Travelshooter
Senior Member
or more simply... shoot a brick wall
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RX100 VI - decentered lens!
- Thread starter rokaroka
- Start date
Jerry045
Forum Pro
I think you might be missing the point. Sure you can shoot a brick wall. What does it tell you? It may look sharp, but is it pushing the full capability of the camera. The brick wall is just not a quantitative target.
Let me offer an example. Suppose you take a photo of the ISO 12233 chart at the correct scale, in other words, fill the viewfinder to cover the area outlined by the red square (for a 3:2 aspect ratio).
Next, take a peek at the center. Can you resolve the 9 lines and spaces?
That camera should be very capable of resolving 2600 lines per height. The lines in the square above are 2000 lines per height. If you can easily see the lines and spaces then the camera is doing what it should. If they are blurry or not resolvable, you got a bad camera. Quick and dirty! What did the bricks tell you?
Next, you can look at the edges.
Yes those fine lines are only 1000 lines per height, but you can certainly compare them with the other three corners to look for edge softness or decentering.
This is not rocket science. You can get a real number for how the camera is performing. Is it up to snuff or not.
The bricks may or may not look sharp, but they can't tell you if the camera is as good as it should be or not.
What is so hard at printing out the chart on a decent printer and snapping a photo of it?
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Jerry
Travelshooter
Senior Member
Sure Jerry... just as easily you can shoot a brick wall and go to each corner for a 100% crop and check the detail.
tbcass
Forum Pro
When checking for a decentered lens a brick wall is good enough. You don't need the fine detail of a test chart.
tbcass
Forum Pro
The only problem with landscapes is finding a scene where everything is at equal distances
tbcass
Forum Pro
That will not reveal decentering that affects the corners, a lens tilting slightly at an angle. Also the very long distances typically found in landscapes may be too far away to show much detail. I believe a brick wall shot at the farthest distance possible to fill the frame is a better bet. A decentered lens will show itself at any distance.
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Tom
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Digital Shutterbug
Veteran Member
Where did you find specifications that give resolution numbers? I haven't seen anything from Sony regarding guaranteed resolution.
You say it should easily resolve 2600 lines per height in the center. At what focal length? At what aperture? I'm sure those numbers will be specified in the Sony specifications you provide for us.
tbcass
Forum Pro
2600 isn't that high a resolution. A 20mp sensor is capable of much more.
sybersitizen
Forum Pro
It's just a reference to what the sensor is capable of resolving, based on pixel count. It says nothing about lenses.
A 20mp camera is not capable of much more.
In order to theoretically resolve 2600 lines, a camera needs at least twice that number of linear pixels. With a resolution of 5472 x 3648, a camera like this theoretically tops out at 2736 lines in the long dimension.
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tbcass
Forum Pro
OK then drop the term "much" and leave it at more.
sybersitizen
Forum Pro
Basically 5% more.
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tbcass
Forum Pro
5% not 1%, not the same.
I was basing what I said on the old DPR tests where they shot resolution charts and what they referred to as the nyquist limit. The A77 with a horizontal resolution of 6000 pixels was able to resolve 3400-3600, well over (12%) the 3000 lp/ph 1/2 of 6000 would suggest.
"The A77's 24MP pixel count pays off in high levels of detail, accurately resolving up to around 3400 lp/ph which puts it amongst the better APS-C DSLRs currently available, as we'd expect from its high pixel count.
Converting your raw files will get a small extra amount of detail but you pay for it with moiré patterning. However, in real-life images this is much less of an issue than it might appear from our test-chart. As always, if detail resolution is your priority, raw files provide a much better starting point than JPEGs (and you can get a lot more out of them than we've managed here, using our standard sharpening settings).
The red Nyquist line in these images represents the limit of our chart's resolution and the (theoretical) limit of the A77's sensor's resolution, but neither the A77's JPEG nor raw output contains much meaningful detail beyond 3600 lp/ph."
https://www.dpreview.com/reviews/sonyslta77/16
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Tom
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Jerry045
Forum Pro
Steve:
The sensor on the RX100 has 3648 pixels in the vertical direction. Due to the combining of the illumination of the surrounding pixels in order to give a color value to each pixel, you need to fudge a little. A decent camera system should be capable of resolving stuff by about 1.4 pixels. So 3648/1.4 = 2606 Lines per height. (I rounded off.) A great camera should do 1.3 pixels or 3648/1.3 = 2806 lines per height. An absolutely ideal perfect camera will do the 3648, assuming each line is perfectly aligned with the pixel boundary. Fat chance on ever seeing that, as it does not exist.
