Yaron Y. Dahan

There are only two things that affect depth of field. 1.) Enlargement size on negative (or sensor) and 2.) f/stop. Since you won't want to change enlargement size (it would give you different framing) your only choice is to shoot as wide open as you possibly can.

well, actually, my question was more how to create the illusion o a shallow depth of field, rather than changing the depth of field itself, which as you mentioned only changes with aperture

thanks everybody for the suggestions and the advice, especially josh who took the time to write out such a long detailed response.

This question just came up in another topic, tangentially, and I wanted to dedicate its own topic to it.

So the question is, how can I minimize the depth of field in order to get a most filmic look?

I am relatively new to video, and I'm not very fond of that evrything always in focus look.

I know that ultimately I have to do tests to figure it out, but I have heard of situations where people played with backfocus, or even removed the lens and held it a couple of millimeters away from the body in order to get a short depth of field. Has anyone tried any of these? Do they work? Do you have any other ideas recommendations as to getting a shallow depth of field? any way to get those drastic changes in focus that one can get with film?

Sometimes when shooting a wide, wide-angle master shot in HD where everything will look in focus anyway (even if I shot wide-open) mainly because nothing is very close to the lens, most of the objects are at a distance, I will light the scene to an f/4, let's say, and shoot the master at that f-stop so that the lens is at its sharpest. Then when I go for tighter coverage, I switch in the ND.60 internal filter and shoot at an f/2.0 to reduce the depth of field. The slight loss of sharpness is fine because now I'm shooting faces, not wide shots of rooms where I want more detail. So I get the shallow focus look for the medium and close shots, but the wide shots are sharp.

Excellent advice. But, and maybe this is a fool's question, does the 2 stop change make that much of a difference? I haven't noticed that in video, well at least not on the level of a 12 inch monitor, its not noticable like it is in film. And correct me if I'm wrong, but doesn't using an extreme Tele give the most filmlike depth of field, because then stuff starts to go out of focus???

Hello,

I am soon to be shooting a short film in which burglars enter a house at night, and I need some lighting tips. I am shooting in DV on the once-pro SONY DSR390.

Basically, I need it to look like an interior night, but still need the characters to be seen in at least some detail.

I am now working on the lighting schema, and my a priori thoughts on this were to take a bunch of redheads and bounce them against foam core in order to bring up the light levels to acceptable levels, maybe blue-gel them to give it all amore "nighty look". Does nayone have experience with this type of situation? Is this a good idea?

Also from a technical point of view, how much under should I be shooting from the aperture reading?? 1 stop, 2???, and what should be the difference between the ambient light and the flashlights? are there any preferences for f-stop to use in this sort of situation?

Any help on this or any other advice is appreciated.

I remember that about a year ago I went to some Digital Cinema Society talk at a film festival, and one of the filmmakers who shot a feaure in HD said that if possible one should always shoot at the widest aperture possible.. he mentioned something to do with either with the way the compression is done or something with the pixels or artefacts.. I can't remember anymore. It was so long ago.

So my question is, does this have any basis? Is this true only for HD, what about DV?

I know for example that in still photography, all else being equal, and disregarding issues of depth of field, usually three f-stops closed down from the widest is considered the "optical center" of the lens. Is this true for video too?

thanks for the advice. I will definately take a look at all the progrmas more in detail, although for the moment, the 3d programs are not really what I am looking for at the moment. I'm looking for a simple way to draw floor plans without having to resort to paint or photoshop.... and i do them by hand for myself, the problem is i cant draw a straight line, and no one understands what I drew...

i have what is known as faulty linear syndrome...

oy

Another way of looking at is this:

 

Master Black (Pedestal) = brightness or value of the darkest black of the image. Raise it and black turns gray; lower it and you crush deep shadow information into black.

 

Black Stretch (Black Gamma) = brightness or value of shadows, approximately 0-30% luminance (that range being adjustable in some cameras).

 

Master Gamma = brightness or value of the midtones. Raise or lower the value and the scene tends to appear overall brighter or darker, while highlight and shadow information stays relatively the same.

 

Just keep in mind that whatever you do in camera and goes to tape is what you're stuck with. Attempting to raise shadows that were lowered too much in camera will result in noise and compression artifacts, and any clipped or crushed values cannot be recovered once they're on tape that way. So play it a little safe. ;)

Thanks michael. thats exatly the information I was looking for. I actually did some camera tests last week, and sort of figured it out at the end.

I think for the situation I described above, I will play around with the M black a bit, because IVe so far been unsatisfied with the way blacks look on the regular "Straight line" Gamma, and the M Black seems (to my eye at least) to somewhat duplicate the filmic "foot" of the gamma.

Thanks again for the help, and for the tip regarding Chroma.

Does anyone know of a program that helps set up and print out lighting floor plans? or does anyone have any ideas for an efficient and simple architecture/design program that i could use to help desing lighting schema??

