Focus wrong? Need help testing Kodak DX7630 AF

Archived from groups: rec.photo.digital (More info?)

Dave G wrote:
> I'm getting (possibly) wrong focusing w/my DX7630 autofocus. It seems
> to be setting the lens about 2/3 of the way to what I would consider
> the target.
>
> Before I send it back to Kodak on warranty, I want to see if it's
> something I'm doing.
>
> What's the right way to test?
>
> (There's no way to set focus manually on this model).
>
> My latest tests involve long-distance focus with a tripod, with and
> without the Retinar 0.6x wide angle converter lens. The scene is on a
> flood control bank of a river with sharp riprap extending from camera
> position to the far distance as well as forest on the other side. The
> figures below refer to the furthest that trees/riprap are the
> sharpest.
>
> W/o the WA lens, with center focus, camera pointed so that the focus
> target includes the line between trees and sky on a hill about 1 mile
> away, the point of sharpest focus on the photo file is about 800 yards
> away. The treeline in the distance is noticeably soft.
>
> With the WA converter, same focus setup, the point of sharpest focus
> is about 300 yards away, an odd bit of data. While this may be
> distortion/degradation from the add-on lens, there seems to be no
> focus problems with it when taking architectural subjects about 50-300
> yards away.
>
> With the camera on "landscape" mode and also landscape SCN mode,
> results are about about the same. From emails to Kodak support, I've
> learned that "landscape," rather than setting the lens at inifnity ,
> instead sets the camera on multi-zone focusing. (Not sure what that's
> about -- I'd think than landscape shots would benefit most from a lens
> set to infinity).
>
> Similarly, in "macro" mode, focus at a nice sharp target at 9"
> (keyboard) sets the lens so that I have to move the camera (with
> shutter button half down) a few inches closer for sharpest focus.
>
> Any help is welcome.
> Dave

Let me see if I understand. You claim that at a distance of 800 yards
focus is good, but things farther away aren't sharp? So, why do you
think there is a focus problem? Maximum focus variation is in the range
of 20 to 50 feet, anything farther away is 'infinity' as far as the lens
is concerned. The lack of sharpness of objects farther away than 800
yards is due to the fact that the size of an object at that distance is
quite probably less than one pixel in size, and thus can't be rendered
clearly. There is a level at which even a 6 mp sensor can't get enough
of an image to produce a clear definition.


--
Ron Hunter rphunter@charter.net

Archived from groups: rec.photo.digital (More info?)

On Fri, 13 May 2005 21:09:08 -0500, Ron Hunter <rphunter@charter.net>
wrote:


>
>Let me see if I understand. You claim that at a distance of 800 yards
>focus is good, but things farther away aren't sharp? So, why do you
>think there is a focus problem?
Because in certain situations, the DX7630's focus is softer than my
1990 Fujifilm 1400 zoom (1.4 Mp). With the Schneider lens and lots
more pixels, shouldn't the Kodak be better?

>Maximum focus variation is in the range
>of 20 to 50 feet, anything farther away is 'infinity' as far as the lens
>is concerned.
As a focus newbie, I don't quite understand this. The camera focuses
well on things up to around 900 yards... 2700 feet... ?

> The lack of sharpness of objects farther away than 800
>yards is due to the fact that the size of an object at that distance is
>quite probably less than one pixel in size, and thus can't be rendered
>clearly. There is a level at which even a 6 mp sensor can't get enough
>of an image to produce a clear definition.
Hadn't thought of that, so I went back to one test image. A large pine
tree jutting out into the sky about 1 mile away is quite soft. The
smallest masses, branches toward the top, are 4 pixels across, and
other elements of the tree are 20-30-50 pixels across.

The full image is at http://www.un-real-estate.com/images/100_0679.JPG
Pine tree in question is along the skyline just to the left of center.
The bridge is 800 yards away. To my eyes, the furthest area of sharp
focus is the trees just behind the bridge. But, admittedly, I don't
really know what to look for.

This was one I took with center spot focus. According to the AF
brackets, I was focusing on the area where the pine tree juts out.
Camera at wide angle (no WA conversion lens attached). Tripod; 1/250;
f/6.7. Compression: fine. Sharpening: normal. 6.1 Mp.

Archived from groups: rec.photo.digital (More info?)

