Exposure question

[george013]

I can. I move a slider called "Exposure Compensation".

That slider called "exposure compensation" is NOT changing your exposure. It's moving the histogram to the left or to the right without passing the extremes.

Without rereading your link yet, it's said that iso-less is using a digital amplifier in staed of an analogue amplifier. And that an analogue amplifier gives better results as a digital. And for what I understood that one reason to do that, is the nowadays better result in the dark area of the sensors. So going for the cheaper digital amplifier.
I'll reread it again.

The summary in the end of that article, practical consideration, counted for photography ffrom the early beginning.

George

[dem]

That slider called "exposure compensation" is NOT changing your exposure. It's moving the histogram to the left or to the right without passing the extremes.

It does this by multiplying exposure values by a number - the same way ISO works in digital cameras. A higher ISO means a higher degree of signal amplification.

[xpatUSA]

Ted, any of the literature that I've read seems to indicate that there is a fairly simple amplifier circuit built into each individual photo site on the sensor chip, so gain is applied at the source (photodiode output). In standard CMOS sensors these are in the top backplane layer, just below the optical elements and in the "back lit" devices they sit between the microlenses and the bottom of the optical path.

Hi Manfred,

Based on that, I must assume that the literature you've read does not include that for Foveon sensors. I should stress that, in this thread, I am only providing information on how Sigma cameras work as examples of "ISO-less" cameras, not as examples of how "standard CMOS sensors" work.

Intuitively this makes sense, as applying gain as close to the source as possible minimizes electrical noise. The downside would be that the circuit elements would have to be quite simple (non-linear?) to fit into the relatively small area. I have no idea as to how the Foveon sensor in the Sigma cameras would be built, but at a high level the electronics would have to sit in each respective colour layer?

Here's how they are built. The circuitry sits in the surface layer of the sensor, above the photodiodes, just like most other CMOS sensors. Here's a Sigma DP1 chip cross-section:



Lots of transistors per 3-layer pixel. Less real fill-factor (54% exclusive of microlens effect). More noise, for which Foveon images are well-known.

I would assume that there would be a secondary level elsewhere on the chip to voltage match the A/D input requirements

The early Sigmas use 3 separate 12-bit ADCs from Analog Devices:




http://www.analog.com/static/importe...ets/AD9235.pdf

The ADC input is preset by the value of VREF to 1V or 2V. Alternatively, an external reference voltage can be applied to an ADC input to set other ranges; I believe this is what Sigma does to match the ADC input to the Foveon chip output of 550mV (saves board space, less noise before the ADC).

[xpatUSA]

That slider called "exposure compensation" is NOT changing your exposure. It's moving the histogram to the left or to the right without passing the extremes.

George

I was joking, George. That's what the at the end of sentence means.

So, no need to SHOUT at me . . .

[george013]

I was joking, George. That's what the at the end of sentence means.

So, no need to SHOUT at me . . .

Well, that leaves the question how you change the exposure unanswered.

George

[Manfred M]

Thanks for clarifying Ted. I always found that Foveon had an interesting concept that was just weird enough never to go mainstream. Somehow, it seemed to have all of the baggage of film (top layer gets most of the light and the bottom layer gets the leftovers) and the inherent noise issues with having to boost the gain in the lower layers.

Much like the Wankel rotary engine; interesting concept, but the four-stroke internal combustion engine was as adventurous as any of the ultra-conservative automobile industry have been willing to get. I wonder when Sigma is going to drop the technology and go mainstream.

[xpatUSA]

Somehow, [the Foveon] seemed to have all of the baggage of film (top layer gets most of the light and the bottom layer gets the leftovers) and the inherent noise issues with having to boost the gain in the lower layers.

Both are popular misconceptions, Manfred. But very hard to dispel. I could post QE graphs galore, absorbance characteristics of silicon, etc., and most people still won't get it. Please accept that the top layer does not "filter" the red light; therefore, the bottom "red" layer needs no "boost" in gain. The reason is that "red" wavelengths have insufficient photon energy to be stopped by the top layer and just pass straight through with no restraint (a highly simplified statement to avoid the introduction of statistics).

Much like the Wankel rotary engine; interesting concept, but the four-stroke internal combustion engine was as adventurous as any of the ultra-conservative automobile industry have been willing to get. I wonder when Sigma is going to drop the technology and go mainstream.

The main advantage of the Foveon is proper color resolution as opposed to the dreaded Bayer interpolation. This thread probably does not need to go into a "Foveon vs. Bayer" comparison but the Foveon's intrinsic detail quality is more like a black-and-white camera than that of a CFA-based camera.

[Andrew1]

Poor Pritam.

[xpatUSA]

Poor Pritam.

Yes, I should not have put up a post that evoked such intense discussion.

Just deleted my last grumpy response to the Gentleman from Nederland, so as to cool it down a bit.

Sorry,

[xpatUSA]

Well, that leaves the question how you change the exposure unanswered.

George

1) "the exposure" is the amount of light presented to the sensor, normally expressed as lux-sec (illuminance x exposure time).

2) I change the exposure by adjusting the lens aperture or the shutter speed.

3) Some people also apply in-camera exposure compensation.

Question answered?

[george013]

1) "the exposure" is the amount of light presented to the sensor, normally expressed as lux-sec (illuminance x exposure time).

2) I change the exposure by adjusting the lens aperture or the shutter speed.

3) Some people also apply in-camera exposure compensation.

Question answered?

No. The question was how to change exposeren in pp.
George

[xpatUSA]

No. The question was how to change exposeren in pp.
George

Then I can not answer the question, because your definition of "exposure" must be different to mine.

I'll repeat my definition, which is "exposure is the amount of light presented to the sensor, normally expressed as lux-sec (illuminance x exposure time)." It should be quite obvious to everybody here that, with that definition, exposure can not be changed in post-processing.

https://en.wikipedia.org/wiki/Exposu...photography%29

Which leads me to ask: what is your definition of "the exposure" in your question?