Warning on Flange Focus Adjust at DVinfo.net

Mike Chandler · April 9th, 2009, 08:18 AM

I just got back from a shoot where the lens simply came off in my hand while shooting. I neglected to run the Auto FB ADJ right afterwards and a lot of my wides were soft. Sony's manual states that "repeated adjustment is not necessary as long as the same lens is used", but I think this should read " if you change or remove lens, run the Auto FB ADJ test".

I finally spotted the problem in the viewfinder and ran the test against a blank wall and it worked.

Not quite sure why the lens popped off--the barrel release is not a snap-lock, rather just a pressure on the flange, and maybe the release lever got bumped when removing the camera from the bag and just took a while to work its way free.

Hope this helps others avoid the problem.

David Issko · April 9th, 2009, 08:23 PM

My lens came off my EX3 lat last year. Cause? In and out of my camera bag which caused the lens to work free of its housing. Glad I was holding on to the lens and body at the time as it was sitting on my shoulder.

As my lens has manual back focus, I refitted the lens and carried out flange focus immediately. All is good.

Max Allen · April 11th, 2009, 12:24 AM

Hi

I think Sony is mistaken in that instruction as well unless they have unbeknown to us modified the laws of physics with new alloys as it pertains to backfocus calibration.

Backfocus should be calibrated any time a lens is mounted, there is change in ambient temperature of 5 degrees or more for an hour or more and before every shoot if the camera has traveled in a vehicle. A backfocus chart should be used whenever possible of course.

Vincent Oliver · April 11th, 2009, 12:32 AM

Backfocus is useful if you intend zooming whilst shooting, for most shots you would set up the focus before shooting. In other words you will not be out of focus as long as the image in the viewfinder looks sharp.

Daniel Epstein · April 12th, 2009, 04:54 PM

Quote:

Originally Posted by Vincent Oliver

Backfocus is useful if you intend zooming whilst shooting, for most shots you would set up the focus before shooting. In other words you will not be out of focus as long as the image in the viewfinder looks sharp.

Vincent, My experience is if the backfocus is off it makes it difficult to judge the overall sharpness on the wide part of the lens. Most viewfinders are still not sharp enough to have complete confidence in their ability to show small focus errors on wide shots. I would check the backfocus with a chart before I started using the camera or after a lens change if possible.

Vincent Oliver · April 13th, 2009, 12:43 AM

Daniel, you are right in sating the backfocus should be set up correctly. However, at the wide setting of the lens there is a lot of depth of field which makes manual focus very difficult.

When on location it is not always practical to perform the backfocus routine, especially if you have the client, talent and other crew members waiting about. On some days I may do two, three or more lens changes.

Mike Chandler · April 13th, 2009, 10:28 AM

Quote:

Originally Posted by Vincent Oliver

Backfocus is useful if you intend zooming whilst shooting, for most shots you would set up the focus before shooting. In other words you will not be out of focus as long as the image in the viewfinder looks sharp.

I would really caution against relying on the viewfinder--It crossed my mind that I might need to re-calibrate, but everything looked fine in the viewfinder. It wasn't until the subject was backlit against a blown-out window that I noticed the fuzz. I think one should re-calibrate every time the lens is changed or removed, even if it means using a blank wall (which I did and which yielded perfectly focused shots thereafter).

Vincent Oliver · April 13th, 2009, 11:03 AM

Quote:

Originally Posted by Mike Chandler

I would really caution against relying on the viewfinder--It crossed my mind that I might need to re-calibrate, but everything looked fine in the viewfinder.

I would strike me as being odd that you can't rely on a viewfinder for accurate focus, surely this is one of its many functions. If you are using autofocus then perhaps viewfinder accuracy is not such a big issue, but then how many professionals actually have 100% confidence in the autofocus. (for any camera)

Yes, re-calibrate often, but also use your eyes to check the focus often.

Mike Chandler · April 13th, 2009, 06:55 PM

I was zooming in on every shot, getting focus, and then pulling back--nothing looked out of focus until I got back to my 42", and virtually every wide was soft. It was not noticeable in the viewfinder.

Daniel Epstein · April 13th, 2009, 08:00 PM

Quote:

Originally Posted by Mike Chandler

I was zooming in on every shot, getting focus, and then pulling back--nothing looked out of focus until I got back to my 42", and virtually every wide was soft. It was not noticeable in the viewfinder.

