Focal Definition and 279 Threads

Hi, I have a fresnel lens from a old big screen tv and it is roughly 1 meter square. The focal point comes down to roughly 2.5cm square (1"). On a sunny day in Hawaii I can melt copper wire after about a minute. Copper has a melting point of 1083°C (1981.4 °F) . That's some serious fun! I...

Hi. If using: f (focal length) = a / ( 2 x arctan (theta / 2)) where a = 13 and is the Field of View the value I get for the focal length is 0.03 and this seems too small. Unless the calculation has not been done right? Thanks.

Hi, Have a query on the back focal plane diameter of an objective. I have got an equation back focal diameter = 320mm X NA / M where NA is the numerical aperture and M is the magnification. Just wondering is there any explanation for it? Thanks

Hi. It asks to calculate the focal length range of a projector of square pixel SXGA is from 4 to 12 m from the screen. It gives the diagonal size of the display (in mm) as well as the horizontal size (in m). The thing that am not sure about is how the focal length would be calculated with the...

Lens -- find the focal length 1. An object 3.0 cm tall is placed 20 cm in front of a converging lens. A real image is formed 10 cm from the lens. What is the focal length of the lens? 2. 1/f = 1/do + 1/di 3. 1/f = 1/do + 1/di 1/f = 1/20 + 1/10 f = 6.667 cm...

Homework Statement Without her contact lenses, Kat cannot clearly see an object more than 70.0cm away. What should be the focal length of her corrective contact lenses?Homework Equations 1/f = 1/p + 1/qThe Attempt at a Solution 1/f = 1/infinity + 1/-70.0cm = -0.0143cm f = -70.0 cm Would anyone...

Lenses and optics: solving for focal point. (SOLVED) (2 points, penalty of 0.5) When a flower pot is placed 1.2 meters on the left of a magnifying glass (converging lens), an image is formed on a screen 0.37 meters to the right of the lens. Find the focal length of the lens. Give your answer...

Homework Statement Veronique is nearsighted; she cannot see clearly anything more than 6.50 m away without her contacts. One day she doesn't wear her contacts; rather, she wears an old pair of glasses prescribed when she could see clearly up to 8.00 m away. Assume the glasses are 2.0 cm from...

Homework Statement Anne is farsighted; the nearest object she can see clearly without corrective lenses is 2.4 m away. It is 1.8 cm from the lens of her eye to the retina. What should the focal length of her contact lenses be so that she can see clearly objects as close as 24.0 cm from...

Homework Statement The diagram shows the eye of a person with normal vision looking at an object that is very far away. a) Determine the focal length of this persons eye. b) Later in this person's life, the focal length will change to between 2.1 cm and 2.3 cm. Will this person suffer from...

Homework Statement When a diverging lens is held 12 cm above a line of print, as in Figure 26.29, the image is 4.1 cm beneath the lens. What is the focal length of the lens? Homework Equations 1/di + 1/do = 1/f The Attempt at a Solution 1/di + 1/do = 1/f 1/4.1 + 1/12 = 1/f f =...

Hi All! Im a bit confused regarding the relationship between focal length and the thickness of a lense. In the lab that we performed, my data seems to be skewed and I am unable to decipher the trend. Can someone explainwhat happens to the focal length as the thickness of the lenses...

Homework Statement A nearsighted person has eyeglasses with a -1D prescription. If the near point is at 23 cm without eyeglasses, where is it when they are put on? Homework Equations (1/f)=(1/do)+(1/di) The Attempt at a Solution I got the answer which is 0.298701298 meters by...

I know that when the focal point is in the inside of a concave mirror. The focal point is greater than zero, and the radius is greater than zero and the lateral magnification is greater than zero. So if the focal point is on the outside of this concave mirror. Would the focal point be...

Homework Statement An object that is 6.00 cm tall is placed 40.0 cm in front of a diverging lens. The magnitude of the focal length of the lens is 20.0 cm. Find the image position and size. Is the image real or virtual? Upright or inverted? Homework Equations / The Attempt at a...

hi again. i totally rocked my physics homework this week, except for this last one. Homework Statement Consider a spherical mirror without making the paraxial approximation (Fig. 36-47, attached as a file). When a ray parallel to the axis makes an angle θ with the radius R at the point of...

