How do the M9 ISO setting reconcile with general exposure conventions?

[A miller]

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I am trying to learn how to determine exposure value without using a meter and I have been spending some time with the Ultimate Exposure Computer Ultimate Exposure Computer

 

According to this, the following ISO levels are full 1 stop exposure values: 100, 200, 400, 800, 1600.

 

The M9 ISO levels include 160, 200, 250, 320, 400, 500, 640, 800, 1000, 1250 and 1600,

 

Question: are each of the ISO levels contained in the M9 intended to represent a full exposure value stop, or are values between each of 100 and 200, 200 and 400, 400 and 800, and 800 and 1600 intended to represent only partial stops? So, for example, is 250 a 1/3 stop greater than 200, 320 a 2/3 stop greater than 200, etc??

 

In addition, when using the "Sunny 16" rule, where aperture is f16 and shutter speed is 125, on the M9 is the ISO 200 (as per the exposure computer contained int he link above) or 160? If the latter, it will call into question my theory that perhaps the ISO levels between 200-400; 400-800 and 800-1600 are 1/3 increments (because there are four increments between the lowest (160) and 400h.

 

Hoping these questions find the computer screens of those of you who actually understand exposure compensation!

 

Thank you!

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[pico]

The M9 ISO levels include 160, 200, 250, 320, 400, 500, 640, 800, 1000, 1250 and 1600,

 

Doubling the ISO is the equivalent of one full F-Stop smaller (larger number). 100, 200 for example is the same as stopping down one full stop. So is 320, 640, and so-on.

 

In addition, when using the "Sunny 16" rule, where aperture is f16 and shutter speed is 125, on the M9 is the ISO 200 (as per the exposure computer contained int he link above) or 160?

 

ISO 125

 

If the ISO is 200, and F-Stop is F/16, then the shutter speed would be 1/200th. ISO 400 would be 1/400th, or rounded up to 1/500th if you wish.It won't make much difference.

 

That chart is far more confusing than necessary. The ratio is very simple. You will be able to do it all in your head. I would not worry about 1/3 stops for now. Stick to whole F-Stops and be happy.

Edited October 22, 2012 by pico

[Jean-Michel]

I am trying to learn how to determine exposure value without using a meter and I have been spending some time with the Ultimate Exposure Computer Ultimate Exposure Computer

 

According to this, the following ISO levels are full 1 stop exposure values: 100, 200, 400, 800, 1600.

 

The M9 ISO levels include 160, 200, 250, 320, 400, 500, 640, 800, 1000, 1250 and 1600,

 

Question: are each of the ISO levels contained in the M9 intended to represent a full exposure value stop, or are values between each of 100 and 200, 200 and 400, 400 and 800, and 800 and 1600 intended to represent only partial stops? So, for example, is 250 a 1/3 stop greater than 200, 320 a 2/3 stop greater than 200, etc??

 

In addition, when using the "Sunny 16" rule, where aperture is f16 and shutter speed is 125, on the M9 is the ISO 200 (as per the exposure computer contained int he link above) or 160? If the latter, it will call into question my theory that perhaps the ISO levels between 200-400; 400-800 and 800-1600 are 1/3 increments (because there are four increments between the lowest (160) and 400h.

 

Hoping these questions find the computer screens of those of you who actually understand exposure compensation!

 

Thank you!

 

 

Hi,

ISO is an arithmetical scale, like the old ASA. A doubling of the ISO number equals a doubling of 'speed' or 'sensitivity'. The one third-stop intermediary 'speed' need to be figured out for each increment of one-third stop, so very roughly 100 -- 133 -- 166 -- 200; then 200 -- 266 -- 332 -- 400.

The no longer used DIN is a geometric scale and far better suited for photography: an increase of 3 in DIN always indicated a full stop increase, and an increase of 1 DIN always indicated an increase if one-third stop. ISO 100 was about DIN 21; ISO 200: DIN 24...ISO 12,500: DIN 42.

 

The ISO numbers, especially the intermediate one, listed in camera menus are probably more a case of convenience than accurate number, the sensitivity is probably accurately set in one-third stops regardless of whether or not the the ISO number is mathematically accurate.

 

The "sunny 16, or 11 in some 'rules'" formula is" for sunny exposure set the aperture at f/16 (or f/11) and set the shutter speed at 1/ISO. So if you set the ISO to 160, you would , the aperture to f/16 and the shutter speed to 1/160, thus the click between 1/125 and 1/250. That formula worked fine in the days of no in-camera light meters and people without hand-held meters. It is good to know it, but really zero need to use it. Better to spend time learning how to use your in-camera meter to meter properly.

 

Jean-Michel

[01af]

ISO is an arithmetical scale, like the old ASA.

No, it's not. Instead, it's an arithmetrical and geometrical scale both. For example, the M9's base sensitivity corresponds to ISO 160/23°. The ubiquituous 'ISO 160' is a common but false abbreviation which actually means ASA 160.

 

 

The one third-stop intermediary 'speed' need to be figured out for each increment of one-third stop, so very roughly 100 -- 133 -- 166 -- 200; then 200 -- 266 -- 332 -- 400.

