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Excellent ''
THat is the ticket!
Ill try it tonight at home. Ill write you back 2morro. Thanks for your tips. I love details like that! |
When all else fails optically and you just have to have that background blurred "silking" is a trick that is sometimes applied in video shooting. Silking is basically the placement of some type of translucent material (sheer fabric, plastic, et.al.), usually stretched on a frame, behind your subjects to blur the background. It can be a very time-consuming production process to ensure that the material is invisible in the shot. Lighting and material selection are critical. But it can be very effective on small, controlled scenes.
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Other than for Ken's last post, I get the feeling you guys are leading Jason to believe that there is actually something he can do to create a narrow depth of field with a quarter inch chip camera, and that simply is not going to happen in a real world situation. (I am not talking about shooting extreme close-ups of the head of a coin) Here are some real world figures to consider:
Using my PD150, (a one third inch camera with LESS depth of field than the Canon at one quarter inch), I shoot a talking head at fifteen feet with a focal length of 12mm at f/2.8. If I were shooting this in 35mm, the lens equivalent would be about 85mm (a good portrait lens). The depth of field in 35mm terms would be: near limit, 14.35 feet. Far limit would be 15.7 feet, for a total depth of field range of a mere 1.34 feet. Great for those who like narrow depth of field. Now back to the PD150 with one third inch chips. The near focus is 7.5 feet and the far limit is (are you sitting down?) 1015.94 feet! Yipes. If you stop down to 1.4 you can get the limit down to around forty feet, but you will still have most background objects in focus in normal interiors. And remember, that far limit does not mean things are immediately a blur in the background; rather they slowly fall off focus. And f1.4 can cause other problems, since it is certainly not the best aperature to shoot at with a zoom lens. Where do I get these outrageous numbers? A very handy depth of field guide from Panavision, to be found at: http://www.panavision.co.nz/kbase/op...alcFOVform.asp There simply is no way to get around the numbers. But I am sure someone will find a way to argue the point. |
The Panavision site uses non-standard values for CoC. The use of non-standard numbers gives exaggerated values. None the less, Wayne is correct in asserting that shallow DOF is difficult to achieve. One method is to use physical effects as Ken suggests.
Another method is to cheat your focus. Wayne's example assumes that you focus on your subject at a distance of 15 feet from the camera. But if you deliberately focus in front of your subject, say 8 feet away, (with your subject still 15 feet from the camera) DOF is from about 5 feet to 16.8 feet. This results in anything beyond 17 feet being out of focus (even with their non standard numbers). If you opened the lens to F1.4 and deliberately focused at 11 feet (with your subject at 15 feet) DOF is from 8 to 17 feet. This is not extremely shallow, but you can knock the background out of focus and a portion of the foreground. This technique will not be very helpful for rack focus etc. But it is one method to use to get a more limited DOF with the tools you already have. |
That is a pretty sophisticated regimen you are recommending, Jeff. It assumes you have a lens with incremental markings for focus, something I haven't seen on the cameras we are talking about. Even the DVX100 would only give you an approximation of the exact distances you are talking about. And that camera won't iris to f1.4, nor will most of the cameras. Even the PD150 will only go to f1.6, and certainly does not perform optimally at that stop. And again, as I mentioned earlier, the background does not become the classic "blur" that most young filmmakers are interested in, but rather, slowly goes further out of focus as the background distance from the subject increases. Very difficult to make this happen in an interior setting.
Basically, I am saying that with small chip cameras, shallow depth of field is not difficult to achieve, it is virtually impossible under normal shooting conditions. The problem is that some of us are creating a false impression that maybe, just maybe, if you wish really hard, and knew the secret tricks, that you will be able to get blurry backgrounds with these cameras, and it simply is not going to happen. I wish there was as much interest in proper lighting techniques, composition, and art direction. But of course these require study and constant practice and offer no "magic bullet" to master. Deep focus is not the enemy to creating striking images. See the movie "Signs" for some great examples in a contemporary film. Additionally look up chiaroscuro. |
Check this out
Go to the site below and once there click on the GL. Next click on the view 360 info. Next, click on documents and after that opens, click on the .pdf and scroll down to page 5. It shows a picture of a couple in focus and the background soft. I think this shows what Jason is trying to achieve.
www.canondv.com |
Yup, the images are meant to highlight the AV (aperture priority) mode. Notice that they are at a marina, and there are no objects in the background for some distance. That would require a technique similar to what I describe. If you focused on the people, you will achieve some pretty incredible DOF and the boats in the background might be in focus.
