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ISO
I shot 35mm and 120mm years ago as a semi-professional, and then pretty much got out of photography for a while. I have recently bought a nice digital SLR, but am struggling to understand what happens when I tell the camera to shoot at a different ISO setting. I know that ISO in film was directly related to the size of the light sensitive crystals in the film emulsion (faster speed=larger crystals=pictures/enlargements with more 'grain'). When I tell my digital camera to use a higher ISO setting-what is the result? Does the picture come out with less color saturation? Does it get 'grainy' when I try to enlarge it? Does the camera boost the exposure in some way?.

Really want to understand.Ron King..

Comments (6)

Banannabiker wrote:.

When I tell my digital camera to use a higher ISO setting-what is the result?Does the picture come out with less color saturation?.

Yes..

Does it get 'grainy' when I try to enlarge it?.

Yes, although technically called "color noise"..

Does the camera boost the exposure in some way?.

It amplifies the sensor sensitivity to a greater degree.Davehttp://pixseal.com..

Comment #1

A higher ISO turns up the gain, thereby amplifying the signal as well as the noise of the sensor. It's kind of like turning up the volume on a stereo receiver, the music will be louder but so will the noise, or static if there is any, as in the case of a weak FM station. (or in the case of photography, a dark subject)...

Comment #2

That has asked about ISO. I hope you find it useful. It is not my document but it sure did help me figure out what ISO was all about..

Since you stated that you were a 'semi-professional' in the 35 mm film days, ISO is equal to ASA. If you will recall, photography was 'limited' to ASA 100, 200, 400basically. But you could push the film to a higher ASA through film development. Also recall, if you were going on a photoshoot how it was almost required that you carried around several bodies with different speed film so you could adapt to the light conditions you encountered?.

With digital SLR cameras, you don't have to carry around two bodies with two different film speeds. Instead you can change your ISO settings to go from one sensitivity to another as often as you take photos. Thus you can have a low ISO in one photo and the next photo you can have a higher ISO settingchanges you can make by a flick of a dial or menu selection..

Here is the chart:.

Http://www.pbase.com/ericsorensen/image/52955921/largeMatt..

Comment #3

Banannabiker wrote:.

When I tell my digital camera to use a higher ISO setting-what is the result?.

The sensor amplifies signals as it increases ISO. This means it also amplifies noise, which is why noise goes up as ISO increases..

Does the picture come out with less color saturation?.

This is a yes and no answer..

If you shoot JPEGs then you camera will (internally) apply noise reduction algorithms to clean up the image. A typical side effect of some of these algorithms is to reduce saturation, something that becomes stronger as more noise reduction is required ( as ISO increases )..

If you shoot RAW then no noise reduction is applied to the image. However you will probably do this yourself at some point in post processing and you hit the same problem. You can control this more when you do noise reduction yourself and you can also boost saturation before applying noise reduction to help the result. However it's a a bit of a balancing act as boosting saturation like this may affect the result of noise reduction negatively..

Does it get 'grainy' when I try to enlarge it?.

Yes. Noise and the effects of noise reduction..

In JPEGs the grain is the processed result of trying to clean up noise. Some cameras apply heavy chroma noise reduction but leave luminance relatively alone. This typically results in low color noise in JPEGs but some grainy effects. Some cameras apply heavy luminance - typically this causes smearing and color bleeding..

Beyond a certain point the noise ( in small sensors usually ) can be so great as to make noise reduction efforts pointless and you just end up with different types of noise after processing ( like big colored blobs )..

Does the camera boost the exposure in some way?.

Yes and No..

It may take the ISO level into account when making it's metering calculation depending on what exposure mode you are in. Obviously on M you're on your own, otherwise it should allow for ISO level. Exposure calculations have not changed since your film days. You should be aware that some cameras ISO values are not accurate - I think some Canon models are like this. Unless you expose manually this is not an issue. The differences are usually small ( say 1/4 to 1/3 stop )..

StephenG.

Pentax K100DFuji S5200Fuji E900PCLinuxOS..

Comment #4

Dherzstein wrote:.

Banannabiker wrote:.

When I tell my digital camera to use a higher ISO setting-what is the result?Does the picture come out with less color saturation?.

Yes..

The better consumer DSLRs hold their colour saturation right up to ISO 1600. Semi-pro cameras like the D300 can do the same at ISO 3200 and the D3 at ISO 128,000!.

And the same goes for the effects of Noise Reduction. ISO 800 is safe to use on all DSLRs. 1600 on most consumer DSLRs, 3200 on modern semi-pro and 128,000 on the D3..

Chris Elliott.

*Nikon* D Eighty + Fifty - Other equipment in Profile.

Http://PlacidoD.Zenfolio.com/..

Comment #5

Banannabiker wrote:.

I have recentlybought a nice digital SLR, but am struggling to understand whathappens when I tell the camera to shoot at a different ISO setting..

Before converting the analog signal recorded by the sensor, it gets amplified via analog amplifiers. It is only after this that the signal is converted into digits (ones and zeros) via an analog-to-digital converter. Some cameras also offer "boosted" sensitivity settings. These latter settings are more like push-processing deliberately under-exposed film..

When I tell mydigital camera to use a higher ISO setting-what is the result? Doesthe picture come out with less color saturation?.

If the camera (or you during raw development) applies too much colour noise suppression, yes. (Colour "noise", also called chroma noise or chrominance noise, takes on the appearance of random coloured dots in your photo, mostly in the shadows. How distracting it is depends more on the size and spatial frequency of these dots than their actual amount - the finer the better of course - as well as on how big you print and how closely you are looking. If unpleasant, chrominance noise can be effectively suppressed without losing detail, but saturation suffers.).

Does it get'grainy' when I try to enlarge it?.

Apart from chrominance noise, there is also luminance noise, which can be, tho not always is, similar in it's appearance to film grain. And yes, it becomes more obvious the bigger you print, although how visible it is will depend on the texture of the photographic paper used, and on viewing distance too..

One thing worth noting is that any current D-SLR, including those sometimes bashed for being "noisy", produce much cleaner prints at any given sensitivity setting than films of corresponding ISO speed. Another thing to note is that when not printing but downsizing to screen resolution (either HDTV or a common computer screen), much if not all of the noise disappears...

Comment #6

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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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