focusing issue

[abc123]

Hi,


Would someone please help me , I have an issue on focusing. I am using both Canon body + lens.


I set up on Manual mode , Manual focus , spot metering , AF point is center. When I focused on the center of the subject then press half way, the subject was focused exactly with red light sound , took the picture , no problem at all . Then I continued to focus on the center , still pressed hafl way to hold down exposure and focusing , when I moved the lens to recomposed , the red light was still on sound and the focus point was changed . I don't know what wrong with it ?


I clearred off all setting , turned off , took out battery and memory card then inserted them again , turned on for the default , it was still the same problem.


Thanks for the help.

[Sinh Nhut Nguyen]

When You focused in the center and recomposed, the focused objectwas not in the center of the frame anymore. Let's say you're usingcenter point AF,the reason you want to focus and recompose is because you don't want your subject to be in the middle. Whatever in the middle nowisout offocused because you never intended that to be in focused in the first place.

[peety3]

Tell us which camera and which lens.


A few things come to mind already:


1) You might not be using the best focus screen for the job. If your lens is faster than f/2.8, the stock focus screen won't show you accurate focus. When the mirror is down, light coming in through the lens is being projected onto the focus screen, and you're looking at the image on the screen when you look through the viewfinder. Some focus screens are optimized for faster lenses, and you might need to change to one of those.


2) Some lenses have focus shift at fairly wide (but not wide open) apertures.


Tell us more, and we'll postulate more.

[abc123]

Thanks Sinh Nhut Nguyen,


As I understand , when we use M mode and Manual focus , wherever we move or recompose ( of course shooting button is on half press ) the focus is still being kept . Let say I recompose the subject at the left corner , after shooting , it is still in focus and clear while the others are blur.

[abc123]

Thanks peety3,


I am using Canon 40D + lens Canon 50 1.8 + lens Canon 70-200 F4 + lens Tamron macro 90 2.8 .


I am aware of the which aperture is compatible with wich lens in the focus screen function.


Anything wrong with the camera body , I mean the focus system ?

[Sinh Nhut Nguyen]

When you in manual focus, the "half press" function should not work because the "half press" function activates the autofocus when the lens is set to AF. I don't understand clearly what you're trying to say, sorry. []

[abc123]

Hi Sinh Nhat Nguyen,


correct me if I am wrong :


1.) using M mode + Manual focus : when press shooting button hafl way, the exposure and focusing is locked then we can recompose the photo and the original focus still there .


2.) using AF mode+ AF focus : press half way and press * to lock the exposure and focus , then recompose.


thanks,

[mark]

an explanation i describrd to some else that shot nikon ... correct me if i am wrong but fous a recompose has seriuos issue ... without the math






<table border="0" width="591" cellpadding="1" cellspacing="0"]
<tbody>
<tr>
<td colspan="2" class="forumsmessagecontainer"]
<div id="forumsmessagetext"]
<p class="justify"].. if you are using a single focus point and focusing and recomposing the the focus is actually going to be off and is more noticable with a large aperture ...this is due to the reality that when you focus and recompose you ar actually changing the focus plane... inother words you focus on something ...move the camera ... it is locked on a particular focus plne ... therefore when you "recompose" that focal plane IE distance changes andanything and everything on the original plane will be somewaht out f focus ...you will get mush better results if you actually shift the focus point from center point to the one that correspondes to the subject you wish to have sharpest ...
<p class="justify"]with out the math do this ... get a piece of stiring and fix it to a point ( represents your center point center point ) take it tight to a wall.... thats is where you are now focus locked ... move up down left or right ... that string no longer is touching the wall .(your original focus Plane ) ..so see waht you thought you focused on it now goint to be OOF(outof focus slightly ... thats the part they dont ell you in the owners manual
<p class="justify"]
</div>
</td>
</tr>
<tr>
<td height="15" colspan="2" class="forumsmessagebottombar"]</td>
</tr>
</tbody>
</table>



ere is your answer

[Sinh Nhut Nguyen]

According to my understanding you want to focus on an object in the middle of the frame and then move it off the middleand still want to have sharp focus on that same object?


First I want to get some of these stuff clear...


- In M mode, you set the exposure and it stays as set until you manually change it.


- When your lens and cameraare in M mode and onManual Focus, pressing the shutter button half way does nothing to the camera.


- When you're in one of the auto exposure modes and Manual Focus, pressing the shutter button half wayonly triggers the camera's meter.


- When you're in one of the auto exposure modes and also on Auto Focus, pressing the shutter button half way triggers the camera's meter and the lensstarts to auto focus.


- Using Auto Exposure, Auto Focus (One Shot AFmode), press the shutter button half way to triggerauto focusing and metering, continue to hold the shutter button half way, press * once to lock the exposure, recompose...if you do all these steps the exposure and the focus will not change after you recompose.


**Keep in mind that when you recompose you don't change the distance between your camera and the subject...that is your cameracannot move closer to or farther way from your subject, doing so will throw your subject out of focus.


**Auto Focus and Recompose work best in One Shot AF.


**An example of Autofocus and Recompose. You're shooting a head &amp; shoulder potrait and you want to focus on the eyes of the model using the Central AF point. You've picked your distance just so your model upper bodywould fill the entire frame. Now you realize that the Central AF point is not atually on her eyes, but on her chest. What you need to do now is to point the centralfocus point at her eyes,half press the shutter button to achieve focus on the eyes, continue to half press the shutter button to keep the focus on the eyes, recompose so the entire model's head and shoulder fill the frame and then take the picture.