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What is a "normal"


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#1 Dan Diaconu M

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Posted 21 June 2009 - 12:16 PM

I have supported for years the following definition of the "normal" lens:
http://en.wikipedia....iki/Normal_lens

without even thinking about it or trying to check it out. It all seemed so....well... logical and in place and used to it (as is) for soooooo many years.....................
Yet, today I bothered to look trough the viewfinder and discover something doesn't add up.
If "normal" means
1"as seen by the naked eye" but at the same time
2"equal to the diagonal of the format",
well.... Huston, we have a problem!
The two do not seem to go together.
One of the two must go (imo). OMG!!!!!!!!! a landslide.

In practical terms: left eye open, right eye in the viewfinder of an SD10, I panned the camera left/right and found 70 (from a 55-200) as the focal length where the two images were seamlessly blending with each other.
In other words, I captured an image "as seen by the naked eye" with the zoom set at 70.
"As seen by the naked eye" means the same perspective and the same size ratio between the elements (buildings in this case) in the frame.
Although, the frame is much smaller (13.8X20.7 mm) than "normal" SLR (24X36mm), that section photographed looks "normal" (imo) reproduction of what I can SEE. (

I captured another image at 25mm (18-50) and compared the two. The latter looks like a wide angle to me. Two prints on the table: which one is "normal"?

Well than, where does "equal to diagonal of the format" fits in the definition than?

If I may call your attention the "double standard" definition in wiki where "normal" is twice the diagonal for motion picture lenses (accounting for viewing distance they say)
Scaling down the projection distance and screen size to a comparable "picture on the table", shouldn't the rule be the same?

I urge you to set aside any dogma and check it out and see for yourself.
What is "normal" for you? Or.... how do you define "normal" ?


Cheers,
Dan Diaconu

PS. I did the same test as above with a SLR (Nikon) 24X36mm and discovered that 55mm produced an image identical with naked eye.
Not 50, not 45 and not the theoretical 43.26.
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#2 David Mullen ASC

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Posted 21 June 2009 - 02:38 PM

PS. I did the same test as above with a SLR (Nikon) 24X36mm and discovered that 55mm produced an image identical with naked eye.
Not 50, not 45 and not the theoretical 43.26.


Why does this matter so much to you? Do you really choose a focal length by what's exactly "normal" or do you choose a focal length by what view and perspective it gives you and how it affects the subject?

All that matters to me is that I know a certain range of focal lengths have a relatively unforced or natural perspective, but that can be a range of 20mm or so. I'm not going to quibble over 5mm...

I mean, technically the SLR full aperture may be the same as 8-perf VistaVision, 37.72 x 24.92, not 36 x 24, so the diagonal would be 45.21mm.

You'll note that the Wiki entry uses terms like "generally" or "about" so they know this is not an exact science either. I mean, if you showed someone a photo shot on an SLR at 43mm, 45mm, and 50mm and told them to pick the "normal" one, most people would say they all looked about the same.
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#3 Dan Diaconu M

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Posted 21 June 2009 - 03:19 PM

Why does this matter so much to you? Do you really choose a focal length by what's exactly "normal" or do you choose a focal length by what view and perspective it gives you and how it affects the subject?


No, it does not matter all that much, just a little bit. I choose a focal by "need" (space available, action, meaning of the dialog, etc) but I would like to have some sort of reference point.

All that matters to me is that I know a certain range of focal lengths have a relatively unforced or natural perspective, but that can be a range of 20mm or so. I'm not going to quibble over 5mm...


Agree.

I mean, technically the SLR full aperture may be the same as 8-perf VistaVision, 37.72 x 24.92, not 36 x 24, so the diagonal would be 45.21mm.


I agree again.

You'll note that the Wiki entry uses terms like "generally" or "about" so they know this is not an exact science either. I mean, if you showed someone a photo shot on an SLR at 43mm, 45mm, and 50mm and told them to pick the "normal" one, most people would say they all looked about the same.


I agree most people will hardly notice the difference, but if pointed out what to look for, they will order them from wide to tight.

The question I asked was related to smaller formats where the "diagonal" doesn't produce the "normal.
In my previous post I mentioned two different focal lengths for the same format (13.8X20.7mm).
The "normal" by frame diagonal turns to be a 25mm. That's a long way to go to the 70 that matches the eye view.
I don't fuss over 5mm (more or less) here David. Generally and about doest cut it either. We have almost three times the difference.
I suppose you have an SLR (film or digital) handy (a digital would actually be better).
What would you call "normal" between a 25 and a 70?
Thanks for contribution.
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#4 John Sprung

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Posted 21 June 2009 - 08:55 PM

There's no such thing as a lens that in any real sense makes the film or electronic image "match" what we see with our eyes. Our cameras have frame lines, we don't. We make carefully crafted compositions with our cameras, but no such concept even exists in ordinary life -- which in large part is what makes the efforts of the cinematographer worthwhile.

It would be better to think in terms of "mid range" rather than "normal" lenses -- in between where we see the distinctive characteristics of wide angle or telephoto lenses.





-- J.S.
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#5 Chris Keth

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Posted 22 June 2009 - 01:33 AM

How did you line up your framelines with the camera's? :blink:

A bit more seriously: there is the optical definition of what a normal lens is for a format. There is also your own definition of what your normal lens is. They don't have to coincide nor do they have to agree. They have different purposes.

Basically, don't worry about it.
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#6 David Auner aac

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Posted 22 June 2009 - 02:47 AM

Hi Dan,

a little tip. Use both eyes! ;)

Cheers, Dave
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#7 Paul Bruening

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Posted 23 June 2009 - 07:58 AM

Hello Dan,

As you may be gathering from the replies, there's probably no actual conclusive answer to your question. We've never arrived at a complete agreement on this topic, here. The reason being, camera lenses don't bend light exactly the same way as the lens in the human eye. A camera lens will represent the human eyes' different aspects at different focal lengths. Each DoP here will pick the aspects that are most important to them and find the focal length that best represents those concerns. As an example, for me, a "normal" lens (for 35mm academy frame) represents all objects at every distance in the same size as seen by the human eye. As you may have observed wide lenses make things in the distance seem small. With long lenses distant object are unnaturally large. So I lean heavily towards a 50mm lens for normal even though it makes for irksomely cramped frame spaces. Lotsa' guys here swear by something in the 35mm range for normal because of completely realistic framing concerns. On top of this is the fact that a zoom lens can bend light in odd ways compared to a prime lens. The differences between them are usually considered a non-issue. But in this comparison I can't account for what subtle things that zoom is doing to your image and observations.
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