ISO on a continuum?
Dec 13, 2014 22:51:10 #
I understand the role of ISO in image taking but am curious . . . .? Is ISO and ASA on the same absolute continuum? Does the film speed of the former Kodachrome 64 as an example fall just below the ISO of 100 on my D750 (slightly slower)? Is the film speed of the old Ektachrome 400 on a par with the ISO of 400 on a DSLR? Finally, is ISO 100 the same amount of measured light for a Canon as for a Nikon?
Dec 13, 2014 23:12:45 #
Frank47 wrote:
I understand the role of ISO in image taking but am curious . . . .? Is ISO and ASA on the same absolute continuum? Does the film speed of the former Kodachrome 64 as an example fall just below the ISO of 100 on my D750 (slightly slower)? Is the film speed of the old Ektachrome 400 on a par with the ISO of 400 on a DSLR? Finally, is ISO 100 the same amount of measured light for a Canon as for a Nikon?
The answer is yes for all your questions. ASA refers to the American Standards Association, ISO refers to the International Standards Organization. The requirements are well documented in the appropriate standards.
Having said that, you might find other differences in characteristics other than light sensitivity. Like grain (or noise). However, in short the f/16 rule still applies, that is the proper exposure in direct sunlight is f/16 at a shutter speed of 1/ISO seconds (e.g. in bright sunlight, with an ISO (or ASA) of 100, your exposure should be f/16 at 1/100 second.
Dec 13, 2014 23:21:23 #
Thank you, LarryFB. I assumed so, but your reply provides an excellent example . . . . the f16 rule would work for any film camera or DSLR. By the way, I love your posted "location"!
Dec 14, 2014 00:12:34 #
Frank47 wrote:
Thank you, LarryFB. I assumed so, but your reply provides an excellent example . . . . the f16 rule would work for any film camera or DSLR. By the way, I love your posted "location"!
Your welcome. Yes, we are full time RVers and have been since 2001 when we retired. Although our actually physical address is in Texas, we spend time all over the place. I've been a photographer for about 60 years, I started digital photography essentially when I retired. I've had several digital cameras since then. However, when we volunteered for the Salton Sea Recreation Area in California, my bridge camera was not good enough so I purchased a Nikon D5200 kit from Costco. WOW, what a difference, In the past 24 months, I have taken over 10,000 photos, not all are great but at least some are.
Dec 14, 2014 01:02:40 #
Frank47 wrote:
I understand the role of ISO in image taking but am curious . . . .? Is ISO and ASA on the same absolute continuum? Does the film speed of the former Kodachrome 64 as an example fall just below the ISO of 100 on my D750 (slightly slower)? Is the film speed of the old Ektachrome 400 on a par with the ISO of 400 on a DSLR? Finally, is ISO 100 the same amount of measured light for a Canon as for a Nikon?
Frank, I'm sure there can be a variation even from camera to camera. It it's probably very small. As long as the meter is working correctly those things shouldn't mater much. I have read that there is also quite a bite of variation from lens to lens and brand to brand on f-stops, as they can be as much as 10% skewed. For example a lens of f1.4 might actually be f1.6.
Even if the ISO is accurate, one may need to tweak the ISO or the speed to bring the exposure back into line. ;-)
Also there are quite a few standards in the world all amounting to the same thing. Such as ISO, Asa, din, ansi and probably many others as well. ;-)
SS
Dec 14, 2014 01:05:00 #
Initially, ISO was intended as a combination of ASA and DIN - both values listed, separated by a slash. Up until not long ago, film boxes and canisters still came with the "ASA/DIN" combination printed on them, as you may recall. Perhaps some film is still packaged that way, I'm not sure. Meanwhile, due to lack of use of DIN for film speed, the DIN value has been unofficially dropped from ISO, so essentially ISO and ASA are now the same thing.
Dec 14, 2014 03:39:50 #
Frank47 wrote:
I understand the role of ISO in image taking but am curious . . . .? Is ISO and ASA on the same absolute continuum? Does the film speed of the former Kodachrome 64 as an example fall just below the ISO of 100 on my D750 (slightly slower)? Is the film speed of the old Ektachrome 400 on a par with the ISO of 400 on a DSLR? Finally, is ISO 100 the same amount of measured light for a Canon as for a Nikon?
For the most part, they are the same. However, the highest ASA standard was 10000; the ASA is now ANSI and no longer certifies film or sensor sensitivity. The IOS issued the highest official ISO, 12500, in 2013; anything beyond that is manufacturer/consumer extrapolation. For "official" purposes, the highest ASA/ISO identical rating in common use is 6400.
But, don't let that slow you down or give you pause. We are talking official standards here, not practical ratings of film or sensors. Beyond 6400 (i.e., 12500), the doubling of ISO sensitivity ratings is equivalent to a one stop increase in sensor capability.
Dec 14, 2014 12:10:48 #
rook2c4 wrote:
Initially, ISO was intended as a combination of ASA and DIN - both values listed, separated by a slash. Up until not long ago, film boxes and canisters still came with the "ASA/DIN" combination printed on them, as you may recall. Perhaps some film is still packaged that way, I'm not sure. Meanwhile, due to lack of use of DIN for film speed, the DIN value has been unofficially dropped from ISO, so essentially ISO and ASA are now the same thing.
I had noticed that -- the missing DIN (log number) -- on a newer box of film. I wonder do film or cameras sold in Germany lack the DIN data as well today? Though for those who purchase a vintage camera or meter with only DIN standards, especially if it has a meter, you'll have to hit the books as they used to say. :wink:
Dec 14, 2014 12:15:36 #
Mogul wrote:
For the most part, they are the same. However, th... (show quote)
The US Gov. had ASA standards for everything. My wife's bosses years ago (just prior to ANSI), a couple aerospace engineers found a ASA standard for a Dry Martini. Was there an "A" & "B" standard for it for Shaken or Stirred? :-)
Dec 14, 2014 13:58:34 #
I appreciate everyone's input. Together it provides a pretty comprehensive picture of a topic that plays such an important role. By the way, it gives me perspective once again on just how "slow" the old Kodak ASA25 films were! 📷
Dec 14, 2014 17:45:37 #
lamiaceae wrote:
The US Gov. had ASA standards for everything. My wife's bosses years ago (just prior to ANSI), a couple aerospace engineers found a ASA standard for a Dry Martini. Was there an "A" & "B" standard for it for Shaken or Stirred? :-)
BTW..
During my working time in the Government Service, I had a copy of the "MIL-SPEC" for Dry Martinis. It also had requirements for making and processing ice cubes and the proper direction to turn the sturrer and for how long.
Also FYI, I had a MIL SPEC for CONDOMS.
Dec 16, 2014 08:47:45 #
Larry, thanks for that explanation, I've thought about that a couple of times.
LarryFB wrote:
The answer is yes for all your questions. ASA refe... (show quote)
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