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ISO versus Exposure Time question
Hi,.

Lets say I want to take a landscape photo in low light using a tripod..

For the best results and least noise should I: -.

Use a low ISO number and a longer shutter speed..

Or.

A higher ISO number and faster shutter speed..

Which is better, or would there be no difference?.

David Colehttp://www.flickr.com/photos/melmoth2008/..

Comments (18)

Hi,.

Lets say I want to take a landscape photo in low light using a tripod..

For the best results and least noise should I: -.

Use a low ISO number and a longer shutter speed..

Or.

A higher ISO number and faster shutter speed..

Which is better, or would there be no difference?.

The former. Increasing ISO also increases noise and reduces image quality. Often you have to do it to get a fast enough shutter speed to prevent blur, but if you are using a tripod and your subject is stationary, shutter speed is not an issue, so use the lowest ISO possible..

The only caveat is if something is moving in the landscape: is wind blowing the trees, are the clouds moving, is there running water? If you want to be sure of freezing those then a faster shutter speed would be necessary. You can always take several shots at different shutter speed / ISO settings and choose the best one afterwards..

Best wishes.

Mike..

Comment #1

DavidCole wrote:.

Hi,.

Lets say I want to take a landscape photo in low light using a tripod..

For the best results and least noise should I: -.

Use a low ISO number and a longer shutter speed..

Yes..

Or.

A higher ISO number and faster shutter speed..

No..

Which is better, or would there be no difference?.

The answer is almost straightforward and simple. Use a low ISO and longer exposure time as required. Since you are using a tripod, also choose the aperture to obtain the desired depth of field. This way you minimise sensor noise which increases with higher ISO..

The one small issue is when exposure times become very long (around 1 second or longer) some cameras are prone to hot-pixels, a type of noise. But this can usually be eliminated if necessary by using the in-camera Dark Frame Subtraction (usually described as Noise Reduction, but should not be confused with software NR which blends the pixels in order to disguise high-ISO noise).Regards,Peter..

Comment #2

The two previous anwers are correct use the low ISO. However I think it is important to understand what ISO means in a DSLR. In the film days you changed film type to get faster speeds. In a DSLR you are increasing amplification when you increase ISO..

This is not much different then turning up the volume on your sound sytem. You amplify both the good AND the bad until you reach a point where the volume amplifier may start to clip or distort the sound. At that point you are amplifying the bad AND making it worse..

Therefore in almost all instances the lower the ISO you can use the better for Image Quality. However some folks go overboard and look at 100% crops and say "look at all the noise" when in an 8x10 print you would never even see it. In almost all DSLRs you can go to ISO800 with little or no noticable noise in the shot.Olympus E-510 and a bunch of stuff to hang on it...

Comment #3

Higher ISO isn't quite like turning up a hi-fi amplifier volume. Although CCDs have an on-chip amplifier that isn't how they increase gain..

"The gain adjustment of a digital CCD camera system defines the number of accumulated photoelectrons that determine each gray level step distinguished by the readout electronics, and is typically applied at the analog-to-digital conversion step. An increase in electronic gain corresponds to a decrease in the number of photoelectrons that are assigned per gray level (electrons/ADU), and allows a given signal level to be divided into a larger number of gray level steps." Nikon's site:http://www.microscopyu.com/articles/digitalimaging/ccdintro.html.

This creates noise because of digitisation errors, not because the noise is made any louder in absolute terms..

Under low light conditions noise in consumer cameras is dominated by read noise, which is a per pixel noise unaffected by exposure duration. Dark noise (the cause of hot pixels) is electrons per pixel per second, so the longer the exposure the more dark noise you will have and the lower the overall signal to noise ratio. You can have hours of fun exploring this with the interactive model athttp://www.microscopyu.com/...ls/java/digitalimaging/signaltonoise/index.html. A less technical acount is athttp://www.cambridgeincolour.com/tutorials/noise.htm..

The other reason to use low ISO and long exposure is that dark noise is easier to remove in post-processing...

Comment #4

Sherwoodpete wrote:.

The one small issue is when exposure times become very long (around 1second or longer).

On many SLR's you will see a camera-induced vibration for pictures of *about* 1/25 second. At this speed, the slap of the Mirror flipping up causes small vibrations that will be seen in the final image..

For pictures faster than 1/25th, the shutter speed is fast enough to eliminate this shake. For pictures lmuch greater than 1/25th, the total exposure time far outweighs any vibration, so it is not seen in the final image..