The ISO chart is set up for 2000 lines per height. If you can't get good resolution there, your camera is not up to snuff.
You may be able to spot decentering on the brick wall, but it won't tell you if your camera is giving you the performance it should.
I am more concerned if my camera is not giving me the performance I paid for. Certainly decentering is a valid issue, but it is not the only factor.
sybersitizen
Forum Pro
My post was already corrected to 5% while you were typing.
Is there a miracle that allows more sampling than the hardware supports? No. These varying figures all come down to how much blurring you're willing to accept and how much contrast you require. To get even 2736 lines at theoretical maximum sharpness and contrast, each line would have to miraculously land directly centered on a pixel row, which probably ain't gonna happen.
More here if you want it:
LP/pix (cy/px)
As we have shown that LP/mm is not a suitable unit for the resolution a digital camera can capture, a different unit is needed. One very common unit is line pairs per pixel or cycles per pixel. In this case we do not have a physical extent in the unit, we just describe how many line pairs can be resolved by one pixel. As a line pair is always a black and a white line, the maximum resolution one can achieve is 1/2 LP/pix. So if one camera can resolve 0.4 LP/pix it reaches 80% of its theoretical maximum resolution. This way one can easily compare two camera and see how well they make use of the amount of pixel they have.
LP/PH
If you only express the resolution in LP/pix, you do not take into account that the sampling itself will reduce the resolution. So if you have camera A with 0.5 LP/pix and camera B with 0.4 LP/pix you would say that A is better than B. But if camera A has only 320 pixel in height and camera A has 2000 pixel, camera B will definitely show more details in the same scene. So to make the test results comparable with the efficiency (LP/pix) and the amount of pixel combined, express the resolution as line pairs per picture height. In this example, this would result in a comparison of 160 LP/PH to 800 LP/PH.
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tbcass
Forum Pro
You can argue with DPR if you want. I'm only repeating what I read as I'm no expert..
sybersitizen
Forum Pro
I assume we're all amateurs here, and I'm not arguing ... just pointing out why there are different numbers wherever you look. It's about how close to perfect contrast and sharpness you'll accept. DPR's figures are almost certainly based on some compromise where lowered contrast and increased blurring are deemed acceptable.
Another Google reference saying the maximum possible LP/PH is exactly half of the pixel count ... and typical measured resolution isn't close to that:
Calculation:
Vertical pixel count sensor = 4000 → max. 2000 LP/PH possible (2 pixels per light-dark transition)
measured resolution: 1600 LP/PH
proportionally: 2000 LP/PH = 100% | 1600 LP/PH = x%
(1600/2000) *100 = 80%
Digital Shutterbug
Veteran Member
But you said the camera should be able to resolve 2600 lines per height. Now you're talking about what the sensor can theoretically resolve. It makes no difference what the sensor can resolve if you hang a crappy lens in front of it. I'm asking where Sony has published what the camera, including the lens, can resolve. That involves all facets of the lens, including the focal length, aperture, contrast, where in the field of view the resolution is being measured, etc.
The OP's issue has no answer if we only discuss sensor resolution. And, sensor resolution is the same in the corners as it is in the center. That's not the case when we talk about a camera because the lens will not be the same in the corners as it is in the center.
Jerry045
Forum Pro
Steve:
You hit the nail on the head. The sensor is the sensor. The maximum possible resolution is just shy of the number of pixels. As I said, there is a bit of fudging because the camera combines the illumination of the surrounding pixels to give a color value to each pixel. This sort of spreads the resultant pixel information a touch wider than just an isolated pixel.
So it is up to the lens to provide the rest of story. A poor lens will not get you the best resolution. Distortion, contrast, chromatic aberration, etc. can combine to degrade your image. A better lens will correct or compensate in those areas and give you a better result.
The OP was concerned with decentering. Someone suggested a brick wall. I suggested a calibrated test target would still allow one to test for decentering and offer even more information about the camera performance. By "the camera", I included the lens and the sensor in my insinuations. After all, you have to deal with both. It is a system, and in the OP's case a fixed lens.
In the case of using the ISO chart, there is a calibrated pattern in each corner. It will allow one to get a feel for just how much decentering is happening. You might be able to put a number on it. You can't do that with bricks. Bricks might tell you IF, but not HOW MUCH.
If you really want to test the camera to its limits, Dr. Jimmy Brown has developed a pretty simple scheme and test target.
Check out: http://www.ianperegian.com/My_FZ35_38_Webpage/FZ50_Testing_files/FZ50 Doc V3.pdf
We are probably diverging from the OP's original question. I would think discussions of camera performance testing might deserve its own thread rather than monopolize this one.
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