hi,

I wonder why this is happening with my EOS 300. When the subject is at the central focusing point, the camera focuses it properly. but when i use one of the other focusing points camera doesn't focuses most of the times. but when i select focusing point, other than the central one, manually, the camera does focus the subject. whats wrong ? is it the camera not functioning properly or am i doing something wrong while focusing. please help.

-- sajeev (chack74@yahoo.co.in), January 30, 2002

Answers

sajeev...

what do u mean by "but when i use one of the other focusing points camera doesn't focuses most of the times" ??

when it is at the defualt focus point selection mode(all points), YOU don't "use" any point...the focus points which achieve focus are indicated in the viewfinder display and the FOCUS ON indicator lights up...sometimes for eg. the right most focus point may not achieve focus as the angle of view to the subject which falls at the right most focus point might not be conducive(or may not have enuff light ?), but the center point would have achieved focus. if u reposition urself such that both the center focus point and the extreme right focus point are positioned correctly over the subjects, u will find that both these points achieve focus....when in automatic mode, often u will find that all the points do not achieve focus..u just need to make sure that the main subjects u intend to capture are covered by the focus points and those points have achieved focus..

and as to when u manually select a focus point it is up to u to make sure that the focus point covers the intended subject in the viewfinder and this will almost always work...u might use it to focus on off center objects...

actually i believe its a pretty important thing...the camera has this AIM metering system..which is supposed to work like.."it meters according to the points which have achieved focus"...so its essential that the elements in the frame that u need to render correctly have to covered by the focus points and achieve focus for them to be exposed correctly. i have noticed that often i ignore this small but important fact...this could be the reason for a lot of snaps lacking the "punch" if u know what u mean...

this is my understanding of the system from what i have read and what replies i have reveived here on this forum...

in case my interpretation is wrong, i'm sure others here will correct me :-)

ciao venkat

-- Venkat (venkat_p_iyer@yahoo.com), January 30, 2002.

what i meant by

"but when i use one of the other focusing points camera doesn't focuses most of the times"

is that,

when i use the AUTOMATIC selection of focusing points, and place the subject at the center, it gets focused properly.

but when i use any other focusing point MANUALLY, and recompose so that, that particular point is on the subject, the subject is not focused. i guess this should be independent of the amount of light available. and in Tv or Av mode, without PARTIAL METERING, i should be able to focus any subject with any of the focusing point IF IT CAN BE FOCUSED WITH THE CENTER FOCUSING POINT.

i hope i have made my question clear.

-- sajeev (chack74@yahoo.co.in), January 31, 2002.

sajeev...

what u mentioned in the last line sounds logical. if a subject can be focussed with the center focus point, it must be able to achieve focus with other focussing points too...

but i'm a bit confused... in the first posting u said.. "but when i select focusing point, other than the central one, manually, the camera does focus the subject. "

but in the second posting u've said... "but when i use any other focusing point MANUALLY, and recompose so that, that particular point is on the subject, the subject is not focused."

i'm sorry yaar...i think i haven't got what ur trying to explain...

ciao venkat

-- Venkat (venkat_p_iyer@yahoo.com), January 31, 2002.

let me make it clear again. instead of using the central point for focusing (AUTOMATICALLY) i.e. the subject is placed at the center for focusing and press the shutter halfway, the object does get focused. but if i use any of the other focusing points (MANUALLY) and place that selected point on the same subject, sometimes the subject is not focused. instead, at times, the subject corresponding to center is focused. this happens mainly in the low light condition.

-- sajeev (chack74@yahoo.co.in), February 01, 2002.

i understood now :-)

but yaar, this hasn't happened to me(rather doesn't)...i tried fiddling about with these focussing points...

what i observed was the same as the first reply i put in... 1. when the focussing points are left to the default(all 7), and i press the shutter release half way down, some or all of the points may/may not achieve focus depending on lighting conditions, subject charateristics etc..whichever points achieve focus, are indicated in the viewfinder display.

2. when i manually select a focussing point, say the extreme right one, as long as i ensure that the point is correctly positioned over the subject, it does focus.

i was not able to duplicate the situation u described. however i shall bear this in mind henceforth when i'm shooting and see if this happens to me too.

sorry about making u explain 3 times and not contribute at all :-( this thing is over n above my head.

ciao

-- Venkat (venkat_p_iyer@yahoo.com), February 01, 2002.

"this happens mainly in the low light condition"

The center sensor is a cross sensor, which means it is sensitive to subjects with both horizontal and vertical lines. All the other focusing sensors are only sensitive to subjects with horizontal lines.

What does this mean? In low light, low contrast conditions, the center sensor will focus more reliably than the other sensors. In good lighting, the single axis focusing sensors can focus on subjects that are primarily vertical (like a wood fence pole) because it can pickup the subjects texture, which allows the horizontal sensor to operate. In low light, subject texture is more difficult to pick up and the AF sensor may fail.

In low light, use the center sensor, or try turning the camera to a 45 degree angle, which may allow the outer sensors to lock onto a vertical subject.

-- Kenneth Katz (socks@bestweb.net), February 01, 2002.

thnx,

i tried the trick by kenneth of tilting the camera by 45 degree and i could really focus that subject properly with the horizontal off-centered focusing points. and for the top-most (or bottom) focusing point there was no problem for focusing. later when i did the same experiement with more light, i had no problem of focusing with any point selected manually.

-- sajeev (chack74@yahoo.co.in), February 08, 2002.