HDTV - shows too dark and murky, inconsistent? (1 Viewer)

[Jeff Gatie]

Why can HD video keep 2 things differing in distance in focus and film can't?

To preface the following, I am not sure if the statement about the depth of field for HD video being greater than film is true, it may be. Given that, here is a possible answer why:

It has to do with the aperture and quality of the lens used. Aperture is the iris in the lens which controls the amount of light being let in. The smaller the aperture, the less scattering of light and the greater the depth of field. However, as the depth of field gets greater, the aperture gets smaller and the amount of light allowed into the camera decreases. If the amount of light decreases, the exposure time must increase in order to expose the film correctly. Since motion cameras have a limit for exposure time, their depth of field is limited; unless super fast lenses or other methods are used to get around it.

HD, being a non-film medium, may circumvent this by collecting much more light than film, thus allowing for a smaller aperture and a greater depth of field.

Note, this is from a still photography background, but the concepts are basically the same (I hope!).

 

[Lew Crippen]

Will film EVER go 30fps or more? If not than I can see it getting phased out in several years. THat is the biggest disturbance to me when watching a movie; when the camera pans and the material looks exteremely choppy.

Never say never, but it is extremely unlikely. This is because viewers have become accustomed to watching movies at 24 fps for a very long time and even if this were not so, there is a substantial investment in projection devices in movie theaters all over the world that only move film at 24 fps.

I accept that you may see the jerkiness and not care for it, but probably most people don’t want a change. For example, think about amount of effort put into simulating 24 fps in playing DVDs. Plus the hot new HD-video cameras are 24 fps capable and filmmakers are choosing those cameras and that rate at ever increasing numbers.

 

[WayneG]

- Will film EVER go 30fps or more?

Last year I saw a bit on TV where a group was demonstrating 48fps film. But with the move to digital and high-def even they seemed to realize it would not become mainstream.

 

[anthony_b]

Last night I saw JAG on CBS-HD and I found it to be a bit on the dark side..my favorite HD broadcast are the local sports events (NY KNICKS-ISLANDERS-RANGERS-METS) I'm really not a fan of either teams but it's just so beautiful to watch !!...(I'm a die hard YANKEE FAN )...

 

[Eric F]

Watch NYPD Blue, it's bright and colorfull. All the things most of the ABC HD shows aren't.

 

[Rob_V]

We just got HD Timeshifting on Rogers Cable here in Canada, it's pretty wicked. Assuming you've got HD Cable/Sat, (as opposed to OTA HD and standard digital Cable/Sat) you should get on your provider to do the same.

 

[Eric F]

Rob, which box did they give you?

 

[Rob_V]

Eric, it's an SA 3100HD. They only upgraded us to that one for VOD, previous to that I believe their standard issue for HD was a 2800HD or 2900HD (can't remember for sure, it's been a while.)

 

[GregHoey]

I noticed a couple of people have raised the HD vs FILM DEPTH OF FIELD QUESTION along with some other interesting questions.

Let me try to give some simple and hopefully useful answers.

Scott L. wrote on 10/24/03:

"3 questions:

- Why can HD video keep 2 things differing in distance in focus and film can't?
- Isn't this all just dependent on the lens? In a film class one of the technical achievments brought up was how a new lens for film could keep more things in focus at the same time.
- Will film EVER go 30fps or more? If not than I can see it getting phased out in several years. That is the biggest disturbance to me when watching a movie; when the camera pans and the material looks extremely choppy."


Scott; Good questions . . . simple basic questions with potentially complex answers so I'll try to keep the answers simple. Forgive me in advance if I over-simply some things in the service of answering the fundamental questions.

1 - DEPTH of FIELD -- there is no definitive answer to this -- it is all relative to many MANY things.

Depth of Field is a TOOL not a standard. HDTV is not "better" because it can have more depth of field than film.

DEPTH OF FIELD / FOCUS DEFINED -- the distance between the "acceptable" near focus and the "acceptable" far focus IE everything in between is "in focus." I used quotation marks here because this can get very subjective.

There is, however, a BASIC optical principle -- the smaller the optical size of the image captured or of the image capture encoder the greater the POTENTIAL depth of field . . . ALL OTHER FACTORS BEING EQUAL.

Very long story very short RE: HD video and 35mm motion picture film.

The imaging array an of an HDTV CAMERA has a diagonal of approx 2/3 of an inch.
The image size of a 35mm motion picture Academy Aperture frame is approx one inch.
The imaging array of a mini DVCAM is approx one third of an inch.

ERGO, HD capturing a smaller image will have more POTENTIAL depth of field than 35mm motion picture and DVCAM would have the most potential depth of field.

The complete explanation is long and hairy and gives me a headache but this is the basic rule and you can take it to the proverbial bank.

That said; when 35mm mopic film is transferred to HD video the depth of field
is unchanged because the DOF is determined by the original capture.


2 - LENSES re; DEPTH OF FIELD

Yes, lenses have a huge effect on depth of field but they are not the controlling factor;
the optical size of the image captured is the controlling factor.

Long story short; the shorter the focal length of the lens IE the wider the horizontal angle of coverage the greater the potential depth of field.

HOWEVER, this is all relative to the size of the image captured which changes with each
"format" IE 35mm mopic, HD, 16mm, DV et. al.

