CB Junior and vertical focus assist..help

[B-H-P]

Hey everyone, I know I have read something on this topic here before but am unable to find it now. Here's what I am shooting with, Canon 20D w/ grip, Canon 550EX, Custom Bracket CB Junior and a Canon 70-200 f/2.8. I am having problems with the auto focus assist beam when shooting in vertical format. The auto focus assist beam is up and to the left of the focus point. So much so that is doesn't intersect with the focus point and the lens just keeps searching. When in horizontal format, it is off a little, but not so much to have caused a problem yet. Has anyone else had this problem? Any help would be appreciated. Thanks.

[rcg]

I haven't run into this on my 580ex. Is the flash body pretty centered on the bracket / down the centerline of the lens. How about moving the flash on the bracket?

[B-H-P]

Well, I have tied center the FLASH (white lite) down the center of the lens and the assist beam shines to the upper left, out of view in the view finder. I have tried moving the assist beam over the lens (white light off to the right) and it still is out of frame. Maybe it is the flash? I don't see any way to adjust the bracket and get that beam where I need it. I must be missing something. Hmmm.

[rcg]

I'm going to mount up the stuff and see if I see anything that might help.

On your 20d what setting are you using in the autofocus setup - single shot, servo. Also any adjustment to the active focus point? What focal length are you attempting?

[rcg]

I just tested the setup and I'm only getting (the expected) offset on the focus assist beam.

I have 580 not a 550 and Im using the 1dm2 not 20d.

[edit]

Oh BTW... my understanding on the focus assist is it is a purely flash function. The beam needs to bounce back to the flash not the camera. The flash simply tells the camera what it sees.

[B-H-P]

I'm going to mount up the stuff and see if I see anything that might help.

On your 20d what setting are you using in the autofocus setup - single shot, servo. Also any adjustment to the active focus point? What focal length are you attempting?

I am using single shot, and I have the center focus point tied to the "*" button on the back of the camera. I just did another attempt at focusing on a picture on the wall in dim lite...I was at 70mm with the 70-200 f/ 2.8.

Thanks for you help by the way.

[B-H-P]

I just tested the setup and I'm only getting (the expected) offset on the focus assist beam.

I have 580 not a 550 and Im using the 1dm2 not 20d.

[edit]

Oh BTW... my understanding on the focus assist is it is a purely flash function. The beam needs to bounce back to the flash not the camera. The flash simply tells the camera what it sees.

I don't know the technical details of the 550EX or 580Ex for that matter. But my understanding is the focus assist if a feature available when the flash is attached to the camera. But that it is not just a flash fuction...but a camera fuction. I believe the flash tells the camera what it sees when it is dealing with the flash output. Not the focus assist.

[Curtis N]

The AF assist light is designed to create lines of contrast on the subject, which helps the autofocus system work when otherwise there isn't enough contrast - Low light situations or subjects without much contrast. In order for the AF assist light to work, it must cast its lines of light on the part of the subject that the active focus point is aimed at.

The camera and flash unit need to be properly alligned. I'm not familiar with the CB Junior so can't advise specifically on how to make that happen. Since the AF assist light on the flash is going to be a foot or so above the lens, it's going to be impossible to line them up at close distances.

[rcg]

No problema on the help....

Sorry I wasn't trying to say the beam assist was for flash photography - sorry If I implied that.

There is definitely going to be an offset for the assist... the flash sits higher by about 3 inches in horizon mode and 6.5 inches higher in the portrait mode.... this doesn't account for the left "push" of the assist pattern. Try covering the emitter on the flash and see what effect you have on the projected pattern. Use a finger and see if you are efffecting the pattern starting from the right side of the emitter... do you have to cover the whole emitter to effect the pattern - eg are you only getting a partial pattern?

Put your 50 1.4 on and see what effect if any that has.