LeicaBraz Posted November 8, 2010 Share #1 Posted November 8, 2010 Advertisement (gone after registration) I know what happens mechanically in the camera when I adjust the aperture and when I adjust the speed. But I don't know what happens (mechanically) when I adjust the ISO value in a film camera. So, what happens? Tks Link to post Share on other sites More sharing options...
Advertisement Posted November 8, 2010 Posted November 8, 2010 Hi LeicaBraz, Take a look here Basic ISO question. I'm sure you'll find what you were looking for!
jaapv Posted November 8, 2010 Share #2 Posted November 8, 2010 You adjust the exposure meter to give the correct data for that ISO value. Basically a rheostat. Link to post Share on other sites More sharing options...
mjh Posted November 8, 2010 Share #3 Posted November 8, 2010 So, what happens? Mechanically? Nothing. As Jaap has said, the ISO value tells the exposure meter how much light will be necessary for an optimal exposure – the higher the ISO number the less light is required. Since the sensor has a fixed native sensitivity, the camera needs to compensate for any deviations from this native sensitivity. For example, if the sensor’s native sensitivity is equivalent to ISO 100 but the selected ISO is 400, the electric charges accumulated in each sensor pixel during the exposure will be 1/4th the amount accumulated when you had been exposing according to ISO 100. The signal read out from the sensor then needs to be amplified by a factor of 4 to compensate. That’s for digital; with an analog camera you compensate by choosing film with the desired ISO rating. Link to post Share on other sites More sharing options...
LeicaBraz Posted November 8, 2010 Author Share #4 Posted November 8, 2010 Very clear, thanks (guess I should have known that). Link to post Share on other sites More sharing options...
wparsonsgisnet Posted November 8, 2010 Share #5 Posted November 8, 2010 Well, I didn't. I was under the impression that at higher iso values the charge across the sensor was increased. Link to post Share on other sites More sharing options...
griffster Posted November 9, 2010 Share #6 Posted November 9, 2010 Well, I didn't. I was under the impression that at higher iso values the charge across the sensor was increased. He's asking about a film camera, dear. Oh how quick we forget... Link to post Share on other sites More sharing options...
jaapv Posted November 9, 2010 Share #7 Posted November 9, 2010 Advertisement (gone after registration) Well, I didn't. I was under the impression that at higher iso values the charge across the sensor was increased. It is called changing film, Bill Link to post Share on other sites More sharing options...
earleygallery Posted November 9, 2010 Share #8 Posted November 9, 2010 Just to add, if the camera doesn't have a meter, but has an ISO dial, it's there just as a reminder and does nothing at all! Link to post Share on other sites More sharing options...
luigi bertolotti Posted November 9, 2010 Share #9 Posted November 9, 2010 Just to add, if the camera doesn't have a meter, but has an ISO dial, it's there just as a reminder and does nothing at all! ..well said... and a final consideration to be pedantic .. with a meter, is anyway a rheostat be it a selenium meter (voltage proportional to light) or a CdS meter (resistance proportional to light)... Link to post Share on other sites More sharing options...
lars_bergquist Posted November 9, 2010 Share #10 Posted November 9, 2010 ..well said... and a final consideration to be pedantic .. with a meter, is anyway a rheostat be it a selenium meter (voltage proportional to light) or a CdS meter (resistance proportional to light)... ... while with a silicon cell meter, it is a gain control. The current from the selenium cell can be fed directly to a microammeter, but that from the Si cell must be amplified. The battery powers the amplifier. While the battery with a CdS meter actually serves as a current reference -- hence the mercury cells which produced a very constant current until they died pretty suddenly. This is why alkaline cells didn't work very well. In a M8 or M9, the ISO adjustment adjusts two gain controls -- one for the amplification of the meter current, as usual, and one for the amplification of the image signal from the sensor. The very pedantic old man from the Selenium Age Link to post Share on other sites More sharing options...
ho_co Posted November 9, 2010 Share #11 Posted November 9, 2010 What ever happened to "You push the button, we do the rest"? Link to post Share on other sites More sharing options...
Michael Geschlecht Posted November 9, 2010 Share #12 Posted November 9, 2010 Hello LeicaBraz, What happens mechanically w/ a manual camera is: As the ISO goes up you turn the shutter speed faster and/or make the lens opening smaller. When the ISO goes down you set the shutter speed slower and/or make the lens opening larger. W/ an automatic camera the camera does the above for you in one of a number of permutations dependent on degree & set-ability of said functions. Best Regards, Michael Link to post Share on other sites More sharing options...
wparsonsgisnet Posted November 9, 2010 Share #13 Posted November 9, 2010 It is called changing film, Bill Gosh ... I'd have to change my mind. They say that a little knowledge is a dangerous thing. It would appear so; I just didn't read far enough to gather adequate knowledge. Now, it's time to ask what film is, as I went cold turkey more than 3 years ago. So, to continue with the inadvertent hijack of the thread, is it true that at a higher iso -- in a damn digital camera -- that more current is fed to the sensor? I see that Lars has answered this. Am I correct in reading that the additional current is applied post sensor? And, yeah, I did know that I couldn't feed any voltage to the film in my M4/6, just money, just like with all the Leica products. It's a good thing they last forever. Link to post Share on other sites More sharing options...
giordano Posted November 11, 2010 Share #14 Posted November 11, 2010 While the battery with a CdS meter actually serves as a current reference -- hence the mercury cells which produced a very constant current until they died pretty suddenly. This is why alkaline cells didn't work very well. Not quite pedantic enough, Lars:D The mercury cells produced an almost constant voltage throughout their life. The current naturally varied with the load, i.e. with the resistance of the CdS cell and the rest of the circuit. Link to post Share on other sites More sharing options...
lars_bergquist Posted November 11, 2010 Share #15 Posted November 11, 2010 Gosh ... I'd have to change my mind. They say that a little knowledge is a dangerous thing. It would appear so; I just didn't read far enough to gather adequate knowledge. Now, it's time to ask what film is, as I went cold turkey more than 3 years ago. So, to continue with the inadvertent hijack of the thread, is it true that at a higher iso -- in a damn digital camera -- that more current is fed to the sensor? No Sir. If you expose at a higher ISO than the sensors basic sensitivity (160), the correspondingly weaker signal from the sensor -- not simply the current -- is amplified so that it reaches full strength. I see that Lars has answered this. Am I correct in reading that the additional current is applied post sensor? Yes, the amplifier is not built into the sensor itself, a.f.a.i.k. The old man, cautiously groping his way in the brave new digiworld Link to post Share on other sites More sharing options...
adli Posted November 11, 2010 Share #16 Posted November 11, 2010 What ever happened to "You push the button, we do the rest"? That was not Leica :-) Actually the slogan dates back to 1897, when some guy called Eastman used it to promote roll film cameras. Roll film was invented a few years earlier and industrialized by Eastmans company (Which today are selling parts to Leica) Link to post Share on other sites More sharing options...
PasMichiel Posted November 11, 2010 Share #17 Posted November 11, 2010 That was not Leica :-) Actually the slogan dates back to 1897, when some guy called Eastman used it to promote roll film cameras. Roll film was invented a few years earlier and industrialized by Eastmans company (Which today are selling parts to Leica) It's called Lumix Link to post Share on other sites More sharing options...
adli Posted November 11, 2010 Share #18 Posted November 11, 2010 Actually, I was thinking about the film substitute in the Leica M series. Link to post Share on other sites More sharing options...
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