TO WIT: in 35mm mopic the so-called "normal" lens is generally accepted to be 50mm
In 16mm the so-called "normal lens" is 25mm because the size of the image captured is SMALLER by one half than that of 35mm mopic.

In HD the "normal lens" is 17.6mm and in DV it is 9.7mm . . . because of the smaller imaging array.

Further, the same focal length lens will function differently optically with each format.

The 25 mm lens will appear "normal" on 16 mm but will appear as a "wide angle"
lens when used on 35 mm mopic. Conversely, the same 25 mm lens would function as a "short telephoto" lens IE less field of view / greater magnification when used on a DV camera.


2 - A - SPECIAL LENSES

There are special lenses which CAN create a greater depth of field. I refer to the Panavision Frazier lens and the Millennium lens. These are defined as RELAY LENSES IE they're sort of like a periscope and move the lens away from the body of the camera.

I have used these lenses and they are pretty neat. HOWEVER, part of the way they get their huge depth of field is by being "slow" IE less sensitive to light -- more detail coming.

Which brings us to the OTHER main component of depth of field -- lens "stop" as in "f stop"

Backing up a notch. The "f" stop of a lens defines the setting of the "iris" which has a variable opening which controls the amount of light which EXITS the lens and hits the film or imaging array -- it does not affect the light ENTERING the lens.


All other things being equal a lens will have more depth of field when "stopped down" IE the size of the IRIS is smaller


WHY DO WE NEED "f stops"

Basically because the sensitivity to light of the film or video imaging array remains a constant but the amount of light in the real world varies considerably . . so you have to be able to control it.

"F stops" are a seemingly arbitrary selection of numbers that define this amount of light.

RULE OF THUMB the larger the "f stop" the SMALLER the size of the iris.

THE OTHER RULE;
each increasing "f stop" lets in HALF as much light as the previous "stop."

conversely each DEcreasing "f stop"lets in TWICE as much light as the previous "stop."

TO WIT; here is a typical range of "f stop" on a lens.

2.8 / 4 / 5.6 / 8 / 11 / 16 / 22.

" f 2.8" lets the most light thru and " f 22" lets the least.
"f 2.8 let's TWICE as much light pass as "f 4"
"f 4" let's HALF as much light pass as "f 2.8" etc etc ad nausea.

Getting back to the Frazier / Millennium lenses; they have a maximum "f stop" of "f 8" or "F 11" depending on the focal length. ERGO, you'll get alot of depth of field ANYWAY. . . . but they do do something else to increase the apparent depth of field and I'll be damned if I know what it is . . but it is neat.


3 - OTHER FILM FRAME RATES

"- Will film EVER go 30fps or more? If not than I can see it getting phased out in several years. That is the biggest disturbance to me when watching a movie; when the camera pans and the material looks extremely choppy."

Yes and no.

Yes, there are film formats other than 24 fps or 30 fps and no, I don't think we'll be "hanging crepe" and burying film anytime soon.

Go see MATRIX REVOLUTIONS in IMAX and see just how great a film print can look albeit film that has been digitally manipulated.

Nearly all features and filmed TV shows are shot at 24 frames per second . . . just cuz that's the film standard and everybody has the equipment and yes, choppy camera pans can be extremely annoying. However,

I hasten to point out that since SAVING PRIVATE RYAN came out deliberate visual strobing and choppy movement have broken out like the proverbial plague with every action film using the effect. That's what you might be seeing as well -- a deliberate stylistic visual choice.

OK, other frame rates;

Special effects guru Doug Trumbull had a system called SHOWSCAN with was 65 mm
film shot AND PROJECTED at 60 fps. It was amazing . . almost three dimensional with no choppy pans. He did a system using OMNI MAX 65mm shot AND PROJECTED at 60 fps for the BACK TO THE FUTURE ride at Universal Studios which was also amazing.
His company also did a system shot and projected at 48 fps for rides at the Luxor Hotel in las Vegas which are most impressive.

IMAX had a system for a while called SOLIDO 3D which was 65mm IMAX 3D shot and projected at 48 fps and it was absolutely awesome.

All these film systems look great but they haven't really caught on because they are expensive and they require new equipment. They exist primarily in theme parks as ride simulations.

There are, however, a couple of neat film formats that ARE catching on . . both from IMAX. One, is the release of feature films in the IMAX format and the other is IMAX 3D using High Definition video cameras for origination and film for presentation.

I've seen the last two MATRIX films, TREASURE PLANET, The LION KING, ATTACK of the CLONES and APOLLO 13 in IMAX and they are wonderful. James Cameron's GHOSTS OF THE ABYSS is VERY impressive in IMAX 3D and Robert Rodriquez
used the same camera system for SPY KIDS 3D which was NOT in IMAX and not as impressive. Cameron has been quoted as saying his next feature film will be in 3D --
shot on 3D - HD video and released on film.

This is ALL good . . . for SPECIAL venues but sadly most commercil movie theatres have at best mediocre image quality. I'm glad we have High End Home Theatre
but it's disappointing that the film exhibitors don't seem to care as much about image quality as we all do.
.

Hope I've shed some light on your good questions. Again, forgive me if I over-explained some stuff and UNDER-explained other stuf.

Good, simple questions are the hardest to anwser.

Best,

Greg