What is Focal: Definition and 292 Discussions

The HP-41C series are programmable, expandable, continuous memory handheld RPN calculators made by Hewlett-Packard from 1979 to 1990. The original model, HP-41C, was the first of its kind to offer alphanumeric display capabilities. Later came the HP-41CV and HP-41CX, offering more memory and functionality.

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  1. Z

    Focal Length: cm-1 Conversion | 0.0759cm-1

    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
  2. H

    Focal length of a concave mirror

    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...
  3. P

    Stargazing What Size and Material Should I Use for My Refractor Telescope Tube?

    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
  4. J

    Calculating Webcam Focal Length and Distortion: A Comprehensive Guide

    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?
  5. R

    Focal Lengths of Two Lenses of a Microscope

    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?
  6. D

    Does the Refractive Index of a Lens Affect its Focal Length?

    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...
  7. I

    How Do You Calculate the Focal Length of a Planar Convex Lens?

    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...
  8. L

    Finding Focal Length of Diverging Lens with Parallel Rays

    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...
  9. M

    Can Refraction in Water Change the Focal Length of a Camera?

    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...
  10. C

    Calculating focal length for aspherical lenses

    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...
  11. R

    Here's a question on light ray optics and focal length.

    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...
  12. M

    Real or virtual, focal length

    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 =...
  13. G

    Focal length calculation and graph Q

    Hi folks, just joined the forums :smile: Hope you don't mind me firing a few questions now and again, i have some reports to do over the weekend which is the last of my HNC in Chemical Engineering :!) A lot of it is basic physics which iv done in the past but its just the odd bit that catches...
  14. A

    Finding the focal length of the lense

    Homework Statement A magnifying glass gives a five times enlarged image at a distance of 25 cm from the lense.Find the focal length of the lense d=25cm M=5 f=? Homework Equations f = d/M The Attempt at a Solution f = 25/5 f = 5 cm But this solution is not correct please help...
  15. W

    Forming a Sharp Image with a Lens: Focal Length Explored

    Homework Statement An object and a screen are separated by 20 cm. A convex lens is placed between them, 5 cm from the object. In this position it causes a sharp image of the object to form on the screen. What is the focal length of the lens? The Attempt at a Solution wouldn't it just...
  16. J

    Figuring Out Focal Length and Object Distance

    Homework Statement An object is located to the left of a thin lens. The image is upright, and the distance between the object and image is 20 cm. What are the focal length and object distance if the lens is 2 times the hieght of the object? Homework Equations 1/p + 1/q = 1/f The...
  17. J

    How does the shape of a lens affect focal lengths?

    Homework Statement Why do two outer rays converge to a different focal point than the inner rays? Homework Equations The Attempt at a Solution The distance to the focal point of the inner rays is shorter than the outer rays, the light has to bend a lot more for the outer rays
  18. M

    Focal Length of Thin Lenses in Different Mediums

    For this question, assume that the index of refraction of diamond is 2.39, that of glass is 1.65, that of water is 1.30, and that of air is extremely close to 1. A thin lens made of glass has a focal length in air of 16.1 cm. A lens of exactly the same shape is then made from diamond...
  19. D

    Find Largest Focal Length Lens for Photo of Poster - 2.79mm

    Homework Statement You take a picture of a poster on the wall of a room and maximum distance you can get from the picture is 3.1 m. The poster is 0.8 m wide and 1.2 m tall and you want it to fit in the 24 x 36 mm frame of the film in your camera. What is the largest focal length lens that...
  20. B

    Finding Minimum Separation of Object and Image in a Converging Lens

    Homework Statement A converging lens of focal length f forms a real image of an object. Show that the smallest separation of the object and the image is 4f. Homework Equations I think: \frac{n_1}{s_0} + \frac{n_2}{s_1} = \frac{n_2 - n_1}{R} small angle approximations. The Attempt at...
  21. J

    What is the correct term for the bright point on the retina in imaging?

    Here is a typical photo of imaging in the eye. The bright point on the retina is called out, in a book on the biology of vision, as the focal point. I am pretty sure the book is wrong, and that this is NOT the rear focal point. The rear focal point would be somewhere closer to the back surface...
  22. S

    Object Distance From Converging Lens for 1% Focal Length Difference

    How far away from a converging lens must an object be ( in terms of focal length, f ) so that the difference between the image distance and the focal lengh is 1% of the focal length? I tried to translate the words into an equation based on the thin lens equation but i don't know if it is...
  23. Amith2006

    Focal length of plano convex lens

    # Diameter of a Plano-convex lens is 6 cm and the thickness at the center is 3 mm. If the speed of light in the material of the lens is 2 x 10^8 m/sec, what is the focal length of the lens? I solved it in the following way: Let R be the radius of curvature of the convex surface. Given that AB...
  24. Amith2006

    Focal length of concave lens using convex lens

    # A convex lens of focal length 10 cm forms a real image of an object placed at a distance of 20 cm from it. Midway between the convex lens and the position of the image a thin concave lens is introduced. The image formed now is at a distance of 5 cm away from the earlier position. What is the...
  25. L

    Solving a Focal Length Puzzle: Find the Image Location and Size

    A converging lens has a focal length of 25cm. A 1.00cm tall object is placed 15.0cm in front of the lens. Find the image location and size, and describe it. Draw a ray diagram. Ok so I get 1/p + 1/q = 1/f rearranged for q=pf/p-f which equals -37.5, so the object is 37.5cm behind the...
  26. M

