Is this diffraction? at DVinfo.net

John Stakes · July 11th, 2009, 07:21 AM

You would think after almost 400 posts I would have asked for advice on my footage by now...well here goes. These are some screen grabs from a recent gig. I'm not sure if this is the best way to get feedback? I will try to post footage tomorrow when I have more time. The client pointed out to me that the models faces were a little distorted at times. Did a quick search, and seems like the problem may be diffraction?? I think the footage is good, but not broadcast worthy.

(from left to right)
1st image: .mov, 2300kbps
2nd image: .mov, 6000kbps
3rd image: .mov, 2300kbps
4th image: .mov 600kbps

2nd and 4th images show the next frame after the others, in which the distortion is more apparent. I don't know if this should be happening?

My settings, to my knowledge, were as follows:
Panavision preset (or was it vividrgb, looks like panny right?)
f1.8
1/48
24f
+6db
standard def

JS

Doug Bennett · July 11th, 2009, 07:43 AM

no - diffraction is caused by small apertures. Using f1.8 you won't get diffraction but you may get a shallow DoF which can also lead to soft focus, particularly when subject is darker than bg

John Stakes · July 11th, 2009, 12:34 PM

yeah there wasn't much light there, but I thought it would be enough for the gig. So is the problem here a soft focus? I didn't bother focusing manually because all the models were not walking to the same location on the stage, and AF has worked great in the past. Sometimes I did have to do a quick manual focus though because I know it's difficult for the AF to function in lower lighting conditions.

Ian Wright · July 12th, 2009, 02:17 AM

was there a dirty sky light filter or something screwed on the end of the lens?

Ian
Festival Video and Audio Previews - Festival Previews Ltd

Doug Bennett · July 13th, 2009, 07:51 AM

shooting at f1.8 in auto focus with a moving subject in front of a bright background you are almost certainly going to have problems with soft focus.

Michael Ojjeh · July 13th, 2009, 10:34 AM

Also shooting at 24f in auto focus in any condition is not a good idea , adding the low lighting condition will make the auto focus a bigger problem.

July 11th, 2009, 07:21 AM	#1
John Stakes Major Player Join Date: Jan 2008 Location: Orlando, FL Posts: 558	Is this diffraction? You would think after almost 400 posts I would have asked for advice on my footage by now...well here goes. These are some screen grabs from a recent gig. I'm not sure if this is the best way to get feedback? I will try to post footage tomorrow when I have more time. The client pointed out to me that the models faces were a little distorted at times. Did a quick search, and seems like the problem may be diffraction?? I think the footage is good, but not broadcast worthy. (from left to right) 1st image: .mov, 2300kbps 2nd image: .mov, 6000kbps 3rd image: .mov, 2300kbps 4th image: .mov 600kbps 2nd and 4th images show the next frame after the others, in which the distortion is more apparent. I don't know if this should be happening? My settings, to my knowledge, were as follows: Panavision preset (or was it vividrgb, looks like panny right?) f1.8 1/48 24f +6db standard def JS Attached Thumbnails $Is this diffraction?-screenshot.jpg$

July 13th, 2009, 10:34 AM	#6
Michael Ojjeh Major Player Join Date: Jun 2006 Location: Boston, MA Posts: 338	Also shooting at 24f in auto focus in any condition is not a good idea , adding the low lighting condition will make the auto focus a bigger problem. __________________ Dragonfly Production http://www.dragonflyproduction.net/ http://www.vimeo.com/user432181

July 11th, 2009, 07:43 AM	#2
Doug Bennett Major Player Join Date: Oct 2004 Location: NYC Posts: 260	no - diffraction is caused by small apertures. Using f1.8 you won't get diffraction but you may get a shallow DoF which can also lead to soft focus, particularly when subject is darker than bg

July 11th, 2009, 12:34 PM	#3
John Stakes Major Player Join Date: Jan 2008 Location: Orlando, FL Posts: 558	yeah there wasn't much light there, but I thought it would be enough for the gig. So is the problem here a soft focus? I didn't bother focusing manually because all the models were not walking to the same location on the stage, and AF has worked great in the past. Sometimes I did have to do a quick manual focus though because I know it's difficult for the AF to function in lower lighting conditions.

July 12th, 2009, 02:17 AM	#4
Ian Wright Regular Crew Join Date: Apr 2008 Location: Edinburgh UK Posts: 94	was there a dirty sky light filter or something screwed on the end of the lens? Ian Festival Video and Audio Previews - Festival Previews Ltd

July 13th, 2009, 07:51 AM	#5
Doug Bennett Major Player Join Date: Oct 2004 Location: NYC Posts: 260	shooting at f1.8 in auto focus with a moving subject in front of a bright background you are almost certainly going to have problems with soft focus.