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Home: Video University Forums: Tech Q & A:
Follow Focus for Digital Shooting

dansen
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Aug 17, 2005, 11:44 PM

Post #1 of 21 (2392 views)
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Follow Focus for Digital Shooting	Can't Post

Hi everyone. Anyone here who has experience shooting with Digital video I'm sure has used a Follow Focus. Can anyone recommend a good place to buy them, particularly for the Canon XL2?

Also, can someone please explain why most people would say it's absolutely necessary to shoot with a Follow Focus. i have only ever shot one Corporate Video but didn't use any sort of extra except a Century Anamorphic lens. I'm not too sure how a Follow Focus could benefit me when making short films or indeed, how it works.. I mean, doesnt the camera focus itself?

Thanks suggestions or answers would be greatly appreciated. Thanks

djtoltz
User

Aug 18, 2005, 12:03 AM

Post #2 of 21 (2389 views)
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Re: [dansen] Follow Focus for Digital Shooting [In reply to]	Can't Post

I was of the understanding that "follow focus" was a technique in which the camera operator (or the camera's autofocus) adjusted as the subject distance to the camera changed. In contrast to "rack focus" where the camera's focus changes to draw attention to a different area of the picture.
---
Douglas Toltzman
Hubert, NC

videobear
Veteran

Aug 18, 2005, 8:41 AM

Post #3 of 21 (2382 views)
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Re: [djtoltz] Follow Focus for Digital Shooting [In reply to]	Can't Post

That's correct, but I believe the poster is referring to a device which performs the function of adjusting the focus without having to touch the camera's focus ring. This device is also called a "follow focus", and, in the movie world at least, is operated not by the cameraman, but by a second person called a "focus puller".

As far as I'm concerned, a follow focus attachment is a very high-end piece of gear, and would not be needed for most corporate shoots. If you're an indie filmmaker and want the most control over your camera's focus, then sure. Note: The Sony FX1 and Z1U HDV camcorders have a feature that simulates this. You set the two focus points, then press a button, and the camera automatically moves from one focus setting to the other.

Regards,
Doug Graham
Panda Productions

mvmaker
User

Aug 18, 2005, 9:03 AM

Post #4 of 21 (2379 views)
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Re: [videobear] Follow Focus for Digital Shooting [In reply to]	Can't Post

Yep, what the bear said.

dansen
User

Aug 18, 2005, 10:03 AM

Post #5 of 21 (2374 views)
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Re: [mvmaker] Follow Focus for Digital Shooting [In reply to]	Can't Post

you only set two focus points? why two? and how do you set them?

mvmaker
User

Aug 18, 2005, 11:09 AM

Post #6 of 21 (2367 views)
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Re: [dansen] Follow Focus for Digital Shooting [In reply to]	Can't Post

In Reply To

you only set two focus points? why two? and how do you set them?

Actually on a film shoot you can have many focus points using a puller what the bear meant was that those two cameras will imitate this by allowing for two automatic focus points. There is no real reason other than that's how many they decided to incorporate into the cams.

Also two focus points is usually all anyone needs within one scene but with a cine cam your puller can set as many focus points you need.

(This post was edited by mvmaker on Aug 18, 2005, 11:11 AM)

djtoltz
User

Aug 18, 2005, 11:34 AM

Post #7 of 21 (2365 views)
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Re: [mvmaker] Follow Focus for Digital Shooting [In reply to]	Can't Post

None of this answers the original question about where to get such a device, but now you've got me curious.

Videobear's first answer made sense to me; especially from a 35mm film perspective where there is much less depth of field than with video cameras, and the cost of mistakes is much higher when burning through film.

However, when I think of a focus point, I think of a specific distance from the camera's focal plane that is sharpest, which is controlled in the camera lens by moving optics. There can only be one focus point at any specific moment in time, using a single lens. Are we talking about multiple cameras? Does the camera move from one focus point to another over a programmable amount of time? Are we selecting multiple points that must all be reasonable sharp at a specific moment, so the lens focus and aperature would be selected to best cover all of the points?

Is this device in the scene, or is it a programmable control on the camera/lens itself?

