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08-29-2018, 02:48 PM - 1 Like   #31
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QuoteOriginally posted by normhead Quote
If the image was in any way superior to increasing the ISO that would make sense. But with out increasing the ISO most of the image will be blacked out even if you can reuse it. So you own't actually know if you have the image you want until you get into post processing. Given that it take bracketing to get the exposure you want. how will you even know if you're n the ball park with your exposure?
That would be possible if there was some way of displaying the 100 ISO image as if it was shot at 400 ISO. Wait, setting your camera to 400 ISO does that for you. What you've essentially done setting at 100 ISO and underexposing, is eliminated the value of chipping... and for what?

Sure you can do it, but why?

Is this whole theory designed to make your life more complicated?
You're still going to lose the dynamic range, using 100 ISO or 400 ISO, one stop ISO makes very little difference.
Or by was it designed by film aficionados who hate chimping, and like waiting until post to see what the image looks like? There are drawbacks to always shooting base ISO and under exposing that are being conveniently ignored. You can. but why?

I can also bang my head against wall whenever i want, but i don't do that either.

The only possible way I'd give up the functionality of using higher ISO would be if it produced a superior result. That has yet to be demonstrated to my satisfaction. If you're going to give up accurate previews, I want something in exchange for that.
Underexposing at low ISO gives you one definite benefit: it increases the amount that you can recover the highlights.

If you have a camera with the accelerator doing noise reduction, lowering the ISO is the only way to turn that off. It's up to you if you consider that a good thing or a bad thing.

Maybe what you want is not to lower the ISO all the way to base, but just to underexpose by a stop or two. The preview will still be usable.

08-29-2018, 05:04 PM   #32
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QuoteOriginally posted by Mark Ransom Quote
Maybe what you want is not to lower the ISO all the way to base, but just to underexpose by a stop or two. The preview will still be usable.
Or as some would say, expose to the right. That being said, we are only talking about situations where their is more EV in the environment than the sensor can cover. If you have a 15 EV camera and an 13 EV scene, Many scenes have more DR than actually needed, so even this is a less than common thing to have to deal with. I'm not sure for a scene that doesn't fink the histogram, shooting at less than say 800 ISO makes an difference at all. Cloudy low contrast days, I'm not sure that even 3200 ISO hurts you with a K-1.

Last edited by normhead; 08-29-2018 at 05:24 PM.
08-29-2018, 06:02 PM   #33
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QuoteOriginally posted by normhead Quote
Or as some would say, expose to the right. That being said, we are only talking about situations where their is more EV in the environment than the sensor can cover. If you have a 15 EV camera and an 13 EV scene, Many scenes have more DR than actually needed, so even this is a less than common thing to have to deal with. I'm not sure for a scene that doesn't fink the histogram, shooting at less than say 800 ISO makes an difference at all. Cloudy low contrast days, I'm not sure that even 3200 ISO hurts you with a K-1.
No, specifically not expose to the right. Suppose that to expose to the right, you determined that you needed F/8, 1/250s, and ISO 1600. Instead you would shoot F/8, 1/250s, ISO 400. The JPEG would be dark but recognizable, and the RAW could be pulled up in post processing. If for example there were some bright clouds in the scene, they would have gotten blown out at ISO 1600 but fully preserved at ISO 400. If your camera is ISO invariant the resulting noise in the picture would be the same under both scenarios.
08-29-2018, 06:31 PM   #34
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QuoteOriginally posted by Mark Ransom Quote
No, specifically not expose to the right. Suppose that to expose to the right, you determined that you needed F/8, 1/250s, and ISO 1600. Instead you would shoot F/8, 1/250s, ISO 400. The JPEG would be dark but recognizable, and the RAW could be pulled up in post processing. If for example there were some bright clouds in the scene, they would have gotten blown out at ISO 1600 but fully preserved at ISO 400. If your camera is ISO invariant the resulting noise in the picture would be the same under both scenarios.
By expose to the right, I mean I'm seeing my exposure so the brightest part of my histogram is close to or touching the right edge of the histogram. I may have to go to minus 3 EV to do that. and I'm going to use 100 ISO.

The first rule, use 100 ISO unless needed for shutter speed, so I'm not even in this position.

Try this some time, see if ISO 400 -2 EV, remember by going to -2 EV you clipped -2 EV off the bottom, you should have the same DR and coverage, but, exact numbers are unpredictable. Remember, you have to end up with similar images. You may have to adjust curves for the 1600 ISO image, but they should be the same. The same amount of light will hit the sensor.

