Critical Focus
by Cadge31
on
Oct 1, 2007 at 3:46:03 pm
Simple question,
Is it easier to obtain critical focus with a Sony Z1U, or a JVC 110U with the stock lens? In other words, which camera doesn't have to be 10 miles away from the subject to obtain critical focus? Or is it 6 of 1 1/2 dozen of the other?
Re: Critical Focus by Mark Suszko on Oct 2, 2007 at 1:39:22 pm
Isn't it hard to give this answer without knowing a few things like the iris opening, the filter, the shutter speed, the overall lighting level? These are how you control depth of field. Or I'm misunderstanding the question too.
Re: Critical Focus by Mark Suszko on Oct 2, 2007 at 4:23:19 pm
Imaging chip size will have a role in that as well. I still don't get the question from a practical point of view.
Strictly judging optics, you look at how many pieces of glass are in the zoom chain and what kind of f-stop range you get.
Every lens has it's own sweet spot for "best" exposure which varies between makes and brands due to different choices and compromises being made by the manufacturers to favor one or more dimensions like price, ruggedness, chromatic abberation, etc. That particular sweet spot exposure setting, coupled with other settings being equal, then gives you a depth of field that you can compare to another camera set at it's own sweet spot and all other variables accounted for, so under those conditions you might be able to say "this one stays sharp for ten feet and that one for eleven". But this seems like nonsense to me from a practical shooter's perspective.
But even given that sweet spot, you still have so many factors that come into play, distance to the subject,overall light level, the shutter, the filtration, etc. that it really is kind of pointless IMO to say one lens has a longer depth of field than another. You can within reason make any lens demonstrate an identical depth of field, that doesn't *prove* anything IMO. DOF is something that you can vary widely if you know your tools and techniques well. Small cheaper DV camcorders tend to come with a huge depth of field, which give a characteristic (some say annoying and amateurish) look compared to bigger lenses with shallower DOF, where you are deliberately directing the eye around the frame by selective focus.
Is that easier to do with a big camera and big lens? Sure.
Is it possible to do with a dinky handicam? Again, yes, within limitations.
So my definitive answer to the question is that it's a definite, possible, 'maybe'.
If you are asking: "which camera can you do the most flexible selective-focus work with", I would say the one with the best low-light sensitivity, and the largest imaging chips and lens you can afford, coupled with a lot of shutter settings and filtration options and a great light kit.
If you have to ask... by Arniepix on Oct 2, 2007 at 4:57:26 pm
If what you're really looking for is shallow depth of field, then you're looking at the wrong cameras. You should be looking at cameras with larger sensors, 2/3" cameras or bigger. Of course, that's going to put you in a whole 'nother price range, plus the price of the glass.
If it were my dime, I'd be looking at the larger Panasonic P2 cameras, Silicon Imaging's SI2k, Red (be prepared for a long wait), or Tompson's Infinity (should it ever get out the door). Not necessarily in that order.
Arnie
Now in post: Peristroika, a film by Slava Tsukerman
Re: If you have to ask... by Cadge31 on Oct 2, 2007 at 5:04:59 pm
I always appreciate the adivce and suggestions I get on Creative Cow. Sometimes, I must say, it is frustrating in the same breath. I mean, it's tough to complain about free advice, but very very rarely do I ever get a straight answer on questions like this.
It's like "which is better A or B", and no one can just give me a straight up answer like "A is better", or "B is better". It seems everyone has a different agenda.
Re: If you have to ask... by Mark Suszko on Oct 2, 2007 at 6:54:32 pm
As in most multiple choice questions, the answer is "C".:-)
You know, you kinda knew the answer when you first posed the question, in that you asked if it was sort of six of one/ half a dozen of the other.
Without digging thru the spec sheets for you for free, all I'm willing to commit to for an answer is if their chips are the same size and the lenses are basically the same, their DOF control is going to be the same, not enough difference to matter.
If your real beef is that you seem to be having to set the camera too far back in a small space, and them zoom in to start getting DOF you can control, well, in the smaller-sized lenses and chips, the only other way to get the effect without the help of distance is to crank in more lights so you can force the iris down to the smallest workable opening and then compensate the iris setting with shutter. I hope I got that right, I always remember it's one extreme or the other but I sometimes flop which one if is, opened-up all the way or closed almost to nothing. When I need to do this stuff in the field I just start tweaking settings until I get what I like, I don't always approach it scientifically.
There's a well-done introduction to depth of field manipulation at the DJTV section of the digital juice website. Check their archives of past episodes. Their short little streaming videos are all quite nice; though generally aimed at less experienced users, they do a good, clear job of illustrating a topic in an overview without talking down to you, and occasionally even I learn something new from some of them. I find some of them good for explaining concepts to clients too.
And an even more specific one, Perry is pretty good...:
http://www.digitaljuice.com/djtv/segment_detail.asp?sid=56&sortby=&page=12&kwid=0&show=all_videos
Re: If you have to ask... by Mark Suszko on Oct 2, 2007 at 7:20:23 pm
See I DID get it switched around, darn it:-) You OPEN the aperture wider, then compensate with shutter or ND filter, plus the distance to get a DOF you can manipulate.
Re: If you have to ask... by Arniepix on Oct 2, 2007 at 7:47:08 pm
[Cadge31]"It's like "which is better A or B", and no one can just give me a straight up answer like "A is better", or "B is better""
Sorry, but sometimes the most straightforward, honest answer is "none of the above". You want me to tell you which one to buy? My answer is niether. Your 2 options are simply not designed to deliver shallow DoF. But it's not my money, so why should my opinion really matter?
[Cadge31]"It seems everyone has a different agenda."
