How To Shoot Manual – Understanding ISO


Last week I did an overview on all three of the settings that directly affect the exposure of an image: ISO, aperture (also known as f-stop) and shutter speed. I gave a few fun exercises and I hope you enjoyed them! Today, I want to dive more into ISO and why it’s so important to understand it more than just letting light in.

Back in the film days (which is still today for me and some of my friends!!), ISO was that number you looked for on the film box. Remember that 200, 400, or 800 film speed you used to commonly see? That was ISO! Today in the digital realm of photography, ISO is simply a way to measure the camera sensor’s sensitivity to light.

As the ISO number gets higher (800, 1600, 6400…) it lets more light in. For example, if you’re outside on a sunny day, you’ll set your ISO as low as possible (somewhere around 100-200). If you’re inside a room and you’re far away from the windows, you might be between 800-1600 or even higher (let’s hope not)! So why is is a higher ISO number not preferable? There is a secondary effect.



See, grain is a style that can be super pretty to some, and not preferred to others. I personally find grain pretty in some cases! Do you see the amount of grain in depicted in the photo directly above as opposed to the first image in this post with less grain? This is a direct effect of a higher ISO setting! Now, it’s not bad to have camera grain if this is something you find artistic or intriguing, but you must understand the cause/effect of ISO settings to better achieve your vision while photographing in different settings.

Below, I’ve included three SOOC (straight out of camera) images to compare what the ISO setting does to the same image.

ISO 25600, Aperture (f-stop) 2.0/f, Shutter 1/250.

This image above has the most grain of the three, because the ISO is higher here than the other two.

ISO 4000, Aperture (f-stop) 1.4/f, Shutter 1/50.

This image has less grain than above. Notice my shutter and aperture were higher above as well. This is because I had to balance the other settings when I let less light in with the ISO setting. I lowered my ISO to let less light in, but I compensated by slowing down my shutter speed and opening up my aperture to allow more light in. By doing this, I eliminated some of the grain while keeping the exposure almost the same!

This image is with flash, just for comparison. The other two above are ambient light (available light) with no flash.
Settings: ISO 800, Aperture (f-stop) 2.0/f, Shutter 1/50.

See how much sharper this image is when I used the flash to add more light and was then able to lower the ISO even more? The lower my ISO setting is, the more crisp the image appears.


I always set my ISO first, because it is one of the settings I change the least. Shutter is my last setting to think about, because I change it so frequently. What I like to do is choose my ISO based on the lighting conditions, and then I choose my aperture and shutter next based on other variables we will get to later!

Here are some starting points you can work with when setting your ISO. Keep in mind this is very rough, and it won’t always work! Use it as a starting point. Adjust your aperture and shutter, and if it’s not working go back and start over with an ISO to let more or less light in.

Outside on a sunny day:
– Shade – 100 ISO (or the lowest your camera allows)
– Full Sun – 100 ISO (or the lowest your camera allows)
– After the sun hits the horizon – 400 ISO (and keep going up as it gets darker! Once you hit 1600 you may need to go home or get a flash!!)

– By a window – 400-640
– Far from a window – 800-1600+

Tip for inside photos! If you can, turn off all of the lights in the room and bring your subject close to the window for nicer photos! This eliminates that sometimes ugly yellow light mixing with blue light.

I hope you’ve enjoyed this post on ISO and feel like you understand it a little better! If you have questions be sure to pot them below! Want to set up a one-on-one coaching session with me to walk you through this in person? Email me!


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  • Heather Richter

    Am I crazy?? The first photo of the ISO examples looks more grainy to me than the second. Maybe it’s because I’m on my phone? Or is there a chance you switched them?ReplyCancel

  • Heather Richter

    Lol whoops I meant the opposite! The second one looks more grainy than the first!ReplyCancel


      Hi Heather! No, not crazy! A couple things that might be happening – (1) Your phone screen won’t give as much detail as your computer, so I would definitely look at these on a larger screen! There is more heavy grain in the image with a higher ISO, which is very apparent to me when I look on my laptop, but not on my iPhone. That may be it! (2) WordPress has sometimes swapped images and moved the order when in mobile version. You may be looking at them in reverse order the more I think about it! I would recommend you (and anyone else) check this post out on a larger screen! I wish I was there to point out the details for you! In the first image of the camera, you can see extra grain especially on the shelf as well as on the camera to the right that is blurred out in the background. In the second image with a lower ISO, the blurred background is a little more “buttery” or smooth! Also, the more you shoot and the more you learn, the more critical your eye sees! So don’t be alarmed if you’re not seeing it yet. It takes a long time to pick up on all of these little details, especially in digital form. If you were to print these out, the differences would be night and day! Just remember what’s important – high ISO = high grain. 🙂 I hope that helped a bit!ReplyCancel

  • Heather Richter

    I came on the computer! You know what I think it was? I’m confusing focus with grain. Now I see it way better on the laptop. The words on the lens and camera are more in focus (to me?) on the first (grainy) one. But now I see the dots of grainyness everywhere 🙂 Thanks Jenna!!ReplyCancel


      Perfect! I was wondering that as well, but I felt like I needed to be sitting in the room with you to talk about that! The blog is just a good starting point hopefully, and I’m always here for questions and additional help!ReplyCancel