Normal perspective with 18-135mm Nikon lens

[varun_r]

I am a beginner photographer and I have been trying to experiment with my D-80

camera and the 18-135mm kit lens. It looks to me that normal perspective is

achieved only when the focal length is set to 50mm on the marker on the lens

body rather than at 28 or 35mm, which would be expected for the DSLR format of

Nikon. I am wondering if I am missing something here or is this normal??

[tonybeach]

"Normal" means your field of view (FOV) is similar looking through the viewfinder to how it appears when you are not looking through the viewfinder. In fact, your absolute FOV is wider than normal but your eye cannot simultaneously focus on details at the periphery and mostly just detect motion outside of about 50 degrees as measured diagonally. It is a useful reference because narrower than normal FOVs make you appear closer to your subject and create flatter perspective while wider than normal FOVs create unnatural depth because they distort normal human perspective.

[ronald_moravec1]

If you consider a 50mm lens normal on film, 34mm is about the same with a digi sensor Nikon like a d80/40/50/200.

 

A normal les is by definition equal to the diagonal of the format, 24x36 film is about 42 mm. 28 will give you the same angle of view on the Nikon digi.

 

Perspective is the relationship in size between near and far objects and has nothing to do with the lens focal length or angle of view, only the camera distance to the subjects.

[vivek iyer]

<i>It looks to me that normal perspective is achieved only when the focal length is set to 50mm on the marker on the lens body rather than at 28 or 35mm, which would be expected for the DSLR format of Nikon. I am wondering if I am missing something here or is this normal??</i>

<p>

The text book definitions of 'normal' are posted above. As regards to your view and the actual question:

<br>

it has to do with the distortions (barrel, etc) projected by the zoom at 28 or 35mm which probably goes unnoticeable around 50mm.

<p>

This should not be 'normal' (or the case). If you don't like this very badly then you need to look for some higher priced zooms like the 17-55 f/2.8 or better yet a prime lens of 28mm or 35mm focal length.

[tonybeach]

"Perspective is the relationship in size between near and far objects and has nothing to do with the lens focal length or angle of view, only the camera distance to the subjects."

 

It is almost impossible to separate perspective from FOV. If the FOV exceeds normal human perception, then there are elements of the scene that will appear unnaturally closer and farther away than we would perceive them if we weren't viewing them through an unnaturally short focal length relative to the format.

[ronald_moravec1]

No Anthony. Crop a 50mm shot enough and it will overlay a 200mm shot perfectly. There is no change in the size relationship between near and far objects from THE SAME POSITION.

 

By moving closer, you can make a near object grow compared to a far.

Just hold your hand out and then move it closer.

[tonybeach]

"Crop a 50mm shot enough and it will overlay a 200mm shot perfectly."

 

If you take two elements of a scene in isolation then this is indisputable. However, my point is precisely that when you don't crop the 50mm shot then different elements of the shot that were cropped will often be closer and those closer items will have a different depth relationship to the viewer. The phenomenon is mostly subtle from normal to telephoto, but becomes increasingly pronounced at wider focal lengths when the various elements and overall FOV no longer resemble what we see without looking through a camera's lens.

[dave_lee6]

I find that when shooting with my F3 and my Nikon 35-70mm f3.5 zoom, that when focused to 70mm the image in the viewfinder is the same as that in the scene before my eyes. More than 50mm, I find 70mm to be "normal" to me.

 

The DX crop makes it difficut to shoot at 50mm in some situations. People get "crop" mixed up with perspective, which are two different things. The DX format is merely a crop, a 50mm lens will still shoot normal perspective (distance from near to far).

[bjørn rørslett]

One should not overlook the effect of finder magnification. With a finder magnification of 0.7x, you need 70mm on the lens to give the impression of a 50mm. Then, the view through the finder will correspond to that of the naked eye in terms of the apparent size of details.

 

Perspective, as stated by several others, depends entirely on the position of the lens/camera in relation to the subject. Field of view and focal length do not influence perspective as such, but these factors are easily confused, since a wide angle lens (of short focal length, thus making details smaller) tends to be used at closer range than a longer lens. The change in relativer position does influence perspective. Convergence of lines is easier to see with a wide angle lens so is mixed up with perspective or "wide-angle distortion", but the fact is that you can get converging lines with any lens.

[vivek iyer]

Bjorn nailed it. It is finder magnification!

[leonard_evens]

Strictly speaking, the word 'perspective' refers to the position of the lens (idealized to a point) with respect to the subject. This determines how three dimensional elements of the scene line up, converge, etc. In this sense, perspective is independent of focal length.

 

But you are talking about something else. If you make a print from your image, you would normally view that print from a certain distance. Suppose you make an 8 x 10 print and view it from about 10-12 inches. Your eye will be placed at a certain position relative to the print. Will it look to you like what you saw when you looked at the scene. In principle, it will come close if the focal length equals the diagonal of the frame. The D80-frame is approximately 16 x 24 mm, and its diameter is about 28 mm. So if you set the focal length to that, the 8 x 10 print will appear similar to what you saw in the scene.

 

What happens if you use a different focal length. You could correct by adjusting the position of your eye when looking at the print, but most likely, you will stay at that same distance, about 10-12 inches. In that case, if your focal length is considerably longer than 28 mm, your eye will be too close to the print, and distances will appear compressed. If the focal length is significantly shorter than 28 mm, your eye will be too far from the print, and the print will look different, objects will appear too small, and spherical objects on the sides of the print will appear ellipsoidal.

 

What if you make a different size print. If it is larger than 8 x 10, most people will get further back from the print and set their eyes at about the diagonal of the print. So the above considerations will still apply. If the print is smaller than 8x 10, most people will still view it from about 8 x 10 inches, so theoretically distortions could appear. However, with small prints, it is probably true that other considerations take over.

 

Of course, all of this depends on certain assumptions about what the people viewing the print expect. That can be changed by individual preferences which might be modified by what sorts of prints they are used to looking at. Many people are used to looking at prints made using a 35 mm camera with focal length about 50 mm. This is actually a trifle long compared to the diagonal of the frame. Having seen so many prints before, such people would prefer a focal length a trifle longer than 28 mm, in this case about 33 mm.

 

Of course, the nature of the scene may affect what people see more than the simple question of the eye's position relative to the print. The eye/brain visual system tends to make corrections based on the subject. For example, when you look at a person's face, you don't see what a camera at the same position would see. If the face is about a meter away, the camera would see the nose as exaggerated in size relative to other features, but your brain sees the face looking normal. It is generally recommended that you place the subject at least two meters from the lens and use a longer focal length lens when doing portraiture. Other kinds of scenes may look more natural when shot with other focal lengths.