Actually, the intermediate ASA values for 1/3 stop increments are: ... 64 - 80 - 100 - 125 - 160 - 200 - 250 - 320 - 400 - 500 - 640 ... and so on. Just as every camera has it.

 

 

The no longer used DIN is a geometric scale and far better suited for photography ...

Whether the DIN scale suits photography better than ASA depends on the particular aspect of photography you are looking at. That's why ISO forges both ASA and DIN into a combined value.

 

 

The ISO numbers, especially the intermediate one, listed in camera menus are probably more a case of convenience than accurate numbers ...

They are pretty accurate and only slightly rounded. For example, ASA 125 actually is 125.99 and ASA 160 really is 158.74. By the way, also most shutter speeds and aperture numbers are rounded.

[giordano]

No, it's not. Instead, it's an arithmetrical and geometrical scale both. For example, the M9's base sensitivity corresponds to ISO 160/23°. The ubiquituous 'ISO 160' is a common but false abbreviation which actually means ASA 160.

 

No: 'ISO 160', 'ISO 160/23°' and 'ISO 23°' all mean exactly the same thing and AFAIR are all countenanced by the relevant standards. 'ASA 160' usually means the same thing in practice but should be consigned to history.

[peterbengtson]

ASA = American Standards Association and ISO = International Standards Organization, another name for the International Organization for Standardization. ISO expanded the ASA ratings to an international standard about 25 years ago. Before ASA we used Weston ratings published by the Weston meter company. These were generally one step lower that The ASA was when it was introduced, ASA 125 = Weston 100.

[Bill W]

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Growing up learning the basics of photography and exposure values is almost lost today with the camera as a computer. A lot of folks don't learn the basics anymore. Keep reading and learning. I get lost thes days in pixels/inch.

[pgk]

Try 'film speed' in google and view the wiki data if you want a great deal more info than is useful.

[johnbuckley]

This is very interesting and informative. I believe I recall that when the M8* came out, Sean Reid wrote that it really had a base of ISO 200, by his measurement, even though its stated base was 160. Does anyone know whether the M9 ISO base of 160 is a 'true' 160? Or is the base ISO measurable as some higher number?

 

* I believe I remember this because, as a Fuji Velvia user with my M7, I was disappointed to be starting at a higher scale. I got excited about the idea that the M9 has a Push 80 level -- until I understood that you are reducing the dynamic range a pretty large amount by utilizing it.

[Jean-Michel]

Hi,

Without going into any arguments, I just want to note that in my earlier post I meant to say that the DIN scale is logarithmic, not geometrical.

 

The log (base 10) of 2 is .3

 

Jean-Michel

[tomlianza]

The concept of ISO speed for digital cameras is fundamentally an anachronism. As digital photography was evolving, there was a strong desire within the professional community to maintain a comfortable relationship with the entrenched ISO exposure concepts. ISO has two very different mechanisms to compute the "native" speed of a camera and a manufacturer may choose one or the other or none of the above. One should remember that there were also multiple mechanisms for determining the ISO speed of film: one for transparency and another for negative. There are also multiple mechanisms for determining the light meter constants used in handheld meters and cameras. The reason for this "softness" in the specifications is based upon photographic preferences. Don't get hung up on the math because it is essentially meaningless in digital photography. Setting an ISO speed is simply setting a gain in the analog pipeline. You can rely upon the fact that doubling the ISO is a full photographic stop, but the "absolute" exposure is really a function of the manufacturer's bias in their calibration procedure. Take pictures, forget the math.

[tobey bilek]

Put ASA in the bin.

[roydonian]

No thanks, I'll keep using it. For all practical purposes, ASA and ISO ratings are interchangeable, and ASA is what I grew up with. Same goes for focal lengths in centimetres - for some mysterious reason my brain still thinks of my 90 mm lenses as being 9 cm and my 135 mm lenses as being 13.5 cm, uses 50 mm and 5 cm interchangeably , but has no problem in regarding the wide-angles as being in mm.

 

Best regards,

 

Doug

Edited October 23, 2012 by roydonian

[earleygallery]

Put ASA in the bin.

 

DIN

[UliWer]

Was the "DIN - System" ever used in Britain?

 

I remember when I was in the UK for the first time in the early seventies, and I wanted to buy a film, but they only had the ASA marks on them, which I didn't know. There was nobody whom I could ask and nowhere (pre-internet times...) I could look up the DIN/ASA comparison. So I just guessed and took the most frequent film hoping it had 18 DIN, which was right.

[giordano]

Was the "DIN - System" ever used in Britain?

 

Not to any extent. There used to be a BSI (British Standards Institute) system which was also in degrees; a film of 18 DIN was about 28° BS. I was learning a lot about photography in the early 70s so knew about DIN and other film speed systems from my textbooks, but BS speeds seemed to be extinct and I never used anything except ASA (or Weston speeds on my mother's old Weston Master II). I have a feeling that the pro film I used gave both ASA and DIN speeds, but can't swear to it.