How many stops from 160 ISO to 320 to 640 etc

[Iron Flatline]

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Hi all.

 

I read (but do not remember) why Leica went with the 160 ISO increments, something having to do with native design of the Kodak sensor. My question is how many stops (roughly) does one increment represent? Is shooting at ISO 320 one stop faster than shooting at 160? Two stops? Something in the middle?

 

I know this is not an exact science, and ultimately I rely on my light meter, but it was puzzling me during a rather boring dinner the other night, and I promised myself I would pose this question here.

 

Any guesses?

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[Bob Ross]

Each doubling or halving of an ISO value is one stop.

Bob

[scott kirkpatrick]

ISO on a digital is like ISO on film. (It's actually from a formula, relating density on the film to aperture, shutter speed and amount of light with the ISO number the multiplicative factor, which we know as the "sunny 16 rule.") But in digital, it really works over a wide range of tones without changing contrast. Just think of each step as shifting the whole image up one bit (x2).

 

scott

[barjohn]

Sean's measurements indicated that ISO 160 was really 200 and 320 was 400 and 1250 was actually 1600 with 2500 being the equal to 3200. Any idea why Leica didn't use the actual ISO but instead selected a value below the actual? It seems to me that a company would want an accurate calibrated value rather than a marketing value, if that is what it is.

[carstenw]

Doubling or halving ISO and shutter speeds gives one stop differences. It is only the aperture which has in between stops.

[l.ceva]

Doubling or halving ISO and shutter speeds gives one stop differences. It is only the aperture which has in between stops.

 

 

On the M8 also shutter speeds have in between stops!

 

Lorenzo

 

http://www.lorenzocevavalla.it

[carstenw]

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I mean it differently. Halving a shutter speed gives you one stop difference. Halving an aperture does not.

 

shutter speeds: 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, ...

apertures: 1.0, 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11.0, 16.0, ...

 

All these numbers are one stop apart from their neighbours.

[Iron Flatline]

I mean it differently. Halving a shutter speed gives you one stop difference. Halving an aperture does not.

 

shutter speeds: 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, ...

apertures: 1.0, 1.4, 2.0, 2.8, 4.0, 5.6, 8.0, 11.0, 16.0, ...

 

All these numbers are one stop apart from their neighbours.

Thanks Carsten, I understand that. My question is how this relates to Leica's atypical ISO values. When I was shooting film, I was told that one ASA increment (100, 200, 400, etc) equals about one stop. That's why I was wondering how this relates to other settings. But I see it relates pretty analogously, it's just a little different 'cos we're Leica!

[wparsonsgisnet]

Iron Man, I don't think there's any "about" to it. I have always seen exactly one f-stop value for either a shutter speed change or an f-stop change. This is true on the M8, the D2, and every camera I have ever used.

 

These things are calibrated and work much better than your speedometer.

[dannirr]

As it relates to ISO speed and sensitivity:

 

It is true that, in general terms, doubling the ISO is equal to one stop of light. However, in reality, this is not exactly true, as it depends the combination of film and developer used and is thus a physical property - but it is close enough to make the assumption. One aperture stop (or shutter speed doubling) is exactly double the light (or half the light depending which way you go)

 

In the digital world, things are different - and the relationship of ISO sensitivity and light is chip dependent and software dependant, and thus doubling or halving the ISO is not a physical property but rather a virtual property - and thus the same relationship exists and is, I believe, more exact (although really fake).

 

I wish the M8 had an Auto ISO feature (a mistake omitting it) - set desired speed and aperture based on effect desired, and let the camera choose the lowest ISO to achieve that.

 

Danni

[Iron Flatline]

Arrghh... I think I'm being misunderstood.

 

My question is does changing the ISO from 160 to 320 mean exactly one stop difference?

[Iron Flatline]

As it relates to ISO speed and sensitivity:

 

It is true that, in general terms, doubling the ISO is equal to one stop of light. However, in reality, this is not exactly true, as it depends the combination of film and developer used and is thus a physical property - but it is close enough to make the assumption. One aperture stop (or shutter speed doubling) is exactly double the light (or half the light depending which way you go)

 

In the digital world, things are different - and the relationship of ISO sensitivity and light is chip dependent and software dependant, and thus doubling or halving the ISO is not a physical property but rather a virtual property - and thus the same relationship exists and is, I believe, more exact (although really fake).

 

I wish the M8 had an Auto ISO feature (a mistake omitting it) - set desired speed and aperture based on effect desired, and let the camera choose the lowest ISO to achieve that.

 

Danni

 

Ah, Danni answered my question while I was posting.

[ron110n]

Arrghh... I think I'm being misunderstood.

 

My question is does changing the ISO from 160 to 320 mean exactly one stop difference?

 

Anything that is x2 push or pull is one stop, regardless if it's shutter speed or aperture.

 

Hope this helps.

 

-Ron

 

 

Creature of Habbits or the Caveman within

[stunsworth]

Ron, no it isn't. One stop slower than f4 is f5.6, not f8 (4 x 2).

[Iron Flatline]

Anything that is x2 push or pull is one stop, regardless if it's shutter speed or aperture.

</Head thumps on desk with desperate, exasperated thud>

 

Yes, I know that about shutterspeeds and apertures. But is it also true of an ISO increment?And if the increments used to be 100, 200, 400, etc, but Leica (for some reason) went with 160, 320, 640, etc, then does that mean it represents a stop as well?

[stunsworth]

Doubling or halving the ISO speed makes a change of one stop regardless of the starting value. So the following series all have a one stop difference between each value

 

100 200 400 800 1600

 

160 320 640 1280 2560

 

1 2 4 8 16

 

10 20 40 80 160

[Iron Flatline]

Thank you for the clear and simple answer. A big hug to you!

[Guest WPalank]

Sean's measurements indicated that ISO 160 was really 200 and 320 was 400 and 1250 was actually 1600 with 2500 being the equal to 3200. Any idea why Leica didn't use the actual ISO but instead selected a value below the actual? It seems to me that a company would want an accurate calibrated value rather than a marketing value, if that is what it is.

John,

Thanks, I think I do remember Sean stating that in his article (I will try to get to ReidReviews and read it later today). That being said:

 

To those people using handheld light meters, would you set the light meter value to 160 or 200 when shooting 160 ISO on camera? (Apologies if this is answered in Sean's article).

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[marknorton]

William, if I use a hand-held or spot meter, I set it to ISO 200 when the camera's on 160.

[ho_co]

Any idea why Leica didn't use the actual ISO but instead selected a value below the actual? It seems to me that a company would want an accurate calibrated value rather than a marketing value, if that is what it is.

John--

Leica's built-in meters have always been biased to give a little less exposure than some people thought best. Leica always remarked of this that "the meter is adjusted to give optimum exposure with color slide film."

 

I would guess that the M8 meter is accurately calibrated, though with a different idea of what 'accurate' means than what others may think. (Canon's meters share the same off-kilter approach according to S Reid.)

 

What is more of interest to me is the fact that Leica has chosen to drop the (standard) 1/3 stop increments:

12 -- 16 -- 20

25 -- 32 -- 40

50 -- 64 -- 80

100--125--160

200--250--320

etc

 

(Note also that Steve's post above http://www.leica-camera-user.com/digital-forum/16411-how-many-stops-160-iso-320-a.html?posted=1#post171930 mentions only parts of the three 1/3 stop ISO sequences, getting Kodachrome 10 but missing Kodachrome 25 and Kodachrome 64, for example.)

 

--HC