Focus...Pull vs Rack vs Repeat vs Measure Focus

A

alumna

Active member
Would greatly appreciate enlightenment on this topic and/or direction to threads where this is covered in some depth.

What is the difference between pulling focus vs measuring focus vs repeating focus vs racking focus? How do they work? What are their implications? (And dare I ask if there are even more tentacles to this focus octopus?!)

How do these various kinds of focus issues relate to the dvx100a and should one consider using certain charts or guidelines in this context? I'm new to this lovely camera and get very nervous when the manual mode is turned on.

Any tips, techniques, tutorials or other nuggets of wisdom would be most valuable. Thanks in advance for your help!
 
Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Pulling focus essentially means adjusting the focus to either keep a moving object or subject in focus as said object/subject changes distance with relation to the camera (i.e., moves closer or farther from the camera, or the camera moves closer to or farther from the subject), or to concentrate attention on a specific object within the frame (e.g., adjusting the focus from a near object to a far object or vice versa).

Racking focus usually refers to a quick focus change; for example you have two people in frame, one in focus, one out of focus, and you rapidly shift focus from one person to the other.

Measuring focus is traditionally done in professional film production, where camera assistants physically or electronically measure the distance from the camera's film plane to the subject, in order to set the proper focus on the lens (unlike the DVX's unmarked lens, professional lenses have focus marks on the barrel). With the DVX, the easiest way to check your focus and get focus marks is to simply zoom in to your subject, focus, then zoom back out to whatever focal length you're using.

There is a chart available on-line somewhere that provides actual distance equivalents for the DVX's focus number readout, but I find it much easier to simply use the DVX's readout for focus reference.

An important thing to remember when shooting with a 1/3" CCD video camera like the DVX is that it has much greater depth of field than 35mm movie or still camera lenses, meaning that you have more leeway with regards to focus, especially at wider angles; getting precise focus isn't as critical or difficult, since more of the image from near to far will look acceptably sharp.

At tighter focal lengths (towards the telephoto end), and at wider apertures, depth of field decreases, making proper focus more critical.
 
Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Wow! Thanks very much for your clear and instructive reply. It was tremendously helpful. Some follow-up questions, if I may.

I now understand how to achieve racking focus with the DVX. (Simply turn the focus ring alternately between the two subjects/objects in the frame?) But what is the best way to pull focus accurately, especially as the subject/object is moving away from or toward the camera? Is this done by designating a start and stop zoom number and then aligning this number with the corresponding focus number on the DVX's readout?

With respect to your point on tighter focal lengths (telephoto and wider apertures) ... what is the proper way to attain sharp focus in those situations?

Also, what is "repeatable" and "follow" focus? I've heard these terms bounced around as well, but don't understand them.

Here's a link to a measuring focus chart kindly posted by HansK in response to a previous question by direktor. http://www.flickerfactory.com/egp/morestuff/dvx100.htm. Is this what you had in mind? (I hope I won't need another lesson in understanding how to read this stuff!)

Thanks again for providing an excellent education!!
 
Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

[quote author=alumna link=board=Events;num=1093065887;start=0#2 date=08/21/04 at 07:14:47]Wow! Thanks very much for your clear and instructive reply. It was tremendously helpful. Some follow-up questions, if I may.

I now understand how to achieve racking focus with the DVX. (Simply turn the focus ring alternately between the two subjects/objects in the frame?) But what is the best way to pull focus accurately, especially as the subject/object is moving away from or toward the camera? Is this done by designating a start and stop zoom number and then aligning this number with the corresponding focus number on the DVX's readout?[/quote]

The most accurate way of pulling focus is to get focus marks for every distance at which your subject will be during a given shot. If, for example, your character moves from point A to B, then to C, get focus marks at all three points; have the subject stand at each of the three points, zoom in, focus, write down the focus readout number for all three points.

Then during the shot, turn the focus ring to the numbers corresponding to the actor's position as you noted. Say point A=50 on the focus readout. And point B=80. Your actor starts at A, close to the camera, so you begin with the focus at 50. Then as your actor moves farther from the camera, to point B, turn the focus ring to 80, preferably at a speed corresponding to the actor's movement. If he's moving quickly, turn the ring quickly, if he's moving slowly, turn it slowly.

[quote author=alumna link=board=Events;num=1093065887;start=0#2 date=08/21/04 at 07:14:47]With respect to your point on tighter focal lengths (telephoto and wider apertures) ... what is the proper way to attain sharp focus in those situations? [/quote]

The easiest way to find your focus marks with the DVX is to zoom in to full telephoto on your subject, focus, then zoom back to your desired focal length.

Just bear in mind that when shooting at longer focal lengths and wider apertures, you'll have less depth of field; i.e., less of the area behind and in front of your subject will be in focus than it would be at a wider angle, so getting the correct focus will be more critical, and it'll be more obvious if your focus is off.

