AF Assist Malfunction - 430 EX II

[BKA]

I just got a new 430 EX II.  I have the flash mounted on my T3i and strangely, when I'm trying to focus with my telephoto zoom the camera is front focusing; I know it is not the lens's problem, because it works without the flash mounted. I also found out that when the 430's af assist  is on, the camera front focuses and when off it works fine. The AF assist also makes auto focus slower for some reason. I've heard that the 600 EX-RT also has the same issue.

 Is their any way to fix this problem? or is Canon just notorious for this problem...because I'm not happy!

Thanks.

[Crista]

Hi BKA! In order for the community to better assist you, we’ll need to know the model camera you are using. This is ensure that the most accurate information is provided. Thank you!

[BKA]

Sure, I use a Rebel T3i.

[digital]

In all the years I have been on forums this is the first time I have heard of this. I'm not sure what would cause the lens to front focus when the flash is on. Focusing has nothing to do wiith the flash. If you watch the canon masterclass series the EXII is not even focus point linked like the EX series was. Even if it was I'm not sure how it could effect it. The flash gets flash exposure information from the camera but has nothing to do with camera funtctions themselves. In other words flash does not control AF.    

See section on ETTL II Metering. 

http://cpn.canon-europe.com/content/education/masterclass/canon_flash.do

As for af asisst issues. You are shooting with a telephoto lens. How far is the subject? There is a point when the af light is just not strong enough to be 100% effective. 

Is this FF problem happening when you are having the af assist issues or does it FF all the time (even when your not using the af assist)?     

[BKA]

Thanks for your reply. I know the flash itself has nothing to do with the focusing...its the AF ASSIST that is messing the focusing up. I don't know why.

[digital]

The distance you are having trouble with?

[BKA]

You mean focal length? I am having problems at all focal lengths with my telephoto lens.

[digital]

I was wondering how far yor subject is? 30', 40', 50' feet away? There is a maximum distance has AF assist has to be effective.

My 600EX-RT is 32.8' in the center and the outer focus points are 16.4'  

[BKA]

I'm not shooting far at all. I shot at 30' and at 3'. Even without the AF assist the lens should focus anyway; there is plenty of light.

[canon-oldman]

First af all this is very annoying problem. I can confirm problem exists.

I'm using Canon 1Ds mark III and Canon 600EX-RT flash.

Depending on whether flash AF assist beam is on or off I need to set different values for focus micro adjustment.

My guess is that:

- When flash AF assist beam is OFF camera is using AF phase detection chip.

- When flash AF assist beam is ON flash will detect distance to the subject and instruct camera to set distance on the lens. In this case phase detection chip might not be used at all. Who knows how lens misallignment and/or AF phase detection chip misallignment is taken into account.

This is why it is critical to have both focusing systems to be aligned properly.

Unfortunately proper solution is to send camera & flash & lens to Canon service for alignment.

I hope they can do this. It would be great if this is covered by Canon warranty.