Is there a difference between digital ASA/ISO versus analog?

[Heimdall]

Whilst trying to make photos with long exposure times i noticed something; my digital photos get considerably lighter (overexposed) compared to my analog-camera (not overexposed) Using the same settings of course.
E.g. taking photos of fireworks; my analog camera handles very long exposure times (even 10 minutes) But the digital one gives a very light sky, and some streetlights ... well..looks like small suns.
I want to make daylight photos with long exsposure times, but is that possible?
and is there a difference between digital ASA/ISO versus analog?

Heimdall

(Canon A70)

[CyberDyneSystems]

The ISO values are "suposed" to be the same as film.. but seeing as how different films can have a ccertain amount of variation.. I'm SURE that different digitals will have variation as well...

[Heimdall]

Thanks!
I havent done any hard research on this, but it seems to me that the difference is more than just a slight one.

Its like there is a LOT of noise when using long exposure times also, but maybe thoose two are interconnected somehow...? (Noise and overexposure that is!)

Well, .. maybe I can add a filter or something to counter this increased "digital-light-sensitivity"

Heimdall

[stopbath]

Thanks!
I havent done any hard research on this, but it seems to me that the difference is more than just a slight one.

Its like there is a LOT of noise when using long exposure times also, but maybe thoose two are interconnected somehow...? (Noise and overexposure that is!)

Well, .. maybe I can add a filter or something to counter this increased "digital-light-sensitivity"

Heimdall
Actually, long exposures with film will normally under expose.

This is due to the film, performing less well during long exposures. Each film is different, but generally you could expect something like a quarter second additional for a second exposure, and maybe even double the exposure needed for something like 10 seconds... (check the films recommendations or do your own testing.) This is known as the reciprocity failure of film...

Digital on the otherhand is straight linear. No over exposure is needed to compensate for the long exposure.

Perhaps what was happening is that a 10 second exposure on film, really metered at 5 seconds. Thus your digital exposure at 10 seconds is double that which was required.

The more noise in the higher ISO images: It seems that the high ISO ratings are just a multipication of the sensor readings. This would also multiply the noise. Also, smaller CCD exhibit more noise than larger CCD. (Maybe they heat up faster which also raises noise levels...)

You can easily take 15 second exposured during the day. Take a reading, then add the required neutral density filters required for however many stops you need to go... Use cloud cover, evening sun ISO, Fstop and other effects to help lower the amount of filters required.