Film Speeds

[johnicm]

why are all digital SLR cameras geared up for fast "film speeds" Starting at 100, and going up to 400,800, etc. why not go the other way for slower "film"

[Cathus]

I'm not sure I really understand the question.

think of it this way, on an ISO of 100 you have 100 bits of noise per photo, with an ISO of 1600, you have 1600 bits of noise, i.e. more, or the 'speed' of your shutter is able to be increased for the same circumstance the higher the ISO number, seems logical to me.

Is that what you meant?

[MattUK]

Perhaps you're confusing the film speed with shutter speed John?

Slow shutter speed allows you to let more light in, and is useful for night shots or smoothing out moving water.

High ISO film speeds are kind of the opposite - they allow you to keep the shutter speed fast when the light isn't so good, to stop blurring at night for example. As Cathus says though, higher ISO settings = more noise in the picture.

[alfbranch]

I agree with Johnicm it make it harder to get long exposures without filters and would we not get less noise at ISO 25

[ABERS]

I think I can see where you're coming from on this johnicm.

With digital it's the camera that sets "the film speed" allowing a wide range of ISO settings, whereas with film it's the type of film used that allows or determines the film ISO/ASA setting.

Film speed started, or should I say still starts at about an ASA rating of 25 going up to 400 ASA. Those figures could be pushed or pulled according to the developer used and the developement time to arrive at the negative you wanted to end up with. You usually ended up with your own special combination to suit your needs.

I'm sure you know this already, but if you go to

http://www.harmanexpress.com/prods/3/ILFORD-Film.htm

Film ratings and types are there.

[OldBoy]

Originally Posted by johnicm

why are all digital SLR cameras geared up for fast "film speeds" Starting at 100, and going up to 400,800, etc. why not go the other way for slower "film"

It because the best image, i.e. less noise/contrast, for a Nikon is 200 whilst a Canon is 100. On some DSLR you can reduce this to 80 or 50 but you lower the contrast as a result.

[cosmicma]

i think what he means is why don't we see iso ratings lower than 100 on dslr's

well some do but not many an example would be the canon 5D MK1 which can go down to iso 50 but from what i have heard you lose dynamic range when using iso 50 on the 5D MK1 so maybe thats the answer

the iso setting on a digital camera is basicly a variable gain callibrated to coinside with film speed and as far as i can tell there is an optimimum setting
on nikon ( and canon i think ) this seems to be iso 200 where the maximum dynamic range is to be had
a higher or lower gain tends to lose some dynamic range but by how much and weather it would be noticable i don't know
maybe below 100 iso it does become noticable just the same as above a certain iso ( depending on camera where this is ) noise becomes noticable

so a simple way of putting it is think of it as a volume control if it's too low you can miss bits and if it's too loud it distorts

EDIT>>
looks like oldboy was typing at the same time

hope this makes sense....

[MattUK]

Originally Posted by OldBoy

It because the best image, i.e. less noise/contrast, for a Nikon is 200 whilst a Canon is 100. On some DSLR you can reduce this to 80 or 50 but you lower the contrast as a result.

Hey OldBoy, I couldn't find anything to support the theory that ISO 200 is the best setting for Nikon - could you point me in the right direction please?

Thx

[OldBoy]

Originally Posted by MattUK

Hey OldBoy, I couldn't find anything to support the theory that ISO 200 is the best setting for Nikon - could you point me in the right direction please?

Thx

If you check the ISO settings in your Nikon Manual you will see that anything below ISI 200 is classed as LO 0.3-LO 1 therefore, the normal lowest ISO is 200.

[KeithT]

In truth, like digital and the noise factor, film also carried with it the anomaly of greater grain particles as ISO values increase. Digital camera makers, for want of a better way to label sensitivity, adopted the International Standards Organisation (ISO) benchmark. I am led to believe that the ISO values of digital sensors are not quite the same as they are with film. My point is, that you should not even try and equate the sensitivity levels of a digital sensor with that of film emulsion. It is purely a guide and nothing more. If you want to gain a slower aperture to light input ratio in order to get similar results as using a slower ISO rating, just use a solid ND graduted filterto coincide with the amount of stops you want to decrease it by on your lens. You will need to set everything manual to retain the difference, and don't forget to use a tripod, as you will get slower shutter speeds as a result.

EDIT: This article might be of use to you: http://dpanswers.com/content/tech_iso.php