Shooting with video, there is always too much depth of field, in my opinion, so "follow focus", as a technique is generally trivial. Especially when, in many cases, the camcorder's autofocus will do the job. Starting out 25 years ago as a photo journalist, I learned to focus rapidly while shooting basketball, and other, fast moving sports. Today, I enjoy the challenge of following someone walking, using manual focus, but with 1/3" CCDs, it's just not that picky.

Finally, to reiterate my original point; we haven't helped the original post find this elusive and mysterious device?
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Douglas Toltzman
Hubert, NC

djtoltz
User

Aug 18, 2005, 11:39 AM

Post #8 of 21 (2363 views)
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Re: [djtoltz] Follow Focus for Digital Shooting [In reply to]	Can't Post

I think I answered my own questions about how this thing works, by re-reading the posts, and pondering the problem. What confused me was the note about someone else controlling the follow focus; I pictured someone walking around the scene with a special device, and my head got all messed up.

I'm understanding now that the follow focus is a device that memorizes two or more focus points and allows you to select them at will. I presume, there is also some sort of speed control, that would allow the camera focus to follow an object moving toward or away from the camera.
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Douglas Toltzman
Hubert, NC

mvmaker
User

Aug 18, 2005, 11:53 AM

Post #9 of 21 (2357 views)
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Re: [djtoltz] Follow Focus for Digital Shooting [In reply to]	Can't Post

In cinematic terms you have a camera man the guy looking through the lens. You also have a guy siting or standing next to the camera adjusting the focus as they film. The focal points are determined when the crew and cast block scenes. This would not be needed except how many scenes are there where the subjects are stationary? Also you have camera movement where predetermined focal points are needed as well.

In some vid cams they have two focal points that can be set. As time rolls along and digitsl cinema pushes the technology you will see more cams with almost unlimited focal points based on memory cards that hold your settings as they do now for certain setups.

videobear
Veteran

Aug 18, 2005, 11:54 AM

Post #10 of 21 (2357 views)
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Re: [djtoltz] Follow Focus for Digital Shooting [In reply to]	Can't Post

Quote

None of this answers the original question about where to get such a device

Try here: http://www.16x9inc.com/...p;catalogno=AC-FF-DV

Quote

Does the camera move from one focus point to another over a programmable amount of time?

Over time, yes. But the automatic feature's speed is fixed, not programmable.

Regarding your other comments:
Video's depth of field can be reduced by
- using ND filters and opening up the iris
- using the telephoto end of the lens, or using a telephoto adapter.

Also, focus is more critical with HDV, because the higher level of detail reveals what would have been acceptable errors in focusing if shot with standard definition equipment. It's so critical that JVC has a "focus assist" feature in the viewfinder of their HD100 camera.

I agree with you that autofocus is fine for many purposes.

Regards,
Doug Graham
Panda Productions

mvmaker
User

Aug 18, 2005, 12:04 PM

Post #11 of 21 (2356 views)
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Re: [videobear] Follow Focus for Digital Shooting [In reply to]	Can't Post

In film-making of course auto focus is not fine but for your needs it might be. There is noauto focus in the world that can be trusted enough to use on an important shoot.

Also might add that cinematic films have done away with the traditional focus puller for a hand held device.

mvmaker
User

Aug 18, 2005, 12:08 PM

Post #12 of 21 (2355 views)
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Re: [mvmaker] Follow Focus for Digital Shooting [In reply to]	Can't Post

http://forums.cgsociety.org/showthread.php?t=221133

A guy asks the same question and gets some very good answers.

djtoltz
User

Aug 18, 2005, 12:53 PM

Post #13 of 21 (2354 views)
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Re: [videobear] Follow Focus for Digital Shooting [In reply to]	Can't Post

Oh, Doug, don't get me started on the mathematics of DOF, etc. That is what I do mostly, as an engineer, is work with precise mathematical models.

DOF is actually determined by the physical distance of the lens from the focal plane, combined with the physical diameter of the aperature, and the distance to the subject. Therefore, a 50 degree field of view, using a 1/3" CCD will yield about 10 times the DOF as that same field of view when focused on a 35mm focal plane, because the first example will need a 4.5mm focal length, and the latter will use a 45mm focal length (approximate numbers). F 1.8 means the aperature diameter * 1.8 = the focal length. If the same field of view is achieved with a lower focal length, the physical aperature size for the same f-stop value is proportionately reduced, so all other factors being the same, depth of field increases.