Mikes experience points out why ignoring checking the backfocus at the beginning of a shoot or when changing the lens can be much more expensive than the time to do the check would cost. Circumstances often drive us into bad decisions as far as the results are concerned. Of course you usually can see a difference in the viewfinder once the backfocus is correct compared to it being off but your eye adjusts to the softness on a small screen pretty easily.

Max Allen · April 13th, 2009, 11:28 PM

Howdy,

Assuming a professional lens with manual back focus adjustment, you can set back focus after every lens change in less than ten seconds by having a chart on the side and panning to it. True some clients don't have 10 seconds but as Daniel points out they may suddenly have it when the costs of missing critical focus is understood. My approach is brightness up, contrast down, peaking minimum. Others prefer a variation of the three. The only problem I see with repeating back focus is throwing off a calibrated viewfinder (VF focus and luminance). Iif you use a separate monitor that's solved.

Using 800 or less lines on a small surface area for critical focus on a 1920 or 1440 image is not the same as using full resolution on a large viewing plane eg. a 20" broadcast engineering HD monitor. Even if you have full res on some theoretical small built-in LCD, the less the physical dimensions of a hi-res display the sharper the image and the less detectable focus. Web clips of footage on video sites from new small format cameras look so good because they're so small. Same footage on a viewer's 46" flatscreen or movie theater is a different experience.

Considering DOF as a product of footcandles as well as focal length, a wide focal length can still have narrow DOF at full open iris and be quite plainly obvious to the eye in certain lighting situations and camera/lens combinations. I've seen this many times in broadcast jobs using jibs where after backfocus was calibrated things improved.

Regards

Vincent Oliver · April 14th, 2009, 12:27 AM

I take the point that a small LCD screen is not the optimum way for accurate focusing. However, short of taking a large monitor on location, we have no other choice. The whole point of the EX1/3 is that it is a portable unit.

Despite what messages I may be giving out, I do backfocus my gear often. I also use the magnify function and peaking to check for accurate focus. And yes, I admit that I also zoom in to my subject to focus and then zoom out again to shoot, in this case you do need to ensure the backfocus is set up correctly.

Mike Chandler · April 14th, 2009, 07:16 AM

Quote:

Originally Posted by Max Allen

you can set back focus after every lens change in less than ten seconds by having a chart on the side and panning to it. True some clients don't have 10 seconds but as Daniel points out they may suddenly have it when the costs of missing critical focus is understood.

Agreed. For just about the same amount of time as going from play to review, you can save your shoot.

Max Allen · April 15th, 2009, 10:47 PM

Quote:

Originally Posted by Vincent Oliver

The whole point of the EX1/3 is that it is a portable unit.

I totally agree Vincent. Portability is the number one biggest feature for me with the EX-1. For my use EX-3 starts to go against the main purpose of a small format camera. So plainly when the production calls for maximum portability the viewfinder/LCD is the option for backfocus.

Glynn Morgan · September 1st, 2009, 08:30 AM

The supplied EX3 lens doesn't have manual backfocus adjustment and my auto adjustment was so hard to calibrate I just took it to a service center and told them my footage was soft on the computer.

Seems to be ok now - I don't want to touch auto FB adjust again. The Fujinon lens should really have a manual FB adjust too.

April 9th, 2009, 08:18 AM	#1
Mike Chandler Major Player Join Date: May 2008 Location: Moab, UT Posts: 264	Warning on Flange Focus Adjust I just got back from a shoot where the lens simply came off in my hand while shooting. I neglected to run the Auto FB ADJ right afterwards and a lot of my wides were soft. Sony's manual states that "repeated adjustment is not necessary as long as the same lens is used", but I think this should read " if you change or remove lens, run the Auto FB ADJ test". I finally spotted the problem in the viewfinder and ran the test against a blank wall and it worked. Not quite sure why the lens popped off--the barrel release is not a snap-lock, rather just a pressure on the flange, and maybe the release lever got bumped when removing the camera from the bag and just took a while to work its way free. Hope this helps others avoid the problem. __________________ www.packcreekproductions.com EX3, Mac Pro, FCP

April 9th, 2009, 08:23 PM	#2
David Issko Major Player Join Date: Jul 2008 Location: Melbourne, Australia Posts: 393	My lens came off my EX3 lat last year. Cause? In and out of my camera bag which caused the lens to work free of its housing. Glad I was holding on to the lens and body at the time as it was sitting on my shoulder. As my lens has manual back focus, I refitted the lens and carried out flange focus immediately. All is good. __________________ David Issko Edit 1 Video Productions