Dave G wrote:
> On Fri, 13 May 2005 21:09:08 -0500, Ron Hunter <rphunter@charter.net>
> wrote:
>
>
>
>>Let me see if I understand. You claim that at a distance of 800 yards
>>focus is good, but things farther away aren't sharp? So, why do you
>>think there is a focus problem?
>
> Because in certain situations, the DX7630's focus is softer than my
> 1990 Fujifilm 1400 zoom (1.4 Mp). With the Schneider lens and lots
> more pixels, shouldn't the Kodak be better?
>
>

Not always. The large pixels of the lower resolution cameras give an
illusion of great 'sharpness', since their edges are more apparent.
Take a picture of the same thing from the same viewpoint, and zoom, and
look at each. The lower resolution at 50% on your screen will probably
appear sharper. Now magnify each of them to 200%. Now which one has
more DETAIL? Which one appears sharper. Surprised? I was.
The picture with the more pixels will appear less sharp because the
extra pixels make lines that appear sharp (if somewhat ragged) while the
greater number of pixels reveals more detail, but appears less sharp.
In either case, picture elements are only so large, and if an object is
so far away that the lens casts the whole image on only a single pixel,
it WILL appear fuzzy.


>>Maximum focus variation is in the range
>>of 20 to 50 feet, anything farther away is 'infinity' as far as the lens
>>is concerned.
>
> As a focus newbie, I don't quite understand this. The camera focuses
> well on things up to around 900 yards... 2700 feet... ?
>
>
>>The lack of sharpness of objects farther away than 800
>>yards is due to the fact that the size of an object at that distance is
>>quite probably less than one pixel in size, and thus can't be rendered
>>clearly. There is a level at which even a 6 mp sensor can't get enough
>>of an image to produce a clear definition.
>
> Hadn't thought of that, so I went back to one test image. A large pine
> tree jutting out into the sky about 1 mile away is quite soft. The
> smallest masses, branches toward the top, are 4 pixels across, and
> other elements of the tree are 20-30-50 pixels across.
>
> The full image is at http://www.un-real-estate.com/images/100_0679.JPG
> Pine tree in question is along the skyline just to the left of center.
> The bridge is 800 yards away. To my eyes, the furthest area of sharp
> focus is the trees just behind the bridge. But, admittedly, I don't
> really know what to look for.
>
> This was one I took with center spot focus. According to the AF
> brackets, I was focusing on the area where the pine tree juts out.
> Camera at wide angle (no WA conversion lens attached). Tripod; 1/250;
> f/6.7. Compression: fine. Sharpening: normal. 6.1 Mp.


--
Ron Hunter rphunter@charter.net

Archived from groups: rec.photo.digital (More info?)

Hi Dave,

Sorry I wasn't here for the last few days. Was off on an assignment and
vacation.

If you have a couple of images that were taken at WA and Tele I will be glad
to review and examine. I would like to review the picture quality as well
as measure for perspective. Do you have an accessory lenses? Also have you
tried resetting the camera to its defaults. If not try doing this to see if
it makes a difference. This should make sure the camera is set to perform
normally as out of the box. You can simply remove the batteries from the
camera overnight and the camera will be reset.

Let me know and send along some pictures. I will review and reply to you, as
well as post here if you like.

Talk to you soon,

Ron Baird
Eastman Kodak Company



"Dave G" <dgehman(at)rcn(dot)com> wrote in message
> I'm getting (possibly) wrong focusing w/my DX7630 autofocus. It seems
> to be setting the lens about 2/3 of the way to what I would consider
> the target.
>
> Before I send it back to Kodak on warranty, I want to see if it's
> something I'm doing.
>
> What's the right way to test?
>
> (There's no way to set focus manually on this model).
>
> My latest tests involve long-distance focus with a tripod, with and
> without the Retinar 0.6x wide angle converter lens. The scene is on a
> flood control bank of a river with sharp riprap extending from camera
> position to the far distance as well as forest on the other side. The
> figures below refer to the furthest that trees/riprap are the
> sharpest.
>

Archived from groups: rec.photo.digital (More info?)

On Sat, 14 May 2005 07:54:43 -0400, Dave G <dgehman(at)rcn(dot)com>
wrote:

> This was one I took with center spot focus. According to the AF
> brackets, I was focusing on the area where the pine tree juts out.
> Camera at wide angle (no WA conversion lens attached). Tripod; 1/250;
> f/6.7. Compression: fine. Sharpening: normal. 6.1 Mp.