One of the reasons I insist on getting a 2/3" or 1/2" sensor on my next major camcorder upgrade is to achieve a higher degree of selective focus. I've done extensive field testing in this area. When shooting portraits on 35mm, I have to focus very carefully on the eyes of the subject, or my 5mm's of DOF will probably be misplaced. The digital camera, with it's much smaller sensor, at the same distance, with the same field of view, and the aperature wide open, renders the background way too sharp for my taste in portraits.

I understand, intimately all about ND filters, aperatures, etc. I've been doing this for a very long time, and physics is an area where I am quite competent, although my artistic ability may come under fire, at times! :)
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Douglas Toltzman
Hubert, NC

videobear
Veteran

Aug 18, 2005, 1:08 PM

Post #14 of 21 (2352 views)
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Re: [djtoltz] Follow Focus for Digital Shooting [In reply to]	Can't Post

You say you want the shallow DOF of a 35mm camera, but don't like the cost of film?
You say you like the simplicity of HDV, but need a more "film-like" image?
Is that what's bothering you, Bunkie?

Well, your problems are over! Just cruise on over to this link!!!

http://www.hdvinfo.net/...hd100mini35test1.php

Smile

This information has been brought to you as a public service of Video University and hdvinfo.net. Void where prohibited by law. Your mileage may vary. No user-serviceable parts inside. Smile

Regards,
Doug Graham
Panda Productions

djtoltz
User

Aug 18, 2005, 1:36 PM

Post #15 of 21 (2348 views)
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Re: [videobear] Follow Focus for Digital Shooting [In reply to]	Can't Post

That is very interesting. Unless my budget plans get changed, though, I'm still going for a minimum CCD/sensor size of 2/3"; for several reasons. That will enhance selective focus ability; compared to 1/3" CCDs. In any case, it will be several months before any purchase, and there is time for lots of research, and maybe some new models of HDV camcorders that will fit the bill. I wish I could say that cost was no option. That mini35 adaptor is definitely worth consideration.

Thank you. I had not yet stumbled across that.
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Douglas Toltzman
Hubert, NC

djtoltz
User

Aug 18, 2005, 1:49 PM

Post #16 of 21 (2346 views)
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Re: [mvmaker] Follow Focus for Digital Shooting [In reply to]	Can't Post

I shouldn't bite on this, but I really have to make a comment here.

Quote
There is noauto focus in the world that can be trusted enough to use on an important shoot.

In my boundless arogance, I've generally assumed that I could focus better than any autofocus system. May camera is always set to manual focus, and I use it that way about 90% of the time, because my subject is not moving, or I want to focus on something that is not centered, or mostly just because I don't trust auto anything; especially if I cannot afford to have it change in the middle of a shot.

However, I must give credit where credit is due. If I have a moving subject that is more or less centered in the frame, and there is nothing in the foreground to confuse the camera, the camera's autofocus system can focus faster, and more accurately than I can; especially given the low resolution of the viewfinder. For me to focus, I must zoom in on my subject, focus, and zoom out, to be sure my focus is accurate. If I have to follow a moving subject, I just can't tell if my focus is precise, as I move it. I use techniques like prefocussing on the starting and ending points, and practicing a smooth transition between them, etc. But, as ego bruising as it may be, my camcorder does it better than I can do it; assuming no obstructions, etc.

I'm of the old school: "Manual everything". I believe the default setup should be all manual, on every camcorder. I just don't think anyone should feel inferior for using the method that produces the best results on any given shot.

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Douglas Toltzman
Hubert, NC

mvmaker
User

Aug 18, 2005, 2:37 PM

Post #17 of 21 (2341 views)
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Re: [djtoltz] Follow Focus for Digital Shooting [In reply to]	Can't Post

You have to remember I come from the world of film-making and while autofocus has gotten better over the years when you are shooting a film even one where you can get instant feedback autofocus is a no no. That's why there is so much preperation involved in camera setups on a film shoot. I have seen a crew take up to 4 hours to get the right focus, depth and predetermined secondary focuses. I think this is over kill but this was a major motion picture and they were using filmstock. Even though I am a digital film-maker I still believe that it's worth the extra effort to block your scenes properly and never use autofocus unless you are making a documentary.

As for the posts above it is better to stay clear of HD on the prosumer level for now. Stick with a 24fps cam with adjustable gamma curves. It won't be long and they will have the whole HD/HDTV figured out but for now it's a cam of worms.

