Expandable ISO: What it is, and why it stinks!

In Photo Basics by Dustin Olsen8 Comments

Newer DSLR cameras are starting to advertise that they have expandable ISO ranges. What does that even mean?

Your camera sensor (the part that captures the image) has a specific range in which it will reasonably be able to react to light before you lose quality in the image.  This is often referred to as the “native” ISO in your camera because the manufacturer has tested it and is willing to claim good quality images within this native range.

Canon_ISO_menu

There are times when you would like to have the ISO go beyond, or expand, the native range so you can achieve the exposure you are looking for your in photo. For right now, it's mostly common to have an expandable ISO range give you an extra stop of light at either end. For example, a native ISO range on a DSLR is 6,400 and the expanded ISO does 12,800. A stop of light doubles the amount of existing light that can reach the imaging sensor.

The way in which the sensor is able to do this is by digitally expanding, or overextending, this native ISO range in the camera. In order for the camera to successfully do this, it will meter the light within the native ISO range and then extrapolate that data to what what it could be if the sensor was actually capable of reaching those extreme low and high ISO ranges. This can be really nice if you find yourself trying to photograph in a lot of dimly lit environments.  However, there is a severe trade-off to having this feature in our newer DSLRs, and that is poor image quality.

Given that the camera is overextending itself through expandable ISO ranges, it will often do a poor job processing the data and give you even more noise/grain in your photos while using these expandable ranges. This is the biggest reason that camera makers don't advertise the “complete” ISO range because they do not want consumers saying their product is broken or producing low quality images at either end of the ISO spectrum.

expandable_ISO isoScene

But really, the reason this all stinks is because nobody likes to have noise in their photos! And if we do have to have that noise, we certainly don't need any of it exaggerated when those high or low ISOs come in handy. Technology is improving greatly and cameras are producing less and less noise at higher ISOs. Before we know it, we will see a decent quality photo with an ISO of 12,800. In the meantime, just because we have expandable ISO doesn't mean we should use it. As a matter of fact, let's create a rule of thumb right now and say that only in EMERGENCIES are we allowed to expand our ISOs and capture that photo we have our hearts set on.

If you would like to learn more about how ISO works in relation to the Aperture and Shutter Speed, and how together they affect the exposure of your photo, click here for Photography Basics #2.


About the Author

Dustin Olsen

Dustin Olsen is a professional photographer living in Boise, Idaho.

Comments

  1. hey dustin and jim, i currently own a nikon d5200 with 18-55 and 33-300 what type of photograpy you think i should do with those lens ? do you think as a beginner TTL speedlite/flash is good to improve my photography..i enjoying your podcast currently @ episode 12 theyre really good

  2. Your tips for beginners have been incredibly helpful. I have basic knowledge of what aperture, shutter speed and ISO do and how they interact, but I’ve been focusing first on lighting. I often don’t know whether to shoot manual or automatic and haven’t been using aperture priority or shutter priority modes much. I just wanted to say thanks for giving me so much direction and for gluing together what was a mess in my head. Things I learned: Decide whether I want shallow or full depth of field, then focus on lighting and how it is affected by ISO and shutter speed. Your tip on using Ap Priority mode was super helpful. I will do just as you say and can’t wait to see the improvement in my ability to capture life as it is happening and to not be the fiddling amateur. Mostly I wanted to say thank you.

  3. What stinks is your comparison. It would have been more fair to compare the last native ISO with the first extended. You talk about 6400 being the last native, so compare it with 12800, not 800 with 25600.

  4. Canon EOS 1200d has 6400 ISO which is expandable upto 12800..is it sufficient to click good pics in dim light

  5. Expanded ISO has one great use, to check composition and focus in very low light scenes without having to wait for a 30 second exposure. I’m talking night time scenes such as astroscapes where you can’t see anything thought he viewfinder or liveview. Set it to Hi1 2, take a 2 second exposure is much more convenient that taking a 30 second exposure at ISO 1600.

  6. Maximum effective ISO is an estimate of the highest sensitivity at which a camera can capture excellent quality photos. 7D has a higher Maximum effective ISO of 1082 vs. 926 with the 70D. It also has a higher extended ISO than the 70D. I have taken pictures in the snow at night capturing moon shadows without a tripod with the 7D and EFS 18-135 mm using an ISO of 16,000. Without a tripod meant a reasonably quick shutter speed. To capture a rocket launch it will be necessary to have a reasonably fast shutter speed. That only leaves ISO and Aperture flexibility in capturing light. The lowest Aperture of the two lenses is the EFS 18-135 mm with 3.5 and 4 with the EF 70-300 mm. A lens with a lower/wider Aperture will capture more light at any given shutter speed or ISO setting. Both lenses work well in low light with the ISO flexibility available in the 7D.
    The contrast and tonal range of a rocket launch at evening or night make capturing the greatest tonal range a greater issue than light sensitivity. To get a truly inspiring photograph you with need set the exposure level for the highlights, and capture the highest tonal range you can afford. A full frame camera would do that best, but I bought the 7D as the highest tonal range I could afford. It also has a highlight alert feature known as “blinkies” that causes blown out highlights to blink in the LCD screen. It is a great tool for setting exposure to capture highlights in the greatest tonal range possible with your sensor.

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