommodation, the pupil constricts to increase the depth of focus of the eye by blocking the light scattered by the periphery of the cornea. (wikipedia.org)

###### area

- Multiplying by the pupil area : Trolands [cd / m^2 * mm^= L * pi * p^2 / 4 = F^2 * Lr ~ 289 * Lr. (wikipedia.org)

###### refer

- The term exit pupil is also sometimes used to refer to the diameter of the virtual aperture. (wikipedia.org)

###### sometimes

- Older literature on optics sometimes refers to the exit pupil as the Ramsden disc, named after English instrument-maker Jesse Ramsden. (wikipedia.org)