OK, that's as far as I go without images, when we look at the same scenario and come to different conclusions about what will happen, there has to be examples. No other way to settle it.

08-29-2018, 09:51 PM   #35
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QuoteOriginally posted by normhead Quote
Ya, people should really just say that. There's really nothing terribly complicated about it. K20D to K-5 12 EV to 14 EV, two more stops of shadow detail.
I think the term is used because ISO-invariant historically came from the time period when cameras were mostly "ISO-variant", which was case 1 I mentioned above. It isn't really a big topic of discussion anymore, but when people refer to it, there's already a term to use, but a term that linguistically has less obvious relevance today. (Though I believe the most recent Canon 6D update was heavily panned because it was pretty much not ISO-invariant.)
08-30-2018, 05:39 AM   #36
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My *istDS can operate at an ISO of 200 at the lowest

My K-1 goes down to 100.

My K-5 has tricks that nominally allow it to operate at, or mimic, a base ISO of 80.

What accounts for the difference? (You would have thought that early CCD sensors would have problems going high, not low, and why the K-1 can't do something the K-5 can is perplexing to me.)

What started this is that when using the AF080C ringflash on the K-5, even at ISO 80 and f/22, I was sometimes blowing highlights (and midtones, and some shadows) at very close range at f/22, and my ND filters being 52mm would have caused issues with mounting the ringflash, necessitating a 49-52mm and a 52-49mm on either side of the filter, and possibly hampered visualisation of fine detail when focusing and composing in the medical photography context. Being able to dial down to ISO 50 or even 25 would have been wonderful and given me great flexibility.
08-30-2018, 05:49 AM - 2 Likes   #37
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QuoteOriginally posted by pathdoc Quote
My *istDS can operate at an ISO of 200 at the lowest

My K-1 goes down to 100.

My K-5 has tricks that nominally allow it to operate at, or mimic, a base ISO of 80.

What accounts for the difference? (You would have thought that early CCD sensors would have problems going high, not low, and why the K-1 can't do something the K-5 can is perplexing to me.)

What started this is that when using the AF080C ringflash on the K-5, even at ISO 80 and f/22, I was sometimes blowing highlights (and midtones, and some shadows) at very close range at f/22, and my ND filters being 52mm would have caused issues with mounting the ringflash, necessitating a 49-52mm and a 52-49mm on either side of the filter, and possibly hampered visualisation of fine detail when focusing and composing in the medical photography context. Being able to dial down to ISO 50 or even 25 would have been wonderful and given me great flexibility.
The two biggest differences are:

1) the well depth which is the maximum number of electrons that the pixel can store. The more electrons the pixel can hold, the LOWER the base ISO.

2) the quantum efficiency which is the average number of electrons generated per incoming photon. The more efficient the sensor is at collecting photons and converting them to electrons, the HIGHER the base ISO.

Last edited by photoptimist; 08-30-2018 at 08:02 AM. Reason: typos
08-30-2018, 12:22 PM   #38
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There's not a very compelling reason to have a lower ISO, just for the sake of a lower ISO. If the base ISO was 400 or 800, but you had the same quality of today's ISO 100, that would be great.

08-30-2018, 01:22 PM   #39
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QuoteOriginally posted by leekil Quote
There's not a very compelling reason to have a lower ISO, just for the sake of a lower ISO. If the base ISO was 400 or 800, but you had the same quality of today's ISO 100, that would be great.
Sometimes if your aperture and shutter speed are constrained by other considerations, it would be nice to have a very low ISO. You can usually use a ND filter, but it's not as convenient.
08-31-2018, 03:05 PM   #40
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I would like to see ISO 50 or 25 also, just for allowing wide open F1.4 shots in any light. The KP does it well with ES up to 1/24000, but MS is better without possible distorsion.
08-31-2018, 08:24 PM   #41
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QuoteOriginally posted by photoptimist Quote
The easiest way to have a really low base ISO is to lower the quantum efficiency of the sensor -- if the photons don't get converted to electrons, the sensitivity is really low. Of course, then the low-light performance suffers.

If you want a sensor with modern quantum efficiency (for good low-light performance) but don't want it to saturate in high light levels, then you need to increase the electrical capacitance of the pixels. That implies building a high surface-area capacitor into each tiny surface-area silicon pixel. For example, one could imagine fabricating tiny tantalum or super-capacitor elements on top of each pixel (to store al the extra electrons generated by longer exposures in bright light) and then flipping the sensor chip for back-side illumination.