Working with DOF is a sophisticated regimen, just like lighting, composition and art direction. It's not easily mastered and requires the right tools. The techniques do not work in all situations. A run and gun production is not ideal for a methodical approach to DOF. It requires a tape measure or optical distance finder, DOF Chart or PDA with DOF program, and an external monitor. The external monitor, though not required, makes checking DOF much easier (especially if your lens lacks a distance scale). Once you have the required tools assembled, it's just a matter of plugging in the aperture, focal length of lens, and different camera to subject distances to learn the DOF limits. Then place your subject at the limits of the DOF. The closer you set focus, the shallower the DOF. Read the article to understand how changing focal length and distance to subject can cancel each other out (Law of Reciprocity). This work method is best used on a set where you have greater control of lighting and other important elements. It requires a slow, methodical approach to your work. Again, it's not a method for run and gun or ENG type production. |
Digi-Cam Buddah's
you guys are coming out of everywhere. Wayne, your absolutely right. It is near impossible to get results indoors. I was trying everything last night at home with a big bluesitup ball about 10 feet away from me and the background around 10 feet behind it. I tried using everyones tricks on here. Im going to give it another go this eve. But probably end up doing it in post if i cant figure it out. Guess it goes with the first thing i read in this forum "shoot, shoot and reshoot!".
Thanks for all the pro-tips guys! |
I have read the article in DVinfo which clearly states that zooming in will not affect DoF as it cancels out the net effect. The only way is to open up the aperture.
But a website suggested from previous posts, http://www.dvcreators.net/media/depthoffield.html suggested that we zoom in as much as possible to get shallow DoF. Are they mistaken? |
It depends on how important the object size is. In their examples, notice how the size of the persons head increases in size. If you can work with your subject size being larger, then changing the focal length will decrease DOF. If the subject size must remain the same size (News Anchors head size) then zooming in (decreasing DOF) will be offset by changing distance to subject. The key is if the subject must remain the same size or not.
DV Creators is correct in a limited way. They do not explain the consequences of changing subject size and the Law of Reciprocity. They are repeating the same misconceptions most people have with DOF. |
Hi Michael,
<< I have read the article in DVinfo which clearly states that zooming in will not affect DoF as it cancels out the net effect. >> Actually that's not what it says... it really reads like this: "If you zoom in without moving the camera back, then DoF will decrease." In other words, the DV Creators tutorial is sort of correct, but the problem with that technique is -- as Jeff states in his article on our site -- that you're now changing the relative size of the object you're shooting... which is going to look weird unless you're shooting the entire production this way (otherwise the resultant change in object size is really going to stand out). Hope this helps, |
Depth of Field
Thanks to Chris Hurd bailing me out of my computer illiteracy, I can post this photo. It's a still from a video clip I shot on my XL-1s. I shot it in manual exposure (F2.8, or 3.6, I forget which), manual focus, frame mode using a 1/2 black promist filter. Great, afternoon low-angle light helped get this look.
http://www.dvinfo.net/media/Image0.jpg |
Indeed, the picture (from the Canon site) portrays what Jason is trying to achieve, but sorry guys, that picture just does not cut it. A high shutter setting is being used, probably at least 1,000 of a second or higher. This will result in a narrower depth of field than a normal shutter setting of 1/60, but will also result in motion jerkiness that is simply not acceptable for normal shooting situations. It also requires a tremendous amount of light to achieve, way beyond the usual interior lighting set-up. And again, the background is a considerable distance from subjects and camera. Actually, the effect in this picture could have been heightened even more by using a longer focal length. As long as the people in frame don't move, the high shutter speed will not be objectionable. High speed shutter has been used quite effectively in movies such as "Saving Private Ryan" and "Gladiator" to add a "special look to" scenes of battle.
