Focal Definition and 279 Threads

I'm designing an eyepiece for fun and want to be accurate. I just realized my physics book equations are approximated for thin lenses only. Suppose I have a convex convex lens or a plano convex lens, lateral parallel rays coming from one side or the other, and a focal point on the opposite...

Homework Statement A biconvex lens with radius of curvature 15 cm has a focal length of 15 cm in air. What is its focal length if it is submerged in water (n=1.33)? Homework Equations 1/f = (n-1)(1/R1 - 1/R2) The Attempt at a Solution 1/f = 1/0.15 = (n-1)(2/0.15) Solving for n...

Homework Statement An object is 12.0 cm in front of a convex mirror. When the convex mirror is replaced with a flat mirror, the image distance is 5.0 cm farther away from the mirror. What is the focal length of the convex mirror? Homework Equations f=-1/2R 1/do+1/di=1/f The...

Homework Statement The image of an object seen in a mirror is twice its actual size. The orientation of the image is the same as that of the object. If the object distance do is 1.7 m, what is the focal length of the mirror? Homework Equations 1/do+1/di=1/f m=-di/do The Attempt...

So I have come across a specification of a narrow field of view camera. The specification states IFOV=30 microrad FOV=2x2 resolution=<.1m at 1 km If I assume a 1K sensor at 9micron pitch and an aperture = 3.7cm I have resolution at .013 m Chip size = 9.2mm Focal length is...

Homework Statement Suppose we have a lens of known focal length, f=100 cm. (a) If light enters the lens from air, but after the lens enters a medium with index 1.33, how far from the lens will focus? (Assume the incident light is collimated.) (b) What if there is instead air after the lens...

Simple question: is there any physical significance of the quantity (focal length of lens)*(wavelength of laser light passing through the lens) ? How does it relate to the size of an image on the image plane? According to my professor, (focal length)*(wavelength)/(constant) is the length of...

Homework Statement When an object is placed 69.0cm from a certain converging lens, it forms a real image. When the object is moved to 39.0cm from the lens, the image moves 19.0cm farther from the lens. Find the focal length of this lens. Homework Equations 1/do + 1/di = 1/fThe Attempt at a...

Homework Statement The barrel of a compound microscope is 15 cm in length (distance between lenses). The specimen will be mounted 1.0 cm from the objective, and the eyepiece has a 5.0-cm focal length. Determine the focal length of the objective lens. Known: f2=5cm, L=15cm, do1=1cm...

Homework Statement A biology student wishes to examine a bug at a magnificaiton of +5.00 by looking through a single lens. the student wants the image of the bug to be a distance of 25cm from the lens. what is the focal length of the lens? Answer:+6.25cm Homework Equations...

I cannot figure out focal distance and the like, is there anyway I can get a walkthrough? the radius of curvature (R) to 0.7 m and the lens’s refractive index (n) to 1.8 . anyone?

Hello, I use a 10x infinity objective as a condenser in a optical trap setup. The collimated forward scattered light is then focused with a 40mm lens onto a QPD. This is the imaging techqnique. There is also BFPI, and I am not clear on this method. My understanding is that I need to image the...

Homework Statement For my high school physics coursework I must investigate factors affecting the focal length of a lens. I have focused on radii of curvature and completed my data collection and verified the accuracy using the lens makers equation. However, in the conclusion I am really...

Homework Statement My physics coursework hypothesis: "As the thickness of the lens increases, the focal length decreases". I tested this using a ray box, a stand to hold lenses and a screen to see where the light is most focused, which is then measured with a metre ruler. The distance 'u'...

Homework Statement "An object 10 cm tall is placed at the zero mark of a meter stick. A spherical mirror located at some point on the meter stick creates an image of the object that is upright, 4 cm tall, and located at the 42 cm mark of the meter stick. Where is the mirror located and what...

Homework Statement The image obtained with a converging lens is upright and 3x the length of the object. The focal length of the lens is 20cm. Calculate the object and image distances Homework Equations I have absolutely no idea how to even start this question The Attempt at a...