That's not really a fair statement. You asked very general question, but want a very specific answer to it. And different professionals may approach it differently, anyway. We all have our biases, fair or not, and differing experience & point of view leads us to different solutions to the same problems.
My personal bias is that it's much better, faster, & cheaper in the long run to do things right. And I'm tired of trying to do more with less. Rather than cutting corners & "fixing" things in post, I'd prefer that film makers do things right in the first place. If that means spending a little more up front, well, then it means raising a little more up front. The odds are that you'll not only save more in post than you spent on a better production, but that you'll be happier with the result.
Arnie
Now in post: Peristroika, a film by Slava Tsukerman
Re: If you have to ask... by adkimery on Oct 3, 2007 at 3:29:18 pm
If you are looking to get a shallower depth of field and can only budget for a sub 10k camera you might want to look at getting a 35mm adapter. W/the exception of the soon-to-be-released Sony EX camera all the sub 10k cameras have similar sized imaging sensors and similar lenses so they'll all have similar DoF.
Re: Critical Focus by Rennie on Oct 17, 2007 at 3:54:47 pm
[Cadge31]"Which of these two cameras with no ad-ons has a shallower depth of field, if either.
"
This is a common misconception. Depth of field (DOF) is dependant on the apature and the film or CCD size. The smaller the imager the greater the DOF.
If your shot list calls for a tight 2 shot of 2 talking heads you could shot it with a telephoto lens from way back. Telephotos have shallow dof but if you took a wide lens which has a deep dof you would need to get right up to the talent to frame the same shot and the dof would be the same because you are so close to the subjects. Lens selection should be a matter of astetics, wide stretches distance while telephoto compresses distance.
It's all relative to the physical world we live in and size of the capture device (CCD or film) and apature we use to record their images. In our world if you filmed the same object with a variety of cameras with different sized imagers at a given apature so that you fill the entire frame DOF will be like this:
A 1/3rd" CCD at F:2.8 = DOF-----[_____________________________________________________]
A 2/3" CCD or 16mm film = DOF [___________________________________________]
A 35mm Film = DOF ----------------[_____________________________]
A 70mm film = DOF -----------------[________________]
To get less depth of field you will need the 35mm converter or you could buy a RED and shoot real 35mm video!
35mm converters typically have a macro lens that attach to your camera lens which focuses on a ground glass the size of a piece of 35mm film. You then use 35mm lenses to focus on that ground glass. In this way you are always filming an image on a ground glass in actuality and in so doing you inherit the dof of the 35mm lenses as they form the image on the ground glass.
Simple answer by Steve Wargo on Oct 16, 2007 at 4:03:20 am
[Cadge31]"Simple question,
Is it easier to obtain critical focus with a Sony Z1U, or a JVC 110U with the stock lens? In other words, which camera doesn't have to be 10 miles away from the subject to obtain critical focus? Or is it 6 of 1 1/2 dozen of the other?"
Simple answer(s): Neither one and both of them.
There is a reason that the big boys have shallow depth of field: They pay for it by using prime lenses on large imagers.
Until you're ready to step up to the plate and put your money down, the only way will be a lens adapter.
This question reminds me of the guys who want to edit 10 bit uncompressed HD on their VAIO laptop and wonder why we can't tell them which model at Best Buy will do just that.
In order to Play, you first must Pay.
By the way, you asked two questions: 1. Which one does, and then, 2. Which one doesn't. If I could only choose between those two, it would be the JVC, because you can switch out the lens. Buy the camera with no lens and then buy a set of 1/3" primes.
And, don't forget to be equally concerned about things like story, lighting, directing, talent, and the all important, critical sound.
Steve Wargo
Tempe, Arizona
It's a dry heat!
Sony HDCAM F-900 & HDW-2000/1 deck
5 Final Cut Pro systems
Sony HVR-M25 HDV deck
Re: Critical Focus by Rennie on Oct 17, 2007 at 3:31:51 pm
Critical focus is just that, how sharp you are focused. Good prime lenses have color coded apature numbers acompanied by focus margin markings on the focus ring. If you look at one of these and turn the focus ring to say, F:8 and the numeral is red there will be 2 red lines on the focus ring. Turn the focus ring to 12' (as if you are filming a tight 3 shot full length). When the 12' mark is in the center (focused line) you can now look at the red lines and everything inbetween is in focus at that apature. Lets say this indicates everything between 16' and 10 ' is indicated to be withing the depth of field. The critical focus point is 1/3 of the way from the closest distance (10') The dof range at this apature and distance is a span of 6' (hypathetically). 1/3 of the way in is 12' which is the critical focus distance. You can now take a tape measure and measure this distance, set the focus ring at 12' and hit record, there is no need to look through the lens other than to frame the shot.
Lets say you take the same shot at F2:8. The lens manufacturer would not have enough room on the focus ring to place the 2 color coded lines on the focus ring to indicate the in focus area so color coding of apature numbers and indicator lines often does not start until F4 or F5.6. A wider (more open apature) has a shallower dof so you may find for the focal lenght there is only 1.5' infocus at F2.8 so everything from 11.5' to 13' is in focus and critical focus is 12'.
There are only 3 parameters used in filmmaking. The 1st is film stock which has a definate asa or light sensitivity. Once loaded there are 2 other controls required to properly expose it. The apature or lens opening controls volume of light hitting the film frame and the shutter also regulates the volume of light hitting the film frame. Together they control proper exposure of the film for a given asa. The apature effects dof while the shutter effects motion blur. The cinamatographer must decide which combination is best or more important for each shot.
Video tape has no asa so the relationship between shutter speed and apature is not crucial like with film but these 2 regulators still maintain their characteristics visually.
