Thread: Focusing

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    Focusing
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    Seems like people are finding that getting precise focusing is not so easy in high-def; certainly not as easy as it was in standard-def. In this post we'll explore focusing and explain the techniques you need to use to get razor-sharp focus out of an HVX200.

    First, let's understand that focus is absolutely critical in high-def. You're dealing with an end frame that has between 2.7 and six times as many pixels as a standard-def frame. Standard-def's low resolution could mask a world of focus errors; high-def's sharpness will point out focus errors blatantly, each and every time. You have to get your focus right.

    Second, let's acknowledge another fact: it's impossible to judge focus at all on the on-camera LCDs. The very best you can do is ballpark; it's mathematically impossible to focus a 2-million-pixel image on a 200,000-pixel display device. No small high-def camera's display is going to be adequate, by itself, to show you proper focus. It's just not possible. If you insist on trying, recognize that the viewfinder has more pixels than the LCD panel does, so it may help you get a little closer to accurate focus, but it's not enough to make the difference you need.

    If you need precise focusing you will HAVE to use something other than the onboard viewfinder/LCD on all the small HD cameras. Even if it's just the magnified focus assist, or the peaking, or a tape measure, or an external full-resolution monitor. You cannot just look at the LCD and judge whether the image is in focus on any small HD/HDV camera.

    With that said, let's talk about what you can do, and what you should do, to get proper focus.

    When setting focus you want to find the exact spot where the focus is pinpoint-sharp. Usually people do this by focusing too far until something starts to go out of focus, and then they pull back until it comes back into focus and then too far so it goes out again, and keep refining this process and splitting the difference until they get the absolute sharpest image. Which is fine, but only if you can actually SEE what you're getting (which brings us back to the monitoring/display situation!)

    There are many focus assist methods you can use to assure you're getting the best focus possible. If you can, use them all -- you're going to find they all are helpful.

    First, there's the magnified FOCUS ASSIST which brings up a square window with a tight center extraction from the frame. This is a wonderful option and I find it absolutely indispensible for achieving sharp critical focus.

    Second, there's the EVF DTL system (also known as "peaking"). Simply put, you MUST use this. Press the EVF DTL button on the back of the camera until the LCD shows "EVF DTL ON". Peaking uses the high-frequency detail in the image to draw an outline or highlight on bits that are in focus. If you don't have EVF DTL on, the LCD will simply look too blurry to get accurate focus; with EVF DTL on you'll see when areas of the image start to "snap" into focus. Combine EVF DTL with the FOCUS ASSIST and you're well on your way to getting sharp precise focus.

    The third focus assist feature is the distance readout in the viewfinder/LCD. This lets you see to an extreme degree of precision just where your lens is being focused at. If you use a tape measure you can focus very accurately just by measuring from the front of the lens to your subject, and then setting the focus ring to that distance setting. Recently we've been using a laser tape measuring device from Home Depot -- aim the red spotting laser at the point you want to focus on, click a button, and it will report the distance down to the inch. Then spin the focus ring to that distance, and voila -- instant perfect focus. A tool like the Leica Disto laser measurer can be very accurate; even the inexpensive A3 claims accuracy within three millimeters over the distance of 100 meters! (Note: don't even waste your time with ultrasonic measurers, you want/need laser if you're going to try this method). And, obviously, lasers should NEVER be shined in anyone's eyes! If you're measuring distance to people or other living things, don't use the laser and doubly don't use a laser around anyone's eyes!! Only use a Class II low-power laser emitting less than 1mW, and never use a Class III or higher around any person's or animal's eyes.

    The final focus assist feature you could want/use would be an external high-resolution production monitor. A native 1280x720 LCD panel will provide enough res to focus accurately with 720p; a 1920x1080 LCD would give you enough pixels to accurately focus 1080i/p.

    If you don't use some or all of these tools, you're fooling yourself. If you use most or all of these tools, your focus is going to be perfect.

    Okay, so now that we know how to use the focus assist devices to get the best results, you now need to know what you want in focus, and how to make sure that it is in focus.

    Typically when shooting people, you want to set the focus on their eyes. Don't focus on the nose or ear or anyhere else -- you want the pupil of the subject's eye to be the crispest focus of the whole shot. And in order to know that the pupil is in crisp focus, you will usually want to check your focus by narrowing your depth of field.

    When judging focus it's obviously so much easier to judge what's in focus if the depth of field is extremely narrow (meaning, very little is actually in focus in the shot; when only the part you want is in focus and everything else is out of focus, it's obviously pretty easy to know that you've properly focused your shot). To narrow the depth of field for checking focus, zoom all the way in (Z99/55.0mm) and open the iris all the way up (f/2.8 or OPEN). If the image gets too bright and blown-out to see what you're looking at clearly, pop in one of the neutral density filters, but the important thing is to be at f/2.8 and Z99 when setting critical focus. That will narrow the depth of field down enormously, letting you choose exactly where to set your focal point. Then, before shooting, you'll zoom back out and set your iris to the proper exposure again.