[quote author=alumna link=board=Events;num=1093065887;start=0#2 date=08/21/04 at 07:14:47]Also, what is "repeatable" and "follow" focus? I've heard these terms bounced around as well, but don't understand them.[/quote]

Repeatable focus usually refers to being able to perform the same focus pull accurately numerous times, which is possible with professional video and movie camera lenses, but generally not with consumer video cameras. On a professional lens, distances are marked, making it easy to set the lens to a specific focus; 10' will always be 10' feet, for example. On a consumer video lens, there are no focus markings, and thus no way of accurately determining the focus save for zooming into the subject to check.

The DVX is an anamoly in this regard, because though it doesn't have a true manual focus lens (the "manual" focus ring actually works via electronic servo), the focus ring allows a nimble enough control to closely replicate the effect of focusing via a true manual lens, thus allowing you to "repeat" a focus move; i.e., turning the focus ring a specific distance will always yield the same change in the focus, rather than the focus change varying in accordance with how fast or slow you turn the ring.

The DVX's focus readout numbers also aid greatly in "repeatable focus," since you can easily do the same focus pull numerous times by using the readout as reference. For example, if you start with the focus at 50, then pull to 80. This essentially allows the lens to function as a pro cine lens, since the readout numbers always represent absolute, unchanging values; 80 will always correspond to 12'4" (according to the handy chart you link to).

On most of Sony's consumer cameras, turning the focus ring rapidly for a short time (say, a quarter of a turn) will yield a focus change equivalent to turning the focus ring slowly for a longer time. Combined with a lack of numerical reference, this makes it very difficult to repeat a focus pull.

As for "follow focus"... a "follow focus" is a system comprised of a gear that interfaces with a lens focus ring and is connected to a knob by which one can pull focus. This is traditionally used on professional film and video cameras to allow a camera assistant to easily and smoothly operate the focus (it's easier to turn a knob that it is to have your hand around the lens, particularly a large cine lens), and facilitates the marking of focus points (the camera assistant will measure the various focus points for a scene, mark them on the lens or follow focus knob, and use these as reference when pulling focus during a shot). Take a look at the Chrosziel follow focus system here (http://www.16x9inc.com/chrosziel/dvcine/dvx100/followfocus/) to see what I'm trying to describe. Hopefully it'll make more sense once you see what it looks like.

[quote author=alumna link=board=Events;num=1093065887;start=0#2 date=08/21/04 at 07:14:47]Here's a link to a measuring focus chart kindly posted by HansK in response to a previous question by direktor. http://www.flickerfactory.com/egp/morestuff/dvx100.htm. Is this what you had in mind? (I hope I won't need another lesson in understanding how to read this stuff!)

Thanks again for providing an excellent education!![/quote]

Here's a site that explains focus-pulling in depth, in a much more clear fashion than I have. Hope this all helps!

http://octopus.drama.bris.ac.uk/OnlineDocs/FocusPulling/
 
Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Thanks so much again for your incredibly lucid explaination. My brain now has a clear focus on this topic.

You're my professor and you rock!!! ;D
 
Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Hello,
I am a newbie and i was looking for PRECISELY the same information that was being discussed here. I got all excited about the link but when i tried it, it didnt work. Could you please tell me how to get the chart for the focus readout?
This would solve my focus questions cos i am planning on making a short film and i was pretty worried about manual focus.
Thank you very much!
 
Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Stas - Thanks for re-sending the link to anu.

anu - Glad to hear you found the thread/link helpful. Stas is a fantastic teacher ... and this is an amazing forum! Let us know how your short film develops and how your manual focus shots work out. :)
 
Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Stas -- excellent posts!
 
Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Thank you Stas!!! Thats fantastic!!! :):) i am THRILLED. You wont believe the amount of discussions we ve had regarding using the follow focus or not, how etc etc etc. This should make it MUCH easier for our DoP!
Thank you again! But err i have another question, can i use the zoe zoom controller or the stealth DVX for smooth focus shifts? I was thinking that in concert with this chart, the zoom and focus controller should be good? what do you think?
Alumna i am learning a lot on here and LOVING it :)
 
Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

As far as I know, there's no way of controlling the DVX's focus via a remote.  The Zoe controller only allows remote operation of the zoom. (The DVX lacks a LANC port, which allows control of both zoom and focus on other mini dv cameras via remote devices like the Zoe and Varizoom).

I remeber Varizoom demonstrating a remote focus controller for the DVX a year ago at NAB, but haven't heard anything about it since.
 
Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

whoa! i didnt know that the DVX doesnt have a LANC port!!!! i am buying a DVX102A here in India. And i assumed it had a lanc port. So i can ONLY go manual mode? maybe i 'll write to Varizoom and find out what they have to say!
 
Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

The DVX does not have a LANC port, and there is no provision for remote focus.

The only way you can get remote focus is with a physical motor/gear combination, which is what Varizoom demonstrated. Problem was that it was bulky and noisy, perhaps too noisy to be practical. But then again, this was over a year ago, so it'd be nice to see what the news is ...
 
Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

Re: Focus...Pull vs Rack vs Repeat vs Measure Focu

I wrote to Varizoom and here is what Colby Eaves from Varizoom said
" Anu,
   If you are referring to the DVX100 our DVX controls will work with your camera. We do not currently have a focus control for Panasonic cameras and have not set a launch date.
Colby Eaves"

so that means no focus control for the DVX 102 a  :-/
 
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