Homework Statement A 2.0-cm-diameter spider is 2.0 {\rm m} from a wall. Determine the focal length of a lens that will make a half-size image of the spider on the wall. Determine the position (measured from the wall) of a lens that will make a half-size image of the spider on the wall...

Hello, I need help with the lens experiment, the aim of which is to determine the focal length of a concave lens by combining it coaxially with a convex lens. Given the focal length of the CONVEX lens is 15cm. and the focal length of the CONCAVE lens is 30cm. Can you give me a set of...

A concave mirror creates an image on the screen 2x larger than the object. Both objects and screen are subsequently moved in order to create an image on the screen 3x larger than the object. 1) If the screen is moved 0.75 m in this process, how far is the object also moved? 2) What is the...

Homework Statement An inverted image is magnified by 2 when the object is placed 22 cm in front of a concave mirror. Determine the image distance and the focal length of the mirror. Homework Equations don't have,sorry The Attempt at a Solution firstly,i use M= -di/do then i got...

Homework Statement The nickel's image in the figure below has twice the diameter of the nickel when the lens is 2.90 cm from the nickel. Determine the focal length of the lens. Homework Equations M = h'/h = - (p/q) The Attempt at a Solution i don't really know how to start this...

Homework Statement Suppose the lens in a human eye has far focal length equal to f0 = 40.1 mm, for distant objects to be in focus. A. An object K is 1.69 m from the lens. How much should the focal length change to focus on the object K? B.What is the magnification ( = image size...

Homework Statement Mastering physics problem 23.76 difficulty rating: two bars=difficult A 2.0-cm-tall object is placed in front of a mirror. A 1.0-cm-tall upright image is formed behind the mirror, 180cm from the object. What is the focal length of the mirror? Homework Equations...

Is there any way to find rough focal length of concave lens and convex mirror without using convex lens? Though I did the experiments(with object and image needles, not candle) very carefully with no parallax errors during my practical class, my readings are incorrect. I want to know if der s...

Homework Statement A 2.0-cm-diameter spider is 1.80 m from a wall. A. Determine the focal length of a lens that will make a half-size image of the spider on the wall. B. Determine the position (measured from the wall) of a lens that will make a half-size image of the spider on the...

Homework Statement I have a two lens system (both are convex lens; converging lens). Say I set lens 1 on left hand side and lens 2 on the right hand side. A)If I place an object within the focal point of lens 1 and the image create by this lens is OUTside the focal distance of lens 2, what...

Homework Statement A converging lens (convex lens) creates an image that is 2 times the size of the object. The object is placed: Homework Equations -di/do = hi/ho 1/f = 1/di + 1/do The Attempt at a Solution I thought the answer was that the object is place two focal lengths...

Can anyone explain to me the procedure that one would follow to you find the focal length of a concave lens using a convex lens? Thanks.

Homework Statement A lens has a focal length of 120 cm and a magnification of 4.0. How far apart are the object and the image? Homework Equations I used the thin lens equation 1/f = (1/di + 1/do)^-1 and M = -d image/d objectThe Attempt at a Solution I have been trying this by rearranging the...

SK15075PEQ3-2 - Diameter/Aperture: 150mm - Focal Length: 750mm - Diffraction-limited secondary mirror support - Paraboloidal (parabolic) primary mirror - 150 primary mirror gathers enough light to reveal deep-sky luminaries. 33% more light gathering power than 130mm, 73% more light than...

This is a simple wording confusion. On one question that I did, the property for a positive focal length image was Real, Diminished and Inverted. On another question of the same type, the property for a positive focal length image was Real, Inverted and Smaller. So, my confusion is the...

Homework Statement If there is a line from the focus of a parabola such that it makes an angle \theta with the x-axis. It intersects the parabola at a point 'P'. I want to find the focal length of the point P as a function of \theta. The Attempt at a Solution The equation of the parabola is...

