Slow Focus in 30F at DVinfo.net

Taky Cheung · April 23rd, 2008, 12:18 AM

Recently I start shooting in 30F. I noticed it takes longer than to focus while zoom-in in 30F than 60i. The scenario is if I have the camera in the widest zoom settings. Then zoom in all the way. The AF takes a very long time to get focus. Sometimes it just won't focus at all. The same situation it focuses a lot faster in 60i. I don't know if I should contact Canon for service on this.

I also have the Canon WA lens adapter so I can't use iAF.

Anybody has a similar experience?

Shiv Kumar · April 23rd, 2008, 01:00 AM

Taky,

Do you know if the aperture settings were the same in your comparison?

I've found that if you stop down the auto focus seems to misfire.

Taky Cheung · April 23rd, 2008, 01:02 AM

It's in the [A] mode.

Petri Kaipiainen · April 23rd, 2008, 01:46 AM

If my memory serves there is a mention in the manual that focus is slow on Frame Mode shooting. Just something even Canon can not do much about apparently.

Annie Haycock · April 23rd, 2008, 01:59 AM

Probably best to zoom in and focus manually, then zoom out and start shooting. Then the subject should stay in focus all the way. I have found that autofocus is really bad in this kind of situation.

Taky Cheung · April 23rd, 2008, 02:06 AM

I have been using the focus ring to adjust. I also found out I was using Hi Speed zoom. That makes it even harder for the A1 to find focus. I turned it off and using normal zoom speed.

So if that's the case, I don't need to send the unit to Canon for service, right?

Taky Cheung · April 24th, 2008, 10:12 PM

Okay, found it. I was browsing Canon support site and search for any focus issue. Here's what I found. Now I feel better as I don't have to send my A1 to service.

- When recording under bright conditions, the camcorder sets a small aperture value, and the picture may appear blurred. This may be more noticeable at wide-angle. When you are using a lens with built-in ND filter, turn it on/off according to the screen display.

- When recording under dark conditions, the focusing range narrows and the picture may appear blurred.

- In 30F and 24F mode, autofocus takes longer than in the 60i mode.

- Autofocus may not work well on the following subjects. In such case, focus manually. Reflective surfaces, Subjects with low, contrast or without vertical lines, Fast moving subjects, Through dirty or wet windows, Night scenes

Shiv Kumar · April 24th, 2008, 10:17 PM

Taky,

That's a great find.

The reason I asked about your aperture settings in my earlier post is for this reason. I've had this experience before. Using the ND filter and thus being able to open up the aperture helps in two regarads:
1. The picture is far sharper
2. The auto focus works better (quicker).

Jason Livingston · April 25th, 2008, 12:02 AM

A contrast AF system works by changing the focus a little and then checking the next frame from the sensor to see if the contrast between neighboring pixels increased or decreased. If it decreases, you then focus in the other direction, if it increases then you continue a little more in the same direction. Then on the next frame, you measure again and repeat. At 60i, you can measure and adjust focus 60 times per second, but at 30p you can only perform half as many measurements and adjustments per second, so it takes longer to achieve focus.

At 24p, the motion blur and low sampling rate can make it very difficult to perform contrast AF. That's why the Panasonic DVX100 was MF-only at 24p, and it's probably the reason that Canon put the active IR focus system on their recent cameras that do 24p.

Shiv Kumar · April 25th, 2008, 12:04 AM

Jason,

Great explanation!

Thank you.

Taky Cheung · April 25th, 2008, 12:47 AM

I do not see the same issue with GL2 Frame mode. Also HV30 also has 24p and 30p. I don't notice any focus delay. I suspect the slow focus in 24F and 30F is related to the extra steps behind to convert the interlace signal to progressive while the internal processor is not fast enough to handle these extra tasks. But that's just my guess :)

April 23rd, 2008, 12:18 AM	#1
Taky Cheung Inner Circle Join Date: May 2007 Location: Los Angeles, USA Posts: 2,114	Slow Focus in 30F Recently I start shooting in 30F. I noticed it takes longer than to focus while zoom-in in 30F than 60i. The scenario is if I have the camera in the widest zoom settings. Then zoom in all the way. The AF takes a very long time to get focus. Sometimes it just won't focus at all. The same situation it focuses a lot faster in 60i. I don't know if I should contact Canon for service on this. I also have the Canon WA lens adapter so I can't use iAF. Anybody has a similar experience? __________________ LA Color Pros Blog RODE Authorized Reseller . Comer LED Camera Lights . TakyBox HTML5 Menu Generator

April 23rd, 2008, 01:00 AM	#2
Shiv Kumar Major Player Join Date: Jul 2007 Location: Gainesville, VA, USA Posts: 327	Taky, Do you know if the aperture settings were the same in your comparison? I've found that if you stop down the auto focus seems to misfire. __________________ Canon XH-A1, Libec LS-55M, Letus Extreme, Steadicam Merlin, PPro CS3

