Why ISO on digital SLR mostly only >200 ?

Hi there,

 

why is it that most digital SLR only come with ISO >200 ? Only a few of Nikon's palette do have the ISO

100 capability. None has ISO 50... Is this due to technical reasons? Or because noone needs anymore ISO

50? My impression, as I look at my D70 ISO 200 results, is quite often that I would think of it as "grained"

and would love to have ISO 100 or even 50...

Digital sensors use a different technology than film. While there's a correlation between ISO and noise in a given sensor, there's no correlation between various sensors and film at the same ISO value. If you need a longer exposure, like for moving water, use neutral density filters.

There is a trade-off between the native sensitivity and how much you can push it by amplifying the data. Using an ISO 100 sensor at ISO 1600 requires a 4 stop push; even two stops loses DR and adds noise.

Consumers tend to use slower lenses so it makes sense to optimize the camera to use ISO 200 rather than ISO 100 however because the D80 and D40x uses more mega pixel within the same size as the D50/D70 series and thereby more noise at higher ISO, the default is ISO 100.

 

If there was a ISO 50 it would actually degrade the image. The reviews on the Canon 5d for example show image degradation from ISO 100 to 50.

Sam,

 

The D80 has a lot less noise than the D70 series due to built-in noise reduction. I have shot

at ISO 1600 with my D80 and the noise is roughly equal to ISO 800 on my old D70/D70s.

 

I shoot at ISO 200 or higher on my D80 all the time. I don't like the look of ISO 100 at all.

 

Dave

I found that the theoretical advantage of being able to change ISO on a digital camera is for the most part hype on the part of digital camera manufacturers.

 

There is no image improvement advantage for using a very low ISO rating. I rarely change the ISO from 200 as this is the optimal speed for my camera (Fuji S2). I find dynamic range reduces at 800 ASA and beyond; so I prefer to under expose and correct in Photoshop. This gives a lot more control and I get less image noise and greater dynamic range as a result. (I may have a different view when I get my hands on a Fuji S5 though )

 

Having a lower ISO would be very useful if you are using a fast lens. In bright sunlight; especially if you are taking photos on the water you will often run out of shutter speed headroom if you are using a F2.8 lens.

 

The cure is quite simple: use a neutral density filter or polarizer, which will effectively cut the ISO from 200 to 100 ASA .

What camera do you have that you're getting a lot of noise at ISO 200? I get very little if any.

Also possible that if you way under-expose the image will be noisier.

Because you only get one sensor that has to do all the speeds. It's easier to manufacture one that gives acceptable results 200-1600 than it is one that does 50-6400.

 

Maybe one day we'll see DSLRs with interchangeable sensors. People who really care about image quality are using interchangeable digital backs on medium format bodies.

Peter asked:

 

What camera do you have that you're getting a lot of noise at ISO 200? I get very little if any.

 

My reply:

 

I see noise in the sky with both the D70 and D200; less at ISO 100 than ISO 200. It's not a lot of noise and disappears when the images are properly resized so that they are viewable on the web. However, it often shows up as digital artifacts when the web application poorly resizes my 1280 pixel images to a smaller size. For example, in this properly exposed ISO 180 shot: http://photos.imageevent.com/tonybeach/mypicturesfolder/april2007/large/_AWB3418.jpg

Anthony,

 

Your example has a very good looking sky.

 

This sounds like it might be a post-processing issue, too in your example. This is why I do

all my sizing in PS and upload. That's a different kind of noise sometimes... jpeg resize

artifacts, etc. When web applications resize photos, all bets are off, and you could have

had a perfect noise-free sky... but not any more.

 

Stefan, does this noise end up being a problem in your final output? Also, I remember

when I first started doing this and I read Ken Rockwell's advice about shooting in jpeg and

ignoring RAW. I did my own quick test and the biggest issue with jpeg out of camera is the

noise in the sky. RAW eliminated it for me. I shoot RAW for critical images. I shoot jpegs

for candid people party shots and times when I have to hand images off to someone

quickly.

I own a D70s and I also resent the lack of ISO 50 and 100. I often want to make long exposures during the day (longer than 1/6 sec) and adding more glass (polarizers and ND filters) lowers the quality of the image. Obviously for such shots I will have to use film and bring my F100 along.

