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Old November 28th, 2015, 02:24 PM   #1
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Aperture for maximum sharpness?

At wide angle, and then at telephoto, anyone happen to know what the optimum apertures are for best clarity and sharpness, and what the limit would be before diffraction softness begins? I have a resolution chart and the 4K option, I might try to figure it out if no one else has a ready made answer. The biggest tell i know to look for is red/green edge chromatic abberations when you rack focus on a high contrast black/white line.

I typically shoot at night at high gain, so I never really iris down, but if I shoot any daylight stuff, would be good to know.

Paul
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Old November 28th, 2015, 02:54 PM   #2
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Re: Aperture for maximum sharpness?

Made some 4K frame grabs, from f4.0 to f9.6. When testing for slightly out of focus CA, I found that stopping down from f4.0 to f5.2-f5.6 helps a lot, ridding the image of soft red/blue edge hazing in the corners. I can't for the life of me see a difference in center sharpness or CA.......go Zeiss. :)

Was trying to upload the frame grabs, but the site said I am missing a security token, and error'd out. :(

Paul
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Old November 29th, 2015, 02:33 AM   #3
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Re: Aperture for maximum sharpness?

Man, I hope the X70 is sharp wide open... it (was) a >$2K camcorder and its only job is to shoot good video. :)
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Old November 29th, 2015, 02:48 AM   #4
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Re: Aperture for maximum sharpness?

Hi Paul,

There is a nice internet site, which describes all kinds of optical performance limits. They also have a calculator online, where you can enter your camera data and get the answer of your question.

Digital Camera Diffraction Resolution, Color & Micro-Contrast
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Old November 29th, 2015, 02:49 AM   #5
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Re: Aperture for maximum sharpness?

All camera's I have owned produced the sharpest image between f4.0 and f5.6, if you shoot wide open and if you pixelpeep you will notice more image softness and it gets worse if you close down the iris completely, especially on small sensor camera's it will give you the impression your shot is out of focus. It's called diffraction and not much you can do about that.
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Old November 29th, 2015, 04:16 PM   #6
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Re: Aperture for maximum sharpness?

Quote:
Originally Posted by Joachim Claus View Post
Hi Paul,

There is a nice internet site, which describes all kinds of optical performance limits. They also have a calculator online, where you can enter your camera data and get the answer of your question.

Digital Camera Diffraction Resolution, Color & Micro-Contrast
I am a bit skeptical of that chart, it doesn't jive with what I am seeing, nor the large sensor size. I run 1/3' cameras that are good until diffraction at f5.6. The X70 definitely is sharper and less CA stopped down a stop or two.

Paul
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Old December 6th, 2015, 03:35 PM   #7
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Re: Aperture for maximum sharpness?

I think I get the best results from my NX5, NX30 or CX700 with iris wider than F4. Certainly closed down more than F5.6 and I see the sharpness decrease on my NX5U for sure. I shoot stage so want as much of stage in focus as possible so try to stay close to F4 most of the time. Since it is often dark in the theatre the full stage unattended cameras are usually wide open anyway.

For me the key was to let the cameras shoot in auto and see what the engineers would like the iris to be !! On most of my Sony's it ends up between F2.8 and F4. On the AX100 it is very similar with all of them preferring to increase shutter speed before shutting down the iris beyond F4. With the NX5U having negative gain it does that too before shutting down the iris. With all of them of course the lenses ramp when zoomed so one is stuck with that anyway. In some respects that is why I try to stay close to F4 on the NX5U as I can then zoom around without be bothered about the ramping.

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Old December 6th, 2015, 03:44 PM   #8
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Re: Aperture for maximum sharpness?

The diffraction effect is much worse when you close the iris down compared to opening it completely up, when you have it wide open, there is some loss in resolution but nowhere near as bad when you close it completely down. I remember when I had my canon xh-a1 I tested this and with the iris almost closed it looked like the image was out of focus. This diffraction effect also seemed much worse on small sensor camera's.
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Old December 6th, 2015, 03:58 PM   #9
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Re: Aperture for maximum sharpness?

Yes , at F8 my NX5U is not good and a noticeable softness compared to F4. I use gain and ND to try and stay close to F4 for my uses.

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Old December 6th, 2015, 10:10 PM   #10
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Re: Aperture for maximum sharpness?

I find my X70 is pretty sharp wide open and actually shoot that way about 85% of the time. One of the main reasons I bought the camera is the noticeably shallower depth of field compared to 1/3 inch chip cameras, so I often shoot to maximize that effect. Over at the X70 FaceBook group the admin, Jody Eldred, says his testing shows 5.6 gives the absolute best sharpness.
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Old December 6th, 2015, 10:27 PM   #11
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Re: Aperture for maximum sharpness?

I would tend to agree with Jody's findings, they match mine. I really do see up to f9.6 in testing seems similarly sharp, and sharper than f4.0 at full telephoto. I am just looking to maximize my 4K resolution, and when you start pushing Ci and digital zoom in 4K, you start magnifying any chromatic abberation of fuzziness in the optics.

f4.0 is slightly fuzzy and softer (enough to notice side by side) than f5.6 when you pixel peep 4K footage. :)

Paul
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