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06-02-2015, 02:26 PM   #16
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QuoteOriginally posted by K David Quote
With digital, an ISO image is being exposed on an ISO 200 (in Pentax) sensor and that means it's being underexposed two stops and the camera is using computing power to guess at what colors and details should look like.
I thought it was using hardware amplification, not software? (Assuming we're limiting ourselves to the full stops, 100-200-400-etc.)

06-02-2015, 03:13 PM   #17
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QuoteOriginally posted by Scintilla Quote
I thought it was using hardware amplification, not software? (Assuming we're limiting ourselves to the full stops, 100-200-400-etc.)
I'm not sure how the hardware would be amplified. But no, ISO compensation uses what light is received and extrapolates image data from that. It's sort of like in-camera push processing.
06-02-2015, 04:00 PM   #18
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I have a roll of ISO 50 Velvia film loaded in my 645 right now.
I almost always shoot ISO 100 if I'm shooting landscapes with a tripod but handheld I'd do like Norm says and use 400.
06-02-2015, 04:08 PM   #19
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QuoteOriginally posted by K David Quote
I'm not sure how the hardware would be amplified. But no, ISO compensation uses what light is received and extrapolates image data from that. It's sort of like in-camera push processing.
I was thinking of amplification in the analog domain, before the analog signal hits the ADC. Was I mistaken about that step happening?

06-02-2015, 04:28 PM   #20
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I think the better question (which I have and has not been addressed) is what iso can be used that avoids in-camera amplification (100 or 200)? I would think that would produce the minimum noise, since it is amplification that brings out noise (assuming no shadow-correction option, etc.). I'm shooting with a K-50. If I have enough light to shoot at my desired aperture and enough shutter speed to avoid motion-blur and camera shake, such that I don't need amplification, then I'd just assume not have it!
06-02-2015, 04:34 PM   #21
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Amplification is a big problem for noise/DR. Use the lowest appropriate ISO, so that you don't have to add brightness in post. The in-camera highlight correction amplifies things, but in my experience it is not too bad.

Oh, and also, if you shoot raw, there is the Expose to the right technique (ETTR), where you basically overexpose photos as much as you can without blowing anything out. Then you darken them in post. Its an interesting theory, might work, might be overhyped.

This is why I say the best rule is not to worry about it too much, but do keep in mind that a) lower ISO=better, b) adding brightness in post will amplify noise (brightness, exposure, levels, whatever its called. other settings might amplify noise as well, for example sharpening)
06-02-2015, 04:59 PM   #22
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QuoteOriginally posted by Newtophotos Quote
I once read an article that ISO 200 was the lowest sensitivity available in film
I would guess that the person who wrote the article was born sometime after the first space shuttle flight.

Of course, I can remember when the slowest, commonly available, was Panatomic-X at ASA 32 and Kodachrome ASA 25. (Yes, ASA, not ISO).

Now where did I put that bottle of Geritol...........


Last edited by Parallax; 06-02-2015 at 05:15 PM.
06-02-2015, 05:52 PM   #23
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QuoteOriginally posted by Parallax Quote
Yes, ASA, not ISO
There are Forum members who were using film when it was rated in DIN.

I'd be curious to know if anyone remembers some of the other older rating systems like Weston, BSI, or GOST. (There are probably some residents of the former Soviet Block here who used GOST.)

---------- Post added 06-02-15 at 05:53 PM ----------

QuoteOriginally posted by Scintilla Quote
Was I mistaken about that step happening?
Answering as not a DSLR engineer, I've never heard of signal amplification as a method. I'm guess that would mean either boosting the power into the sensor or running it through a booster afterward to increase the signal. I suppose that could have benefits for signal-to-noise ratio. So, maybe? I have always heard of ISO increases as being a software solution, but that doesn't mean that I'm right.
06-02-2015, 06:05 PM   #24
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ASA and DIN were both in use at the same time, prior to ISO. ASA in the U.S. and DIN in Europe, but DIN has been around about 9 years longer than ASA.
06-02-2015, 06:34 PM   #25
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QuoteOriginally posted by Newtophotos Quote
I once read an article that ISO 200 was the lowest sensitivity available in film and therefore ISO 100 in a digital camera doesn't mean anything. Is this true or is ISO 100 50% less sensitive then ISO 200 in a current Pentax dslr? If so then ISO 125 or 160 is also real and less sensitive than ISO 200.
Film went way down to ISO 25 at least when I shot film starting int he 1980's

As for digital, on my *istD , I ran a test and found no appreciable difference between ISO 200 and 400. So I shot 400 unless it was really really bright.

Try for yourself and decide where you want to shoot. On my K5 I use auto ISO with the upper limit set to 5000
06-02-2015, 09:50 PM   #26
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In film, slower film does tend to be contrastier. Faster black and white films have two layers, one for highlights and the other for shadow detail. That is why tri-X and HP5 (ISO 400) are famous for tonality. The old Agfapan 25, Kodak Panatomic-X and current Ilford Pan-F and anything slow are one layer. Ansel Adams would tell you to overexpose and underdevelop to increase tonality, but you still will get more dynamic range with the higher speed films. With Digital, you amplify the existing information to increase the ISO. The shadow detail goes away when you "underexpose" and amplify the rest of the information to increase the effective ISO, which causes less dynamic range. Imaging sensors have a "native" ISO. If you go below the native ISO you don't gain much.
06-03-2015, 05:51 AM   #27
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Neither am I, but I've played with software

QuoteOriginally posted by K David Quote
. . . Answering as not a DSLR engineer, I've never heard of signal amplification as a method. I'm guess that would mean either boosting the power into the sensor or running it through a booster afterward to increase the signal. I suppose that could have benefits for signal-to-noise ratio. So, maybe? I have always heard of ISO increases as being a software solution, but that doesn't mean that I'm right.
Well, my k200d claims a 12-bit-per-channel sensor with 12-bit-per-channel output format (RAW). If the ISO setting in the camera just changes bit-shifting in software, that should mean that I could always shoot ISO 100 and bring up exposure in post-processing (since all 12 bits are written for each channel). However, the results are not the same, so I'd guess there's some sort of signal amp in there.


Don't forget that the dynamic range would drop off at the same rate as you brought up the highlights if the camera didn't have an analog amp before the ADC.
06-11-2015, 01:30 PM   #28
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How do I get the legendary 80 iso on the k-5? Mine seems only 100.
06-12-2015, 08:41 PM   #29
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Set Expanded Sensitivity to "On"

Menu Item C - 1 - 3
06-13-2015, 05:51 AM   #30
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Kodachrome 25 was one awesome film for detail. Shot in medium or large format cameras rendered fantastic detail. I used a few rolls of 3200 ASA Ektachrome to shoot the stars once in awhile. With film that fast you have to use it quickly after you get it as it tends to fog over time. I always stored mine in a freezer.
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