What is a purpose of focal point in optics,especially in human eye? I don t understand,why is required to make a focal point in retina?Everywhere in articles are pictures of this problem clarified by one principle:Object,which we see reflects rays in all directions,and those which are parallel...

Homework Statement In Sears' Optics, chapter 4, Sears claims that the first and second focal lengths (distance from first and second focal points to the first and second principal points, respectively) are equal, and he seems to imply that this is true in general, without proof. I am a...

Any help much appreciated - this is driving me crazy! Homework Statement Show that the focal length of a half ball lens, in air, (in the paraxial limit) is given by: f=R/n-1 Homework Equations Equation (from Hecht- Optics), for refraction at a spherical interface: nm/s0 + nl/s1...

Hello everyone, I'm an optometry student who is currently doing Optics 1, and I have a general question about focal points. I can do the math regarding F1, F2, and the nodal ray, and I am decent at drawing the ray traces, but I would like to know more about the actual real world applications...

Can an ellipse's focal points be outside the ellipse? I have tried googling this, but without any good explanations or answers. According to my calculations, the focal points of the ellipse defined by x^{2} + \frac{y^{2}}{4} = 1 are (-\sqrt{3},0) (\sqrt{3},0)) . I maybe wrong of course...

ok so here is the quesiton.. An object is loacted 3.5 cm from the optical centre of a lens. The lense produces an image of magnification that is +0.667 the size of the object a) is this lens a diverging or converging lens? explain b) Find the position of the image and the focal length...

My question is as follows: Does the focal length of a concave lens change when put into a medium such as water? Initially the focal length of the lens is 20 cm in air. Would it get larger or small in water?

Hello! I am preparing an exam about optics and I can't understand a formula.my problem is at the end of the second page (the explanation is in Italian, but the formulas are easy to read for everybody). I can't understand how in the last step f=R/2 - (1+b) * r^2/4R etc they found -(1+b)...

Lenses - magnification, position, focal length help! ok so here is the quesiton.. An object is loacted 3.5 cm from the optical centre of a lens. The lense produces an image of magnification that is +0.667 the size of the object a) is this lens a diverging or converging lens? explain b)...

Radius of curvature and focal distance question? Hi everyone! Really struggling on these two questions and have spent way too many hours coming up with the wrong answers. Below are the questions and my attempts. Any help would be greatly appreciated! 1. Calculate the radius of curvature...

I am a bit of confused with the following terms involved in the study of lenses: Diameter of lens Aperture of Lens Are these terms synonomous? And how are they related to focal length of a lens?

is it true when we use concave lens, we can obtain focal length when we get the sharp image.. is it possible to get more than one sharp image when we change the object distance (distance between object and lens)

Hello all. I am in the process of designing a mechanism for collimating laser diodes for a personal project. I don't have training in optics so I am stuck with this problem: I need to determine the focal length of a lens that can be used to collimate a laser beam with divergence 45 degrees...

Homework Statement A telescope has a focal ratio of f/7.5. You wish to use it with a spectrometer that requires an f/10 beam at its input. Compute the focal length of a 50mm diameter lens that, when inserted in the beam 150mm in front of the unmodified focal plane, produces the required beam...

Hi I am trying to design a three mirror off axis telescope. The free parameters are the offset between the apertures and distance betwen the surfaces. My question is for a system with 'n' elements/surfaces (n=3 in my case) is there a relation between optical path length and focal length of...

Hi all, I'm looking for an equation which will give me the focal length of a biconvex lens given that we know both Radii of curvature, the thickness of the lens and the refractive index inside and outside. An equation is given on wikipedia here http://en.wikipedia.org/wiki/Focal_length as I...

I have a problem with the determination of the correct focal curve of an achromatic double. I'm considering here a doublet formed by a biconvex Flint Glass lens attached to a plano-concave crown glass lens. ( I know that the typical design of the doublet is a biconvex crown lens attach to a...

