What happens to images if objects are at focal length

[UIUCstudent]

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What happens to images if objects are at focal length for concave, convex, diverging and converging lens. Does anyone know?
I know objects can't be behind the convex mirror, but it could happen in a lens/mirror system I think.

 

[Isoprop]

Use the lensmaker's equation to figure this out. Ex) If we have a converging lens, and f = +1 m, and we put the object at +1 meters, then the image would be at infinity.

edit: what this means is that the rays would never converge and no image would be produced.

 

[UIUCstudent]

Oh that makes sense. so di=infinity
But would this image at infinity be to the left or right of lens (virtual or real?)

I'm asking this because of a question in practice exam. No. 14

http://www.screencast.com/users/trinhn812/folders/Jing/media/b0326c22-e0ad-47d2-b52e-a582cd834f53

 

[Isoprop]

Oh that makes sense. so di=infinity
But would this image at infinity be to the left or right of lens (virtual or real?)

I'm asking this because of a question in practice exam. No. 14

http://www.screencast.com/users/trinhn812/folders/Jing/media/b0326c22-e0ad-47d2-b52e-a582cd834f53

There is no image so it's neither virtual nor real.

Hmmm... As for the answer to questino 14... it should be false because the image from the lens on the left doesn't exist so it can't become the object of the lens on the right.

It's been a while since I looked at thin lenses so I'm not exactly sure.