topic Re: AF Assist Malfunction - 430 EX II in Speedlite Flashes

AF Assist Malfunction - 430 EX II

BKA — Wed, 19 Dec 2012 20:45:51 GMT

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.

Re: AF Assist Malfunction - 430 EX II

Crista — Wed, 19 Dec 2012 14:58:35 GMT

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!

Sure, I use a Rebel T3i.

BKA — Wed, 19 Dec 2012 20:45:29 GMT

Sure, I use a Rebel T3i.

Re: Sure, I use a Rebel T3i.

digital — Thu, 20 Dec 2012 13:18:00 GMT

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)?

Re: AF Assist Malfunction - 430 EX II

BKA — Thu, 20 Dec 2012 18:32:06 GMT

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.

Re: AF Assist Malfunction - 430 EX II

digital — Fri, 21 Dec 2012 00:18:50 GMT

The distance you are having trouble with?

Re: AF Assist Malfunction - 430 EX II

BKA — Mon, 24 Dec 2012 18:14:39 GMT

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

Re: AF Assist Malfunction - 430 EX II

digital — Mon, 24 Dec 2012 18:46:01 GMT

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'

I'm not shooting far at all. I shot at 30' and at 3'. Eve...

BKA — Sat, 29 Dec 2012 00:00:05 GMT

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.

Re: I'm not shooting far at all. I shot at 30' and at 3'. Eve...

canon-oldman — Wed, 03 Feb 2016 17:22:15 GMT

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.

Re: I'm not shooting far at all. I shot at 30' and at 3'. Eve...

kvbarkley — Thu, 03 Mar 2016 20:22:23 GMT

http://www.bobatkins.com/photography/technical/focus_vs_light_source.html

Oh, and the flash has no distance measuring at all.

Re: I'm not shooting far at all. I shot at 30' and at 3'. Eve...

Waddizzle — Thu, 03 Mar 2016 21:17:36 GMT

@kvbarkley wrote:

[link deleted]

Oh, and the flash has no distance measuring at all.

Why do you persist in posting links so often? I don't click on miscellaneous links. It also violates the TOU agreement.

Re: I'm not shooting far at all. I shot at 30' and at 3'. Eve...

Danny — Thu, 03 Mar 2016 21:31:11 GMT

Hi!

To clarify, if someone uses a link to help illustrate a point and the page you land on isn't overtly trying to sell you anything, we will generally allow it to stay up. Links that we usually take down include ones that are irrelevant to the conversation, ones that contain objectionable content, or where the site's purpose is intended to solicit sales. This is not necessarily an exhaustive list of criteria, and each link's viability is at the discretion of the forum moderators.

In this case, we checked kvbarkley's link and it satisfies our criteria. We'll allow it to stay up.

We hope this helps!

Re: I'm not shooting far at all. I shot at 30' and at 3'. Eve...

canon-oldman — Thu, 03 Mar 2016 22:48:17 GMT

kvbarkley, you might be surprised how complex AF assistant beam is. It is not a simple light.
Article is interesting. I wonder if there is IR filter in the front of AF-phase detection sensor?

Another interesting observation/speculation.
Considering IR light causing back focus. Notice that AF assistand beam has lots of IR light.
Is there any compensation coefficient Canon using to correct AF in the case when Flash AF assistant light is on?
I guess it should if using AF-phase detection chip, and should NOT if measuring distance using flash.

Re: I'm not shooting far at all. I shot at 30' and at 3'. Eve...

kvbarkley — Thu, 03 Mar 2016 22:45:50 GMT

I know it is a complex pattern. Still doesn't measure distance, though. Just provides illumination for the camera's AF system.

As for the link, it is to a technical photography website that describes this issue exactly. It appears that IR light can move the focus point a bit.

Re: I'm not shooting far at all. I shot at 30' and at 3'. Eve...

canon-oldman — Thu, 03 Mar 2016 22:50:42 GMT

kvbarkley, light flash AF beam and check if you can see split lens or even pair. It looks similar to old style split focusing screen.

Re: I'm not shooting far at all. I shot at 30' and at 3'. Eve...

kvbarkley — Thu, 03 Mar 2016 22:57:02 GMT

Yes, it is a matrix pattern. But the flash has no sensor to read the light - unlike my old Vivitar 8^). It is all done by the camera. After all, disco-flash works just as well to focus without the complex pattern or even the external flash.

Besides the distance from the *flash* to the subject is irrelevant - you could be using off-camera flash. What counts is distance from the *camera* to the subject.

Re: I'm not shooting far at all. I shot at 30' and at 3'. Eve...

canon-oldman — Thu, 03 Mar 2016 23:12:32 GMT

There is US patent, not sure if Canon goes this way, but their flash AF assist is not that simple as one might think.
Autofocus assist lighting used for rangefinding in very low light conditions.

http://www.google.ch/patents/US20100158495