How to force autofocus to focus on a specific object?


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commonjunks

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Jul 23, 2009
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#1
Hi,

I took this picture and i want to focus on Penguin but using autofocus it is impossible.
Or only answer is manual focus?

 

Diavonex

Senior Member
Sep 23, 2008
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#2
Use spot focusing; watch out for camera shake.
 

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Octarine

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Jan 3, 2008
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#3
Use single AF point that is directly above the penguin. See manual for further details.
 

ricleo

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Mar 13, 2004
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#4
or use the centre focus point, focus on the penguin and then recompose the framing while your finger is half-depressed on the shutter button.
 

commonjunks

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Jul 23, 2009
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#5
Use spot focusing; watch out for camera shake.
Use single AF point that is directly above the penguin. See manual for further details.
or use the centre focus point, focus on the penguin and then recompose the framing while your finger is half-depressed on the shutter button.
Thank you guys.
ricleo i will try you method :D.
 

Octarine

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#6
or use the centre focus point, focus on the penguin and then recompose the framing while your finger is half-depressed on the shutter button.
This could throw off the focus, especially with such a shallow depth of field. Nobody is a born tripod, chances are good to shift in more than one direction. That's the point where multiple AF points come in handy.
 

commonjunks

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Jul 23, 2009
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#7
This could throw off the focus, especially with such a shallow depth of field. Nobody is a born tripod, chances are good to shift in more than one direction. That's the point where multiple AF points come in handy.
Will keep in mind.
I was looking at this picture, aperture is only 2 and it very sharp/clear.
Does it mean increasing .2 will make picture that clear?

http://www.greaterbostonphotography.com/wp-content/uploads/2009/04/unearthly-oak-aged-souther-tier.jpg
 

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ziploc

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Jan 17, 2002
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#8
Will keep in mind.
I was looking at this picture, aperture is only 2 and it very sharp/clear.
Does it mean increasing .2 will make picture that clear?
No. The problem with your pic is not due to the aperture but because you've gotten too close to the subject. All lenses have minimum focusing distance (check the manual of your camera/lens); if you're closer then the minimum focusing distance the lens/camera will not be able to focus. E.g. if a lens' min focusing distance is 0.5m, you can only focus starting from 0.5m or more.
 

hongwen37

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May 19, 2009
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#9
TS,

No part of your photo looks sharp to me... How near are you to the subject? Do you know that if you are too near to the subject, you are not able to focus anything at all, even with manual focus?

Also, did you take that photo with autofocus or manual focus? let us know so we can help you...

The f/1.8 allows your subject to be sharp too... Just that you need to know how to focus...
 

Rashkae

Senior Member
Nov 28, 2005
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#10
Many first-time DSLR buyers tend to think that using the kit lens will be just like a point-and-shoot and immediately give tham a "macro" mode. it does not; you need to take your minimum focus distance into consideration.

As for selecting your focus point, there is a section in your camera manual that details how to switch to spot focus and then select the point.
 

commonjunks

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Jul 23, 2009
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#11
Many first-time DSLR buyers tend to think that using the kit lens will be just like a point-and-shoot and immediately give tham a "macro" mode. it does not; you need to take your minimum focus distance into consideration.

As for selecting your focus point, there is a section in your camera manual that details how to switch to spot focus and then select the point.
Thank you i will look at my manual. Maybe i give example of wrong picture, i will try to post some of my sons picture (those pictures are taken from distance and taken handheld 1/200 @ 1.8 aperture).


TS,

No part of your photo looks sharp to me... How near are you to the subject? Do you know that if you are too near to the subject, you are not able to focus anything at all, even with manual focus?

Also, did you take that photo with autofocus or manual focus? let us know so we can help you...

The f/1.8 allows your subject to be sharp too... Just that you need to know how to focus...
Sorry it is taking autofocus (camera was able to focus), distance about 25~30 centimeters.
 

Rashkae

Senior Member
Nov 28, 2005
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#12
Thank you i will look at my manual. Maybe i give example of wrong picture, i will try to post some of my sons picture (those pictures are taken from distance and taken handheld 1/200 @ 1.8 aperture).
If you're at f/1.8, you need to consider how thin your depth-of-field will be.
 

zac08

Senior Member
Feb 21, 2005
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#13
Thank you i will look at my manual. Maybe i give example of wrong picture, i will try to post some of my sons picture (those pictures are taken from distance and taken handheld 1/200 @ 1.8 aperture).




Sorry it is taking autofocus (camera was able to focus), distance about 25~30 centimeters.
It's too close to autofocus. Your lens has a minimum focusing distance. Do watch for that.
 

Jun 11, 2009
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#14
What focusing point are you using?

You need to tell the camera where to focus at by selecting the focus point in order to test front/back focus. Otherwise, with auto focus-point selection, the camera might not focus on where you want it to focus or sometimes it will focus on in between the two points it thinks you want to capture. It is not a problem at smaller aperture, but at f/1.8, you really need to pin point the focus point on where you want it to focus at.
 

commonjunks

Senior Member
Jul 23, 2009
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#15
What focusing point are you using?

You need to tell the camera where to focus at by selecting the focus point in order to test front/back focus. Otherwise, with auto focus-point selection, the camera might not focus on where you want it to focus or sometimes it will focus on in between the two points it thinks you want to capture. It is not a problem at smaller aperture, but at f/1.8, you really need to pin point the focus point on where you want it to focus at.
I think tonight i need to read manual. I was hoping to skip it but seems :nono:. Funny thing is last month i got 50mm f1.8 lens and result was very clear but i returned it (due to misunderstanding between me and shop) and now i buy from another shop and not that good result. But again, i will read manual and try to keep the things in mind for my next shot.
 

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