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Movies Forum Index » Movie Technology Forum » Lens Focal Length Conversion
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| Hollywords, LLC |
 Posted: Sun Mar 09, 2008 9:25 pm |
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Can someone provide me with (or point me to a Web site that provides)
the conversion factor to translate the angle of view/focal length of a
35mm still camera image to a standard (4-perf/Academy aperture) 35mm
flat image?
For example, if I shoot something with a 50mm lens on a 35mm still
camera, to get the same sort of image with a 35mm film camera, I
assume I need to use a slightly shorter lens (since the image area is
smaller). Given that, I assume there is a scaling factor that will
allow me to take shots with a still camera and calculate what sort of
lens I'd need on a film camera to get that same angle of view/achieve
the effect of that same focal length lens.
If someone's feeling ambitious, I'd also be interested in the scaling
factors between 35mm 4-perf (Academy Aperture) and...
* 35mm Anamorphic
* Super-35
* 16mm
* Super-16
* Super-8
* 65mm
* IMAX
* Any digital camera formats that come to mind.
(I figure I may as well cover my bases.)
Thank you in advance.
--Richard |
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| Peter |
| Posted: Mon Mar 10, 2008 1:59 am |
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On 2008-03-09 19:25:33 -0700, "Hollywords, LLC" <info@hollyword.org> said:
Quote: For example, if I shoot something with a 50mm lens on a 35mm still
camera, to get the same sort of image with a 35mm film camera, I
assume I need to use a slightly shorter lens (since the image area is
smaller). Given that, I assume there is a scaling factor that will
allow me to take shots with a still camera and calculate what sort of
lens I'd need on a film camera to get that same angle of view/achieve
the effect of that same focal length lens.
You could use the image diagonal as a scaling factor.
50mm was still more-or-less standard for Academy, although the Academy
aperture's image diagonal is less than one-half the image diagonal of
35mm still.
VistaVision Large Aperture is the same size as 35mm still, although the
1.66:1 extraction is somewhat smaller.
The image diagonal of 'Scope is one half the image diagonal of VVLA and
35mm still.
40mm was the standard lens for 'Scope.
IIRC, the ACM Handbook has equivalent focal lengths for the then extant
processes.
--
CinemaScope®: The Modern Miracle You See without Special Glasses!
--
Peter |
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| Neil Midkiff |
| Posted: Mon Mar 10, 2008 2:29 am |
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Hollywords, LLC wrote:
Quote: Can someone provide me with (or point me to a Web site that provides)
the conversion factor to translate the angle of view/focal length of a
35mm still camera image to a standard (4-perf/Academy aperture) 35mm
flat image?
For example, if I shoot something with a 50mm lens on a 35mm still
camera, to get the same sort of image with a 35mm film camera, I
assume I need to use a slightly shorter lens (since the image area is
smaller). Given that, I assume there is a scaling factor that will
allow me to take shots with a still camera and calculate what sort of
lens I'd need on a film camera to get that same angle of view/achieve
the effect of that same focal length lens.
If someone's feeling ambitious, I'd also be interested in the scaling
factors between 35mm 4-perf (Academy Aperture) and...
* 35mm Anamorphic
* Super-35
* 16mm
* Super-16
* Super-8
* 65mm
* IMAX
* Any digital camera formats that come to mind.
In most photography books you'll find the rule of thumb that a "normal" lens has
a focal length approximately equal to the diagonal measurement of the film
frame. For 35mm still pictures (24 x 36mm "Leica" format) that's about 43.3mm,
and indeed you used to find some 35mm still cameras sold with 45mm instead of
50mm normal lenses.
Similarly, for a 4"x5" view camera, the "normal" lens would be about the
diagonal for it: 6.4", or about 160mm.
For the Academy aperture of 1.37:1 the frame diagonal is about 26mm in the
projector, or about 60% of the diagonal measurement of the 35mm still camera
frame. So your scaling factor is about 60%.
For other sizes, you can look up the frame sizes (for instance
http://en.wikipedia.org/wiki/List_of_film_formats )
and do the math yourself based on the film height and width and the good old
Pythagorean theorem.
I don't think I've ever seen any studies on how viewers perceive the field of
view versus camera focal length for widescreen film formats. Does the diagonal
measurement still make sense as a basis for the rule of thumb when the image is
2:1 or wider?
