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Can anyone explain why the "ISO" setting exists on digital SLR cameras? It seems like this is an unnecessary holdover from film cameras. I ask this as an owne

by drblast 15y ago

Can anyone explain why the "ISO" setting exists on digital SLR cameras? It seems like this is an unnecessary holdover from film cameras. I ask this as an owner of a Canon Digital Rebel that knows very little about photography. What does changing the ISO setting get you that changing the exposure time or aperture wouldn't?

sbierwagen 15y ago
ISO is sensor sensitivity. Higher settings multiply the numbers that come from individual sensor elements by increasingly large amounts. Image sensors are not perfectly noiseless, of course, and the higher the ISO is, the noisier the image, which appears as random speckles of colored dots. You don't notice the difference, though, because you're probably shooting in JPEG mode, not in RAW. In JPEG, the Rebel tries very hard to cover up its sins, and will blur away sensor noise, which is hard to notice unless you grovel over areas of fine detail at 400% magnification. Second time I've linked this in this thread, but http://www.dpreview.com/reviews/nikond5100/page20.asp http://www.dpreview.com/reviews/nikond5100/page20.asp shows some great examples of what sensor noise looks like over a range of ISO values. Edit: Useless editorializing: A SLR isn't a great purchase for someone who knows very little about photography. A point-and-shoot is lighter, cheaper, more durable, easier to use, and in the vast majority of situations, will produce identical results to a SLR. You then graduate to a real camera when get fed up with the various fiddly technical limitations of a point-and-shoot; and bonus, you still have the small camera, which is the one you take with you when climbing mountains, or on vacation, rather than lugging around five kilograms of japanese glass. Tedious polemic: I dearly hope you have more than one lens. The enormous price premium of a SLR is mostly for the privilege of being able to change lenses. If you just stick with the kit lens, then you will have spent rather a lot of money to accomplish nothing a point-and-shoot couldn't do.
- bradleyland 15y ago
  Just as a counterpoint (not to pick a fight), I'd disagree with a lot of what you said in the latter portion of your post. Entry level SLRs are great, even for people who don't know anything more than point-and-shoot. The advantage of an SLR is that it will focus faster, meter faster, and ultimately take the photo faster. This is a huge advantage for parents, whose children are fast moving targets. What's not necessarily a good idea, is buying the biggest, most expensive SLR you can find. Canon and Nikon both make entry-level SLRs that have modes specifically targeted at novice photographers who will never leave full-auto mode. Buying a more expensive model primarily gets you features. Features that you won't use. The hardware is remarkably similar until you get up in to cameras that cost thousands of dollars. Many people believe that the huge lens is what makes SLR photos clearer in more conditions, but that's not the whole story. The lens is large because of an aspect of the SLR that you'll probably never see: the sensor. The single greatest reason for the increased image quality of an SLR is sensor size. When you shoot with a compact point-and-shoot, you're capturing light with a sensor the size of your pinky fingernail. You could shoehorn the fastest, largest, most expensive SLR lens on to a compact point-and-shoot, and the photos it takes wouldn't compare to an SLR with even a modest lens. The sensor in an SLR camera is closer to the size of a postage stamp, and this makes all the difference. Keep in mind that compacts these days shoot comparable resolution (megapixels) to SLRs. This means that each "pixel" in a compact is microscopically small when compared to the "pixels" in a SLR sensor. This means less area for light to fall, and less light collected. So, even with one lens, and in the hands of a novice, a reasonably priced SLR can result in sharper, more well timed photos in a more diverse range of conditions.
  - ajkessler 15y ago
    Also not to pick a fight, especially since your post has a lot of merit if this were 2009, but point and shoots and bridge cameras have come a long way. You can essentially get all the benefits of an SLR in the higher end point and shoots for several hundred dollars less than even entry level SLR kits. There are a number of point and shoots with the same size sensors as entry level DSLRs, same instant on, equivalent lack of shutter lag, equivalent metering, etc. etc. For most people, the upsell to the DSLR probably isn't worth it at this point.
    - barrkel 15y ago
      There's a tradeoff between the physical size of your lens, the physical size of your sensor, and your maximum optical zoom. The way you put it, you make it sound like you can have it all in a compact, but that's just not the case. A bridge camera with a substantial zoom and large sensor size will be as about as big as a DSLR with a lens of similar capability. A compact point and shoot will either have a smaller sensor or a less capable optical zoom, and probably both. I have a fairly high end compact, albeit one from late 2009 (Canon S90), and it is nowhere near as capable as an entry-level DSLR in terms of focus speed, continuous shot rate, instant on etc.; and the S95 from late 2010 isn't much more capable (720 HD video, stereo mics and firmware update).
      - mtw 15y ago
        imho the 2 biggest differences between a DSLR and a compact is the focus speed and the dynamic range. DLSRs have larger sensors, so by laws of physics, they gather more light and will always have more dynamic range than compacts or smartphones
        ajkessler 15y ago
        Mostly yes, but there are a number of compact cameras that now have aps-c sized sensors; the same ones used in entry level dslrs.
        15y ago
esun 15y ago
ISO is a trade-off between noise and speed. Sometimes you need the speed, like at a nighttime party or sports, and sometimes you need the perfect details, like shooting landscapes. In general, you want to shoot at the lowest ISO which works in any given situation. A longer exposure can result in object or camera shake blur. Wider aperture reduces depth of field, making it harder to focus. Sometimes, you'll need all three to get enough light in the shot: A hot sensor, a longish exposure, and a wide aperture.
ajkessler 15y ago
ISO is certainly not an unnecessary holdover from film cameras. It's actually very, very useful. To understand, you really need to get a grasp on the basics of exposure. This may be helpful: http://www.ajkesslerblog.com/understanding-exposure/ http://www.ajkesslerblog.com/understanding-exposure/ When a photon hits a pixel it produces an electrical signal. You can think of the ISO as the amount that signal is amplified. So, if you want to keep aperture and shutter speed at certain levels, you can adjust the ISO to produce a usable image. The tradeoff is that when you amplify a signal a great deal, it gets noisy.
- wtallis 15y ago
  So, does that make the ISO setting a no-op in RAW mode? It sounds like it's entirely a post-processing option.
  - andrewjshults 15y ago
    Changing the ISO at time of exposure actually increase the amplification at the sensor level. Changing the exposure in post processing just shifts bits around (the advantage of RAW is that, depending on the camera, it captures between 12-16 bits vs. 8bits for jpeg images and it's not compressed so shifting the bits around doesn't have quite as noticeable an effect).
  - danssig 15y ago
    Depends on the camera. On medium format digital backs it is, as well as the Nikon D7000.

