Is ISO the same on different DSLRs?

[forestgnome]

We had an earlier thread on high-ISO bodies, but I have a question. I'm drooling over the new Canon T1i.

http://www.bhphotovideo.com/images/images345x345/613611.jpg

This has the crazy ISO. Is 1600ISO on this body the same or different than 1600ISO on earlier Rebels?

Also, do you have to shoot RAW to get a nice image at high ISO? Do I get graininess because I've used only Large/Fine?

thanks

 

[Grumpy]

If I am not mistaken, ISO stands for International Standards Organization. In Photography, it is a standard indicator (measure) of a film or image sensor’s sensitivity to light, upon which an exposure computation to determine correct f/stop and shutter speed combinations can be based.

In film days we used what some people call the “sunny 16 rule.” It works this way:

* Set your shutter speed at the reciprocal of your ISO (1/ISO).

* Then, if you are shooting a front-lit subject in bright sun, set aperture to f/16.

* If light is “cloudy bright” (hazy or high, thin clouds over the sun) use f/11.

* In plain cloudy conditions, use f/8. In dark cloudy conditions use f/5.6.

To answer your question about ISO 1600 on older and newer cameras:

Just like all films of a given ISO not being equal in image quality (or characteristics) during the film days, all sensors are not equal in quality or characteristics in the digital era. Furthermore, sensor technology has advanced rapidly, and continues to be refined. So image quality at ISO 1600 on your older digital camera may not be as good as it would be at ISO 1600 on a newer model.

As for shooting in RAW vs JPG … The advantage in using RAW format is that you record virtually all image data, which you then can tweak using a computer program. JPG images are processed and “optimized” in the camera. In my experience, the “graininess” issue can become as severe in RAW capture images as any others.

The “graininess” in digital images, as I understand it, is really a form of electronic “noise.” Photoshop provides some noise reduction controls that will help clean up some of this. But the real solution is a sensor that produces less noise.

G.

 

[w7xman]

I believe Grumpy is correct. The higher ISO's are an amplification of the sensitivity to light of the origional signal of the sensor.

ISO 1600 should let the same amount of light in on all cameras, as there is a standard for the aperature, shutter speed and ISO that is kept fairly uniform across the industry.

However, what will be different as Grumpy said is how well the sensor handles that amplification. My 20D is terribly grainy and unusable at ISO1600, but I drool at some of the clarity of the new cameras.

Worth the upgrade! Especially for you who could always benefit from a higher shutter speed in those low light moosings that you do...

 

[DougPaul]

This has the crazy ISO. Is 1600ISO on this body the same or different than 1600ISO on earlier Rebels?

As others have noted, the ISO number describes the sensitivity of the sensor (analogous film speed). Ideally all sensors will have the same sensitivity for the same stated ISO, in practice there is some manufacturing variation.

Also, do you have to shoot RAW to get a nice image at high ISO? Do I get graininess because I've used only Large/Fine?

Not necessarily. Canon cameras have built-in noise reduction which generally reduces the resolution (reduction of fine detail) to reduce the noise, so there are compromises. Some bodies allow adjustment of the noise reduction process in their menus. The reduction of RAW to JPEG also loses some information (once lost, it cannot be recovered).

If you shoot raw, you get to control the processing steps to get what you think is best. One can often do better than the standard built-in processing. (I generally shoot RAW+JPEG for such pictures so I can choose based upon the results.)

The noise comes from several sources.
* Light itself is noisy because it comes in discrete photons. The intensity is the average number of photons which have a noise (standard deviation) equal to the square-root of the average. Thus the percentage of photon noise is inversely proportional to the square-root of the intensity and brighter images (ie lower ISO shots) have less photon noise.
* The sensor pixels collect electrons knocked loose by the photons. It adds noise because electrons can leak in or out of the pixels. (This gets worse at higher temps and longer exposures.)
* The electronics (amplifiers and A/D converter) that reads out the number of electrons collected in each pixel also adds noise. (This is also worse at higher temps.)

All else being equal, larger sensors (ie larger sensor pixels) have less noise because they require larger apertures (for the same F-stop) which capture more light. (Thus the 5D2 has lower noise than the XTi.) Fewer pixels for the same sensor size also have less noise. (The marketing race for more pixels is increasing the noise.)

Ultimately, the noise is fundamentally limited by the number of photons detected by each pixel. Improvements in technology, however, can reduce the noise contributed by the other sources.

There is lots more info on the topic at http://www.clarkvision.com/imagedetail/#sensor_analysis and http://www.clarkvision.com/imagedetail/.

Doug

 

[Brambor]

noise reduction

The noise reduction on some of the newer DSLR's is better in jpegs at iso 1600 and larger. You would not normally get the noise reduction quality if you processed straight RAW. You would then have to use other 3rd party applications (i.e. noise ninja) to get equal or better quality (of the in camera noise reduction jpg mode).