580 ex auto focus assist Beam Pattern?

[william_powell1]

No one at Canon can tell me why with different lens I get different

patterns projected by the Auto focus assist beam.. I am using the

Mark II .. zoom lens gives a wide beam at all focal lengths and the

fixed focal a narrow vertical beam.. Can this be changed?

[jimstrutz]

Which Mark II, 1D or 1Ds? Which zoom lens? Which fixed focal lens? What AF points are you using with each?

 

Are you sure you want it changed?

[yakim_peled1]

What? Have I understood correctly? The width of the 580EX's AF assist beam is changed with the lens' focal length?

 

Happy shooting,

Yakim.

[ydvu]

Hi, Bill

 

My guess (just guess) is that the focus pattern varies with change of focusing pattern. That's what happens to my system (D60+420ex). When I use automatic mode the flash emits a flat pattern so all the fucusing points can "see" the pattern. When I use just one focusing point (in advanced modes) the flash emits a narrower pattern just to cover than focusing point. This is to increase the autofucusing performance, I guess.

 

Yuqing

[ydvu]

Changing a typo here:

 

My guess (just guess) is that the focus pattern varies with change of focusing points.

 

Yuqing

[steve_dunn2]

<p>Are you using the same AF points in every case? Most of Canon's more recent flash units project a pattern which matches the AF point(s) in use on the specific body at that moment. For instance, on my Elan 7E, four of the seven points are sensitive only to horizontal lines, two only to vertical lines, and one to both. If I pick a horizontal-only AF point, the 420EX' AF assist system only projects horizontal lines. If I pick a vertical-only AF point, it only projects vertical lines. If I pick the cross sensor, or let the camera pick a sensor for me, it projects both horizontal and vertical lines.</p>

 

<p>A previous discussion, several weeks ago, reveals that the 580EX works the same way with at least one body (I think it was a discussion about the 20D but I'm not certain); the pattern it projects depends on the AF point(s) selected. Is it possible this is what you're seeing?</p>

[alexandru_petrescu]

420EX on Rebel T2 and Elan 7Ne: AF assist beam pattern is vertical if any vertical focus point is manually/eyeally selected, horizontal if any horizontal point is selected and both horiz/vert if automatic AF focus point (no manual no ECF). If the center point is manually selected the beam pattern is vertical. If the flash is in Slave mode the pattern is periodic and vertical. All the above for focals between 16 and 200, I don't think the focal lengths influence the beam pattern for the mentioned bodies.

<p>

Now I wonder how the pattern is with a 20D's 9-point focus points, or with the 3's I-don't-know-how-many focus points.

[joey_conta]

Sorry for necro-posting, but I couldn't find any recent topic thats appropriate for this info...

 

With some experimentation with a 40d and an 580ex II I've come to learn that the AF assist pattern, is dependant on the AF point selected.

 

On the 580ex II the top two lamps project horizontal lines, with the one on the right (if front of the flash is pointing towards you) projecting ,three brighter "Inner" horizontal lines, and the left lamp projecting three dimmer "Outer" lines with sit on top and below the "inner" projected lines.The bottom AF assist lamp, projects one Vertical column, which is the brightest of the three.

 

On the 40d and the 350d when the camera is set to Auto AF point selection, the Bottom Lamp, and the Top Right Lamps light up, projecting the Vertical column and the Inner horizontal Lines.

 

When the Center or the two AF points above or below the centre AF point are selected manually, only the Bottom lamp lights, projecting only the vertical beam.

 

When any of the Other AF points (ie: NOT the centre AF point, and the ones above and blow it) are selected manually, only the top lamps light, projecting only the horizontal lines.

 

http://tinyurl.com/2t2t67 (youtube, Af assist lamp video)