Question

You have two lenses with focal lengths of f1=+150 mm and f2=+75 mm. Use these lenses to design a compound microscope.

1. Use the 75 mm lens as the objective to produce an intermediate image with a magnification of –3. At what position with respect to the lens should the object (specimen) be placed?

2. The 150 mm lens will be the eyepiece. What is the magnification of the eyepiece?

3. Where should the eyepiece be placed with respect to the intermediate image?

4. What is the tube length, LL, of your microscope?

5. Calculate the magnification of the microscope.

6. Draw a ray diagram of the microscope to scale using the principal rays through the eyepiece and the objective.

Answer 1

Basic theory is below, anything with suffix e is it belongs to eyepiece example U​​​​​​e it means object distance from eyepiece where U means object distance. Similarly suffix o means it is related to objective, example V​​​​​​0​​​​​ , it means image distance from objective. V means image distance. All measurements we will do from the centre (pole) of the lens.

We are considering here D as 25 cm.

Now solutions of the question: taking equations from above theory.

Last part of the question ray diagram is same as the Ist ray diagram we did in the theory part. All values u can put accordingly.

You might get little confused there are two formulates of final magnification.

1. Near point other M​​​​​​infinity , here we have used near distinct point as final image is at 250mm. Would have been the final image at infinity we will choose the other formulae. Though total magnification in this question was not asked, it deals only with individual magnification.