    As you zoom out, the depth of field becomes deeper, which brings more and more of the frame into focus. And as you stop the iris back down to the proper exposure, more and more of the frame comes into focus. So if you can nail the focus at f2.8/Z99, then as you zoom out and stop down you can be assured that the focus is just getting better and better, crisper and sharper.

    Don't go too far though! F/5.6 is about as small an aperture as you want to use; maybe f/8 but that's it. Don't go to f/9.6 or f/11 when shooting high-def, or the image will get softer again due to the principle of diffraction. Stick between 2.0 and 5.6 whenever possible.

    Another focus assist tool is autofocus -- if you can't get focus any other way, you can press and hold the "PUSH AUTO" button until autofocus locks in. That's no guarantee that your focus will be accurate, however; autofocus may not choose to lock onto the part of the frame that you prioritize as being most important. If you have no other way of double-checking your focus, temporary autofocus is probably better than nothing, but it certainly shouldn't be your primary focus assist tool.
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    Focusing for drama/film: have a production monitor handy. Zoom in to Z99, and open the iris to f2.8. Measure to the subject using a tape or (if eyes are not in the shot) a laser measurer, and start the focus ring based on what the tape/laser says. Then refine the focus by watching the monitor until you've found pinpoint sharpness. (if you don't have a monitor, use the FOCUS ASSIST and EVF DTL, and make arrangements to get a monitor!)

    Focusing for events/run & gun: learn to estimate distances. Practice with a laser tape or an actual tape and learn to judge distance accurately. Ballpark focus using the distance meter, and fine tune using EVF DTL and FOCUS ASSIST (when possible). Also, avoid full telephoto and wide-open iris; if you can stay around f/4.0 or f/5.6 you'll have much deeper depth of field, and keeping the lens wider (under 20mm) will also give deeper depth of field.
    Last edited by Barry_Green; 04-30-2006 at 01:24 AM.


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    Senior Member Chris Messineo's Avatar
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    Barry,

    As always great information.

    Regarding number 3, when trying to measure the distance between the camera and your subject, where in the viewfinder does it display the distance. I see focus as displaying a number between 0 and 99. Does that translate to inches? Am I missing something obvious? Also from where on the camera should I measure (on the DVX we used to use the shoe on top)?

    Thanks,

    Chris


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    Senior Member JoeNash's Avatar
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    chris did you finally get that big order in ?


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    Yes you're missing something Chris -- go into the menus into display setup, and change from NUMBER to FEET/MM (or, for our Metric friends, mm/mm). That'll give you a readout in feet or meters instead of inches.


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    Senior Member Chris Messineo's Avatar
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    Barry, I made the change - very cool. I am going to pick up a laser measure tomorrow.

    Joe, The big order did arrive and I am like a kid at Christmas.

    Chris


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    Senior Member JanBee's Avatar
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    Quote Originally Posted by Barry Green
    Recently we've been using a laser tape measuring device from Home Depot -- aim the red spotting laser at the point you want to focus on, click a button, and it will report the distance down to the inch.
    Thanks a lot for the sticky!

    I wonder if you're really referring to a laser-only device. The ones I've checked out are 400 Euros++, and there are some inexpensive ones for 50 Euros that have a laser to aim and use ultrasonic to measure the distance with an error of about 5mm (well, that's what they claim). I guess the home-depot thingy you've mentioned is not a very expensive one, right?

    Sorry, I just want to make sure I buy no crap. :-)
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    Senior Member Anders Holck's Avatar
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    You need a real Laser mesure like barry says, Laser pointers with Ultrasonic mesure only works for large surfaces at straight angles. They wont work for small targets or off axis mesurements.

    And beware that you can easily ruin someones vision permanently with theese devices. Be a pro when operating them and do it with care. Never ever try to mesure for a closeup at the forehead of someone. Keep a small tape mesure for that kind of stuff....
    Last edited by Anders Holck; 03-12-2006 at 08:12 AM.


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    Senior Member dougspice's Avatar
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    What is the point of measurement for judging distance? Is there a mark equivalent to the "film plane", or does Panasonic consider the measurement from the front of the glass?

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    Senior Member for_mlove's Avatar
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    I did some looking around, and this looks to be the least expensive unit that would work well. Can you tell us which unit you were using Barry?

    http://www.stanleytools.com/default....tance+Measurer

    You can find this unit at Home Depot oniline, Amazon and several other online stores, but they all seem to be the same price, about $100.

    *edited to change link that didn't work*


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    Thanks, barry. As always, your writing is so clear and inspiring.
    So, any more info on the timetable for the HVX book?


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