(This post was edited by mvmaker on Aug 18, 2005, 2:39 PM)

djtoltz
User

Aug 18, 2005, 2:49 PM

Post #18 of 21 (2339 views)
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Re: [mvmaker] Follow Focus for Digital Shooting [In reply to]	Can't Post

You may have noticed in one of my recent posts that I'm not ready to invest in HDV; even though I have no doubt that the resolution is higher. A couple of the camera's I'm considering are;

The AJ-SDX900
Three 2/3" 520,000 Progressive CCD imagers

�

24P/30P/60i recording capability

�

Captures film-like 24-frame images using CineGamma

�

50 Mbps DVCPRO50 3.3:1 compression/25Mbps DVCPRO 5:1 compression switchable

�

Switchable 16:9/4:3 aspect ratios

�

12-bit DSP (6 pole matrix, 12 pole color correction)

�

18MHz sampling frequency

�

Dual Stage Filter Wheel

�

High Sensitivity: F13 at 2000 Lux

�

Minimum illumination: .11 Lux at +48dB gain

�

Shutter speeds and Synchro-scan shutter

�

Wireless microphone receiver pocket built-in

�

4-channel digital audio recording

�

SD Memory Card for scene file swapping

�

Three User Programmable buttons for such capabilities as: Luminance, Reference, Digital Zoom, Black Stretch, Digital Gain, Channel 1 or 2 Front Volume Control or Auto Trace White Balance

�

Remote control using simple AJ-EC3, Studio RCU with 26 pin adapter or Digital Triax

�

Ideal for program production, independent filmmaking and content creation

�

Pre-Recording Board option offers 15 second caching or single frame intervalometer

�

SDI Option allows for Digital Monitoring
Or the AJ-SDC915
A lesser DVCPro 50 16:9, 2/3" CCD, and many of the features cited above for about $14K (body+viewfinder).

Since I'm not buying right away, I'm just comparing features and checking out new models as they appear. The Panasonic HD that shoots on solid state cards looked good, until I started to compute in the cost of 4GB cards, the recording capacity of those cards, and the other accessories. It also does not support interchangeable lenses.

Everything is speculation, at this point. At the end of the year, I will know how much money I have to spend, before the start of a new fiscal year (for income tax purposes).
---
Douglas Toltzman
Hubert, NC

dansen
User

Aug 19, 2005, 2:23 PM

Post #19 of 21 (2295 views)
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Re: [djtoltz] Follow Focus for Digital Shooting [In reply to]	Can't Post

so in relation to my initial question, when do I use a follow focus and can i use it with a Canon XL2 or does the focus on the camera have to have special grips on it to accomodate the Follow Focus mechanism? cheers

hlanden
The Dean / Moderator

Aug 21, 2005, 10:41 AM

Post #20 of 21 (2264 views)
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Re: [dansen] Follow Focus for Digital Shooting [In reply to]	Can't Post

Imagine you are shooting a close-up of a famous star who is walking toward the camera. This star only has a few minutes to do the shot so the entire shot must be in focus. A person called an assistant cameraman in the US or a focus puller in England changes the focus barrel as the star walks toward camera. But before doing the shot, the assistant cameraman marks distances on the focus barrel of the lens so when the actor is at point #1, let say a bed of flowers, the assistrant "pulls" the focus till the barrel is at point#1 he or she has previously marked on the focus barrel. The next mark, #2, might be a spot on the ground. So you pull the focus barrel so your focus is at #2 when the actor is there. Lens focus is a logarithm function so the closer the star gets to the camera, the faster you have to pull the barrel.

It's a lot easier when the subject is not moving and you are just pulling or racking focus from one stationary object to another which is a different distance from the camera. In these cases some kind of automatic focus pull would be just right.

In some camera configurations the assitant has a radio controlled device which can change the focus barrel. "Pulling focus" is more of a challenge when working with a shallow depth of field. Before becoming a cameraman some years ago, I worked as a union assistant cameraman on TV shows, commericials, feature films and more.

Hal
Produce Profitable Special Interest Videos

ssvp
User

Aug 25, 2005, 2:22 PM

Post #21 of 21 (2180 views)
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Re: [dansen] Follow Focus for Digital Shooting [In reply to]	Can't Post

In Reply To