Michael, regardless of what format you shoot with, be it 35mm motion picture film, 16mm, 2/3" chips or 1/3" chips, depth of field is a result of focal length and aperature (iris). The basic rule is: the longer the focal length and/or the wider the aperature (lower numbers, eg f/1.6), the narrower the depth of field. The shorter the focal length and/or the narrower the aperature (higher numbers, eg f/16), the greater the depth of field. This is true for all formats, bearing in mind that larger image surfaces, such as 35mm will yield narrower depth of field, and smaller image surfaces will yield much greater depth of field, but the predeeding rule still applys. This is physics and cannot be ignored. So the narrowest depth of field any given format is capable of, will be found using the widest aperature at the longest focal length. This can be confirmed using the Panavision depth of field guide I mentioned above. (Be wary: zoom lenses seldom perform optimally at their longest focal length at widest aperature) Charles lovely picture is an example of long focal length and wide aperature equals narrow depth of field. But what it teaches budding filmmakers is never shoot an actor with a head bigger than a duck. |
Wayne... "the picture (from the Canon site)" -- I'm trying to get away from it being known as a Canon site; it's actually an "everything site" now, with some Sony stuff up there too, and JVC and Panasonic material forthcoming. If you have anything that's non-Canon that you'd like to contribute, I'd warmly welcome it!
Any other DoF image examples, anybody? |
<<<-- Originally posted by Chris Hurd : Wayne... "the picture (from the Canon site)" -- I'm trying to get away from it being known as a Canon site; it's actually an "everything site" now, with some Sony stuff up there too, and JVC and Panasonic material forthcoming. -->>>
I think there is some confusion Chris. I was referring to the link in James Emory's post, www.canondv.com. If that isn't the Canon website, I must be having an halucination. Which would not be all that unusual. |
DOF's just ducky
Wayne:
It's a goose. Goosies go: "honk, honk." Duckies go: "Aflac." |
Wayne -- thanks for the clarification, looks like the confusion was all mine, hallucenogenics aside.... that's what I get for not following the thread as closely as I should.
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Just to reinforce just how "deep" DOF on a 1/3" camera can be...
I was recently making some test shots in which I was trying to shoot a close subject while keeping a local landmark, visible through a window, in identifiable focus. I tried a wide variety of exposure and subject lighting combinations, 22 all told. In the end, the landmark remained easily identifiable and only a few shots markedly blurred it. The landmark was over 1 (straight-line) mile away. Perhaps the best way to envision the effect of aperture on DOF is to try the poor-man's glasses trick, particularly if you're near-sighted. Curl your index finger until there's only a tiny opening. Then peer through it and adjust the opening until you can see some object clearly. As you widen the opening the object blurs. That's basically what's happening in the camera with respect to the iris. |
I dont wish to be argumentative but I would like to dispel the notion that DOF has anything to do with CCD size - it does not
The Three Factors which affect DOF are 1 Focal Length 2 Aperture - f-stop 3 Camera to Subject distance CCD size will introduce telephoto compression effects which enter play for smaller CCDs http://www.8mm.filmshooting.com/community/articles/dof.php has an article which should be read since it is an extract from Ilford Manual of Photography, 4th Edition, 1949. Pages 14 to 17 Also for shallow DOF effect you should be aware that Circle of Confusion extends one third in front of subject focal plane and two thirds behind subject focal plane so using this for the background blur effect you need - arrange your camera to subject distance to be approx 1/4 (or less) of the distance of the camera to the background. Then the aperture will act as a background blur control (small f number - more blur) hope this helps |
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<<<-- Originally posted by Jeff Donald : It depends on how important the object size is. In their examples, notice how the size of the persons head increases in size. If you can work with your subject size being larger, then changing the focal length will decrease DOF. If the subject size must remain the same size (News Anchors head size) then zooming in (decreasing DOF) will be offset by changing distance to subject. The key is if the subject must remain the same size or not.
DV Creators is correct in a limited way. They do not explain the consequences of changing subject size and the Law of Reciprocity. They are repeating the same misconceptions most people have with DOF. -->>> So , from what I understand, is this. To achieve a shallow DoF, we either zoom in, or we put the camcorder closer to the subject. Both will have the same result as long as the object size remain constant rite? Which also means, the bigger the object size, the shallower the DoF since both method, zooming in and putting the camcorder closer will increase the object size, rite? |
I don't think you are being argumentative John, but I do think you are in error, or perhaps making a semantic argument that went way over my head.