by drblast 15y ago

sbierwagen 15y ago

ISO is sensor sensitivity. Higher settings multiply the numbers that come from individual sensor elements by increasingly large amounts. Image sensors are not perfectly noiseless, of course, and the higher the ISO is, the noisier the image, which appears as random speckles of colored dots. You don't notice the difference, though, because you're probably shooting in JPEG mode, not in RAW. In JPEG, the Rebel tries very hard to cover up its sins, and will blur away sensor noise, which is hard to notice unless you grovel over areas of fine detail at 400% magnification. Second time I've linked this in this thread, but http://www.dpreview.com/reviews/nikond5100/page20.asp http://www.dpreview.com/reviews/nikond5100/page20.asp shows some great examples of what sensor noise looks like over a range of ISO values. Edit: Useless editorializing: A SLR isn't a great purchase for someone who knows very little about photography. A point-and-shoot is lighter, cheaper, more durable, easier to use, and in the vast majority of situations, will produce identical results to a SLR. You then graduate to a real camera when get fed up with the various fiddly technical limitations of a point-and-shoot; and bonus, you still have the small camera, which is the one you take with you when climbing mountains, or on vacation, rather than lugging around five kilograms of japanese glass. Tedious polemic: I dearly hope you have more than one lens. The enormous price premium of a SLR is mostly for the privilege of being able to change lenses. If you just stick with the kit lens, then you will have spent rather a lot of money to accomplish nothing a point-and-shoot couldn't do.

