# Solving the Mystery of the Broken Projector: +5.5 or +6.5?

• baileya

## Homework Statement

You have paid big bucks to see Season of the Witch at the 3-D IMAX theater in Vancouver. Just before the movie is about to begin, the theater staff tell you that the lens for the projector has just broken! You really want to see the movie and decide that it should be simple to set up a single lens system to project their 60mm film onto a 9 meter tall screen - if you just had a lens!? Fortunately you are there with your great aunt who wears REALLY thick glasses. One of her lenses has an optical power of +5.5 m-1, and the other has a power of +6.5 m-1 (optical power is 1/f). If the screen is 27-m away from the lens, can you save the day and fix the "projector" with one of these lenses?
Which lens would work best?

## Homework Equations

1/p+1/q=1/f m=hi/ho

## The Attempt at a Solution

I can draw ray diagrams, etc. and figure that all out... I just don't know how one would work better than another?

One would work better in terms of producing a better image.

what m-1 means?

what m-1 means?

so you mean to say that the +6.5 would work better?

No I'm asking what m-1 means in power? :rofl:

oh m-1 is the same as 1/focal length

you have height of image, object, image distance
you an find object distance

the use object distance, image distance to find and then find power!
the use lens having value closer to your value

so the best lens is the lens with the highest power?

so the best lens is the lens with the highest power?

The better lens makes the better picture on the screen. Bigger power doesn't necessarily mean better picture (focus) on the screen. It depends on the geometry of the lens and such.

You must work the numbers out and see which one forms an image close to where the image needs to be created (screen).

The better lens makes the better picture on the screen. Bigger power doesn't necessarily mean better picture (focus) on the screen. It depends on the geometry of the lens and such.

You must work the numbers out and see which one forms an image close to where the image needs to be created (screen).

power is related to focal length and focal length is related to image distance, then how is power is not related to making better image?
and both lenses will form image at screes at one or other point ... what will matter will the size of object!

@ baileya

i told you that the power closer the the power you'll find will be the better lens! in this case it might be the lens with more power but this is not always true!

power is related to focal length and focal length is related to image distance, then how is power is not related to making better image?
and both lenses will form image at screes at one or other point ... what will matter will the size of object!

@ baileya

i told you that the power closer the the power you'll find will be the better lens! in this case it might be the lens with more power but this is not always true!

? I didn't say power isn't related. All I said was the goal of choosing the right lens was trying to get the best picture. I was hoping to hint to him the reason to choose a certain lens over the other as opposed to just telling him. I know power is related to focal length.. The more 'power', the smaller the focal length right?
An image is in best focus at its focal length, regardless of its power.