In regards to chip size and depth of field, may I offer the following from tvtechnology.com: The Elusive Film Look by Randy Hoffner 4/7/03 http://www.tvtechnology.com/features/Tech-Corner/f_rf_technology_corner.shtml "You might recall that the depth of field is the range of object distances from the camera lens over which everything appears to be in focus. As lens aperture or f number decreases, depth of field increases, and, if the f number is held constant, as the size of the image decreases, depth of field also increases. The result is that for the same f number, a 2/3-inch CCD camera will have about 2.2 times the depth of field that a 35mm camera will have. As many 35mm movie lenses are designed to function optimally at maximum aperture, which may be as much as f/1.6, there is no chance that a 2/3-inch video camera will achieve the same depth of field as a movie camera. So while it is technically possible to use a 35mm movie lens with a 2/3-inch video camera, the angle of view and depth of field will not mimic 35mm film at all. One solution is to mount the 35mm lens so that its image is generated on a ground-glass screen outside the camera (increasing the image size to that of a 35mm film frame), and using relay optics to route the image to the CCD sensors. This would increase the size, complexity and price of the video camera system." If a 2/3inch video camera has 2.2 times the depth of field of a 35mm camera, how much greater is the depth of field of a 1/3 or 1/4 inch camera? Additionally I disagree with your contention that distance to subject affects depth of field. Only in so far as you may use a longer focal length for subjects that are farther away, as in the case of Charles' duck, er, goose. Only focal length and aperture affect dof. In comparing the chart from the super 8 site with the Panavision guide, I find them quite compatible. (Using the 1/4 inch video on the Panavision) No conflict here. This is an interesting discussion, but I am afraid it only serves to add to the confusion for the newbies, who are probably figuring, "Hey, if these guys can't agree, there must be some way to get blurred backgrounds for my movie with my GL1 (or whatever)." But unfortunately there is not, unless you want to shoot your entire movie outside at the longest focal length you have with a wide open aperture. |
Quote:
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Duck!
And sometimes you have to step in goose poop.
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The formula for determining DOF must have distance from camera to subject. The Panavision site requires it, as well as any other DOF chart or scale. The formula from my article is directly from the eighth edition of the American Cinematographers Manual, pages 698 and 699. Without the distance from camera to subject you can only determine hyperfocal distance (which is required for DOF). Let's not reinvent physics here, it's required, end of subject.
DOF does not always extend 1/3 in front and 2/3 behind the subject. It varies with the hyperfocal distance and many times is 1/2 and 1/2. There are five factors that effect DOF and not three. They are stated in my article. CCD size or target size effects DOF as stated in my article. If your subject must stay a certain size (News anchors head on TV) then CCD (or negative size) will effect DOF. Why? Because you must change one of the variables to keep target size the same. When you change one of the variables, you change DOF, end of subject. If you have questions, read the article. If there is something you don't understand, post back. All questions are welcome. |
ok guys!
I have a huge page to print out now. THis weekend i'll give it a go with the new GL2. I'll get back to you all with what works and what doesn't. Thank-you all for the insight ( no pun intended ). I love this forum. Everyone is so into filming here!
Chat soon |
I don't quite know how to respond to Jeff's last post, as he seems to be getting a bit tite about all this. I have visited his tutorial, and while there is nothing there to rabidly disagree with, I feel that it is way more information than is necessary to resolve the dilemma of depth of field. For instance, Circle of Confusion is a rather arcane subject that is not often brought up when calculating depth of field on the set. CoC varies with different lenses of similar focal lengths, from different manufacturers. It really is not going to affect depth of field calculations of a fixed lens on a mini dv camcorder.
