net focal length of combination of lenses

Could someone supply the formula for the resulting focal lengths when elements of convertible lenses are combined? Procedure FOCAL LENGTH AND POWER OFCOMBINATION OF THIN LENSES FOR Board, NEET and JEE. If focal length of one of the lenses is 20 cm, then power of the other lens is (a) +6 ∙0 D (b) –3 ∙75 D Combination of Lenses I. Discussion in 'Large Format' started by keith_pitman, Jun 1, 2001. keith_pitman. If f 1 and f 2 be the focal lengths of the two lenses and F be the focal length of the combination. Diagram. Find the net focal length of a combination of lenses whose focal length are Ask for details ; Follow Report by Anyajain6435 21.03.2019 Log in to add a comment ... Focal Length of Convertible Lens Combinations. Find the combined focal length. Two thin lenses separated by some distance : If two thin lenses are held a distance d apart from each other, then focal length of the combination is given by the relation, 1/F = 1/f 1 + 1/f 2 – d/f 1 f 2 Practice Problems : 1. The focal length of combination will be (a) 1 cm (b) 20 cm (c) 100 cm (d) 100/11 cm 15. Two thin lenses are in contact and the focal length of combination is 80 cm. Both of these have the same value of the refractive index. Two converging lenses of equal focal length 'f' are placed in contact. The combined focal length for two thin lenses separated by a distance a (Figure 2) is given by the equation: $\endgroup$ – user4552 Jun 23 '19 at 15:52 It may be true as an approximation when the lenses are close compared to their focal length. A bi-convex lens of focal length = 10 cm and a bi-concave lens of focal length = 20 are kept in contact with each other. With a convex lens, the real image of a distant object is formed at a distance equal to its focal length. \mathrm{A}$ second converging lens, this one having a focal length of $60.0 \mathrm{cm},$ is located 300.0 $\mathrm{cm}$ … Photo.net Photography Forums. $\begingroup$ I don't think it's true in general that the combination of two thin lenses acts like a thin lens. The reciprocal of focal length in metre is called power of lens in dioptre (D). A focal System. While dealing with the combination of lenses or compound lenses, you may come across the following terms. Find the focal length of the combination. A 1.20 -cm-tall object is 50.0 $\mathrm{cm}$ to the left of a converging lens of focal length 40.0 $\mathrm{cm} . Combined focal length (F): =f 1 f 2 /[f 1 + f 2] F = 10x(-20)/[10-20] = +20 cm The focal length of the combination is positive and so it acts as a convex lens.