Many higher-end SLR's have either a mirror delay and/or a Mirror Up (MUP) function. In mirror delay, when you release the shutter, the mirror is raised, and then a short time later (1/40th second?), the shutter is tripped. In MUP, the mirror is raised, then at YOUR command, the shutter is tripped..

Warm regards,DOF..

Comment #5

4 times the ISO results in 2 times the noise for a particular pixel..

That is, photon noise is proportional to the square root of ISO..

It is a bigger problem with small pixel sensors than with large pixel sensors (displayed at the same sensor pixels per display inch); Noise/Signal for an individual pixel is proportional to Square_Root_ISO/Pixel_Length.

Exposure time does not inherently affect photon noise, although the probability of vibrations and thermal noise increases with exposure time...

Comment #6

Hello,.

As ISO is increased, noise will also increase. However, as exposure time is increased ( beyond a couple of seconds, depends on sensor?) image quality will also deteriorate due to the 'hot pixel' issue already mentioned, plus thermal noise. It definitely pays to experiment I think..

Generally, low ISO = better pic quality, and that is where I would start...

Comment #7

[Recurring rant...].

You will often learn more by trying than by asking..

You have a camera.You have a computer.You have the software.Go take some pictures and try out some variations..

Waiting until the event to try a new shooting technique is just a recipe for disaster. You will likely lose some great shots by trying unfamiliar things and paying attention to the camera instead of the subject. Be familiar with the techniques beforehand.[End of Rant.].

In this case, you could have shot a few tests in the time it took to ask a question on the forum and get five (redundant) replies..

[ e d @ h a l l e yc c ] http://www.halley.cc/pix/..

Comment #8

I was trying to keep it simple. LOL..

JImOlympus E-510 and a bunch of stuff to hang on it...

Comment #9

Harumph! You used "exposure time" in the subject...correctly. I was going to compliment you on that, but I see you regressed to using "shutter speed" here. .

DavidCole wrote:.

Hi,.

Lets say I want to take a landscape photo in low light using a tripod..

For the best results and least noise should I: -.

Use a low ISO number and a longer shutter speed..

Or.

A higher ISO number and faster shutter speed..

Which is better, or would there be no difference?.

David Colehttp://www.flickr.com/photos/melmoth2008/.

Charlie DavisNikon 5700, Sony R1, Nikon D300HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #10

Thanks for the information everyone..

Much appreciated..

David Colehttp://www.flickr.com/photos/melmoth2008/..

Comment #11

Dad_of_four wrote:.

Sherwoodpete wrote:.

The one small issue is when exposure times become very long (around 1second or longer).

On many SLR's you will see a camera-induced vibration for pictures of*about* 1/25 second. At this speed, the slap of the Mirror flippingup causes small vibrations that will be seen in the final image..

For pictures faster than 1/25th, the shutter speed is fast enough toeliminate this shake. For pictures lmuch greater than 1/25th, thetotal exposure time far outweighs any vibration, so it is not seen inthe final image..

Many higher-end SLR's have either a mirror delay and/or a Mirror Up(MUP) function. In mirror delay, when you release the shutter, themirror is raised, and then a short time later (1/40th second?), theshutter is tripped. In MUP, the mirror is raised, then at YOURcommand, the shutter is tripped..

Canon cunningly continues to hide the MLU function to make it difficult to access, but it's there (in DSLR models anyway). Apparently a direct print button is more important on models that have one (and users can't select it to be a MLU button instead)..

Cheers from John from Adelaide, South AustraliaJohn Harvey Photography http://johnharvey.com.auCanon 40D, Canon 20D & Fuji F10..

Comment #12

Les Olson wrote:.

Higher ISO isn't quite like turning up a hi-fi amplifier volume.Although CCDs have an on-chip amplifier that isn't how they increasegain..

"The gain adjustment of a digital CCD camera system defines thenumber of accumulated photoelectrons that determine each gray levelstep distinguished by the readout electronics, and is typicallyapplied at the analog-to-digital conversion step. An increase inelectronic gain corresponds to a decrease in the number ofphotoelectrons that are assigned per gray level (electrons/ADU), andallows a given signal level to be divided into a larger number ofgray level steps." Nikon's site:http://www.microscopyu.com/articles/digitalimaging/ccdintro.html.

This creates noise because of digitisation errors, not because thenoise is made any louder in absolute terms..