Now, that I look at my photos again, I realize that this noise effect is mostly related with dark

surfaces. Look at the attached cropped 100% image. Ok, it's a little bit out of focus due to

heavy winds. But it shows the phenomena.<div></div>

And here is another one, daylight, but again, dark background:<div></div>

My Contax ND (First full frame 35 mm digital SLR) had an ISO range of 25 to 400. ISO 25 was great for studio work. If the camera had not had the major problem of only being good for 55 shots before needing new batteries, I never would have sold that beauty, even thought it was only 6 megapixels. ISO 25 with 6 megapixels rivals ISO 200 with 10.2 megapixels (Nikon D20!).

 

Michael.

Anthony Beach said, "even two stops loses DR and adds noise."

 

Anthony, try and S5 :)

 

regards, michael

Peter wrote:

 

Your example has a very good looking sky.

 

This sounds like it might be a post-processing issue, too in your example. This is why I do all my sizing in PS and upload. That's a different kind of noise sometimes... jpeg resize artifacts, etc. When web applications resize photos, all bets are off, and you could have had a perfect noise-free sky... but not any more.

 

My reply:

 

Close examination of the original file shows noise, but you don't see that in the full sized web version, but those digital artifacts are coming from the noise getting mixed into the website's resizing algorithm and becoming exaggerated. Here's an ISO 125 example: http://photos.imageevent.com/tonybeach/mypicturesfolder/april2007/large/_AWB5531.jpg

 

 

Michael wrote:

 

Anthony, try and S5 :)

 

My reply:

 

Thank you for the suggestion Michael, but I think not. My D200 does just fine for the vast majority of my photography and my only complaint is that I would like it to be 35FF and have more resolution. The S5 costs nearly as much as a used D2x. The D2x will be my next camera because it is widely considered the best low ISO performer (yes, many of us shoot a lot at low ISO, I personally rarely even get to ISO 800); and it has a lot of extras like better AF and more resolution, something that I wouldn't get if I spent my money on an S5.

Michael Hahn wrote:

 

ISO 25 with 6 megapixels rivals ISO 200 with 10.2 megapixels (Nikon D20!).

 

My reply:

 

Prove it. It takes a lot of noise to wipe out resolution, a lot more than my D200 exhibits at ISO 100, 200, or even 400. Too many people obsess about noise and destroy detail in their images using NR applications to wipe out the noise; I simply avoid sharpening noise.

Stefan,

<p>

As others have noted, a lower ISO would not resolve graininess issues - the sensor on your D70 is optimized for ISO 200 and above, and like the 5D's poor ISO 50 response, your D70 image quality would suffer if Nikon allowed you to set it to ISO 100 or lower.

<p>

As to your dark background images, the first one appears to be a long exposure. Have you enabled your Long Exposure NR? It's a big help in situations like that. As to the flower background, if that's a correctly exposed image, then all I can suggest is selecting the background and do some noise reduction or blur on it to even out the spotting - it looks like random noise of some sort, or possibly JPEG artifacting if you are saving to JPEG in the camera.

<p>

There's a good article at <a href="http://www.photo.net/learn/dark_noise/">http://www.photo.net/learn/dark_noise/</a> covering the basics of dark noise (and some compensation techniques which you won't need because your D70 already uses Dark Noise Subtraction when in Long Exposure NR mode).

Ah, "Long Exposure NR".... what's that? Haven't heard of it... Well, gonna google for it. Thanks

for the tipp.

Yeah, that really bugs me. In fact, one of the reasons I switched from film to a DSLR is the ISO sensitivity. I was hoping it would go down to 50, but it only goes to 100.

Kieran, DSLRs have about a two stop sensitivity advantage of noise versus grain (i.e., ISO 200 is the same as ASA 50). However, if you want slower exposures to deliberately blur your scene, than film is a better media because you can use a less sensitive film and film is a better format because you can stop down the lens more with less diffraction (this is complicated since in the DX format a 6 MP sensor is good to f/16, 10 MP to F/13, and a 12 MP is good to f/11; film shows the same amount of diffraction at f/22).