# OPEN SOLUTION PROBLEMS IN THE FIELD OF OPTICAL INSTRUMENTS

This paper develops problems with generic statements for resolution by the students of the instrumental optics subject in the optics and optometry degree. Such problems are different from the typical problems because they are a generic problem, without any particular fact or event, so that students develop a theory that covers all possible cases related with the problem. Then the students will be asked to summarize the difficulties that have been found to solve it.

The motivation for this type of problem is that students begin to develop problems with real open solution. To do this, they have to do a good approach to the problem with precision and to say what are the beginning premises to solve the problem. They should then make assumptions for solving the problem that covers all possible cases. They have to look for information about the subject, develop strategies for the resolution and, finally, check that the results are consistent with the assumptions made.

In the course of Instrumental Optics, students essentially have to distinguish between objective and subjective optical instruments studying geometric and photometric characteristics of some of the most representative instruments, for example, camera, projection systems (objective instruments) and the magnifying glass, oculars and microscope (subjective instruments).

For example, to understand the functioning of the camera and projection systems in optical terms, the professors propose problems as follows to the students:

"You want to take a picture to an object. Describe under what conditions should be done it to get a good picture (assuming you want to take the picture by day or night). Once the photographs are taken, you want to make a presentation with all of them, what type of projection system you use and why? "

Among the parameters that describe the conditions to make a good photograph, the student has to take into account the distance that the object is photographed. They have also decided what type of lens must be put in the camera and the focal of this lens. Moreover, they must decide the diaphragm number and the exposure time. Also they have taken into account if the chosen parameters are the most suitable for photographing the entire object (they have to calculate the field that can be seen) and also to decide the sensitivity of the film. And this study has to be done in the case to take the photograph by day or night (depending of the light of the object these parameters will change when the picture they take it).

With respect to the projection system, they have to decide what is the place where they want to do the presentation, that is to say, the projection distance from the projector to the screen; and also they have to decide what kind of elements will be used to mount the projector, so that the projected image has the size you want and also decide the light source so that the image is properly illuminated.

Once students have solved problems of this kind, we have asked to give their points of view and comments the difficulties they have had to resolve the problems, and also to compare this kind of problems with the closed solution problems. What do you think about this kind of problems? What kind of problems you have been more difficult to solve? With which of the two types of problems you may think you learn best? These are some of the questions they ask students to answer.