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10-28-2012, 05:42 AM   #1
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Sweet spot for best image quality

Hi!

I'm wondering wheter there is something like an ideal setting of ISO, aperture and shutter speed for the best image quality from the sensor. Of course under the assumption that one can adjust the light accordingly for correct exposure. I'm curious from a rather technical perspective.

Brian


10-28-2012, 06:01 AM   #2
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I could be mistaken but I think you'll get the best image quality at the lowest ISO you can go, depending on the situation. ISO is entirely dependent on the camera's sensor, while aperture is more a function of the lens. Most lenses produce their sharpest images when they're stopped down a bit. I don't think shutter speed has much to do with image quality aside from allowing motion blur if the shutter speed is too slow.
10-28-2012, 06:15 AM   #3
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QuoteOriginally posted by sbh Quote
Hi!

I'm wondering wheter there is something like an ideal setting of ISO, aperture and shutter speed for the best image quality from the sensor. Of course under the assumption that one can adjust the light accordingly for correct exposure. I'm curious from a rather technical perspective.

Brian
Keep iso low (iso 100 on K5), f stop around 5.6 (beyond that diffraction occurs), camera on tripod, shutter delay to avoid vibration induced by mirror movement; shutter speed should not matter if the subject is still

Hope that helps
10-28-2012, 06:22 AM   #4
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Ive always thought the baseline ISO was 200 ISO but a lot state 100 ISO but either will serve you well. As for the apreture.... the majority of lense perform at there best closed down a couple of stops. So if you have say an F4 lens it will perform best at F8 etc etc etc. Also watch your shutterspeeds ! I try to conform to using a shutter speed twice the number of the focal lengh you are using IE if you are set to 50mm then you need at least 100th of a second speed or if at 20mm then 40th of a sec etc etc

10-28-2012, 09:19 AM   #5
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Everything DxOMark measured on the K-5 indicate the best ISO is 80 under ideal conditions. Just the dynamic range value is barely under the D800s 14.4 where a 12 is considered excellent. From what I can see the on the K-5's score; at ISO 80 the Ev is 14.1 while at ISO 100 it is 13.5 and at ISO 200 its still good at 12.8 but way below the optimal ISO of 80. Tonal range, color sensitivity etc. follow that trend.
10-28-2012, 10:02 AM   #6
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Like Westmill and Halfspin allready said: it depends on the lens being used. ISO 80 (if you updated the firmware of your K-5) has the best DR.
10-28-2012, 10:26 AM   #7
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QuoteOriginally posted by TenZ.NL Quote
Like Westmill and Halfspin allready said: it depends on the lens being used. ISO 80 (if you updated the firmware of your K-5) has the best DR.
Now I'm a bit curious... how and which update improved the picture quality?
10-28-2012, 10:28 AM   #8
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Halfspin stated that ISO 80 has the best dynamic range according to DXOmark, IIRC that came with a firmware-upgrade. Before that the lowest iso-value was 100.

10-28-2012, 10:46 AM - 1 Like   #9
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If you go to photozone and look up the lens in question you get an idea of thier characteristics.

For example from this page...

Pentax SMC-DA 15mm f/4 AL ED Limited - Review / Test Report - Analysis



What I can tell from that is... the DA 15 has excellent center sharpness..peaking at F5.6 but way beyond "sharp" from f4 to F8. It also tells me that at F4 it is relatively weak at the borders F4 and F5.6 but has excellent borders at F8. So if I'm shooting landscape and want excellent edge to edge sharpness, I'm going to shoot at F8. If I'm shooting a subject where I want it to be centre sharp but soft on the borders for bokeh... I'm probably going to shoot 5.6 or F4. You pretty much have to look at the charts for the lens you use and decide what exactly you'd use the lens for at what F-stop. If you wanted best centre sharpness, 5.6 if you want best edge to edge, F8. There's not just one best answer.
10-28-2012, 11:04 AM   #10
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QuoteOriginally posted by TenZ.NL Quote
Halfspin stated that ISO 80 has the best dynamic range according to DXOmark, IIRC that came with a firmware-upgrade. Before that the lowest iso-value was 100.
Nope, ISO 80 was there from the start if not then please point me to the firmware update you're talking about.
10-28-2012, 12:26 PM   #11
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QuoteOriginally posted by Anvh Quote
Nope, ISO 80 was there from the start if not then please point me to the firmware update you're talking about.
+1
iso 80 is referred to in the manual.
10-28-2012, 12:36 PM   #12
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QuoteOriginally posted by K(s)evin Quote
+1
iso 80 is referred to in the manual.
Oke, thanks for pointing me out, Kevin. I really thought that came with an upgrade.
10-28-2012, 03:59 PM   #13
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For every image there probably is an ideal sweet spot, where an image can be captured. However, it depends on a variety of things.
  • Light - or lack of light - This is going to change for each image opportunity. What is good in the afternoon will not work at night, etc. You have to adjust to the available light at the moment, or add some from some source.
So, how do you do that. Well, for the light available, and the gear that you have, I would put forth the following:
  • P mode - The camera determines the optimal settings, based on the environment that it sees, and takes the image.
Or
  • I use Av mode, with the ISO at 80, and the aperture at f8 (i.e., Norm's example, or what I remember being the sharpest f stop for the lens), then....
If there is not enough light, I then....
  • Increase the ISO to about 1600 and if there is still not enough light (maintaining a reasonably fast shutter speed)
  • Increase the aperture from f8 to what ever the lens allows - f2.8 and if there is still not enough light (maintaining a reasonably fast shutter speed)
  • I might actually switch lenses to a faster lens, if I have it with me (31Ltd at f1.8)
  • Increase the ISO beyond 1600 till there is, always trying to keep the shutter speed fast enough for hand holding - 1/(2*focal length).
If there still is not enough light, then break out the tripod (which is usually the case, because I shoot at night). Actually, I start off with the tripod, since I know that there is not enough light...

10-28-2012, 04:28 PM   #14
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If you care about sharpness, you'll break out the tripod sooner rather than later. There's no point even talking lens sharpness if you're hand holding. Your lens will drop at least one category. AN excellent lens becomes a very good lens or even a good lens. It may be good enough for what you do, but if you want test condition sharpness, you have to use a stable tripod to achieve it.

Second, don't be afraid of the higher f-stops. There are lots of images where a sharp image will have a very narrow sweet spot, and the rest of the image is out of focus. ANd because of the predominance of soft areas the image looks soft. You stop down to F-16 or F22, and if you analyzed it diffraction will actually have caused some lack of sharpness, but the whole image looks sharper. More of the image is acceptably sharp, less of it is razor sharp, but unmagnified, the F-22 image just looks sharper. IN the case of digital, as long as your diffraction doesn't exceed a pixel, the image will actually be just as sharp, even when enlarged.
10-28-2012, 05:27 PM   #15
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And if you want the camera to decide on the best combination of settings to get the best IQ from your Pentax lens, choose the MTF option on your P mode menu item on the camera.
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