bradleyland 15y ago
Just as a counterpoint (not to pick a fight), I'd disagree with a lot of what you said in the latter portion of your post. Entry level SLRs are great, even for people who don't know anything more than point-and-shoot. The advantage of an SLR is that it will focus faster, meter faster, and ultimately take the photo faster. This is a huge advantage for parents, whose children are fast moving targets. What's not necessarily a good idea, is buying the biggest, most expensive SLR you can find. Canon and Nikon both make entry-level SLRs that have modes specifically targeted at novice photographers who will never leave full-auto mode. Buying a more expensive model primarily gets you features. Features that you won't use. The hardware is remarkably similar until you get up in to cameras that cost thousands of dollars. Many people believe that the huge lens is what makes SLR photos clearer in more conditions, but that's not the whole story. The lens is large because of an aspect of the SLR that you'll probably never see: the sensor. The single greatest reason for the increased image quality of an SLR is sensor size. When you shoot with a compact point-and-shoot, you're capturing light with a sensor the size of your pinky fingernail. You could shoehorn the fastest, largest, most expensive SLR lens on to a compact point-and-shoot, and the photos it takes wouldn't compare to an SLR with even a modest lens. The sensor in an SLR camera is closer to the size of a postage stamp, and this makes all the difference. Keep in mind that compacts these days shoot comparable resolution (megapixels) to SLRs. This means that each "pixel" in a compact is microscopically small when compared to the "pixels" in a SLR sensor. This means less area for light to fall, and less light collected. So, even with one lens, and in the hands of a novice, a reasonably priced SLR can result in sharper, more well timed photos in a more diverse range of conditions.
- ajkessler 15y ago
  Also not to pick a fight, especially since your post has a lot of merit if this were 2009, but point and shoots and bridge cameras have come a long way. You can essentially get all the benefits of an SLR in the higher end point and shoots for several hundred dollars less than even entry level SLR kits. There are a number of point and shoots with the same size sensors as entry level DSLRs, same instant on, equivalent lack of shutter lag, equivalent metering, etc. etc. For most people, the upsell to the DSLR probably isn't worth it at this point.
  - barrkel 15y ago
    There's a tradeoff between the physical size of your lens, the physical size of your sensor, and your maximum optical zoom. The way you put it, you make it sound like you can have it all in a compact, but that's just not the case. A bridge camera with a substantial zoom and large sensor size will be as about as big as a DSLR with a lens of similar capability. A compact point and shoot will either have a smaller sensor or a less capable optical zoom, and probably both. I have a fairly high end compact, albeit one from late 2009 (Canon S90), and it is nowhere near as capable as an entry-level DSLR in terms of focus speed, continuous shot rate, instant on etc.; and the S95 from late 2010 isn't much more capable (720 HD video, stereo mics and firmware update).
    - mtw 15y ago
      imho the 2 biggest differences between a DSLR and a compact is the focus speed and the dynamic range. DLSRs have larger sensors, so by laws of physics, they gather more light and will always have more dynamic range than compacts or smartphones
      - ajkessler 15y ago
        Mostly yes, but there are a number of compact cameras that now have aps-c sized sensors; the same ones used in entry level dslrs.
        15y ago

esun 15y ago

ISO is a trade-off between noise and speed. Sometimes you need the speed, like at a nighttime party or sports, and sometimes you need the perfect details, like shooting landscapes. In general, you want to shoot at the lowest ISO which works in any given situation. A longer exposure can result in object or camera shake blur. Wider aperture reduces depth of field, making it harder to focus. Sometimes, you'll need all three to get enough light in the shot: A hot sensor, a longish exposure, and a wide aperture.

ajkessler 15y ago

ISO is certainly not an unnecessary holdover from film cameras. It's actually very, very useful. To understand, you really need to get a grasp on the basics of exposure. This may be helpful: http://www.ajkesslerblog.com/understanding-exposure/ http://www.ajkesslerblog.com/understanding-exposure/ When a photon hits a pixel it produces an electrical signal. You can think of the ISO as the amount that signal is amplified. So, if you want to keep aperture and shutter speed at certain levels, you can adjust the ISO to produce a usable image. The tradeoff is that when you amplify a signal a great deal, it gets noisy.

wtallis 15y ago
So, does that make the ISO setting a no-op in RAW mode? It sounds like it's entirely a post-processing option.
- andrewjshults 15y ago
  Changing the ISO at time of exposure actually increase the amplification at the sensor level. Changing the exposure in post processing just shifts bits around (the advantage of RAW is that, depending on the camera, it captures between 12-16 bits vs. 8bits for jpeg images and it's not compressed so shifting the bits around doesn't have quite as noticeable an effect).
- danssig 15y ago
  Depends on the camera. On medium format digital backs it is, as well as the Nikon D7000.