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12-15-2009, 11:59 PM   #31
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QuoteOriginally posted by er1kksen Quote
f4 is a lot shallower on FF than you think (given the same perspective). There have been APS-C test shots where the focus was far enough off to throw some parts OOF while the face and focus target remained sharp. I really think focus is the main factor in those crops.
So how shallow do you think the depth of field is?

If you look at the EXIF data the Nikon D3S does include:
focused distance = 1.88m;
focal length = 70mm
aperture= f/4.

These are enough to calculate the DoF.

Using the standard circle of confusion of 1/1000th the focal length -
this would give a DoF = 408.7mm = 16.1" = 1ft 4.1"

Personally I would have thought this was plenty for the scene -
especially if one looks at the face and the two focusing markers and see these are all very well focused.

So do you still think this is a focus or DoF issue? -
that does not take away what I initially said
I am still surprised by the textural area when compared to the rest of the photo.


Last edited by UnknownVT; 12-16-2009 at 12:11 AM.
12-16-2009, 01:56 AM   #32
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The K-x is an excellent little camera and focuses very well even in low light. It has perfectly usable ISO 3200, and even 6400 with a bit fiddling. Video performance is very nice - well the images are. The built-in microphone picks up noise from the camera, especially the SR system (which can be turned off for video if you want better sound).
I say that the video is entry level consumer video.

And yes, the FA 50 f/1.4 gets mixed opinions about AF speed because it performs different on different bodies. No surprise there. The K-x has the same new algorithm AF system as the K-7 so it is faster, but the K-7 is even better in low light because of two things - built in separate AF assist lamp and extra colour sensitive sensor for the AF.
K-x can misfocus slightly in tungsten light because it lacks colour sensitive AF.
12-20-2009, 04:23 AM   #33
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QuoteOriginally posted by UnknownVT Quote
So how shallow do you think the depth of field is?

If you look at the EXIF data the Nikon D3S does include:
focused distance = 1.88m;
focal length = 70mm
aperture= f/4.

These are enough to calculate the DoF.

Using the standard circle of confusion of 1/1000th the focal length -
this would give a DoF = 408.7mm = 16.1" = 1ft 4.1"

Personally I would have thought this was plenty for the scene -
especially if one looks at the face and the two focusing markers and see these are all very well focused.

So do you still think this is a focus or DoF issue? -
that does not take away what I initially said
I am still surprised by the textural area when compared to the rest of the photo.
The other crops donīt suggest overactive noise reduction (retaining more detail than the K-x, at least) so I donīt think thatīs the issue. Focus issues (which are a known inconsistency in IRīs test images) seem to me the most likely culprit. Not necessarily DoF; but the shallower DoF does make it easier for focus issues to occur than it does for APS-C test images (many of which also have inconsistent focus).
12-20-2009, 10:21 AM   #34
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QuoteOriginally posted by er1kksen Quote
The other crops donīt suggest overactive noise reduction (retaining more detail than the K-x, at least) so I donīt think thatīs the issue. Focus issues (which are a known inconsistency in IRīs test images) seem to me the most likely culprit. Not necessarily DoF; but the shallower DoF does make it easier for focus issues to occur than it does for APS-C test images (many of which also have inconsistent focus).
Looking at the Nikon D3S ISO200 shot of the same scene -
I can still see the "blurriness" of the necklace area -
so I think you are right about a "focus issue" -
but it is probably DoF rather than mis-focus.

IR images have defined focus points in the scene and one can examine those and there is NO mis-focus.

However despite my own calculations for the DoF (I re-checked and they are correct) -
my mistake was forgetting we are examining the image at 100% - or actual pixel level -
whereas the standard "classic" DoF calculation is based on examination of a print probably for 10x8 - this means we are looking at an image on the screen at 100% actual pixel level which is about 20-36X the area of a 10" print - so the DoF would be much more critical under this kind of scrutiny.

So I think your initial suggestion of being full-frame and having shallower DoF was most likely correct.

And the reason I was surprised by the comparison of the necklace area was exactly as you said all the other crops do show the Nikon D3S having better IQ -
the reason why the necklace area was blurrier on the Nikon D3S was most probably due to the shallower DoF and therefore OOF (out of focus) compared to the K-x.

Thanks for the discussion and pointing that out in the first place.

12-22-2009, 05:12 PM   #35
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QuoteOriginally posted by UnknownVT Quote
Looking at the Nikon D3S ISO200 shot of the same scene -
I can still see the "blurriness" of the necklace area -
so I think you are right about a "focus issue" -
but it is probably DoF rather than mis-focus.

IR images have defined focus points in the scene and one can examine those and there is NO mis-focus.

However despite my own calculations for the DoF (I re-checked and they are correct) -
my mistake was forgetting we are examining the image at 100% - or actual pixel level -
whereas the standard "classic" DoF calculation is based on examination of a print probably for 10x8 - this means we are looking at an image on the screen at 100% actual pixel level which is about 20-36X the area of a 10" print - so the DoF would be much more critical under this kind of scrutiny.

So I think your initial suggestion of being full-frame and having shallower DoF was most likely correct.

And the reason I was surprised by the comparison of the necklace area was exactly as you said all the other crops do show the Nikon D3S having better IQ -
the reason why the necklace area was blurrier on the Nikon D3S was most probably due to the shallower DoF and therefore OOF (out of focus) compared to the K-x.

Thanks for the discussion and pointing that out in the first place.
Glad we could get that sorted out. To be honest I have very little technical knowledge of DoF calculations and their relationship to output size and etc. since I just try to use whatever works, but itīs good to have someone who does to check the facts.
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