Question about ISO's

[Toad]

I was recently reading through PlanetNeil.com and was noticing that on some of the pictures he was putting the iso speeds are some pretty strange (to me) numbers. How does one pull of a iso speed of 1250, 640, or 500? I have a Rebel XT, and the iso speed options are 100, 200, 400, 800, and 1600... I don't see a 500 or 640 anywhere in there.
So, are these just iso settings that are available on other cameras, or is there some button I didn't know I could press?
Toad

[Shane]

You are correct, each camera has various ISO's and they step up in various increments.

[venchka]

Those numbers are 1/3 stop increments between the whole stop increments on your Rebel. You could simulate those 1/3 stop ISO increments by setting your Rebel to 400 and then setting your exposure to +1/3 stop=ISO 320, sort of. You pays your money and you gets your ISOs.

PS: The whole ASA/ISO scale is usually labeled on most good hand meters. Or at least mine have them. My old Gossen Luna-Pro is marked from 0.8 to 25,000. That's how us Fossils can figure out these digital camera questions without ever owning one.

[ramblinray]

I think those are the only ones available for your model. Pay more money and you can get a bigger selection of ISO values and a bunch of other options too. As the old adage goes, you get what you pay for.

[venchka]

It also helps in understanding the whole range of ASA/ISO numbers if you've dealt with a variety of film manufactured in different speeds.

I don't quite get the whole digital ISO concept myself. Why labor along with the film speed concept for an electronic sensor? Do any of these GeeWhiz DSLRs have an ISO mode? I pick shutter speed & aperture and the camera picks the correct exposure? HUH?

[Toad]

Originally Posted by ramblinray

As the old adage goes, you get what you pay for.

Oh yes, I've always believed that. It's just that sometimes what you want isn't always what you can afford.
Besides, as an ameture starting out, I wasn't going to go get the top of the line, drool inducing professional camera. Especially if this whole photography thing turned out to not be for me. It seems though that I am enjoying it quite a lot at the moment, so I will most likely in the distant future be upgrading to something a little more capable. Like a 1Ds Mark II.

Toad

[CaptainTom]

If you are in dim light and you want maximum depth of focus and you meter at F2 at 1/25, how do you get the aperture to f8 without decreasing (longer) the shutter speed ? Increase the effective sensitivity of the sensor (film if you will). Sure it's hocus pocus on a digital, but if you want maximum control you have to be able to control all the factors.

[venchka]

Originally Posted by CaptainTom

If you are in dim light and you want maximum depth of focus and you meter at F2 at 1/25, how do you get the aperture to f8 without decreasing (longer) the shutter speed ? Increase the effective sensitivity of the sensor (film if you will). Sure it's hocus pocus on a digital, but if you want maximum control you have to be able to control all the factors.

I know that. Why don't these digital bodies adjust their sensor "speed" as required? As you suggest, I select f2.8 @ 1/160 and the camera picks "ISO 567" or whatever is needed?

[Toad]

Originally Posted by venchka

I know that. Why don't these digital bodies adjust their sensor "speed" as required? As you suggest, I select f2.8 @ 1/160 and the camera picks "ISO 567" or whatever is needed?

I think that the Nikon D80 has an "auto" setting for their ISO speeds. Maybe somebody else can confirm this.

Toad

[CaptainTom]

If you want to control DOF then you would need to "tell" the camera you want increased/decreased DOF. I suppose it would be possible. I think we are still very much stuck in the terminology and techniques developed in the film days. Why do we still compare DSLR's to 35mm? Because that's what we are used to. My camera shoots full frame as far as I'm concerned. It may not be the field of view it would have it were 35mm, but also not the same at 2 1/4 or 6x7.

[venchka]

I hope Nikon is paying attention and giving us auto ISO.

Suppose you want to control DOF AND subject motion. With film you were stuck until you could change rolls. If these GeeWhizBang electronical gizmos are going to give us total freedom, then auto ISO is the way to go. Assuming the user is clever enough to know when to lock in slow or fast as his/her needs dictate.

[billbunton]

Originally Posted by venchka

I hope Nikon is paying attention and giving us auto ISO.

They have been for quite a while. Below is cut and paste from the firmware 2.0 update manual for the D2x. Original firmware had the mode, but didn't have the min shutter speed or max sensitivity settings:


Custom Setting b1: ISO Auto Control (Page 188)Custom Setting b1: ISO Auto Control (Page 188)
This menu now contains the options shown below.
Option Description
Off
(default)
ISO sensitivity remains fixed at value selected by user, regardless of whether optimal exposure can be achieved at current exposure settings.
On
If optimal exposure can not be achieved at ISO sensitivity selected by user, ISO sensitivity is adjusted to compensate, to minimum approximately equivalent to ISO 100 and maximum selected using Max. sensitivity option. In exposure modes P and A, ISO sensitivity will be adjusted if photo would be overexposed at shutter speed of 1/8,000 s or underexposed at value selected for Min. shutter speed. Otherwise camera adjusts ISO sensitivity when limits of exposure metering system are exceeded (mode S) or when optimum exposure can not be achieved at shutter speed and aperture selected by user (mode M). ISO sensitivity can not be set to values over 800 while this option is in effect.

Max.
sensitivity
Menu shown at right is displayed. Press multi selector up or down to highlight
desired ISO sensitivity and press to right to return to ISO auto menu.
Min.
shutter
speed
Menu shown at right is displayed. Press multi selector up or down to highlight
desired shutter speed and press to right to return to ISO auto menu.

[venchka]

Canon is oblivious to this mode of operation? Copyright/patent protection on Nikon's part?

[jeffkohn]

Originally Posted by venchka

I don't quite get the whole digital ISO concept myself. Why labor along with the film speed concept for an electronic sensor? Do any of these GeeWhiz DSLRs have an ISO mode? I pick shutter speed & aperture and the camera picks the correct exposure? HUH?

You can do this on Nikon's. There's not an "ISO Mode" on the mode dial but you can use Auto-ISO functionility to achieve exactly the same effect. And what's interesting is that the ISO's the camera will select are sometimes more granular that 1/3 stop, which means this could actually be the most accurate way to get the exposure the meter wants.

[Duffy Pratt]

The Camera companies still have not adjusted to the idea that ISO can now change with every shot. With film, you would almost always have one ISO setting/roll, so there was no need to make the ISO adjustment real easy, or to make the ISO information immediately available. Thus, on the digital cameras, switching ISO is typically more difficult than changing Aperture or Shutter Speed, and the cameras didn't show ISO in the viewfinder.

With more experience, I think people are coming to realize that there are three adjustments that one can make on every exposure. Aperture (which changes DOF and bokeh), Shutter Speed (which mostly deals with subject blur), and ISO (which varies the noise level). So now, I think, there are finally some cameras coming with the ISO info in the viewfinder. Maybe the companies will also make ISO easier to adjust, and give some more sophisticated AI for different modes of shooting.

Duffy