Shutter Speed v High ISO.

awa355 · 01-18-2017, 09:58 AM

I have searched my query before posting here as the threads I found were specific to a particular photographic technique. My query is about B.I.F. in the late evening when I assume I need my iso kept down a bit for light gathering purpose's.

Many articles refer to upping the ISO to allow an increase in shutter speed. If my Tv speed is set to 1/1600, doesn't the camera use that speed regardless of whether the ISO is set at 100 or 3200?.

Whoa. I just realized what a silly question I put up. If Tv is set to1/1600, it is going to fire off at that speed anyway. A higher ISO will help give a quicker shutter speed if using other modes. Correct??.

Last edited by awa355; 01-18-2017 at 10:16 AM.

BrianR · 01-18-2017, 10:15 AM

Originally posted by awa355

Many articles refer to upping the ISO to allow an increase in shutter speed. If my Tv speed is set to 1/1600, doesn't the camera use that speed regardless of whether the ISO is set at 100 or 3200?.

Yes. It would shoot at 1/1600, and try to adjust f/stop and iso (if auto-iso is enabled) to balance the exposure. If you have auto-iso disabled, it would try to adjust the f-stop only to balance the exposure. No matter what, in Tv mode, the shutter speed will be whatever you set it to.

As to why the articles are suggesting you increase the iso.... suppose a 'proper' exposure was iso100, 1/200s, f/4. If you just up the shutter speed (pretend you're in full Manual mdoe) and shoot at iso100, 1/1600s, f/4, your image will be very dark. So the suggestion is to up the iso one stop for each stop of shutter speed you add. All the following would work:

iso100, 1/200s, f/4
iso200, 1/400s, f/4
iso400, 1/800s, f/4
iso800, 1/1600s, f/4

As we move down the list, we gain motion stopping power, but we'll take a hit with a noisier photo (with the caveat that iso800 is still pretty high quality on any modern dslr

). The f/stop could also be changed to let in more light at the 'cost' of less Depth of Field. All three variables, iso, f/stop, and shutter, are a compromise in one way or another. Choose the compromise that works for your photo, and choose the shooting mode (Tv, Av, TAv, M, etc) that lets you work the variables in the most convenient way.

awa355 · 01-18-2017, 10:20 AM

Originally posted by BrianR

Yes. It would shoot at 1/1600, and try to adjust f/stop and iso (if auto-iso is enabled) to balance the exposure. If you have auto-iso disabled, it would try to adjust the f-stop only to balance the exposure. No matter what, in Tv mode, the shutter speed will be whatever you set it to.

As to why the articles are suggesting you increase the iso.... suppose a 'proper' exposure was iso100, 1/200s, f/4. If you just up the shutter speed (pretend you're in full Manual mdoe) and shoot at iso100, 1/1600s, f/4, your image will be very dark. So the suggestion is to up the iso one stop for each stop of shutter speed you add. All the following would work:

iso100, 1/200s, f/4
iso200, 1/400s, f/4
iso400, 1/800s, f/4
iso800, 1/1600s, f/4

As we move down the list, we gain motion stopping power, but we'll take a hit with a noisier photo (with the caveat that iso800 is still pretty high quality on any modern dslr

). The f/stop could also be changed to let in more light at the 'cost' of less Depth of Field. All three variables, iso, f/stop, and shutter, are a compromise in one way or another. Choose the compromise that works for your photo, and choose the shooting mode (Tv, Av, TAv, M, etc) that lets you work the variables in the most convenient way.

Brian, thank you. I was editing my post as you were replying. All makes sense now.

photoptimist · 01-18-2017, 10:21 AM

First, there's some confusion in what you wrote. A low ISO does not cause the camera to gather more light, it actually makes the camera less sensitive to light. For low-light situations you actually want to increase the ISO to make the camera more sensitive to light.

If you set the shutter speed, set the aperture, and set the ISO to some value (i.e., use M mode), the camera will do exactly that but the picture may be quite over-exposed or under-exposed.

If you set the shutter speed, set the aperture, and let the camera pick the ISO (i.e., use TAv mode), the camera will increase the ISO as the light levels decline.

If you set only the shutter speed, and let the camera set the aperture and ISO (i.e., use Tv mode with Auto-ISO), the camera will generally use low ISO and open aperture until light levels get so low that it must also increase the ISO as the light levels decline further. (If you don't use Auto-ISO, the camera will use whatever ISO you've set).

Sagitta · 01-18-2017, 10:24 AM

The way I look at it is this:

You can fix noise a lot more easily than you can fix blur in post.

awa355 · 01-18-2017, 10:27 AM

Originally posted by photoptimist

First, there's some confusion in what you wrote. A low ISO does not cause the camera to gather more light, it actually makes the camera less sensitive to light. For low-light situations you actually want to increase the ISO to make the camera more sensitive to light.

If you set the shutter speed, set the aperture, and set the ISO to some value (i.e., use M mode), the camera will do exactly that but the picture may be quite over-exposed or under-exposed.

If you set the shutter speed, set the aperture, and let the camera pick the ISO (i.e., use TAv mode), the camera will increase the ISO as the light levels decline.

If you set only the shutter speed, and let the camera set the aperture and ISO (i.e., use Tv mode with Auto-ISO), the camera will generally use low ISO and open aperture until light levels get so low that it must also increase the ISO as the light levels decline further. (If you don't use Auto-ISO, the camera will use whatever ISO you've set).

Yes, I should have said a wider aperture, not a lower ISO. re light gathering. Thank you.