April 11th, 2009, 12:32 AM	#4
Vincent Oliver Trustee Join Date: Sep 2004 Location: Chislehurst, London Posts: 1,724	Backfocus is useful if you intend zooming whilst shooting, for most shots you would set up the focus before shooting. In other words you will not be out of focus as long as the image in the viewfinder looks sharp. __________________ Eyes are a deaf man’s ears. Ears are a blind man’s eyes

April 13th, 2009, 12:43 AM	#6
Vincent Oliver Trustee Join Date: Sep 2004 Location: Chislehurst, London Posts: 1,724	Daniel, you are right in sating the backfocus should be set up correctly. However, at the wide setting of the lens there is a lot of depth of field which makes manual focus very difficult. When on location it is not always practical to perform the backfocus routine, especially if you have the client, talent and other crew members waiting about. On some days I may do two, three or more lens changes. __________________ Eyes are a deaf man’s ears. Ears are a blind man’s eyes

April 13th, 2009, 06:55 PM	#9
Mike Chandler Major Player Join Date: May 2008 Location: Moab, UT Posts: 264	I was zooming in on every shot, getting focus, and then pulling back--nothing looked out of focus until I got back to my 42", and virtually every wide was soft. It was not noticeable in the viewfinder. __________________ www.packcreekproductions.com EX3, Mac Pro, FCP

April 11th, 2009, 12:24 AM	#3
Max Allen Regular Crew Join Date: Mar 2004 Location: NY Posts: 186	Hi I think Sony is mistaken in that instruction as well unless they have unbeknown to us modified the laws of physics with new alloys as it pertains to backfocus calibration. Backfocus should be calibrated any time a lens is mounted, there is change in ambient temperature of 5 degrees or more for an hour or more and before every shoot if the camera has traveled in a vehicle. A backfocus chart should be used whenever possible of course.

April 13th, 2009, 11:28 PM	#11
Max Allen Regular Crew Join Date: Mar 2004 Location: NY Posts: 186	Howdy, Assuming a professional lens with manual back focus adjustment, you can set back focus after every lens change in less than ten seconds by having a chart on the side and panning to it. True some clients don't have 10 seconds but as Daniel points out they may suddenly have it when the costs of missing critical focus is understood. My approach is brightness up, contrast down, peaking minimum. Others prefer a variation of the three. The only problem I see with repeating back focus is throwing off a calibrated viewfinder (VF focus and luminance). Iif you use a separate monitor that's solved. Using 800 or less lines on a small surface area for critical focus on a 1920 or 1440 image is not the same as using full resolution on a large viewing plane eg. a 20" broadcast engineering HD monitor. Even if you have full res on some theoretical small built-in LCD, the less the physical dimensions of a hi-res display the sharper the image and the less detectable focus. Web clips of footage on video sites from new small format cameras look so good because they're so small. Same footage on a viewer's 46" flatscreen or movie theater is a different experience. Considering DOF as a product of footcandles as well as focal length, a wide focal length can still have narrow DOF at full open iris and be quite plainly obvious to the eye in certain lighting situations and camera/lens combinations. I've seen this many times in broadcast jobs using jibs where after backfocus was calibrated things improved. Regards

April 14th, 2009, 12:27 AM	#12
Vincent Oliver Trustee Join Date: Sep 2004 Location: Chislehurst, London Posts: 1,724	I take the point that a small LCD screen is not the optimum way for accurate focusing. However, short of taking a large monitor on location, we have no other choice. The whole point of the EX1/3 is that it is a portable unit. Despite what messages I may be giving out, I do backfocus my gear often. I also use the magnify function and peaking to check for accurate focus. And yes, I admit that I also zoom in to my subject to focus and then zoom out again to shoot, in this case you do need to ensure the backfocus is set up correctly. __________________ Eyes are a deaf man’s ears. Ears are a blind man’s eyes

September 1st, 2009, 08:30 AM	#15
Glynn Morgan Regular Crew Join Date: Feb 2009 Location: Australia Posts: 119	The supplied EX3 lens doesn't have manual backfocus adjustment and my auto adjustment was so hard to calibrate I just took it to a service center and told them my footage was soft on the computer. Seems to be ok now - I don't want to touch auto FB adjust again. The Fujinon lens should really have a manual FB adjust too.