The Focus Pulsing 'Feature' - Error or with every Camera?

Richard Alvarez · July 19th, 2007, 12:48 PM

Daniel,

DO you normally shoot only the nose and lower chin of your interview subjects? That's what your clip primarily shows.

Autofocus is looking for sharp deliniations in the subject material. Its looking for contrast. Different manufacturers asign the 'search area' to different parts of the screen. I suspect that canon's 'search area' for focus is primarily center weighted. IN your shots, the center of the screen is all one value... all extreme closeups of your face, with soft lighting... no sharp lines at all. Thus the camera is hunting on something to focus on... your nose? Your lips? Your chin? AND you keep moving. YUP, confusing for the algortithm.

I concur with Chris. This camera is not for you. Sell/return it and stay with the camera that meets your PRIMARY need... good autofocus for your particular shooting style. You'll have to just make do with you secondary needs not being met.

It's always a trade-off.

Daniel Raebiger · July 19th, 2007, 01:46 PM

Quote:

Originally Posted by Richard Alvarez

Daniel,

DO you normally shoot only the nose and lower chin of your interview subjects? That's what your clip primarily shows.

Autofocus is looking for sharp deliniations in the subject material. Its looking for contrast. Different manufacturers asign the 'search area' to different parts of the screen. I suspect that canon's 'search area' for focus is primarily center weighted. IN your shots, the center of the screen is all one value... all extreme closeups of your face, with soft lighting... no sharp lines at all. Thus the camera is hunting on something to focus on... your nose? Your lips? Your chin? AND you keep moving. YUP, confusing for the algortithm.

I concur with Chris. This camera is not for you. Sell/return it and stay with the camera that meets your PRIMARY need... good autofocus for your particular shooting style. You'll have to just make do with you secondary needs not being met.

It's always a trade-off.

thanks for your thoughts! i agree on how confusing the poor AF might have felt seeing only my chin ;) i've first encountered the problem while having the camera sitting on my lap, zooming veeeerrry slowly back from my keyboard / monitor i have in front of my pc.

i think i'll test the camera under real conditions next week and return it if i'm not able to handle it with the AF mode. Do you know any other cameras with similar features (HDV, XLR) for a reasonable price? :)

Henrik Reach · July 19th, 2007, 02:19 PM

Ok, i have to adjust my previous statement about AF working for some situations..

After reviewing a lot of footage I have shot today, the focusing when in AF is simply hopeless, and pulsates A LOT, even in a lot of the shots where I thought it would surely do allright.

I guess it's all manual for me when shooting in HD from now.

Anyone tested the difference in AF when shooting in DV/HDV? Is it better in DV?

(And btw, is AF this bad in the consumer HDV/AVCHD etc cameras too?! If so, they're practically worthless..)

Daniel Raebiger · July 19th, 2007, 02:47 PM

Quote:

Originally Posted by Henrik Reach

they're practically worthless..)

my thoughts exactly. the funny thing is: even my 299 bucks thingy does better focus than the A1. Have the FX1 and an HC1E at hand, both do just fine in terms of autofocus.

Chris Hurd · July 19th, 2007, 02:56 PM

After reviewing the clip, I must agree completely with the assessment from Richard Alvarez. There are two problems at work, and neither is the fault of the camera. First, not enough light. Auto focus needs to see contrast in order to work, and insufficient light equals insufficient contrast. The second problem is in the second half of the clip... the lens is zoomed in too far for focus to work at such a close distance to the subject. In other words, the distance to the subject is too close for the minimum focusing distance of that particular focal length.

Sorry, clearly an example of operator error here.

1. Add more light.

2. Increase the distance from the camera to the subject, or decrease the focal length (zoom out).

Daniel Raebiger · July 19th, 2007, 03:23 PM

gonna try to film some test footage handheld in bright daylight tomorrow, hopefully with better results :)

despite the obviously poor light - my very cheap two other cams did just fine ;)

Bill Watson · July 20th, 2007, 02:03 AM

Just out of interest. Are you on Normal AF or Instant AF?