Frame rate will also affect dof, but that is hardly an issue for video cameras, except the DVX100, and once you set it, it becomes a constant. Filtration will affect depth of field, if you use an ND. But this is not mentioned in most discussions of dof, because what you are really doing is changing the aperture. Distance to subject must be known to calculate dof, but then it is constant. If you move to a different distance to the subject, you must re-calculate the dof. 1) The longer the focal length, the narrower the depth of field. The wider the focal length, the greater the depth of field. 2)The wider the aperture setting, the narrower the depth of field. The narrower the aperture setting, the greater the depth of field. Here are a few pictures to illustrate these points: (Charles Newcomb, this duck's for you) http://www.digitalprods.com/Ducks.jpg Here are some publicity comments on the unveiling of the Arricam: "Camera assistants will become “system’s managers” as they master the Lens Data System (LDS) that “shows relevant information from the lens in use, such as focus and iris settings, the focal length, as well as the resulting depth of field, all on a convenient display.” Note that "relevant information" is; focus (distance to subject) plus iris setting plus focal length equal depth of field. No need for a long discussion, or, as Jeff likes to put it, "end of subject." Please go to the following link for more excellent information on depth of field: http://octopus.drama.bris.ac.uk/Onli.../FocusPulling/ Finally, in no way is my intention to denigrate the hard work Jeff Donald has put in on his tutorial on depth of field, but I do feel that for the person who may be new to this concept, and is trying to apply it in a practical situation, that maybe he has gone a bit overboard with the information. In the Army, they say there are two kinds of information; Need to know, and nice to know. It is my humble opinion that in the discussion of depth of field, items 1) and 2) above are "need to know" and all else is "nice to know." |
Quote:
Circle of Confusion The diameter of a circle formed by a lens imaging a true point. The largest circle which the eye will perceive as a point, without producing perceptible unsharpness (lack of focus). Is the primary factor in determining image sharpness to the viewer. As the aperture is stopped down, the Coc is reduced in diameter. However, spherical aberration causes the plane of sharpest focus to shift or move along the optical axis, toward the CCD. The smallest area of intersection for crossing light rays produces not a point, but a circle. This is the origin of the term Circle of Confusion. If the circle has a diameter of 1/3000 of the viewing distance, or less, it is perceived by the eye to be a point (therefore sharp and in focus). As the viewing distance increases, physically larger diameter circles are perceived by the eye to still be a point. The diameter of the Coc is not a fixed number, nor is it's size agreed upon as an industry standard. The 1/3000 figure is the most commonly accepted. It translates to a size of .01 inches or .25mm. For many applications 1/300 of an inch is the standard. The bottom line is sharpness, or the lack there of, is in the eye of the beholder. What appears sharp to me may not appear sharp to you, or vice versa. Why do I dwell on accuracy in discussing things of a technical nature? Well, to put it quite simply, I teach photography. Each term I have students take my classes that want to reinvent DOF or Coc. They have their own limited knowledge and personal experience with trying to deal with it and learn it. There are several threads here where members have tried to invent the formula for DOF from their experimentation around the kitchen table. It doesn't work that way. We need to have agreed upon standards and definitions so that an intelligent discussion can take place. What happens if people only have the information they "need to know." Well, in science they make false and/or inaccurate assumptions. Complete and accurate information is required for intelligent discussion. I don't think the army wants to encourage too much intelligent discussion. But this information might be too hard for me? I doubt it. I've had students from 18 to 80 take my classes and have no problem understanding DOF or Coc. The biggest problem is many of my students have "learned" misinformation or inaccurate information about DOF. They've been to web sites, read articles, talked to so-called experts and been misinformed or received half truths. I feel it is our responsibility to see that does not occur at DV Info. |
<<<-- Originally posted by Jeff Donald : Do you have a link to the article, I'd like to read it? I suspect it does not show Coc because it would be fixed data and would not change, why clutter the display with information that would not change. -->>>
http://www.cameraguild.com/interviews/chat_alsobrook/alsobrook_machines5.htm Gee, Jeff, that's kind of my point. Why get into discussions about CoC when it really does not enter into determing depth of field for a camera with a built in lens? And even with a camera with interchangeable lenses, such as the Canon XL1s, how would the user determine the CoC and apply that information to his set-up? Coc is of interest when your choice is between a Cooke Prime and your Panavision Zoom, but I have a hard time seeing the value to a quarter inch chip camera, and just how does this apply to Jason's original question: "I have been trying to get the camera to focus on people a few feet away and then blur the background. What is the trick to this with the GL2?" Again, my point is that narrow depth of field is impossible to achieve with small chip cameras under normal conditions, so rather than fighting it, work with it and use other methods to give separation to your background. And very often the added depth of field will work in your favor. I hear people complain that they can't get a remote focus for their DVX100 to use when the camera is mounted on a jib. Hey, when you are shooting full wide at f/4, everything from 2 feet to infinity is in focus, so what are you worrying about focus? See, every cloud has a silver tinted lining. |