"Recorded by the chip" is not the correct phrase -- the chip can't record, it can only respond to light, converting photons into voltage. Yes, after that, signal processing is applied before the image is recorded to tape. But certain things do affect the exposure information recorded, and if it's not recorded, it's not there in post for you to play with. Knee compression is the most obvious thing, hence why all Sony pro cameras have a "DCC" switch on them ("auto knee") to hold more overexposure detail. Black stretch / black gamma can do the same thing at the other end.

 

...

On the other hand, if you're talking about a DVCAM camera, I'd try and get halfway there in-camera and with lighting rather than save it all for post.

Hmm.. yes, I should have said, "senses" the information

That's quite interesting. I didn't realize that the camera doesn't record all that the sensor "sees"

He's wrong. For example where the adjustment of knee point and knee slope is concerned that will cram in more highlight information. You couldn't leave the camera on a default setting and hope to bring that back in post. Thats why the likes of the F900R have hypergamma, and the Varicam has Film Rec gamma.

 

Then there are issues of noise. The camera has coring and level depend adjustments which can minimise the noise in certain areas of the picture (such as the darker areas). This is more difficult to achieve in post. The fact is that you will get a cleaner picture by having these adjustments made in-camera.

Also interesting. Instead of continuing on abstract level, why don't I describe my specific upcoming shoot, and maybe get some advice. I am shooting with a pro DV cam (Either DSR 300 or 390). The scence will be a low key scene, with one decent size highlight that I want to go out of range and be bruned out. I want to keep a dark, nice tonal range in the picture keeping the colors nice and deep. If you had to shoot this what changes would you make in-camera? What would you save for post?

Thanks...

That's a great question. I don't know.

Okay, So I finally caved in and called Sony. Talked to some guy named Dominick. He told me that all of the changes in Gamma and M Black, etc. were made after the Image was recorded by the chip. I asked him what the point was then, if this stuff if usually done in post production, and he said that there really wasn't any. So why would you want to change stuff in camera at the time of the shoot? So you can see the "feel" of the shoot on the monitor? Dominick told me that it transform the image without any loss, but is this really possilbe? If I boost the contrast to the max, and then in post, I realize it was too much, isn't the information lost, becuase I discarded the mid tones??? I don't really know enough about how video works.

As I understand it, stretching the black levels is a way of decreasing the contrast difference from the lower to mid range gamma signals as compared to the brightest parts of the scene. It's a form of electronic contrast reduction since the darker parts of the picture are made more visible while the brightest parts of the scene stay at the leve they are at.

Thanks Alessandro.. So stretch, would be the equivalent of axpanding the low t- mid range tones?? Essentially the same thing as changing the bottom half of the gamma curve? Do you know how it does this? or to be more precise at the expense of what?

Stretching the blacks can often be a good thing. However remember to make the distinction between black level and black gamma(stretch).

 

The black stretch will not affect the absolute black level. I like deep blacks (ie when something is black, I want it to look black, not grey.) Often I find that the standard black level setting on cameras is too high for my liking. I nearly always end up adjusting it in post. As long as you don't go below the zero line on a waveform with the master black you will not crush detail. So I wonder if getting a good master black setting, and then using black stretch to bring back some detail might be the best way to go?

thats a very interesting question, and I will have to do some tests and get back to you on that. Actually the project I am working on calls for low key deep images, and I want to emphasise the entire lower range of colors and hues, and then have some bright spots that will go out.

Unfortunately, I have no access to a wavceform monitor for the moment, so from a purely scientific point of view, I wont be able to know exactly.

You're getting into very complex issues that have people on both sides of the issue thinking they are right and those with a differing opinion are wrong. I think you can actually lose detail even if the darkest part of the signal is barely above the zero black (aka IRE of 1,2,3) compared to leaving set-up at 7.5 and making 7.5 equal zero black.

 

Keep in mind I think there is a difference between graphics images and real life images. Graphics images seem to handle zero black fine, but real life images can easily lose detail in the darks if one uses zero IRE (for NTSC) as a standard and some of the picture information is right around the 1-5 IRE range.

Hmm. Interesting stuff. So what about the difference beetween M. Black and Gamma? If M Black changes the whole line of black how is it different from Gamma? OR does M Black just lower the gamma line, and the Gamma changes the curve???

But I still have one question that is still amystery to me, and I posted it actually in the next post, but since its linked I'll allow myself to ask it again. All of these settings changes - M Black Gamma, etc.... do these changes affect the sensitivity of the chip or are they "in camera post production" changes, and they're just doing "as if"?

Hi,

I am somewhat of a newbie to video, and I am usind the Sony DSR300, and have some confusion

so, from a visual perspective, I noticed that all three of these essentailly affect the contrast, but what is the difference from changing on or the other? both from a technical point and a visual point? any help is appreciated.

Hello there,

So, I come from a film background (stills) and I'm starting to move into video a bit, and I'm trying to figure out how everything works. I am shooting with a DSR 300, and my question is about the Gamma adjustments. I know that for example in film, a high contrast situation will lay better on a more severe slope of the gamma, and a low contrast situation will fit better on a softer slope. the question is in video does adjusting Gamma in the camera change the range of what the chip itself sees, or is it only processing that happens after the chip reads it? (which would essentially make it useless to play with)