    Finding Focal Length of 2 Lenses Combined

    Hello everyone, I'm confused on this issue. How can I tell if the focal length is going to be postive or negative when 2 lens are combined like the ones below: Here is the directions: You grind the lenses shown in Figure 34-49 from flat glass disks (n = 1.5) using a machine that can grind a...
  27. J

    Image distance / focal length relation

    Let O be the object, L be the lense, I be the image, and S be a screen for projecting an image. The lens can be placed anywhere between O and S. Let f be the focal length of the lense. Prove that for an image to be clearly formed on screen S, OS > 4f must be true. A figure of a "too...
  28. 1

    Power and focal length of human eye

    I am extremely stuck on this question and do not know how to go about it. Could somebody help me? 1. (a) If the human eyeball is 4cm from lens to retina, what is the range of the power and focal length of the eye lens when focussing an object an infinite distance away and one at the normal...
  29. A

    How Does Focal Length Affect the Focus Point of a Lens?

    Hi .I am reall y confused about the focal length of lens.i understand that it is the length from the lens to the point where parallel beams coming from infinity after passing through the lens cross one each other.My question ,knowing thew focal length wher exactly does it help?does it have any...
  30. Z

    Stargazing 14mm reflector with a 900mm focal length

    Here is a shot of the transit of venus as seen from Swansea, South Wales i used a 114mm reflector wiht a 900mm focal length with a Mylar solar filter. A universal t-mount fitter with a 20mm eye piece. mounted on the t mount was a Canon EOS 50E loaded with Fuji Superia XTRA ISO 200 film...
  31. S

    Finding Focal Lengths of Microscope Lenses

    Can someone tell me what sort of equation I would use for this question, I can't use the magnification as I have two unknowns. At least I don't know how to apply the magnification equation to this question. A microscope is made in a tube 25.0cm long. It magnifies 5.00 x 10 to the 2 times...
  32. B

    Lenses: If given object height and focal length, is it possible to calculate

    the image's height? If so, how? I have the formulas, but see no way of making a substitution. If you wanted to know the problem, it states: The focal length of a camera is 35 mm and the radius of the moon is 1.74 x 106 m. Calculate the diameter of the moon's image that appears on the...
  33. S

    Experimenting with a Diverging Lens: Discovering the Focal Point

    Hey all, I recently did an experiment using a diverging or convex lens, to produce different images according to the focal point. For the experiment I found the focal length, and set up the lens and light source at that distance. I used just paper for a screen to produce the real images created...
  34. A

    Object at focal point of converging lense

    I have a simple question that I can't seem to answer... why is it that when an object is at the focal point of a converging lense, the image is at infinity? How can you show this through ray diagrams?
  35. K

    What Determines the Focal Length of an Einzel Lens in TOF Mass Spectrometry?

    Hi, Im working on a project in designing a (TOF) mass spectrometer and want to include an einzel lens in order to help focus the ion beam onto the detector. I know the basics behind the operation of the lens, but am struggling to find any equations for the focal length of an einzel lens...
  36. N

    Understanding Elliptical Formulas: Focal Point Discrepancy Explained

    Confused as why these two formulas do not match up. Or do they? http://www.geocities.com/thesciencefiles/ellipse/facts.html c^2=a^2-b^2 This does not seem to match up with the fact that the focal point should be 1/2 the distance of the radius of curvature. If you make a = b in the...
  37. C

    Image Location for a Double Concave Mirror (-20 in Focal Length)

    if a double concave mirror with a focal length f = -20 inches is used , where does the image seem to be located , if the image is 30 feet away from the lens first i converted the 30ft to inches and got 360inches used formula 1/p + 1/q = 1/f .0028 + 1/q = -.05 1/q = -.053 q = -18.9...
  38. M

    How Do You Calculate Focal Length in a Lens Lab Experiment?

    In my physics lab, we have been assigned to find the focal length of a lense that was given to us. The professor says it can be found by using this formula: Object distance over 1 plus 1 over the Image Distance will equal one over the Focal Length. So, we put a piece of white paper at ground...
  39. M

    Calculating Focal Length Given L & U: Uncertainties Explained

    I am trying to find F, i have L = 60cm and U = 31cm, how would i calculate f (focal length)? and also how would i find the uncertainties? thank you very much
  40. X

    Help with A-level physics coursework. focal lengths of lenses

    hi! im in a bit of a panic at the moment i have 2 days to complete my physics coursework on focal lengths. the title is: "you are given two convergin lenses of different lengths. you are to devise an experiment:- -to measure the focal length of each lense -to measure the focal...
  41. A

    Formulas and reasoning behind finding focal length

    hey can someone give me the formulas and resoning behind finding focal length, magnitude of radius curvature, and other optic stuff. Thank you.
  42. J

    Compute the focal length in air of a thin biconvex lens

    Compute the focal length in air of a thin biconvex lens (n=1.5) having radii of 20 and 40 cm. Locate and describe the image of an object 40cm from the lens. my answer: 1/f = (n-1)(1/R1-1/R2) 1/f = (1.5-1)(1/20-1/40) 1/f = .5(.025) f = 1/.0125 = 80cm (convering lens because f is...
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