Homework Statement A thick lens has an index of refraction of 1.560, thickness of 3.0cm, and radii of curvature of R1= -4.50cm, R2= -3.60cm. Calculate the positions of the focal points (relative to the vertices). Homework Equations \frac{n}{s}+\frac{n'}{s'}=\frac{n'-n}{R} ffl =...

Homework Statement When an object is at distance u1 and u2 from pole of concave mirror, images of same size are formed. Find the focal length of the mirror. Homework Equations 1/v+1/u=1/f The Attempt at a Solution Can u please ray diagram for this question. I think their is only...

Can you have an "anti" focal point of a lens? Hi, Imagine putting a convergent lens in the path of a laser beam. I put a small light meter at the focal point of the lens. If I move the lens along the beam will there be positions of the lens where the light paths through it completely...

From what I recall, determining the focal length of a double convex lens just involves an infinite light source and holding the lens close to an image-capturing surface such as a wall and adjusting the distance until the image is at its sharpest...the distance from the lens to the surface is the...

I am trying to find the focal length of a convex lens, so i let the sun shine through my window to create an image on my wall. Is that image the focal point or is it just the distance of the image? And if it is the distance of the image, how do I put it into the thin lens equation, since the...

So I bought a magnifying glass for a project and I need to find out the focal length of it in order to use it. I'm given the magnification of the converging lens, which is 5, but I don't any methods or how I could find out the focal length given only the magnification. I attempted to set...

A diverging lens is used to form a virtual image of an object. The object is 88.0 cm in front of the lens, and the image is 44.0 cm in front of the lens. Determine the focal length of the lens. 1/f = 1/do + 1/di since do is 88cm infront of the lense, that would keep the 88 positive, and...

Homework Statement Suppose that you wish to construct a telescope that can resolve features 7.0 km across on the Moon, 384,000 km away. You have a 2.2 m-focal-length objective lens whose diameter is 10.5 cm. What focal-length eyepiece is needed if your eye can resolve objects 0.10 mm apart...

Homework Statement A microscope has a 13.0 x eyepiece and a 57.0 x objective lens 20.0 cm apart. Calculate the focal length of each lens. Where the object must be for a normal relaxed eye to see it in focus? Homework Equations M=m(objective)*m(eyepiece)=f(objective)/f(eyepiece)...

Homework Statement For a lens with a focal length f, find the smallest distance possible between the object and its real image. Homework Equations 1/s + 1/s' = 1/f The Attempt at a Solution I tried plugging in different numbers for the solution, but I'm not sure how to reach the...

Homework Statement A person had a near point of 80 cm. What focal length lens would be required to correct this persons near point to 30cm, allowing then to read at this distance Homework Equations Maybe: 1/di + 1/do = 1/f = P I found another similar question which used 1/(the...

In my Optics book (Hecht, 4th edition) the author discusses how, when dealing with a multiple lens system (say, with n many lenses), one can think of the system as a single lens system, with an effective focal length given by: 1/f(effective) = 1/f1 + 1/f2 + ... + 1/fn My question is this...

Hi, i have a simple optical system composed of: 1. objective with 50 mm focal lenght 2. CCD camera that can not be mounted behind the objective, for mechanical reasons... it can only be mounted 1-2 cm far behind the objective. So i need to "translate" the focal point of the objective 1-2 cm...

Is it possible to build a large mirror array (around 10 km²) with adjustable focal length (from 10 meters to around 400 kilometers)?

Homework Statement A lens forms an image of an object. The object is 16 cm from the lens. The image is 12 cm from the lens on the same side as the object. (a) What is the focal length of the lens? Is the lens converging or diverging? (b) If the object is 8.5 mm tall, how tall is the image...

I know that for concave lenses, the focal length is one half the length of the radius of the circle. Is this also true for convex lenses? Thanks

I've been doing some calculations on lenses, and I'm a little confused about some of the diagrams I've seen. Looking at a ray diagrams, I see the light passing through the lens, at one angle, and then converging on a focal point from there. Using snells law to calculate refraction through the...