Why did manual focus fail? at DVinfo.net

Greg Clark · July 26th, 2010, 07:25 PM

I was shooting a dance on a stage and set the focus for the upstage area. XH-A1 for the most part kept the focus but when I zoomed in at the end for a closeup in the downstage area blur occurred. Knowing why it happened will help me in the future.

Michael Ojjeh · July 26th, 2010, 08:22 PM

Did you Zoom in all the away and focus first before you start shooting ?

Peter Manojlovic · July 26th, 2010, 08:34 PM

Were you shooting 30F or 60i?
What was the lighting condition?
Do you have Instant AF on?
Did you give it several seconds to find itself??

Allan Black · July 26th, 2010, 10:53 PM

Greg, to understand the problem try and repeat it .. lighting, A1 settings, distances, everything.

Maybe the distance from the lens to your focused upstage area, was different to the distance from the lens to the downstage area you zoomed out to.
Cheers.

Chris Soucy · July 27th, 2010, 12:05 AM

You as much as answered your own question.

You had focussed on the Upstage area. By zooming into the Downstage area (which must have been at a different distance) it must, certainly, be out of focus.

I infer from your (brief) post that you were in MF, so the lens wouldn't have corrected itself (even if it could figure out what to focus on) and even if you had been in Auto Focus mode, the lens cannot focus and zoom at the same time (if it was a A1, not a s) so would have taken some time to aquire the target, even if it could figure out what target to aquire.

The moral is: Keep an eye on that LCD and ride the focus ring if shooting close (zoom in), on subjects with depth, the camera can't do that for you.

Pulling it off in real time with a single camera is almost impossible, BTW.

Without a B cam shooting wide to cut to, whilst the A cam operator gets his (zoomed in) sh*t together, seamless just ain't possible.

CS

Greg Clark · July 27th, 2010, 07:11 AM

Would it be true that if I zoomed in fully on the upstage area and focused the focus should hold everything between that point and my camera at the back of the audience? I was shooting 60i. It is hard to see when the focus changes on the small XH-A1 LCD.

Michael Hutson · July 27th, 2010, 02:53 PM

Greg,

This is what I am hearing you say: You set your focus on an object upstage like the back curtain or wall. After doing this, you expect everything between that point(i.e. the back wall) and the camera to remain in focus. That is an incorrect expectation.

What you CAN expect IS after you focus on the backstage, you can zoom in and out and the backstage will remain in focus. Any subjects downstage will not be in focus when zoomed in on them downstage. They are at a different distance from where you set your focus. You may not see it when are not zoomed in, but it will become very noticable when you zoom in......as you have witnessed......if I am hearing you correctly. You must refocus for closeups at a different distance. Hope this helps.

Greg Clark · July 27th, 2010, 07:32 PM

Wow am I wrong. I guess my only choice is Autofocus or keep my finger on the focus button on the XH-A1 at all times. Especially when I'm not using my large external LCD.

Les Wilson · July 27th, 2010, 08:57 PM

Greg,
Research something called Depth of Field or DOF. Here's a nice tutorial:
Interactive Depth of Field Tutorial

Bottom line is that the area in focus has a depth. Usually just in front of your focus point and some distance behind. How deep it is from front to back is a function of focal length (zoom) and iris (f-stop).

July 26th, 2010, 07:25 PM	#1
Greg Clark Major Player Join Date: Sep 2004 Location: Surprise Arizona Posts: 297	Why did manual focus fail? I was shooting a dance on a stage and set the focus for the upstage area. XH-A1 for the most part kept the focus but when I zoomed in at the end for a closeup in the downstage area blur occurred. Knowing why it happened will help me in the future.

July 26th, 2010, 08:22 PM	#2
Michael Ojjeh Major Player Join Date: Jun 2006 Location: Boston, MA Posts: 338	Did you Zoom in all the away and focus first before you start shooting ? __________________ Dragonfly Production http://www.dragonflyproduction.net/ http://www.vimeo.com/user432181

July 26th, 2010, 10:53 PM	#4
Allan Black Inner Circle Join Date: Sep 2006 Location: Sydney. Posts: 2,928	Greg, to understand the problem try and repeat it .. lighting, A1 settings, distances, everything. Maybe the distance from the lens to your focused upstage area, was different to the distance from the lens to the downstage area you zoomed out to. Cheers. __________________ Drink more tap water. On admission at Sydney hospitals more than 5% of day patients are de-hydrated.

July 27th, 2010, 12:05 AM	#5
Chris Soucy Inner Circle Join Date: Feb 2007 Location: Fairfield, Dunedin, New Zealand Posts: 3,691 Images: 18	Hi Greg....................... You as much as answered your own question. You had focussed on the Upstage area. By zooming into the Downstage area (which must have been at a different distance) it must, certainly, be out of focus. I infer from your (brief) post that you were in MF, so the lens wouldn't have corrected itself (even if it could figure out what to focus on) and even if you had been in Auto Focus mode, the lens cannot focus and zoom at the same time (if it was a A1, not a s) so would have taken some time to aquire the target, even if it could figure out what target to aquire. The moral is: Keep an eye on that LCD and ride the focus ring if shooting close (zoom in), on subjects with depth, the camera can't do that for you. Pulling it off in real time with a single camera is almost impossible, BTW. Without a B cam shooting wide to cut to, whilst the A cam operator gets his (zoomed in) sh*t together, seamless just ain't possible. CS

July 27th, 2010, 07:11 AM	#6
Greg Clark Major Player Join Date: Sep 2004 Location: Surprise Arizona Posts: 297	Excellent Comments for Thought Would it be true that if I zoomed in fully on the upstage area and focused the focus should hold everything between that point and my camera at the back of the audience? I was shooting 60i. It is hard to see when the focus changes on the small XH-A1 LCD.

July 26th, 2010, 08:34 PM	#3
Peter Manojlovic Major Player Join Date: Jun 2007 Location: Hamilton Ontario Posts: 769	Were you shooting 30F or 60i? What was the lighting condition? Do you have Instant AF on? Did you give it several seconds to find itself??

July 27th, 2010, 02:53 PM	#7
Michael Hutson Major Player Join Date: Nov 2008 Location: Elgin, IL Posts: 249	Greg, This is what I am hearing you say: You set your focus on an object upstage like the back curtain or wall. After doing this, you expect everything between that point(i.e. the back wall) and the camera to remain in focus. That is an incorrect expectation. What you CAN expect IS after you focus on the backstage, you can zoom in and out and the backstage will remain in focus. Any subjects downstage will not be in focus when zoomed in on them downstage. They are at a different distance from where you set your focus. You may not see it when are not zoomed in, but it will become very noticable when you zoom in......as you have witnessed......if I am hearing you correctly. You must refocus for closeups at a different distance. Hope this helps.

July 27th, 2010, 07:32 PM	#8
Greg Clark Major Player Join Date: Sep 2004 Location: Surprise Arizona Posts: 297	Wow am I wrong. I guess my only choice is Autofocus or keep my finger on the focus button on the XH-A1 at all times. Especially when I'm not using my large external LCD.

July 27th, 2010, 08:57 PM	#9
Les Wilson Inner Circle Join Date: Jan 2004 Location: Boca Raton, FL Posts: 3,014	Greg, Research something called Depth of Field or DOF. Here's a nice tutorial: Interactive Depth of Field Tutorial Bottom line is that the area in focus has a depth. Usually just in front of your focus point and some distance behind. How deep it is from front to back is a function of focal length (zoom) and iris (f-stop).