Why does overexposing cause shots to look out of focus? at DVinfo.net

Jonathan Nicholas · April 1st, 2005, 03:20 AM

Just curious as even slightly over exposing can make the picture lose its sharpness.

Cheers

Jon

Hugh DiMauro · April 1st, 2005, 10:47 AM

I noticed the same thing with my PD 170. As soon as I activated the ND filter the picture sharpened. You are not imagining that. I noticed it to.

Don Bloom · April 1st, 2005, 10:58 AM

One reason is that overexposure blows out the highlites and when that hapens the edges become soft. So when they become soft, it looks out of focus.

One way to combat that is to use the manual controls for exposure, white balance, iris and shutter speed. This will give you much more precise control of the camera to help counteract the very thing you're seeing. The NDs will cut your iris by 1 and 3 stops (IIRC) on the 150/170 so you need to be careful as with the iris open like that, sometimes your focus can be a bit out.

Better to be 1 or even 2 stops UNDER than a half over. Digital doesn't handle overexposure very well.

HTHs
Don

Nick Jushchyshyn · April 1st, 2005, 03:02 PM

Another issue is the nature of CCD technology.

Each pixel is something of an electron bucket, collecting & storing electrons created when photons hit the silicon until the frame is read off the chip.

These "buckets" have a finite capacity and can literally overflow, allowing and electrons to spill into adjacent pixels. As a result, some blurring occurs in over exposed areas of the CCD.

April 1st, 2005, 03:20 AM	#1
Jonathan Nicholas Regular Crew Join Date: Sep 2004 Location: Birmingham, UK Posts: 90	Why does overexposing cause shots to look out of focus? Just curious as even slightly over exposing can make the picture lose its sharpness. Cheers Jon

April 1st, 2005, 10:47 AM	#2
Hugh DiMauro Trustee Join Date: Jun 2003 Location: Central Florida Posts: 1,207	I noticed the same thing with my PD 170. As soon as I activated the ND filter the picture sharpened. You are not imagining that. I noticed it to. __________________ Interesting, if true. And interesting anyway.

April 1st, 2005, 10:58 AM	#3
Don Bloom Inner Circle Join Date: Jan 2003 Location: Chicago, IL Posts: 6,609	One reason is that overexposure blows out the highlites and when that hapens the edges become soft. So when they become soft, it looks out of focus. One way to combat that is to use the manual controls for exposure, white balance, iris and shutter speed. This will give you much more precise control of the camera to help counteract the very thing you're seeing. The NDs will cut your iris by 1 and 3 stops (IIRC) on the 150/170 so you need to be careful as with the iris open like that, sometimes your focus can be a bit out. Better to be 1 or even 2 stops UNDER than a half over. Digital doesn't handle overexposure very well. HTHs Don

April 1st, 2005, 03:02 PM	#4
Nick Jushchyshyn Major Player Join Date: Feb 2004 Location: Philadelphia, PA, USA Posts: 548	Another issue is the nature of CCD technology. Each pixel is something of an electron bucket, collecting & storing electrons created when photons hit the silicon until the frame is read off the chip. These "buckets" have a finite capacity and can literally overflow, allowing and electrons to spill into adjacent pixels. As a result, some blurring occurs in over exposed areas of the CCD.