<<<-- Originally posted by Wayne Orr : Again, my point is that narrow depth of field is impossible to achieve with small chip cameras under normal conditions, so rather than fighting it, work with it and use other methods to give separation to your background. -->>>
I wholeheartedly disagree with this. My experience with the small camera format goes from Canon 814 & Nizo 2056 Super8, right through Video8 and Hi8 and now to DV with VX2k , 950, 900. Follow my advice given earlier and slim DOF (blurry foreground or background ) is a cinch. |
Then John, I am sure you will be happy to post a clip or two for our examination. Earlier you wrote:
"so using this for the background blur effect you need - arrange your camera to subject distance to be approx 1/4 (or less) of the distance of the camera to the background. Then the aperture will act as a background blur control (small f number - more blur)" So, if we are shooting an actor that is ten feet from the lens, to get the blur effect the background must be an additional thirty feet away? That's handy. |
Wayne
check back tomorrow and the shots are yours its a bit dark over here at the moment |
Wayne,
Quote:
You ask why discuss Coc when it does not enter into determining DOF? It's very simple. You can not determine DOF without having a value (size) for Coc. Every chart, scale, guide, Palm program will allow you to add a value or uses a predefined one. The Panavision site uses predetermined Coc in their equations. You can not define sharpness without Coc. Most people have a curiosity about those things. If all this is old hat, I'm sorry. Gloss over my instructions, but understand, many members and guests want to learn as much as they can (I've already received 3 emails on the subject). |
Chris,
"Any other DoF image examples, anybody?" I have a couple of DOF frames but need some advice on how to post them. Thanks, Bob |
Ball of Confusion
Jeff writes, "I didn't bring up Coc in this discussion. It was brought up by you and Jay."
Excuse me, Jeff, but the first mention of Circle of Confusion (aptly named for this discussion) was brought up by you in an earlier response to my recommendation of the Panavision site. You wrote: "The Panavision site uses non-standard values for CoC." A few other comments. You did not respond to my quote on the Arricam: "...the Lens Data System (LDS) that “shows relevant information from the lens in use, such as focus and iris settings, the focal length, as well as the resulting depth of field..." No mention of the two missing factors from your "5 factors for determining depth of field," although later you did say; "I suspect it (the LDS) does not show Coc because it would be fixed data and would not change, why clutter the display with information that would not change." But later you said, "The diameter of the Coc is not a fixed number, nor is it's size agreed upon as an industry standard." How can it be "fixed data" one moment, and then "not a fixed number, nor its size agreed upon," the next? Later, I asked, "just how does this apply to Jason's original question:" which was "I have been trying to get the camera to focus on people a few feet away and then blur the background. What is the trick to this with the GL2?" No reply from J.D. You write: "You can not determine DOF without having a value (size) for Coc. Every chart, scale, guide, Palm program will allow you to add a value or uses a predefined one." Oh? The "Kelly-Wheel" which is used by film camera assistants to determine depth of field does not list the Circle of Confusion. One final reference: "The depth of field in an image is controlled by three factors: the distance to the subject, the focal length, and the aperture used to capture the image." "For users of compact digital cameras, depth of field is a subject of special interest becuase depth of field is more difficult to control with a compact digital camera than with earlier film cameras. The small imaging sensors of compact cameras require the use of short focal lengths, and this in turn gives these cameras an unusually long depth of field when compared to 35mm cameras. Thus, intentionally getting a shallow depth of field is more difficult." http://www.megapixel.net/cgi-bin/fs_...ticle-dof.html (this is an excellent site with good graphics to explain depth of field) For John Jay, who writes, "Follow my advice given earlier and slim DOF (blurry foreground or background ) is a cinch." "The bad news is that it is much more difficult, using a digital camera, to blow the background out of focus, which is a pleasing effect in portrait and nature photography. You will have to use the longest possible focal length, and keep your lens wide open. Well, there is no free lunch. I'm not retiring my 35 mm SLRs yet. (2002 note: I'm lying! In the last year I went through just two rolls of film.) In close-up photography, the greatly increased depth of field is a lifesaver. I never had so good, sharp tabletop pictures as I have now, in the digital domain." http://www.wrotniak.net/photo/dof/ Andrzej (Un-jay) Wrotniak Wayne Orr Caveat Emptor |
I stand corrected, I did mention Coc first, because of the Panavision use of non standard Coc values for some formats. My apologies to you and Jay.