01-18-2017, 09:58 AM	#1
awa355 Veteran Member Join Date: Sep 2016 Posts: 331	Shutter Speed v High ISO. I have searched my query before posting here as the threads I found were specific to a particular photographic technique. My query is about B.I.F. in the late evening when I assume I need my iso kept down a bit for light gathering purpose's. Many articles refer to upping the ISO to allow an increase in shutter speed. If my Tv speed is set to 1/1600, doesn't the camera use that speed regardless of whether the ISO is set at 100 or 3200?. Whoa. I just realized what a silly question I put up. If Tv is set to1/1600, it is going to fire off at that speed anyway. A higher ISO will help give a quicker shutter speed if using other modes. Correct??. Last edited by awa355; 01-18-2017 at 10:16 AM.

01-18-2017, 10:15 AM	#2
BrianR Veteran Member Join Date: Dec 2010 Location: Ontario Photos: Gallery Posts: 3,332	Originally posted by awa355 Many articles refer to upping the ISO to allow an increase in shutter speed. If my Tv speed is set to 1/1600, doesn't the camera use that speed regardless of whether the ISO is set at 100 or 3200?. Yes. It would shoot at 1/1600, and try to adjust f/stop and iso (if auto-iso is enabled) to balance the exposure. If you have auto-iso disabled, it would try to adjust the f-stop only to balance the exposure. No matter what, in Tv mode, the shutter speed will be whatever you set it to. As to why the articles are suggesting you increase the iso.... suppose a 'proper' exposure was iso100, 1/200s, f/4. If you just up the shutter speed (pretend you're in full Manual mdoe) and shoot at iso100, 1/1600s, f/4, your image will be very dark. So the suggestion is to up the iso one stop for each stop of shutter speed you add. All the following would work: iso100, 1/200s, f/4 iso200, 1/400s, f/4 iso400, 1/800s, f/4 iso800, 1/1600s, f/4 As we move down the list, we gain motion stopping power, but we'll take a hit with a noisier photo (with the caveat that iso800 is still pretty high quality on any modern dslr). The f/stop could also be changed to let in more light at the 'cost' of less Depth of Field. All three variables, iso, f/stop, and shutter, are a compromise in one way or another. Choose the compromise that works for your photo, and choose the shooting mode (Tv, Av, TAv, M, etc) that lets you work the variables in the most convenient way.

01-18-2017, 10:20 AM	#3
awa355 Veteran Member Join Date: Sep 2016 Posts: 331 Original Poster	Originally posted by BrianR Yes. It would shoot at 1/1600, and try to adjust f/stop and iso (if auto-iso is enabled) to balance the exposure. If you have auto-iso disabled, it would try to adjust the f-stop only to balance the exposure. No matter what, in Tv mode, the shutter speed will be whatever you set it to. As to why the articles are suggesting you increase the iso.... suppose a 'proper' exposure was iso100, 1/200s, f/4. If you just up the shutter speed (pretend you're in full Manual mdoe) and shoot at iso100, 1/1600s, f/4, your image will be very dark. So the suggestion is to up the iso one stop for each stop of shutter speed you add. All the following would work: iso100, 1/200s, f/4 iso200, 1/400s, f/4 iso400, 1/800s, f/4 iso800, 1/1600s, f/4 As we move down the list, we gain motion stopping power, but we'll take a hit with a noisier photo (with the caveat that iso800 is still pretty high quality on any modern dslr). The f/stop could also be changed to let in more light at the 'cost' of less Depth of Field. All three variables, iso, f/stop, and shutter, are a compromise in one way or another. Choose the compromise that works for your photo, and choose the shooting mode (Tv, Av, TAv, M, etc) that lets you work the variables in the most convenient way. Brian, thank you. I was editing my post as you were replying. All makes sense now.

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01-18-2017, 10:21 AM	#4
photoptimist Pentaxian Join Date: Jul 2016 Photos: Albums Posts: 5,123	First, there's some confusion in what you wrote. A low ISO does not cause the camera to gather more light, it actually makes the camera less sensitive to light. For low-light situations you actually want to increase the ISO to make the camera more sensitive to light. If you set the shutter speed, set the aperture, and set the ISO to some value (i.e., use M mode), the camera will do exactly that but the picture may be quite over-exposed or under-exposed. If you set the shutter speed, set the aperture, and let the camera pick the ISO (i.e., use TAv mode), the camera will increase the ISO as the light levels decline. If you set only the shutter speed, and let the camera set the aperture and ISO (i.e., use Tv mode with Auto-ISO), the camera will generally use low ISO and open aperture until light levels get so low that it must also increase the ISO as the light levels decline further. (If you don't use Auto-ISO, the camera will use whatever ISO you've set).

01-18-2017, 10:24 AM	#5
Sagitta Veteran Member Join Date: Feb 2011 Location: Maine Photos: Gallery Posts: 3,081	The way I look at it is this: You can fix noise a lot more easily than you can fix blur in post.

01-18-2017, 10:27 AM	#6
awa355 Veteran Member Join Date: Sep 2016 Posts: 331 Original Poster	Originally posted by photoptimist First, there's some confusion in what you wrote. A low ISO does not cause the camera to gather more light, it actually makes the camera less sensitive to light. For low-light situations you actually want to increase the ISO to make the camera more sensitive to light. If you set the shutter speed, set the aperture, and set the ISO to some value (i.e., use M mode), the camera will do exactly that but the picture may be quite over-exposed or under-exposed. If you set the shutter speed, set the aperture, and let the camera pick the ISO (i.e., use TAv mode), the camera will increase the ISO as the light levels decline. If you set only the shutter speed, and let the camera set the aperture and ISO (i.e., use Tv mode with Auto-ISO), the camera will generally use low ISO and open aperture until light levels get so low that it must also increase the ISO as the light levels decline further. (If you don't use Auto-ISO, the camera will use whatever ISO you've set). Yes, I should have said a wider aperture, not a lower ISO. re light gathering. Thank you.