Tuesday 21 April 2015

optics - Why are objects far away inverted through a lens but not through the viewfinder?


When I look through a lens the image of objects far away are inverted but when looking the the viewfinder on my camera they are not. Why is this?


I am having a hard time understanding why objects far away are inverted in the first place.


Could anyone provide an explanation or ray diagrams (Preferably using a point source on an object and including the lens in the human eye)?


EDIT: Thanks everyone I now understand why objects far away from a lens appear inverted. But can anyone now explain how the camera elements make far inverted objects appear right way up without also making close normal objects appear upside down?


EDIT 2: I can't provide an image right now because I am at school but you know how when you look through a magnifying glass and far objects will be inverted and blurry but close objects will be sharp and erect (normal)?


That is what is happening when I look through my camera lenses while they are not attached to the camera, but when they are attached to the camera and I look through the viewfinder (or at processed film) the objects in the image produced are all of the same orientation.


Does this mean that lens doesn't actually produce images like a magnifying glass would because the objects on the images produced on film are all of the same orientation? Or does this mean a magnifying glass doesn't actually produce objects with different orientations?? If a magnifying glass doesn't, then why does it look like it does and are the convex lens diagrams wrong (they show a virtual image upright for close objects and real upside-down images for far objects)? Isn't a magnifying glass just a convex lens?


It DOES look like a magnifying glass when I look through the lens. That's why I thought that then lens was producing objects with different orientations. This also goes with the convex lens diagrams below that show objects with different orientations.


So does the lens produce objects with different orientations or doesn't it??? If not why does it look like it does when I look through the lens, and also based on the convex lens diagrams it seems like it should. If it doesn't then how do the other lenses in a camera lens attachment correct the convex lens. And if it does then why does film and the viewfinder show objects with the same orientation?



Sorry for asking so much. This is just so confusing!


EDIT 3: This is how I thought a camera lens would work: Lenses


I forgot to mention in EDIT 2 that it seems that close objects shouldn't even appear on film based on the diagrams.


I still don't understand... =(


EDIT 4: So objects really close to the camera lens should not appear on film, correct?


So...Why do all objects in the viewfinder appear upright??? Since my eye is reviving both the light rays from close objects (virtual upright images) and far objects (real inverted images) shouldn't really close objects and objects farther away have different orientations? Just like looking through the lens directly? How does the viewfinder change anything?


EDIT 5: Thanks so much everyone. Thanks for the help.


"Anything close enough to form a virtual image is not focused onto the focusing screen"


So lets say I put a pen right in front of the lens and look through it directly. The image I see is upright so this means it is a virtual image. Now lets say I attach the lens to the camera and look through the viewfinder. I can still see the pen but it is blurry (because the focal length is longer, right?). The lens forms a virtual image of the pen but I can still see it in the viewfinder. Why is this? If the viewfinder shows me exactly what would be on the film it should not show the pen at all (based on the diagrams in the image above) should it?


EDIT 6: Maybe it should form a blurry image. Like a pin hole camera or something. In any case thanks for all the help everyone. I know it can be frustrating trying to teach me. I can be pretty dense sometimes.





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