Homework Statement This is a follow on question. The first few questions ask about finding the numerical answer. The question that I am confused about and cannot do seem to do properly says: Complete the ray diagram to locate the position of the image shown on the retina when effective focal...

why does the spot size increase with lower f#. Lets says you have 2 lens of the same material, and diameter, just different focal length. F/2 has higher spot size than F/3 but F/2 is faster. Is spot size a characteristic of a lens? So if your detector is fixed in size you need to get a lens...

So I got a lab to plan and design an experiment to determine the focal length of a convex lens and involve the use of lens eq. and by means of plotting a graph...I have a basic rundown of what needs to be done and all but I am somewhat in a dilemma i don't have any access to any of the apparatus...

Can you tell me the need & use of the pocal points on a lens , why do we need to have them , why do we measure them . focal points can be used for various measurements but other than that ?

Homework Statement A person with presbyopia can see distant objects clearly, but is unable to accomadate to see near objects because of hardening lens. one person cannot see objects nearer than 1.5m. a)the focal length of the eye glasses needed to see objects as close as 25cm. Homework...

Homework Statement An object is placed in front of a converging lens in such a position that the lens (f = 15.0 cm) creates a real image located 21.0 cm from the lens. Then, with the object remaining in place, the lens is replaced with another converging lens (f = 16.0 cm). A new, real image...

I am doing an assignment for school about the focal length of a concave mirror. I found that the focal length for the mirror was 0.0759cm-1 But, how much is that really in terms of cm? So basically, 0.0759cm-1 = ?cm Thanks ;D

Homework Statement Focal length of a concave mirror. This was an experiment, done in class. I was required to collect a light globe:(of course with a power source) for the object, paper:screen/image, and a concave mirror. I created the images, of the globe filament, to the screen...

so i am building a refractor telescope and i don't know what size to make the tube and what material to use for it? please telll me this is a huge % on my grade

Is there a formula for calculating the required focal length for a webcam given the width of the field of view and the distance away from the subject the camera is? Also is there a relationship between the focal length of a webcam and the 'fish-eyedness' or distortion of the picture?

A microscope is made in a tube 25.0 cm long. It magnifies 5.00 x 102 times, 50.0 times by the objective lens and 10.0 times by the eyepiece. What are the focal lengths of the two lenses?

I just have one question regarding the focal length of a lens. I had a test today and there was a fill in the blank section regarding how the focal length of a lens is determined (there was two empty spaces.) Wouldn't there be three possible answers. The curve of the lens, the index of...

Light is falling on the planar side of a thin planar convex glass lens. The curvature radius |r| is 50cm. I have to calculate the distance of the focal point to the curved surface of the lens, which to my understanding is the focal length, since it's a thin lens. Additionally I am supposed to...

Homework Statement I'm trying to find the focal length of the diverging lens. The converging lens is 24cm behind a diverging lens. The focal length of the converging lens is 31cm. I know that parallel light strikes the diverging lens and then affter passing through the converging lens the...

Hi, I need to know whether Refraction changes current focal length of a camera..I have a camera focused at the bottom of a water tank(without water). After filling water to the tank i cannot see the bottom anymore focused..I need to calculate how much should I move the camera vertically to...

How is it done? I've done a little research on Wikipedia and found the lensmaker's equation, but one of the values needed to compute focal length is the radius of the lens curvature. Strictly speaking, an aspherical curvature wouldn't have a set radius, would it? The reason I'm asking is because...

Here's a question on ray optics. We say that the focal length of a lens is half times the radius of curvature, right. Now, consider any lens(say convex), made of any material(say glass). Now a beam of light parallel to the principle axis, passes through the lens. All the rays in the beam will...

A positive lens has a focal length of 12cm. An object is located a distance of 3 cm from the lens. How far is the lens from the image? Is the image real or virtual, erect or inverted? My attempt f = +12cm o = +3cm i =? 1/o + 1/I = 1/f 1/i = 1/f – 1/o = 1/12cm – 1/3cm = 1/12 – 4/12 =...