# Object Distance for Mirrors versus Lenses

1. Apr 29, 2015

### C. Long

We are finishing up light and I'm a little confused on when the object distance would be negative when we are talking about mirrors and not lenses. The definition we were given is that the object distance is negative if the incoming light is on the opposite side of the mirror then the object is. I don't understand how\if that would make any images of the object, wouldn't the mirror be in the way of the incident light?

Thanks for any clarification.

2. Apr 29, 2015

### sophiecentaur

I googled sign convention lens mirror and, amongst a lot of hits, http://www.physics.gla.ac.uk/~johannes/optics_lecture/overheads06_1_3_7-1_4_3.pdf [Broken]. Any use?

Last edited by a moderator: May 7, 2017
3. Apr 29, 2015

### C. Long

Thanks. It still looks like there wouldn't be any way the light could create an image if they are on opposite sides of a mirror.

4. Apr 29, 2015

### sophiecentaur

I haven't read the actual passage that you are quoting from. Are you sure it isn't talking of the image being behind the mirror? IS it just a translation problem?

5. Apr 29, 2015

### C. Long

I can understand how the image distance can be positive or negative, I just don't see any instance when the object distance would be considered negative and you still get any kind of image. If the physical object is on one side of the mirror and the incident rays are coming from the other, then that tells me there would be no image formed real or virtual.