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Will Increased ISO Make Your Images Sharper?

July 24th, 2017

Waldo in South Carolina says:

Am I crazy or does shooting with a higher ISO result in sharper looking photos? I accidentally shot a house at ISO 640 instead of my usual 400 and I was surprised how good the photos looked. What causes this? I would have thought effect on sharpness would have been just the opposite.

Increasing ISO can allow you to shoot at a higher shutter speed or a smaller aperture either of which could make for a sharper image. If you are shooting on a solid tripod the higher shutter speed shouldn’t make a difference but shooting with smaller aperture could be what you are seeing. Without knowing more details it’s hard to tell exactly what is happening.

Traditionally, a higher ISO means grainer images but with today’s DSLRs and mirrorless cameras, you can still get very good results at a high ISOs so don’t be afraid to boost your ISO when needed.

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8 Responses to “Will Increased ISO Make Your Images Sharper?”

  • So am I crazy? I do everything I can to keep the ISO low.

  • Interesting… I did a comparison of two images at different ISO settings (100 and 200) with aperture constant and I found that the 200 ISO actually “appears” sharper. The reason for this, I think, is not an improvement in actual image sharpness at the higher ISO (let’s face it the lens hasn’t changed between shots!) but a slight boost in contrast due to the slightly more compressed tonal scale of the higher ISO setting. Viewing in Lightroom side by side, I removed all sharpening and clarity settings from both images and viewed at 100 percent and had a good look at the shadow areas. The 100 ISO version actually “scores” in terms of smooth tonal rendering : the dynamic range is slightly greater than the 200 ISO version, whose shadow areas (while pretty good) were a bit more blocked up and “grittier” by comparison. Oddly, the effect of the slightly increased noise in the shadow areas is a bit like pulling the blacks slider down very slightly: this compresses the really subtle shadow detail and in so doing actually provides a bit of “bite” to the image. On the 100 ISO version the very darkest areas still have a bit of information/ luminosity to them. One of the factors contributing to perceived sharpness in an image is contrast, so my feeling is that the higher ISO settings are actually recording less tonal information (slightly inferior dynamic range) but at the same time producing a punchier result. I am sure you could bring the lower ISO up to that level of the perceived sharpness of the higher ISO shot with small adjustments of the blacks and/ or clarity sliders in Lightroom (to close up the shadows very slightly). But if you start trying to lighten the shadow areas of a high ISO image in post then that digital noise is going to start to look very obvious. So I would say if you are shooting for HDR or Enfuse or even ETTR with a single shot and looking to get the widest tonal spread for your image, then shoot lowest ISO possible (to capture greatest/ “cleanest” shadow detail) but if you are using flash (and thereby helping out the shadows with a bit of fill and not looking to raise them in post) you can afford to shoot higher ISO settings if that helps you. I would want to have a good look at settings of 800 ISO and beyond before putting this into practice, but to be able to shoot ISO400 is potentially a real help to the RE photographer if you wish to use just one compact flash, for example, or even allow yourself a slightly smaller aperture than usual with your usual lighting set up.

  • We might want to consider what the native iso of the camera is. For my 6d, the native iso is apparently 160, so an iso 200 image might be cleaner than an iso 100 image.

  • I agree with Simon.

    The perception of sharpness is based on a number of factors that affect the subjective response to an image.
    Contrast and noise provide the perception of sharp transitions that imply sharpness.

    Back in the film days we observed that TRI-X film often looked much sharper than Plus-X and especially Panatomic.
    When enlarged greatly one could see the increased sharpness and detail of the slower films but at normal 8×10 print sizes the fast film won.
    Printing on a grade higher paper often made an image appear sharper. Ralph Gibson’s use of very high contrast gave an impression of high sharpness to his work.

    In my lab days (owned a commercial lab) we would add noise to low res images to increase apparent sharpness.
    We labor over ultimate IQ but so frequently lose sight of the goal.
    An impactful image at 1200pixels relies very little on ultimate sharpness and DR but on composition, lighting and post processing.
    Those same rules also apply to a 12,000 pixel image.

  • Last winter after bumping my ISO up to 1600 to reduce streaks of rain, I accidentally shot the whole house that way.
    Even though my Nikon DSLR is several years old (D7100), the images were great.
    Still, 320 – 400 ISO is my preferred inside range

  • Sharpness owes a lot more to perceptual characteristics such as contrast, lighting and noise than many will acknowledge.

    In our race to ultimate IQ we search for the sharpest lenses and the cameras with the “best” sensors.

    Back in our film days we learned how to increase apparent sharpness by adjusting our lighting and printing on higher contrast paper.

    In digital files i have added noise to increase apparent sharpness.
    The corollary is that very slow films were prized for their sharpness yet often looked less sharp in final print than the print form faster film.

  • I am not certain either way about increasing ISO for more sharpness. I do know I have long been using what I call ‘native’ ISO for Canon products, starting at ISO 160, then 320, then 640, etc. I heard anecdotally some time ago that the Canon sensor was developed for ISO 160. I do not know or particularly care if it is true or not, as my results have been fine. I shoot real estate at 640 or 1280, both being multiples of the native 160. My clients are happy with the product, so I am happy. I made this comment because the original post mentioned hitting 640 and finding it sharp, 640 being a multiple.

  • You’re not crazy, it’s probably just a ton of variables at play.

    However, you might want to insure that camera of yours. I’ve never held a camera that gets sharper when you crank up the iso. Want to trade, lol.

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