Beginner Why is 50mm so important?

Blank_Canvas said:
I've made my point. Just out of interest if you wanted to record a scene with a normal perspective as possible (in 35mm context) what focal length would you use ?
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Focal length is not a consideration in choosing 'normal' perspective, as focal length does not affect perspective.

But to answer your question - if perspective were to be my primary element of the shot, i would choose where to stand to get the desired perspective.
I would then use a focal length that gives the framing i wished.
 
Rapscallion said:
Focal length is not a consideration in choosing 'normal' perspective, as focal length does not affect perspective.
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Scientifically, no. Perceptually, yes. Photographs taken with longer lenses appear to have compressed perspective. The images they make look 'flattened' and therefore not normal. The reverse applies to wider lenses.
 
Ed Sutton said:
Scientifically, no. Perceptually, yes. Photographs taken with longer lenses appear to have compressed perspective. The images they make look 'flattened' and therefore not normal. The reverse applies to wider lenses.
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This is lost on some people or they have failed to grasp how important this is when recording a crime scene, how choosing the wrong focal length can change the 'perspective / viewpoint' of the recorded scene. Failure to record, distort or add artistic licence, subjective framing has no place in forensic photography, it is unlike any other photographic discipline and I include medical photography in that genre.
 
Ed Sutton said:
Scientifically, no. Perceptually, yes. Photographs taken with longer lenses appear to have compressed perspective. The images they make look 'flattened' and therefore not normal. The reverse applies to wider lenses.
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Perhaps you can take 2 pictures to show me this whilst stood in the same place? Because i havent seen this in my own photos.
 
If we'd only stop using the word "perspective" this debate might get somewhere - it's the wrong word and too much discussion seems to be dancing around it's definition. Which creates a circular ar$e-kicking contest when it doesn't fully relate to the original question.

How we see the world is perception, not perspective. Perspective is a very small part of this. A "normal" lens produces an image that very closey approximates how a human perceives the world.
 
This is universally documented even in some really basic photographic books and on photographic websites.
 
Rapscallion said:
Perhaps you can take 2 pictures to show me this whilst stood in the same place? Because i havent seen this in my own photos.
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Then you probably don't understand what I'm saying. It's not about shooting from the same place.

Telephoto compresses space:

DL2_8037.jpg


To achieve similar framing with a wide angle involves moving closer, which alters perspective AND opens out the space:

DL2_8038.jpg


If the top picture doesn't look 'flatter' than the bottom one to you, then you're weird. :D
 
Alastair said:
If we'd only stop using the word "perspective" this debate might get somewhere - it's the wrong word and too much discussion seems to be dancing around it's definition. Which creates a circular ar$e-kicking contest when it doesn't fully relate to the original question.

How we see the world is perception, not perspective. Perspective is a very small part of this. A "normal" lens produces an image that very closey approximates how a human perceives the world.
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The brain perceives things. However perception is the correct terminology to use when discussing focal lengths as the the angle of view will change, for example the shorter the focal length the wider the field of view, the longer the focal length the narrow the field of view. It is the change in these focal lengths that affects the actual (not perceived) perspective. Hopefully that makes sense.
 
Ed Sutton said:
Then you probably don't understand what I'm saying. It's not about shooting from the same place.

Telephoto compresses space:

DL2_8037.jpg


To achieve similar framing with a wide angle involves moving closer, which alters perspective AND opens out the space:

DL2_8038.jpg


If the top picture doesn't look 'flatter' than the bottom one to you, then you're weird. :D
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But what you have shown is exactly what i have been saying, it is the movement that changes the perspective, not the lens!


EDIT
please post the same shot, using different focal lengths while stood in the same location.That way we are discounting any other factors apart from the focal length.
 
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Blank_Canvas said:
The brain perceives things. However perception is the correct terminology to use when discussing focal lengths as the the angle of view will change, for example the shorter the focal length the wider the field of view, the longer the focal length the narrow the field of view. It is the change in these focal lengths that affects the actual (not perceived) perspective. Hopefully that makes sense.
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No, it doesn't. The only thing that affects perspective, perceived or otherwise, is distance. Not focal length.

