whats up with my FZ200 images

Started 8 months ago | Discussions thread
gardenersassistant
Contributing MemberPosts: 823
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Re: f/8 (like f/22) isn't always a no-no
In reply to sherman_levine, 8 months ago

sherman_levine wrote:

Nick,

At least in the range 2.8-5.6 at full zoom, the differences in quality seem negligible. We had a bunch of discussion about this when the camera was first released.

I cited the FZ150 only because it's pretty much fixed aperture at full zoom, and people don't complain about fuzzy

Sherm

I just did a test that seems somewhat consistent with the earlier conclusions.

I took the achromats out of the equation, and just used the camera as is.

I set up a test chart and photographed it, using (centred) single point autofocus, from about 10ft using full zoom, and using f/2.8, f/4, f/5.6 and f/8. The camera was on a tripod and I used a wired shutter release. IS was off. I captured RAW and JPEG.

I then set the zoom to 16X and moved the camera towards the test chart until the framing was as nearly the same as I could get it. I then took another four shots with the same apertures. Then moved in again and took another four shots at 8x, and another four very close to the target at 1X.

I then imported the images into Lightroom, with no adjustments. I did a crop from the centre of the image for one of them, and also upped the exposure by 0.4 stop to make it easier to see what was going on. (I had the camera set to underexpose by one third of a stop.) I then got lightroom to make exactly the same crop and exposure adjustment to all of the images. I exported the crops to JPEG, with no sharpening, resizing or anything else.

I then did the same for a crop right at the top of the image and quite near to the left hand edge.

I then resized the uncropped images to 1100 pixels high, which is what I work to these days.

I have posted here at flickr some images taken from the RAW captures. These are, for all the apertures and zooms: The centre crop; The upper left crop; Whole image, resized to 1100 pixels high.

I have flicked back and forth between various of the images. I used Faststone Image Viewer to do the comparisons, because this enabled me to select pairs and larger sets of images to flick between, using the arrow keys to change between images without having to take my eyes off a particular part of the screen. I find this is the most powerful way of seeing fine differences between images, when one image/version exactly (or in this case nearly) overlays the previous one.

There is some random variation, but some patterns did seem to emerge (although caution is needed because there was no repitition in the observations and so the random effects might be predominating). That said ...

It seemed to me that for the centre crops, the f/5.6 crops were sharper than the f/8 crops, and the f/4 crops were sharper than the f/5.6 crops. However, in both the centre and corner crops, f/2.8 seemed less sharp than f/4. I suspect this may have to do with dof. The test chart was the midde two sections of a four section fold-out , so there was a crease down the middle, meaning that it was not absolutely flat. Also, the camera surely cannot have been absolutely straight on to the test chart; the extent of this would have varied with the amount of zoom, as moving between zoom factors meant physically moving the camera and tripod. The f/4 crops might be sharper because the slightly larger dof compensated for irregularities in positioning the camera in relation to (that part of) the target. That said, the area of the centre crop was where I was focusing, so I'm a little sceptical of the dof explanation. Is it possible that f/4 is in fact a bit sharper than f/2.8?

For the top left crops it appears that the f/5.6 versions may be sharpest. Again, this makes me wonder about dof effects.

And what is the likely impact of these differences, at least for my images at 1100 pixels high? Looking at the whole images resized to 1100 pixels high the differences in sharpness are still visible, although not massive to my eye. It depends on where you look, centre, middle edges or corners, but f/2.8 still seems generally to be less sharp than f/4 around the edges. At the corners f/5.6 may be fractionally sharper than f/4, with f/4 and f/5.6 level pegging at the middle edges. f/2.8 and f/4 seem be sharpest at the centre, sometimes one and sometimes the other in no pattern I can discern.

It's a matter of interpretation as to exactly what words to use to describe these differences. I don't feel entirely comfortable with "negligible", although that seems to me to be quite close to how I feel about it. The differences certainly don't seem to me to be, in practical terms, as large, or as unambiguous, as one might be led to expect by some of the rather unqualified assertions that are sometimes made about this subject.

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