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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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Viewfinders flip the image for you, on SLRs that little pyramid looking block on top of the camera is a pentaprism (5 sided prism) that does the optical magic and on electronic cameras it's just wired that way. On old TLR and view cameras the image is, indeed, upside down and flipped on the "screen." Someone else will have to handle the optical diagrams for you =) –  Patrick Hughes Mar 20 '12 at 1:27
    
I don't know much about optics (Maybe you could ask this question on the physics SE or something), but The concept is similar to when you hold a magnifying glass at arm's length and look through it. –  J. Walker Mar 20 '12 at 1:42
2  
Far away objects and near objects will have the same orientation with the same lens. Otherwise, pictures with both near and far objects would look very strange! –  mattdm Mar 20 '12 at 3:46
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On the edit: they don't. Can you post a picture illustrating what you are seeing? –  mattdm Mar 20 '12 at 12:23
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Regarding Edit 4: When you look through your camera's viewfinder, you're not looking directly through the lens. Besides the inverting prism and viewfinder optics, you're looking at a focusing screen or ground glass that shows the image formed by the lens. It's at the same distance from the lens as the film or sensor. Anything close enough to form a virtual image is not focused onto the focusing screen, so you don't see it as magnified image in the viewfinder. You don't have the clear path to the lens that you do when you remove the lens from the camera and hold it up to your eye. –  coneslayer Mar 20 '12 at 22:12

3 Answers 3

"Anti-focusing" of objects closer than 1 focal length to lens:

  • This addresses one of the questions which arose during your "Edits" but is not implied in your subject line.

The Question: This is a precis of your question - all text is yours.

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

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

  • "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.


What you are describing is exactly what happens, but because the defocusing of objects closer than a focal length from the lens is progressive as distance inside the focal point increases - just as your diagram suggests - they do not just "vanish" as they come inside the critical distance - rather they become progressively more indistinct the closer they get to the lens face.

The pictures below show reasonably extreme examples of this 'feature' being used to good effect to nearly completely remove closeground items from the photo - in this case vertical bars and a reasonably heavy mesh are nicely "vanished by being defocused and spread so widely as not to be noticed.


Foreground objects (in this case a heavy mesh and cage bars) which are closer to the lens than its focal length are "anti-focused" to the point of near invisibility.

Your diagram 3 with cage bars added:

enter image description here

This is one of my standard "tricks" for photographing objects in cages and similar environments where there is an incomplete obscuring layer that you can get right up against. An extremely useful "trick".

In this photo there are cage bars very close to the front element of the lens - as close as I could get them. I use this method to sucessfully "drop out" even quite solid bars. In this case it's normal thickness cage bars. Distance to front element is under 50mm and it's a 50 mm f1.8 lens. There ARE some optical effects present but they are not normally noticed by most viewers. Higher res version of this is here and click download icon 2nd from right at top of photo. This gives a much better look at what you CAN'T see.

CAGE BARS BETWEEN BIRD & VIEWER

enter image description here

This is an even better example, in that there is a small pitch very thick square mesh between the camera and the subject (I think not more than 20mm squares - I can check other photos). This was using an 18-250 lens at 18mm, f6.3 * See photos showing mesh that was present in 2nd photo below. Visually the mesh ruins the bird's presentation and the camera "sees" the bird far better than the eye can.
Same photo on facebook here

VERY THICK & UGLY SQUARE MESH BETWEEN BIRD & VIEWER

enter image description here

enter image description here


(*) I originally said that this was taken with a 50mm f1.8 lens but after checking the original I have changed the details, as above.

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It is "easy enough" to explain the basic question with a ray diagram or similar means - see below
BUT it is important to realise that the answer to why viewfinder or human eye images are not inverted are "by design" or "because" (choose one, both the same essentially) - ie the system requires the outcome to be a certain way so whatever steps are required to implement it are provided.

In the case of a viewfinder, extra lenses, mirrors or prisms (or a combination of these) are added as required to achieve the final result. The real question becomes not "why is this this way up" but, how is this done.

In the case of the human eye, the image on the Retina IS inverted and the brain looks after getting it "right way up" as far as the viewer is concerned.

The information below from this excellent site with much on this and similar topics shows how basic inversion works.

enter image description here

Also see -> More on Ray Diagrams


In the case of the eye, the image is inverted:{ From here - low tech but interesting }

enter image description here

http://www.quantumtheatre.co.uk/Lights%20&%20Sounds%20notes%20Key%20Stage%202_files/image022.jpg


IMPORTANT:

Note that while the above image grabs your attention as it deonstrates inversion, it actually does a very bad job of showing bow the eye lens works - the more so as the eye lens is embedded in the Cornea and the air Cornea interaction does most of the 'lensing' while the Cornea-lens interface only manage about 10% of the total bending.

An excellent discussion of this is available here - see the In your eye and a reasonably corre t image of how light is actually veny by the eye is shown below.

enter image description here

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Can people please stop saying that the brain turns the image around! The projected image is as much "turned around" by the brain as it is by the software in a camera - there is nothing requiring that the sensor (in the eye or digitally) should be oriented the same way as the subject is... –  SoftMemes Mar 20 '12 at 20:35
    
Hmm, never thought of it that way. –  Brandon K Mar 20 '12 at 21:37
    
@Freed - if you'v tried looking in a mirror to control your world you may reconsider :-). I know what you mean BUT the need is that what is to your right physically is perceived to be your right and where eg your right hand is. For you to interact with reality consistently it helps (but is not essential) if all sensors have a consistent rule set. eg Dentists become expert at working inverted or not as the situation requires. The "brain inverts the image" is a useful shorthand for meaning that it presents the information in a manner that integrates wll with the overall sensor system. –  Russell McMahon Mar 21 '12 at 2:28
    
@Russel, it's exactly for the reasons you describe that I disagree with saying that the brain inverts the image. It gives the impression of there being extra mental effort involved in seeing because what is up in the outside world is down in the image projected on the eye. –  SoftMemes Mar 22 '12 at 22:12
    
@Freed - similar to those kids' toys with multifaceted lenses which claim to simulate insect vision. No! If insects had that perception of the world they could not function. –  mattdm Mar 24 '12 at 12:44

This link provides a good (sometime complex) answer to your question.

In short:

  • One normal lens element magnifies but is limited to a certain magnification factor
  • Complex Lens-combinations can get more magnification and may invert the picture due to the different attributes of the lenses and their use in the objective. (You might catch the beam of a lens behind its focal point and refocus it with another lens-> inverts the image)
  • A pentaprism inverts the image when it is sent to the viewfinder, so you have the final "look" of the image and can work with it.
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