The two are closely linked however, because for example, we tend to use longer lenses from greater distance. But it is the changed distance that alters perspective, not the lens - as per the football pitch shots above.
 
Blank_Canvas said:
This is universally documented even in some really basic photographic books and on photographic websites.
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And incorrectly so!

Apologies if i come across as a contrarian, but i believe that this idea should not be perpetuated as it is plain wrong!
 
HoppyUK said:
No, it doesn't. The only thing that affects perspective, perceived or otherwise, is distance. Not focal length.

The two are closely linked however, because for example, we tend to use longer lenses from greater distance. But it is the changed distance that alters perspective, not the lens - as per the football pitch shots above.
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Not so. It's a combination of both distance and focal length. The two are intrinsically linked.
 
Blank_Canvas said:
Not so. It's a combination of both distance and focal length. The two are intrinsically linked.
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OK, perhaps we can try to extricate these two.

Experiment one
Take two pictures from different locations using the same focal length.

Experiment two
Take two pictures from the same location with different focal lengths.

The results will show that the perspective will have changed in experiment one, but not in experiment two. The only deduction from this is that moving changes perspective and not focal length.
 
Blank_Canvas said:
Not so. It's a combination of both distance and focal length. The two are intrinsically linked.
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They are two halves of the same coin certainly, but they're not locked together with a 50mm focal length for perspective to look natural.

For example, a head and shoulders portrait looks best with a longer lens, in the 85-135mm range on full-frame. It doesn't look right with a 50mm, because you'd have to shoot at something like 18in distance and that's closer than we normally view other people. Hence, perspective appears exaggerated in an unflattering way, and it's actually invading their personal space making expressions look a bit uncomfortable.
 
Blank_Canvas said:
Not so. It's a combination of both distance and focal length. The two are intrinsically linked.
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Ok, I typically teach that perspective is caused only by working distance. And this is true in that, for any given working distance the perspective will be the same with any lens (discounting lens distortion).

However, if you change the distance and simultaneously change the focal length to keep the framing of the subject the same, then you significantly affect perspective AND "compression." This is because the change in distance negates the change in magnification *at the subject distance.* But the change in distance does not negate the change in magnification at all other distances.

Example:
You use a 50mm lens for a subject at 10ft with a BG at 20ft.
You then switch to a 100mm lens which is 2x the magnification. And you move back an additional 10ft to 20ft from the subject so that the subject is 1/2 the size perceptual/same size recorded. But you have NOT doubled the distance to the BG, you have only increased the distance by 50% (now 30ft to BG). So you get 50% more magnification of the BG than in the previous (50mm) situation.
But now, in this new situation, if you change focal lengths without changing the distance the relative sizes/magnifications of the subject/BG will stay the same and the perspective will remain the same.

Simply put, a change in distance changes the perspective. A change in focal length combined with a change in distance changes the magnification ratio *along with the perspective.*
 
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Rapscallion said:
OK, perhaps we can try to extricate these two.

Experiment one
Take two pictures from different locations using the same focal length.

Experiment two
Take two pictures from the same location with different focal lengths.

The results will show that the perspective will have changed in experiment one, but not in experiment two. The only deduction from this is that moving changes perspective and not focal length.
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Number 1 is a given ( Linear perspective)

Number 2 is what I was referring to when I said it's well documented in books etc and on the web.

If you stood in the same place with a camera on a tripod and took three exposures with differing lenses of a hair pin bend on the road from a distance of 150 meters The 18mm, would give an impression that the same bend was further away than an image taken with 50mm. The same image taken with a 200mm lens would convey the impression that the bend is closer than it was. This is lens perception. The 50mm is used to record the field of view or perspective of the human eye. Or as close to as possible to it.
 
Blank_Canvas said:
Number 1 is a given ( Linear perspective)

Number 2 is what I was referring to when I said it's well documented in books etc and on the web.

