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-   -   Tests (Picture Profiles And Sharpness) (https://www.dvinfo.net/forum/sony-nxcam-avchd-camcorders/499017-tests-picture-profiles-sharpness.html)

Alec Moreno July 30th, 2011 05:21 AM

Tests (Picture Profiles And Sharpness)
In light of some recent posts here about sharpness issues with the NX5, I decided to go out today and do a bunch of tests to see if I could first duplicate the problem and then determine how to avoid it. Afterward, I ran some more tests with the picture profiles to see if I could find something better than what I've been using.

The results...success on both counts.


We know that the iris and zoom determine the depth of field. (For anyone who is not aware of this, you may have read that ND filters and gain are what cause this, but that's true only to the extent that adjusting these two settings may cause you to adjust your iris as well.) There's the primer for what follows.

In the sunlight, I chose some flowers about 17 meters away and focused on them (manual focus, manual iris, manual gain, ND1). Because I was using ND1, I was forced to run the iris up above 8. The picture seemed to look fine in the viewfinder. I then repeated this process twice more with camera set to ND2 and then ND3, lowering the iris each time to maintain somewhat the same exposure. When I got to ND3, I noticed that the picture was incredibly "blurry." (Problem duplicated!) At this point I played with the focus and found that the blurriness was not a fault of the camera, but that my focus had simply been off to begin with...by 6 meters!

Scratching my head over how I could have been so far off, I repeated the shots at the new focus setting, but this time starting with ND3, and working down to ND1. The picture remained in focus throughout. However, the picture was noticeably blurry at ND1 (of course, because of the high iris required at this setting). At this point, I intentionally messed up the focus and tried to set it from scratch. Again, I could not focus correctly due to the blurry picture caused by the iris' high setting. I confirmed this by running the camera up to ND3 again and seeing that I indeed had not been able to nail the focus using the blurry image while at ND1.

My conclusion is that the high iris setting will cause blurriness in the picture...(this is expected if you've fiddled around with a DSLR's crazy high aperture settings)...to such an extent that focusing becomes unreliable if you intend to select a higher ND setting after focusing. The advice then would be to focus at a high ND setting when possible, and then dial it back down if you need to for the particular look you're going after. Just keep in mind the trade off you're making between crispness and blurriness (aka: wider depth of field).

The blurry pictures in my test looked pretty much like the ones others have posted in recent threads, and I suspect that the above reasons played some part in causing their images to come out poorly as well. Some people have also mentioned that this camera is not as sharp as other HD cameras. I can't speak on that other than…compared to a Sony Z1, the NX5 has superior sharpness. I'll have to test the detail settings on another day.

I've spent a lot of time with the profiles since getting this camera, and today I came full circle. Starting tomorrow, I'm going with no picture profile at all (which is the same as PP1 at the factory setting). This is because it seems to my eye that PP1 does a better job of maintaining skin tones than anything I was able to come up with.

The picture is somewhat flat as others have mentioned, but this does not make for a bad image. Actually, I like shooting slightly flat, as I want some room to adjust the picture in post. A lot of the profiles people have shared are fairly aggressive and designed for particular scenes. That's the point of having profiles after all, but for my purposes as an event filmmaker, I want a universal profile that simply works under all conditions…and PP1 is it for me. There's a reason why this is the factory setting…so a layman would have a good "all around" camera out of the box.

If I did not have the ability to color correct and tweak the exposure in post, I might sing a different song, but not one clip makes it off my timeline without "the treatment" anyway, so that is a non-issue in my case. My personal recommendation to anyone searching for profiles is this…don't under estimate the factory settings on this camera, and for sure conduct your tests of other profiles under a variety of lighting conditions.

Alec Moreno
Wedding Art Films - Southern California - Los Angeles - Orange County - Video

David Heath July 30th, 2011 08:28 AM

Re: Tests (Picture Profiles And Sharpness)

Originally Posted by Alec Moreno (Post 1671210)
My conclusion is that the high iris setting will cause blurriness in the picture...to such an extent that focusing becomes unreliable if you intend to select a higher ND setting after focusing. The advice then would be to focus at a high ND setting when possible, and then dial it back down if you need to for the particular look you're going after.

What you are describing is diffraction limiting - diffraction is the way light will bend around a solid edge. It's a characteristic of all wave motion, and the amount is dependent on wavelength. Because the wavelength of light is so small, it becomes a problem only with very small physical dimensions - hence why it is so much more pronounced at small apertures (high numbers) than larger.

The aperture - the f stop is dependent on two things - physical size of iris, and focal length of lens. For a given angle of view, the focal length will vary with sensor size, such that f5.6 on a 1/3" sensor will be physically half the size (a quarter the area) of the aperture as f5.6 on a 2/3" camera.

And this is why 1/3" cameras are not generally seen as acceptable for a lot of broadcast work, not in an unrestricted way, anyway. The exception is the Canon XF305, which partially overcomes the problem by diverging the light around the area of the iris (so a physically larger iris can be used), then reconverging. Trouble is, that's expensive to get the optics right, so it's generally just better to use a larger chip size. (Which also has sensitivity advantages.) I'm not sure it's possible to pull the trick with interchangeable lenses, either.

The issue is far more serious now we're in the HD world, and, especially, the 1920x1080 world. The really clever bit about the EX cameras is that they got 1/2" chips and associated optics into the size and form more normally associated with 1/3", and at comparable prices. Yes, 2/3" would be better still, but 1/2" is still better than 1/3". That's what nobody other than Sony has so far managed to do.

As far as focussing goes, then no, don't focus on one ND, then flip to the other. But it's normally a good idea to zoom tight on an object, focus, then pull out to desired shot size. That's assuming the lens tracks well, but that's a whole new story........

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