April 23rd, 2008, 01:02 AM	#3
Taky Cheung Inner Circle Join Date: May 2007 Location: Los Angeles, USA Posts: 2,114	It's in the [A] mode. __________________ LA Color Pros Blog RODE Authorized Reseller . Comer LED Camera Lights . TakyBox HTML5 Menu Generator

April 23rd, 2008, 01:59 AM	#5
Annie Haycock Major Player Join Date: Dec 2007 Location: Pembrokeshire, Wales Posts: 734	Probably best to zoom in and focus manually, then zoom out and start shooting. Then the subject should stay in focus all the way. I have found that autofocus is really bad in this kind of situation. __________________ Canon XH A1; Canon XF100; Nikon D800

April 23rd, 2008, 02:06 AM	#6
Taky Cheung Inner Circle Join Date: May 2007 Location: Los Angeles, USA Posts: 2,114	I have been using the focus ring to adjust. I also found out I was using Hi Speed zoom. That makes it even harder for the A1 to find focus. I turned it off and using normal zoom speed. So if that's the case, I don't need to send the unit to Canon for service, right? __________________ LA Color Pros Blog RODE Authorized Reseller . Comer LED Camera Lights . TakyBox HTML5 Menu Generator

April 23rd, 2008, 01:46 AM	#4
Petri Kaipiainen Major Player Join Date: Apr 2007 Location: Espoo Finland Posts: 380	If my memory serves there is a mention in the manual that focus is slow on Frame Mode shooting. Just something even Canon can not do much about apparently.

April 24th, 2008, 10:12 PM	#7
Taky Cheung Inner Circle Join Date: May 2007 Location: Los Angeles, USA Posts: 2,114	Okay, found it. I was browsing Canon support site and search for any focus issue. Here's what I found. Now I feel better as I don't have to send my A1 to service. - When recording under bright conditions, the camcorder sets a small aperture value, and the picture may appear blurred. This may be more noticeable at wide-angle. When you are using a lens with built-in ND filter, turn it on/off according to the screen display. - When recording under dark conditions, the focusing range narrows and the picture may appear blurred. - In 30F and 24F mode, autofocus takes longer than in the 60i mode. - Autofocus may not work well on the following subjects. In such case, focus manually. Reflective surfaces, Subjects with low, contrast or without vertical lines, Fast moving subjects, Through dirty or wet windows, Night scenes __________________ LA Color Pros Blog RODE Authorized Reseller . Comer LED Camera Lights . TakyBox HTML5 Menu Generator

April 24th, 2008, 10:17 PM	#8
Shiv Kumar Major Player Join Date: Jul 2007 Location: Gainesville, VA, USA Posts: 327	Taky, That's a great find. The reason I asked about your aperture settings in my earlier post is for this reason. I've had this experience before. Using the ND filter and thus being able to open up the aperture helps in two regarads: 1. The picture is far sharper 2. The auto focus works better (quicker). __________________ Canon XH-A1, Libec LS-55M, Letus Extreme, Steadicam Merlin, PPro CS3

April 25th, 2008, 12:02 AM	#9
Jason Livingston Regular Crew Join Date: Feb 2006 Location: Maryland, USA Posts: 71	A contrast AF system works by changing the focus a little and then checking the next frame from the sensor to see if the contrast between neighboring pixels increased or decreased. If it decreases, you then focus in the other direction, if it increases then you continue a little more in the same direction. Then on the next frame, you measure again and repeat. At 60i, you can measure and adjust focus 60 times per second, but at 30p you can only perform half as many measurements and adjustments per second, so it takes longer to achieve focus. At 24p, the motion blur and low sampling rate can make it very difficult to perform contrast AF. That's why the Panasonic DVX100 was MF-only at 24p, and it's probably the reason that Canon put the active IR focus system on their recent cameras that do 24p.

April 25th, 2008, 12:04 AM	#10
Shiv Kumar Major Player Join Date: Jul 2007 Location: Gainesville, VA, USA Posts: 327	Jason, Great explanation! Thank you. __________________ Canon XH-A1, Libec LS-55M, Letus Extreme, Steadicam Merlin, PPro CS3

April 25th, 2008, 12:47 AM	#11
Taky Cheung Inner Circle Join Date: May 2007 Location: Los Angeles, USA Posts: 2,114	I do not see the same issue with GL2 Frame mode. Also HV30 also has 24p and 30p. I don't notice any focus delay. I suspect the slow focus in 24F and 30F is related to the extra steps behind to convert the interlace signal to progressive while the internal processor is not fast enough to handle these extra tasks. But that's just my guess :) __________________ LA Color Pros Blog RODE Authorized Reseller . Comer LED Camera Lights . TakyBox HTML5 Menu Generator