Noa Put · July 20th, 2007, 02:38 AM

I often film under dark circumstances as a weddingvideographer, especially during the party in the evening. I actually use the autofocus of my vx2100 a lot, just because it is so good and switch to manual whenever necessary and then use the "one push" button to fix the focus to a certain object. Only when it gets real dark the autofocus won't manage but for situations as was shown in the example clip I'm sure that my Sony will give a sharp image zoomed in or not.
Also a big difference I noticed is that the autozoom reacted real quick on the A1 which makes it even more noticable, my Sony does the focus adjustments more slower so it looks more natural if it would loose it's focus and restores it.
I was planning to buy an hd cam by the ending of the year or beginning next year and looking at the autofocus capabilities of the canon (It is the XHA1, right?) this will not be a camera for me. Most of you will probably say use the manual controls but having used my vx2100 allmost 3 years it has never let me down on that part and manual focussing on such a sony isn't particilary easy were you have to deal with too many things which can change in an instant. A good "point and shoot" camera should be able to deal with most of these changes without a problem so you only need to switch to manual in a few occasions.
If you are in a controlled situation then it's completely different because you have the time to set everything right, then you should use manual control at most times.

Daniel Raebiger · July 20th, 2007, 07:39 AM

Noa, yes this is the XH A1. I Sort of expected that a 3,5k Camera inherits all the features from a 900 Bucks Cam like the HC1E and improves them (like the AF^^)

The sort of things we do seem to compare a lot. Dark Environment (Party, Church/Event), constantly changing subjects and no time or way to focus manually. I'm heading out to the wilderness in a few minutes and try to shoot in bright daylight (having 100K right now^^) and am trying to get some handheld shots of moving objects and some stills with zoom in/out on objects with high contrasts and stuff. hopefully there's no pulsing :)

gonna post my video here.

one last thing before i go: the focus-speed option in the camera-setup menu only controls the focus preset switches speed, right? so where do i set the AF Focus speed lower?

thanks :)

@Bill
Instant AF - but Normal AF gives me exactly! the same results with my chin :)

Henry Cho · July 20th, 2007, 08:49 AM

hi daniel,

there is no way to set the auto focus speed i'm aware of.

Quote:

Originally Posted by Daniel Raebiger

The sort of things we do seem to compare a lot. Dark Environment (Party, Church/Event), constantly changing subjects and no time or way to focus manually.

i don't think this has to be the case. news crews almost never use auto focus, just because of the issue we're talking about here, focus hunting, and shooting breaking news is fairly dynamic. in all fairness, they have true manual lenses with markings on the barrel.

back when the xl1 came out, the servo driven focus ring was a fairly major point of concern, especially for event videographers. there were no markings on the lens barrel, and working in manual focus for dynamic event work was difficult (to put it mildly). it became pretty common practice, and a very workable solution, to put the xl camera's lens into manual mode and hit the 'push AF' button whenever the subject was framed. i've shot dozens of events this way and it's a very comfortable way of shooting for me. even for the zoom-happy, most zooms i find i edit out, but even if i'm shooting a zoom to keep in, i use the tried and true: i zoom in, set focus, zoom out, and zoom in again at the desired zoom speed.

even when shooting on a stabilizer where i can't really touch the camera, i'll try not to use auto focus. i'll usually keep the camera at full wide to keep a large DOF and set the focal length just below infinity (or occassionally use a focus/zoom controller).

on a side note, when i got my xha1 back from factory service recently, i noticed that "I AF" was replaced by "S QUICK AF". it seems to behave exactly the same, so not sure what the story is there.

Daniel Raebiger · July 20th, 2007, 08:56 AM

sounds pretty interesting :) have to try that on a concert or something with fast moving talents. just was outside and shot a few ducks and stuff. :)

July 19th, 2007, 02:56 PM	#20
Chris Hurd Obstreperous Rex Join Date: Jan 2001 Location: San Marcos, TX Posts: 27,368 Images: 513	After reviewing the clip, I must agree completely with the assessment from Richard Alvarez. There are two problems at work, and neither is the fault of the camera. First, not enough light. Auto focus needs to see contrast in order to work, and insufficient light equals insufficient contrast. The second problem is in the second half of the clip... the lens is zoomed in too far for focus to work at such a close distance to the subject. In other words, the distance to the subject is too close for the minimum focusing distance of that particular focal length. Sorry, clearly an example of operator error here. 1. Add more light. 2. Increase the distance from the camera to the subject, or decrease the focal length (zoom out). __________________ CH Search DV Info Net \| 20 years of DVi \| ...Tuesday is Soylent Green Day!

July 19th, 2007, 03:23 PM	#21
Daniel Raebiger Regular Crew Join Date: Jul 2007 Location: Landshut, Germany Posts: 143	gonna try to film some test footage handheld in bright daylight tomorrow, hopefully with better results :) despite the obviously poor light - my very cheap two other cams did just fine ;) __________________ Important notice: There's still soup left!