I still stand by my assertion that many members and guests have an interest in DOF and Coc. Many are film photographers and while they can't apply all of this to video, it is very applicable to their traditional film photography and darkroom work. This is quite obvious by the number of views this thread is getting and the number of emails I'm receiving. I've not commented on the link I asked for because it is a lengthy article and I could not easily find the quote. I can't find where Alsobrook is talking about Arricam. When I have more time I'll read the article. Sorry. The Kelly-Wheel uses a fixed Coc, like the Panavision site. All five factors are listed in the DOF Skinny thread and DV Info article. The Coc value changes with the size of CCD or negative used. Once established for your size CCD the value will remain fixed. You have noted the larger format cameras have less DOF. Why? They have a different value Coc. I thought your asking of Jason's original question was a sort of rhetorical question or something on your part. My answer to Jason's original question is contained in previous posts. Jason stated he would experiment with the suggestions and post back results and further questions. Now I'm pretty much trying to help you understand it. I previously mentioned that a great many articles and web sites have errors and half truths. This is evidenced by your continued reference to these sites that list only 3 factors for DOF. I thought the American Cinematographers Manual, 8th edition (published by the America Society of Cinematographers) and their published formula would be good enough for you. Their formula requires five values. 1. focal length of the lens 2. f-stop number (size) 3. Coc 4. distance from camera to object (subject) 5. Hyperfocal distance (derived from first 3 values) In the article and Ultimate thread I list the fifth value as "The viewer's personal standard of the permissible degree of sharpness (or unsharpness)". This is after all a subjective medium. I don't argue sharpness. If you insist your image is in focus, who am I to argue with you. |
More balls
I'm sure that would get me a lot of work. Yeah.
Jeff, you and I are never going to walk down the aisle. I think you are obfuscating a subject that to people using camcorders should not be so complicated, based on my considerable experience. It would be totally out of the realm of reality to expect someone with a GL1 shooting a "movie" to sit down and "do the math" in the formula for depth of field you refer to, everytime they set up a shot. It also does not answer the original question, "how do I blur the background?" Wayne Orr Caveat canem |
<<<-- Originally posted by Wayne Orr : Again, my point is that narrow depth of field is impossible to achieve with small chip cameras under normal conditions, so rather than fighting it, work with it and use other methods to give separation to your background. -->>>
Wayne, you asked for some frames.... Technical Data f1.6 shutter 425 subject distance 1.6m background distance 6.3m Optical zoom 50% approx 22mm Axe : Sony TRV950E Ambient temperature 16 C Weather Cloudy Dull Frame Rate 50i Procedure - record to DV then grab stills to Memory stick 640x480 then upload to yahoo briefcase as below DOF examples of background blur (dofbg) and foreground blur (doffg) found here http://photos.yahoo.com/bc/agentpurp...c=ph%26.view=t http://photos.yahoo.com/bc/agentpurp...c=ph%26.view=t |
John, I hardly know what to say. I guess then, your advice to someone looking for the blurry background would be:
Shoot wide open, at 22mm, at shutter speed of 425 (never mind the jerky motion), make sure your background is at least 20 away, and your subject is the size of a liter of Coke, and you will end up with a somewhat blurry background. Perfect. May I recommend to you the movie, "The Patriot," starring Mel Gibson. I think you will find some of the blurry background pictures in that film are more in keeping with what Jason had in mind. And no motion effects from the hi speed shutter used in your pix. Sorry, John, no sale. Wayne Orr Veni, vidi, vici |
DOF Dummy (that's me)
The way I do it is like this... it's very technical, so try to stay with me.
Okay. I point the camera at the subject and fuss around with the lens and exposure settings. If I get it to work, cool. If I can't, I blame it on poor lighting or Canon... sometimes both. |
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