Hi Les. It's actually more than that, as I suspect you know. Lower image signal levels mean a lower signal to noise ratio for a given amount of noise. However you look at it, in addition to digitisation errors, the lower number of photos assigned per grey level at higher ISOs mean that noise becomes amplified along with the image signal you want. Digitisation errors add to that noise..

Cheers from John from Adelaide, South AustraliaJohn Harvey Photography http://johnharvey.com.auCanon 40D, Canon 20D & Fuji F10..

Comment #13

John down under wrote:.

Canon cunningly continues to hide the MLU function to make itdifficult to access, but it's there (in DSLR models anyway)..

Hmmm... How would Canon do a MLU function on their P&S models? I guess one of their brilliant marketing types could claim a "permanent MLU", then hide how to activate it? .

Charlie DavisNikon 5700, Sony R1, Nikon D300HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #14

Ed Halley wrote:.

[Recurring rant...].

You will often learn more by trying than by asking..

You have a camera.You have a computer.You have the software.Go take some pictures and try out some variations..

Waiting until the event to try a new shooting technique is just arecipe for disaster. You will likely lose some great shots by tryingunfamiliar things and paying attention to the camera instead of thesubject. Be familiar with the techniques beforehand.[End of Rant.].

In this case, you could have shot a few tests in the time it took toask a question on the forum and get five (redundant) replies..

[ e d @ h a l l e yc c ] http://www.halley.cc/pix/.

Why do you read/post in beginners questions if you find us so annoying? I'm scared about asking any questions about other than gear because of answeres like this. I know I know nothing about photography, and that's why I want to ask and learn. Please don't rub in how stupid we are. Stay away from beginners questions if you think we are to stupid or anoying...

Comment #15

Tibia wrote:.

Why do you read/post in beginners questions if you find us soannoying? I'm scared about asking any questions about other than gearbecause of answeres like this. I know I know nothing aboutphotography, and that's why I want to ask and learn. Please don't rubin how stupid we are. Stay away from beginners questions if you thinkwe are to stupid or anoying..

You took away the wrong impression. My intent was to allay fear: you can't break your equipment by USING it, and that's the most effective way to learn..

Have fun asking, but your first instinct should be to TRY THINGS and EXAMINE RESULTS. Always try first, and it's much more rewarding for you and everyone else (newcomer as well as experienced amateurs and professionals) if you come to us with samples and questions about "I don't understand why this one's so grainy when the exposure levels were the same!".

[ e d @ h a l l e yc c ] http://www.halley.cc/pix/..

Comment #16

You're asking a hypothetical when in the "field" you can check your results by looking at histogram and the image. If in doubt, try both exposures you mentioned and see what the results are..

With recent DSLR's the usual problem is "blown highlights" so make sure you get into a good filter system, I recommend Cokin and learn to use neutral density filters, split filters and polarizers. That longer shutter speed you mentioned sends a warning light to my brain to watch over exposed areas. so easy to over expose. If you have a function in your camera to turn on over exposed highlight areas warning, turn it on and check it..

Http://www.cokin.com/ico3-p0.html.

One of the benefits of landscape photography is that almost always you have time to check the photo and make adjustments.Rationally I have no hope, irrationally I believe in miracles.Joni Mitchell..

Comment #17

Mike703 wrote:.

Hi,.

Lets say I want to take a landscape photo in low light using a tripod..

For the best results and least noise should I: -.

Use a low ISO number and a longer shutter speed..

Or.

A higher ISO number and faster shutter speed..

Which is better, or would there be no difference?.

The former. Increasing ISO also increases noise and reduces imagequality. Often you have to do it to get a fast enough shutter speedto prevent blur, but if you are using a tripod and your subject isstationary, shutter speed is not an issue, so use the lowest ISOpossible..

The only caveat is if something is moving in the landscape: is windblowing the trees, are the clouds moving, is there running water? Ifyou want to be sure of freezing those then a faster shutter speedwould be necessary. You can always take several shots at differentshutter speed / ISO settings and choose the best one afterwards..

I totally agree with that. Very often the "movement" adds a great deal to a photo..

Indeed sometimes the "movement" MAKES the photo..

I love moving/flowing water especially, but even blur in trees and clouds (and "sports" photos) can add a great deal of dramaticism and actually "be" the photo..

People talk a lot about creativity using DOF. I personally think creative use of shutter speed offers 100x more options..

Best wishes.

Mike.

Thanks for reading .... JoePhoto.

( Do You Ever STOP to THINK and FORGET to START Again ??? )..

Comment #18

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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