July 20th, 2007, 07:39 AM	#24
Daniel Raebiger Regular Crew Join Date: Jul 2007 Location: Landshut, Germany Posts: 143	Noa, yes this is the XH A1. I Sort of expected that a 3,5k Camera inherits all the features from a 900 Bucks Cam like the HC1E and improves them (like the AF^^) The sort of things we do seem to compare a lot. Dark Environment (Party, Church/Event), constantly changing subjects and no time or way to focus manually. I'm heading out to the wilderness in a few minutes and try to shoot in bright daylight (having 100K right now^^) and am trying to get some handheld shots of moving objects and some stills with zoom in/out on objects with high contrasts and stuff. hopefully there's no pulsing :) gonna post my video here. one last thing before i go: the focus-speed option in the camera-setup menu only controls the focus preset switches speed, right? so where do i set the AF Focus speed lower? thanks :) @Bill Instant AF - but Normal AF gives me exactly! the same results with my chin :) __________________ Important notice: There's still soup left!

July 20th, 2007, 08:56 AM	#26
Daniel Raebiger Regular Crew Join Date: Jul 2007 Location: Landshut, Germany Posts: 143	sounds pretty interesting :) have to try that on a concert or something with fast moving talents. just was outside and shot a few ducks and stuff. :) __________________ Important notice: There's still soup left!

July 19th, 2007, 12:48 PM	#16
Richard Alvarez Inner Circle Join Date: Sep 2002 Location: San Mateo, CA Posts: 3,840	Daniel, DO you normally shoot only the nose and lower chin of your interview subjects? That's what your clip primarily shows. Autofocus is looking for sharp deliniations in the subject material. Its looking for contrast. Different manufacturers asign the 'search area' to different parts of the screen. I suspect that canon's 'search area' for focus is primarily center weighted. IN your shots, the center of the screen is all one value... all extreme closeups of your face, with soft lighting... no sharp lines at all. Thus the camera is hunting on something to focus on... your nose? Your lips? Your chin? AND you keep moving. YUP, confusing for the algortithm. I concur with Chris. This camera is not for you. Sell/return it and stay with the camera that meets your PRIMARY need... good autofocus for your particular shooting style. You'll have to just make do with you secondary needs not being met. It's always a trade-off.

July 19th, 2007, 02:19 PM	#18
Henrik Reach Regular Crew Join Date: Jun 2007 Location: Halden Posts: 106	Ok, i have to adjust my previous statement about AF working for some situations.. After reviewing a lot of footage I have shot today, the focusing when in AF is simply hopeless, and pulsates A LOT, even in a lot of the shots where I thought it would surely do allright. I guess it's all manual for me when shooting in HD from now. Anyone tested the difference in AF when shooting in DV/HDV? Is it better in DV? (And btw, is AF this bad in the consumer HDV/AVCHD etc cameras too?! If so, they're practically worthless..)

July 20th, 2007, 02:03 AM	#22
Bill Watson Major Player Join Date: May 2007 Location: Noosa Queensland Australia Posts: 248	Just out of interest. Are you on Normal AF or Instant AF?

July 20th, 2007, 02:38 AM	#23
Noa Put Inner Circle Join Date: Jun 2007 Location: Belgium Posts: 9,510	I often film under dark circumstances as a weddingvideographer, especially during the party in the evening. I actually use the autofocus of my vx2100 a lot, just because it is so good and switch to manual whenever necessary and then use the "one push" button to fix the focus to a certain object. Only when it gets real dark the autofocus won't manage but for situations as was shown in the example clip I'm sure that my Sony will give a sharp image zoomed in or not. Also a big difference I noticed is that the autozoom reacted real quick on the A1 which makes it even more noticable, my Sony does the focus adjustments more slower so it looks more natural if it would loose it's focus and restores it. I was planning to buy an hd cam by the ending of the year or beginning next year and looking at the autofocus capabilities of the canon (It is the XHA1, right?) this will not be a camera for me. Most of you will probably say use the manual controls but having used my vx2100 allmost 3 years it has never let me down on that part and manual focussing on such a sony isn't particilary easy were you have to deal with too many things which can change in an instant. A good "point and shoot" camera should be able to deal with most of these changes without a problem so you only need to switch to manual in a few occasions. If you are in a controlled situation then it's completely different because you have the time to set everything right, then you should use manual control at most times.