If you stood in the same place with a camera on a tripod and took three exposures with differing lenses of a hair pin bend on the road from a distance of 150 meters The 18mm, would give an impression that the same bend was further away than an image taken with 50mm. The same image taken with a 200mm lens would convey the impression that the bend is closer than it was. This is lens perception. The 50mm is used to record the field of view or perspective of the human eye. Or as close to as possible to it.
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But the perception of depth compression with the longer focal length is an optical illusion. The only difference between the three images is that the 50mm and 200mm are succesively closer crops of the 18mm image - with exactly the same perspective.

Blank_Canvas said:
The brain perceives things. However perception is the correct terminology to use when discussing focal lengths as the the angle of view will change, for example the shorter the focal length the wider the field of view, the longer the focal length the narrow the field of view. It is the change in these focal lengths that affects the actual (not perceived) perspective. Hopefully that makes sense.
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Again, getting perception and perspective muddled. And field of view and perspective are different things again.

(BTW, I agree with what I think is your intended point - 50mm is the closest to human perception. It's just that when you start arguing perspective it's all going a bit pear-shaped)
 
Just to butt in, I'm finding this extremely interesting, purely from an academic point of view (from all parties).
I might try some experiments of my own, to accompany the , 50mm => 82mm equivalent or just crop factor argument which also about perception, perspective, distance to subject and focal length.
I'll just sit here with my proverbial pint and continue to ear-wig/learn!
 
It's clear in my mind. Irrespective of the lens used. The three dimensional image recorded in two dimensions. The final image when produced will display a 'perspective' a view, vista, impression or aspect by definition.
 
Rapscallion said:
But what you have shown is exactly what i have been saying, it is the movement that changes the perspective, not the lens!


EDIT
please post the same shot, using different focal lengths while stood in the same location.That way we are discounting any other factors apart from the focal length.
Click to expand...
I said moving alters perspective (that's a given), but was trying to show how longer lenses flatten apparent space - as per the first photograph.

Go stand in the middle of a railway line and take wide and tight shots. The angle between the lines won't change (perspective), but the sleepers will appear closer together in the tighter frame (apparently compressed space). That may not be an altered 'perspective', but it is an alteration of the perception of perspective in a colloquial sense.
 
Blank_Canvas said:
Number 1 is a given ( Linear perspective)

Number 2 is what I was referring to when I said it's well documented in books etc and on the web.

If you stood in the same place with a camera on a tripod and took three exposures with differing lenses of a hair pin bend on the road from a distance of 150 meters The 18mm, would give an impression that the same bend was further away than an image taken with 50mm. The same image taken with a 200mm lens would convey the impression that the bend is closer than it was. This is lens perception. The 50mm is used to record the field of view or perspective of the human eye. Or as close to as possible to it.
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This is 3 different images, taken with three different lenses from the same distance, and the wider FOV images cropped to match. The perspective is the same in all of them.

3.jpg


Original images and more in the article here: http://photographic-academy.com/creating-a-picture/85-creating-a-picture/133-more-on-lens-selection
 
Hi Steven - thanks for posting the pictures, saved me going out myself.
 
sk66 said:
This is 3 different images, taken with three different lenses from the same distance, and the wider FOV images cropped to match. The perspective is the same in all of them.

3.jpg


Original images and more in the article here: http://photographic-academy.com/creating-a-picture/85-creating-a-picture/133-more-on-lens-selection
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Yes you can do this, I know that it can be done that and have even done this myself. However, you failed to grasp my point and given an example completely out of context to what I was articulating.

You don't crop or alter the image in crime scene photography, you don't change the perspective or alter the image in anyway. To do do is misleading - you could mislead the courts and jury. You use a correctly exposed and unedited original file. Two are produced and a working copy is viewed. This and the original as a master are both exhibited.

I used the bend in the road as an example it could be closer or further away depending on the viewpoint, distance and focal length - discussed at length.

That's why you photograph the scene with a 50mm lens as it's near as damn it to the human eye(s) it's an accurate perspective as if can be and this is widely accepted evidence in courts as being accurate. This is important when someone's liberty is at stake. Forensic photography / evidence is not just to prove that someones is guilty but also to disprove their involvement in the offence. Mess around with the view of the road, the perspective and this places a totally different interpretation on recorded events which could lead to a miscarriage of justice.