To be honest, to me it doesn't appear to be any more out of focus
at the greatest distance than it does at some of the closer parts of
the picture. It may appear that way because of the bright
backlighting of the sky leaking through the most distant objects. I
don't know if your manual mentions it, but the one for my Fuji
describes the types of objects that are suitable for focusing and
types of objects that don't work very well. Not only is the
'jutting' pine tree a poor object to focus on, there really isn't
any distant object that's suitable either. It may be that your
camera focused much closer than you suspect. Just because you
placed the pine tree in the focusing brackets doesn't guarantee that
your camera (or any AF camera) will be able to focus accurately on
that object. The focusing mechanism needs clearly defined
horizontal or vertical edges and contrasting colors. This is the
type of picture where I think a manual focusing lens would be able
to focus more quickly and more accurately. Does your camera have a
"landscape" picture mode that might force the camera to focus at a
great distances? To get a better idea of where the camera actually
is focusing you might want to maximize the lens's aperture.
Whatever is closely in focus should appear about the same as in your
picture, but the out of focus areas will be much more blurred.

Archived from groups: rec.photo.digital (More info?)

ASAAR wrote:
> On Sat, 14 May 2005 07:54:43 -0400, Dave G <dgehman(at)rcn(dot)com>
> wrote:
>
>
>>This was one I took with center spot focus. According to the AF
>>brackets, I was focusing on the area where the pine tree juts out.
>>Camera at wide angle (no WA conversion lens attached). Tripod; 1/250;
>>f/6.7. Compression: fine. Sharpening: normal. 6.1 Mp.
>
>
> To be honest, to me it doesn't appear to be any more out of focus
> at the greatest distance than it does at some of the closer parts of
> the picture. It may appear that way because of the bright
> backlighting of the sky leaking through the most distant objects. I
> don't know if your manual mentions it, but the one for my Fuji
> describes the types of objects that are suitable for focusing and
> types of objects that don't work very well. Not only is the
> 'jutting' pine tree a poor object to focus on, there really isn't
> any distant object that's suitable either. It may be that your
> camera focused much closer than you suspect. Just because you
> placed the pine tree in the focusing brackets doesn't guarantee that
> your camera (or any AF camera) will be able to focus accurately on
> that object. The focusing mechanism needs clearly defined
> horizontal or vertical edges and contrasting colors. This is the
> type of picture where I think a manual focusing lens would be able
> to focus more quickly and more accurately. Does your camera have a
> "landscape" picture mode that might force the camera to focus at a
> great distances? To get a better idea of where the camera actually
> is focusing you might want to maximize the lens's aperture.
> Whatever is closely in focus should appear about the same as in your
> picture, but the out of focus areas will be much more blurred.
>
Yes, the camera has a landscape setting, and the OP needs to read his
manual, and follow the advice in it. Setting the camera on landscape
will set 'infinity' for focus, greatly reducing both the time, and
energy drain for taking such pictures, and will then adjust the exposure
and aperture for good depth of field. Manual focus is never as fast as
AF, unless the camera has very poor autofocus performance. I have NEVER
seen a manual focus I can adjust in less than .2 seconds.


--
Ron Hunter rphunter@charter.net

Archived from groups: rec.photo.digital (More info?)

On Sat, 21 May 2005 09:02:39 -0500, Ron Hunter wrote:

>> This is the type of picture where I think a manual focusing lens would
>> be able to focus more quickly and more accurately.
>
> Yes, the camera has a landscape setting, and the OP needs to read his
> manual, and follow the advice in it. Setting the camera on landscape
> will set 'infinity' for focus, greatly reducing both the time, and
> energy drain for taking such pictures, and will then adjust the exposure
> and aperture for good depth of field. Manual focus is never as fast as
> AF, unless the camera has very poor autofocus performance. I have NEVER
> seen a manual focus I can adjust in less than .2 seconds.

Nor I, but for the type of picture we're discussing (where the
camera's AF has nothing good to focus on) even if it takes 5 seconds
to focus manually, you're assured of getting a pretty accurate
focus. For the same difficult subject, the camera using AF would
either focus inaccurately (albeit relatively quickly, which is
useless) or would waste a lot of time 'hunting', without assuring
the photographer that the picture would be focused properly when it
finally stops. This last, BTW points out a limitation with optical
viewfinders, at least in the digital P&S cameras I've seen. If the
camera is misfocused you have no indication of it, only an
indication that the camera has focused on something, somewhere.
Only by looking at the LCD display (or an EVF), with sufficient
resolution and perhaps a zoomable center area, can you tell if the
camera is focused where it's intended to be.