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How to tell if autofocus is spot-on?

 
 
SS
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      03-05-2006
I would like to know if there is some way I can check my camera is finding a
pin sharp focus on autofocus but here is the problem: I am looking at
distant tree branches on my photos, however as I zoom in on PSP details
starts to go and they look fuzzy - BUT - shortly followed by obvious
pixellation i.e. I am getting to the limit of the sensor (7MPX) which of
course causes detail to go, even if focus is spot on. Its a Canon A620 which
gets excellent reports and has a manual focus system if required but I find
it very hard to use as you tend to 'overshoot' using the focus buttons so
never sure if its spot on (is it best to zoom in then focus then zoom out
for the shot?).


 
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=?iso-8859-1?Q?M=E5ns_Rullg=E5rd?=
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      03-05-2006
"SS" <(E-Mail Removed)> writes:

> I would like to know if there is some way I can check my camera is finding a
> pin sharp focus on autofocus but here is the problem: I am looking at
> distant tree branches on my photos, however as I zoom in on PSP details
> starts to go and they look fuzzy - BUT - shortly followed by obvious
> pixellation i.e. I am getting to the limit of the sensor (7MPX) which of
> course causes detail to go, even if focus is spot on. Its a Canon A620 which


Make a few test shots of a small object grass or some other surface
with small details. It should be easy to see if the focus plane lines
up with the intended target.

> (is it best to zoom in then focus then zoom out for the shot?).


No. Zooming often changes focus.

--
Måns Rullgård
http://www.velocityreviews.com/forums/(E-Mail Removed)
 
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bmoag
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      03-05-2006
It isn't much better using a digital SLR which has a dim, non-pentaprism
viewing system, looking through an F4 (or smaller) lens in less than optimal
light through a focusing screen that has no critical focus adjustment
features, e.g. split image.
This is a real problem with all dSLRs except the very top end. Even then the
viewing systems and viewing screens are not optimal.
This is why some sort of heads up, projectied live EVF view of the scene may
(emphasis on may) be helpful. Olympus has announced such a system and I
believe it will become mainstream.
If you can put your camera on a tripod you actually have to bracket focus
under these circumstances and use as small an f-stop as practical for at
least one of your shots.


 
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Prometheus
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      03-05-2006
In article <6ADOf.18810$(E-Mail Removed) >, bmoag
<(E-Mail Removed)> writes
>It isn't much better using a digital SLR which has a dim, non-pentaprism
>viewing system, looking through an F4 (or smaller) lens in less than optimal
>light through a focusing screen that has no critical focus adjustment
>features, e.g. split image.
>This is a real problem with all dSLRs except the very top end. Even then the
>viewing systems and viewing screens are not optimal.
>This is why some sort of heads up, projectied live EVF view of the scene may
>(emphasis on may) be helpful. Olympus has announced such a system and I
>believe it will become mainstream.


So a low resolution and slow responding power consuming 'viewfinder'
will be better than the high resolution and fast responding live
pre-view on my SLR!

--
Ian G8ILZ
 
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Jim Townsend
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      03-05-2006
SS wrote:

> I would like to know if there is some way I can check my camera is finding a
> pin sharp focus on autofocus but here is the problem: I am looking at
> distant tree branches on my photos, however as I zoom in on PSP details
> starts to go and they look fuzzy - BUT - shortly followed by obvious
> pixellation i.e. I am getting to the limit of the sensor (7MPX) which of
> course causes detail to go, even if focus is spot on. Its a Canon A620 which
> gets excellent reports and has a manual focus system if required but I find
> it very hard to use as you tend to 'overshoot' using the focus buttons so
> never sure if its spot on (is it best to zoom in then focus then zoom out
> for the shot?).


Here's a web site dedicated to checking the focus of cameras.

http://www.photo.net/learn/focustest/

One thing to consider when 'zooming in' on your images and viewing them on
your monitor. When zoomed to 100%, you're looking at an image that was
created by a sensor the size of your little fingernail and then enlarged to
approximately 3 Feet X 2 Feet. At 200%, it's 6 feet X 4 feet.

A lot of the 'blur' you see is caused by the fact the lens isn't absolutely
and totally perfect. Such a lens doesn't exist.





 
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Tesco News
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      03-05-2006
"SS" <(E-Mail Removed)> wrote in message
news:jdCOf.73213$(E-Mail Removed)...
>I would like to know if there is some way I can check my camera is finding
>a
> pin sharp focus on autofocus but here is the problem: I am looking at
> distant tree branches on my photos, however as I zoom in on PSP details
> starts to go and they look fuzzy - BUT - shortly followed by obvious
> pixellation i.e. I am getting to the limit of the sensor (7MPX) which of
> course causes detail to go, even if focus is spot on. Its a Canon A620
> which
> gets excellent reports and has a manual focus system if required but I
> find
> it very hard to use as you tend to 'overshoot' using the focus buttons so
> never sure if its spot on (is it best to zoom in then focus then zoom out
> for the shot?).
>
>

Hi.

A terrific amount of time is wasted by people worrying about the Resolution
of their lenses, and the accuracy of the Auto Focus system.

If your Lens or Camera has a fault, you will soon be aware of it, unless of
course you can't tell good quality results from bad.

If you really must test your AF, get yourself outside in nice bright light,
set a high shutter speed so that your aperture is at is maximum, and take
photos of a wooden fence or brick wall, from an angle. Stick something to
the wall or fence for you to focus on. When you examine the results the
wall or fence nearest to you should be unsharp, and gradually get sharper,
and then start to become unsharp again. The sharpest point should be at
your marker.

Roy G



 
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Rich
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      03-06-2006
Buy this:

http://www.dslrfocus.com/
 
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Ron Hunter
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Posts: n/a
 
      03-06-2006
SS wrote:
> I would like to know if there is some way I can check my camera is finding a
> pin sharp focus on autofocus but here is the problem: I am looking at
> distant tree branches on my photos, however as I zoom in on PSP details
> starts to go and they look fuzzy - BUT - shortly followed by obvious
> pixellation i.e. I am getting to the limit of the sensor (7MPX) which of
> course causes detail to go, even if focus is spot on. Its a Canon A620 which
> gets excellent reports and has a manual focus system if required but I find
> it very hard to use as you tend to 'overshoot' using the focus buttons so
> never sure if its spot on (is it best to zoom in then focus then zoom out
> for the shot?).
>
>

It is much more likely you are at the resolution limit of your
lens/sensor set.
 
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Kennedy McEwen
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Posts: n/a
 
      03-06-2006
In article <%gKOf.76978$(E-Mail Removed)>, Tesco News
<(E-Mail Removed)> writes
>
>A terrific amount of time is wasted by people worrying about the Resolution
>of their lenses, and the accuracy of the Auto Focus system.
>

It will all
become irrelevant soon anyway.
http://www.photonics.com/spectra/tec...49/QX/read.htm
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's ****ed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)
 
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Tesco News
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Posts: n/a
 
      03-07-2006
"Rich" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Buy this:
>
> http://www.dslrfocus.com/


Hi.

I like that.

It should keep all the worriers very busy for a very long time.

Roy G


 
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