P.S. Film has really low quantum efficiency -- about 1/25th that of silicon sensors -- which is why it has such low base ISO and such humongous grain for high ISO films.
That also explains why film takes over-exposure better than digital.
08-31-2018, 09:34 PM - 1 Like   #42
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QuoteOriginally posted by timw4mail Quote
That also explains why film takes over-exposure better than digital.
Does it, though? The would imply that a older, less efficient digital sensor would take over-exposure better too, but I don't think that's really how that works.
09-01-2018, 01:47 AM - 1 Like   #43
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QuoteOriginally posted by normhead Quote
OK, that's as far as I go without images, when we look at the same scenario and come to different conclusions about what will happen, there has to be examples. No other way to settle it.
Well I OPed this thread which shows some examples --

Iso invariance - PentaxForums.com


And pasted this example elsewhere -

and
Is that what you mean?
As for being complicated once you get your head around it utilising Iso invariance simplifies your photography - there is only two variable inputs to your sensor - shutter and aperture . So set to Raw, choose the widest aperture and slowest shutter that are appropriate for your environment and check you are not clipping the highlights. You are now at best practice - how simple can that be!!
Oh and the Iso invariance principle and ETTR are totally compatible because ETTR is only valid at base Iso.
09-03-2018, 07:19 AM - 2 Likes   #44
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QuoteOriginally posted by timw4mail Quote
That also explains why film takes over-exposure better than digital.
Actually, the reason film handles over exposure is because of the statistical nature of the binary grains of silver halide. That is, each grain either develops to black if by statistical chance it was hit with photons or develops clear if it was not.

Imagine a piece of film with 100 grains of silver halide in it.

Now expose the film with just the faintest amount of light needed to get one grain in 100 to develop to black. Now there's 1 black grain , 99 clear grains.

Next, double the exposure so that 1 of the remaining 99 unexposed grains develops to black. Now there are 2 black grains , 98 clear grains.

Next, double the exposure a second time so that another 2 of the remaining 98 unexposed grains develops to black. Now there are 4 black grains, 96 clear grains.

Next, double the exposure a third time so that another 4 of the remaining 96 unexposed grains develops to black. Now there are 8 black grains, 92 clear grains.

Imagine increasing the exposure until about 50 of the 100 grains are developing to black and 50 remaining clear grains.

Next, what happens if you double the exposure again? What are the chances that the 50 remaining unexposed grains become black? The added light only ensures that each unexposed grain has another 50% chance of turning black so the result is that doubling the exposure only brings the black level from 50% black to 75% black. There are still 25 unexposed grains.

What happens if you double the exposure again to 4X the light needed to create a 50% black negative? Each of the remaining 25 unexposed grains has a 75% chance of turning black. Thus another doubling of the exposure only brings the black level from 75% black to about 94% black.

The point is that it takes exponentially more and more light to ensure that the few remaining unexposed grains become black. That implies that even the brightest highlights have some gradation in tonality.


In contrast, a silicon sensor is almost perfectly linear. Doubling the exposure when the sensor is already at 50% exposure level results in a 100% exposure level and saturation.


Note: I've greatly simplified the math, physics, and the chemistry for this. But the point remains that film has a nonlinear response to light which gives it extra latitude for over-exposure. Silicon sensors are linear but saturate which makes them unforgiving to over-exposure.
09-03-2018, 07:38 AM   #45
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QuoteOriginally posted by GUB Quote
Well I OPed this thread which shows some examples --

Iso invariance - PentaxForums.com


And pasted this example elsewhere -

and
Is that what you mean?
As for being complicated once you get your head around it utilising Iso invariance simplifies your photography - there is only two variable inputs to your sensor - shutter and aperture . So set to Raw, choose the widest aperture and slowest shutter that are appropriate for your environment and check you are not clipping the highlights. You are now at best practice - how simple can that be!!
Oh and the Iso invariance principle and ETTR are totally compatible because ETTR is only valid at base Iso.
Looking at the example images.... I don't really care. Shooting at base ISO is best practice. That is what I see in those images. I've been saying that for a long time before someone made up ISO invariance. Funny how someone takes a simple concept, and turns it into some thing complicated.

The explanation, base ISO uses more light to form the image. More light means less noise.. No need for a term like ISO invariance to explain it. I fail to see the advantage of getting all complicated.

ALlthe images are noisy, so the claim is that one bad image is better than another bad image. I'm not sure I care based on the examples provided. It would have been better if they were de-noised and then compared.

Last edited by normhead; 09-03-2018 at 07:46 AM.
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