I would guess that more difference in the perception of effects of widescreen
lens angle comes from whether the viewer is seeing a projected image that is
width-limited or height-limited based on the architecture of the theater (or on
the dimensions of the viewing screen, in electronic formats). That's an overly
fancy way of saying that sometimes widescreen really means "shortscreen" -- if
the proscenium of a classic movie house is just filled with a 4:3 screen, you
have to reduce the image height (using a longer projector lens) in order to get
the full width of a Super Panavision film onto the screen. Similar things
happen in letterboxing widescreen video for older monitors. The viewer will get
a different experience of angle of view in a theater built for a wider screen
ratio....scenes shot with the same camera lens will have a different look in the
two different theaters.
-Neil Midkiff |
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| Peter |
| Posted: Mon Mar 10, 2008 1:03 pm |
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On 2008-03-10 00:29:01 -0700, Neil Midkiff <nmidkiff@earthlink.net> said:
Quote: For the Academy aperture of 1.37:1 the frame diagonal is about 26mm in
the projector, or about 60% of the diagonal measurement of the 35mm
still camera frame. So your scaling factor is about 60%.
True, but 50mm remained the "normal" lens for Academy, much as it was
the "normal" lens for Silent/Full.
That 40mm would become the "normal" lens for 'Scope is somewhat
interesting, as 40mm with a 2:1 squeeze is equivalent to a 20mm lens,
and 18mm lenses, for "flat", only became available and thereby popular
in the 1950s, so 24/25mm might have before been the widest available
for Academy.
--
CinemaScope®: The Modern Miracle You See without Special Glasses!
--
Peter |
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| Martin Hart |
| Posted: Mon Mar 10, 2008 5:08 pm |
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Get yourself a copy, ANY COPY, of the ASC Manual. There are all sorts
of lens tables providing angular coverage, depth of field, and more.
Marty
The American WideScreen Museum
In article <nt49t3t026k80ki53kaebmqv41h4vpjdkr@4ax.com>,
info@hollyword.org says...
Quote: Can someone provide me with (or point me to a Web site that provides)
the conversion factor to translate the angle of view/focal length of a
35mm still camera image to a standard (4-perf/Academy aperture) 35mm
flat image?
For example, if I shoot something with a 50mm lens on a 35mm still
camera, to get the same sort of image with a 35mm film camera, I
assume I need to use a slightly shorter lens (since the image area is
smaller). Given that, I assume there is a scaling factor that will
allow me to take shots with a still camera and calculate what sort of
lens I'd need on a film camera to get that same angle of view/achieve
the effect of that same focal length lens.
If someone's feeling ambitious, I'd also be interested in the scaling
factors between 35mm 4-perf (Academy Aperture) and...
* 35mm Anamorphic
* Super-35
* 16mm
* Super-16
* Super-8
* 65mm
* IMAX
* Any digital camera formats that come to mind.
(I figure I may as well cover my bases.)
Thank you in advance.
--Richard
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| Peter |
| Posted: Mon Mar 10, 2008 9:20 pm |
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On 2008-03-10 15:08:43 -0700, Martin Hart <oldtornperf@nospam.net> said:
Quote: Get yourself a copy, ANY COPY, of the ASC Manual. There are all sorts
of lens tables providing angular coverage, depth of field, and more.
That's definitely the FIRST place to look, although it is titled "ASC
Handbook", not "ASC Manual".
The issue of "normal" focal length for a particular format is largely a
function of time, in general, and lens and camera technology, in
particular.
Back in the days when Mitchell Standard or Bell & Howell 2709 cameras
were housed in portable sound-proof booths, complete with their
operator and assistants, the "normal" focal length for Academy was
relatively long, perhaps 75mm for a wide-angle shot, 100mm for a
"normal" shot and 152mm for a close-up shot. This was required because
the booth was not really "sound proof", and for other, logistical
considerations.
When Mitchell blimped its Newsreel Camera (NC), thereby creating the
Blimped Newsreel Camera (BNC), cameras got quiet enough to use 50mm as
a "normal" lens. But, only three BNCs were completed before the onset
of WW-II.
So also with the impressive, completely silent, yet completely
unblimped Fox Studio Camera, which came on-line about the same time as
the BNC, but Fox had TWENTY of these magnificent cameras to three of
Mitchell's BNCs.
(A completely unblimped, sound production camera would not be created
again for another three decades, the BNC and its Mitchell derivatives,
and its Panavision derivatives, too, being considered "quiet enough",
at about 26 dB, give-or-take).