This thread has gone way off focus. The original question was why is the 50mm lens important ( or similar ). I offered up one reason - because it"s use conveys an accurate perspective to the court when used properly. Not a perceived view !

In the literal sense and by definition the photograph that is produced is a 'view' or 'perspective' that accurately reflects the scene from the camera / 50mm lens as recoded.

There are many factors to consider in forensic photography this is just one very small tiny aspect. I don't have the time to go Into this in any detail and will detract from the original question by the OP.
 
I said that about 30 posts ago :LOL:

the other reason that lots of people who've been shooting since the days of filum have them is that prior to the advent of a decent zoom , the 50mm f1.8 was the standard kit lens on most SLRs
 
Blank_Canvas said:
Yes you can do this, I know that it can be done that and have even done this myself. However, you failed to grasp my point and given an example completely out of context to what I was articulating.
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So what you actually meant was the recorded FOV and not the perspective/compression...
I agree with that.
sk66 said:
"Normal" comes down to the camera recording an ~45* FOV on the sensor.
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justinminns said:
The reason everybody gets a 50mm is because they are a cheap fast prime not because of the focal length
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"Cheap and fast" are the only reasons to get one IMO... but there is a lot of talk about "normal," perspective, and "compression." And a lot of nonsense about "zoom with your feet."
 
you can zoom with your feet , its simple









but the need to take your shoes and socks off and lie on your back does limit the practical utility :LOL:
 
big soft moose said:
you can zoom with your feet , its simple
but the need to take your shoes and socks off and lie on your back does limit the practical utility :LOL:
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Damn, I almost missed the second line! LOL!
You must be a bit more flexible than I am... I find framing the shot quite problematic.
 
Great debate guys
I enjoyed reading through the thread

My take is that the 50mm is cheap and fast :sneaky:
 
sk66 said:
So what you actually meant was the recorded FOV and not the perspective/compression...
I agree with that.
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No not quite.......

I'm still right, I know what I meant !

When I produce a photograph taken with a 50mm lens the below definition is correct. It is defined in the English dictionary:-

..... as representing three-dimensional objects on a two-dimensional surface so as to give the right impression of their height, width, depth, and position in relation to each other.

You are not wrong to suggest field of view. However, 'View' is a synonym of 'perspective' which is also the correct usage of the word in this context.
 
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Blank_Canvas said:
..........When I produce a photograph taken with a 50mm lens the below definition is correct. It is defined in the English dictionary:-

..... as representing three-dimensional objects on a two-dimensional surface so as to give the right impression of their height, width, depth, and position in relation to each other.
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Hi Nick - it is the bold part that i am struggling to see. As is shown in the photos above, focal length doesn't have any effect on the relative size and position.

Another way of looking at this. Create a wooden frame in the proportions 3:2. By holding this at different distances from your eye it will mimic the field of view of a given focal length. At any distance you choose to hold it, the view you see through the frame will look natural, you are never at any point changing the perspective of what you see by moving the wooden frame closer or further away.
 
As I showed, focal length alone does not change the representation "of their height, width, depth, and position in relation to each other."

It really does come down to recording a FOV and then presenting/viewing it so that it occupies the same FOV. In TV videography a "normal lens" is ~ 2x the FL of what it would be for still photography because the viewing distance is typically ~2x as far.
IMHO, the whole thing is somewhat arbitrary because it's about recording and presenting a scene so that it "feels normal" to the viewer... and there's absolutely no "standard" for that. Anything from ~40-60mm is accepted as "normal" for FF 35mm.
 
Blank_Canvas said:
I'm still right, I know what I meant !
You are not wrong to suggest field of view. However, 'View' is a synonym of 'perspective' which is also the correct usage of the word in this context.
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Blank_Canvas said:
I'm not going to go down the route of playing semantics - I'm out.
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Ok...
And if we take FOV/view and perspective as being synonymous in this context, then I agree that what you intended to convey and what "you meant" are correct... I "get it." I just don't think you're communicating it particularly well.
 
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