An indication of how quiet the Fox Studio Camera was is the fact that
for CinemaScope, 40mm was considered "normal", yet this combination of
a very quiet camera, and a very, very wide horizontal field, was
equivalent to 20mm, which was wider than most lens families then
included.
(18mm was considered to be "super-wide" in the 1950s, and the 25mm
Bausch & Lomb CinemaScope "combined" lens of 1954 was equivalent to
12.5mm)!
With today's hand-held, or Steadicam-assisted principal photography,
the point of view of the camera is dramatically different from the BNC,
Fox Studio Camera, and early Panavision days.
Today, totally silent, and easily portable cameras are _de rigour_, and
at the camera-to-subject distances which these production cameras
encourage, if not demand, 25mm or less could be considered "normal".
--
CinemaScope®: The Modern Miracle You See without Special Glasses!
--
Peter |
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| Scott Dorsey |
| Posted: Tue Mar 11, 2008 9:34 am |
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Hollywords, LLC <info@hollyword.org> wrote:
Quote: For example, if I shoot something with a 50mm lens on a 35mm still
camera, to get the same sort of image with a 35mm film camera, I
assume I need to use a slightly shorter lens (since the image area is
smaller). Given that, I assume there is a scaling factor that will
allow me to take shots with a still camera and calculate what sort of
lens I'd need on a film camera to get that same angle of view/achieve
the effect of that same focal length lens.
You can figure it out yourself!
angle of view = frame height / ( focal length * 57)
With a non anamorphic system, the vertical angle of the image on the
film equals the height of the frame on the film, divided by the focal
length divided by 57.
Same thing works for width. Get the width, divide by the focal length
times 57, and you'll get the usable angle in degrees horizontally.
Units all work out, so if you use millimeters for image size, you get
millimeters in focal length. Or inches for inches.
That 57 is actually a 180/pi if you want it more precisely. (This is actually
why people use radians instead of degrees, to avoid that fudge factor).
Aperture sizes can be found in the SMPTE book, or in a nifty handout that
Arri will give you about their illuminated finders.
--scott
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"C'est un Nagra. C'est suisse, et tres, tres precis." |
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| Peter |
| Posted: Tue Mar 11, 2008 11:16 am |
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On 2008-03-11 07:34:21 -0700, kludge@panix.com (Scott Dorsey) said:
Quote:
That 57 is actually a 180/pi if you want it more precisely. (This is actually
why people use radians instead of degrees, to avoid that fudge factor).
By definition, a circle contains 2Ï€ radians.
Electrical engineering is performed in units of radians/second, not in
cycles/second (equivalent to circles/second) nor in Hertz (Hz).
--
CinemaScope®: The Modern Miracle You See without Special Glasses!
--
Peter |
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| Steve Kraus |
| Posted: Mon Apr 07, 2008 9:05 pm |
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Peter wrote:
Quote: That's definitely the FIRST place to look, although it is titled "ASC
Handbook", not "ASC Manual".
The title is American Cinematographer Manual, not handbook. That's what
the two in my lap (editions 5 & 7) say and that's what the current edition
(#9) is called although the ASC store website refers to it as the ASC Film
Manual.
http://ascmag.com/store/product.php?productid=7600&cat=258&page=1 |
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| Peter |
| Posted: Fri Apr 11, 2008 12:46 pm |
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On 2008-04-07 19:05:41 -0700, Steve Kraus
<screen@SPAMBLOCKfilmteknik.com> said:
Quote: That's definitely the FIRST place to look, although it is titled "ASC
Handbook", not "ASC Manual".
The title is American Cinematographer Manual, not handbook. That's what
the two in my lap (editions 5 & 7) say and that's what the current edition
(#9) is called although the ASC store website refers to it as the ASC Film
Manual.
My experiences with that publication go back to Edition 1, which, IIRC,
covered the Three-Strip and Fox Studio cameras, as well as the various
Mitchell, Bell & Howell and ACME/Producers Service Corp cameras then in
current production or in common use.
I have a current edition on order. Likely, I'll not find the
Three-Strip, Fox Studio, Mitchell, Bell & Howell or ACME/Producers
Service cameras in there.
I suspect all of us are right, in whole or in part, in that the title
has changed over the years from "American Cinematographer ..." and "ASC
...." as well as "... Handbook" and "... Manual", in various
combinations thereof.
--
CinemaScope®: The Modern Miracle You See without Special Glasses!
--
Peter |
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