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bjanes

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« Reply #80 on: February 26, 2007, 11:34:48 am »

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Can you give a lin to what Roger Clarke says? Is Clarke saying that "electron densities" of 1600e/sqmicron was available 20 years ago?
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Here is [a href=\"http://www.clarkvision.com/imagedetail/does.pixel.size.matter/index.html] Roger's[/url]  link. Look in the section Unity Gain Sensitivity. Roger is a very knowledgeable guy, but everything he says may not necessarily be true.

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P. S. These numbers also suggest that reduced feature size is greatly reducing the disadvantage of CMOS and interline CCD sensors relative to FF CCDs in fill factor and electron well capacity for given pixel size, which might mark the beginning of the end of FF CCD. Maybe that is why Kodak has for the first time used interline CCD instead of FF CCD in a sensor for astro-photography and FourThirds cameras, the new KAI-10100.
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That's a good point, but CMOS has its limitations also as described [a href=\"http://www.dalsa.com/shared/content/pdfs/CCD_vs_CMOS_Litwiller_2005.pdf]here.[/url]  With deep submicron fabrication techniques, CMOS sensors develop problems in the analog portion of the chip. Below 0.25 μm supply voltages drop from 5 volt levels, imposing constraints on dynamic range. Below 0.35 μm, linearity of the transistor performance suffers. As Micheal pointed out in his sensor essay, all of the high end MF backs are CCD.

Bill
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gdeliz

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« Reply #81 on: February 26, 2007, 12:40:16 pm »

See Canon's full frame whitepaper http://www.robgalbraith.com/public_files/C...White_Paper.pdf

An explanation of Canon's noise reduction techniques is on page 17.


George Deliz
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BJL

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« Reply #82 on: February 26, 2007, 12:42:05 pm »

Thanks for the links and new information.
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Roger is a very knowledgeable guy, but everything he says may not necessarily be true.
[a href=\"index.php?act=findpost&pid=103251\"][{POST_SNAPBACK}][/a]
Indeed, he just asserts that this 800 to 1600 has been about the same for 20 years, whereas my evidence shows significant improvements over a far shorter time period. More data from his site: Canon's CMOS DSLR sensors in his tables have densities around 1000, whereas the new smaller Sony CMOS improves this too 1600; again showing that considerable downsizing of DLSR photosite size is still possible while increasing electron density, thus potentially giving higher DR with smaller pixels.
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... but CMOS has its limitations also ... With deep submicron fabrication techniques, CMOS sensors develop problems in the analog portion of the chip. Below 0.25 ?m supply voltages drop from 5 volt levels, imposing constraints on dynamic range. Below 0.35 ?m, linearity of the transistor performance suffers.
[a href=\"index.php?act=findpost&pid=103251\"][{POST_SNAPBACK}][/a]
Interesting; thanks. That does still leave prospects for interline CCD replacing FF (as in FourThirds with the E-400?) And even with those depth limits, that new Sony 1/1.8" 6MP 2.5 micron CMOS sensor has a higher electron density than any FF CCD I know of.
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As Micheal pointed out in his sensor essay, all of the high end MF backs are CCD.
[a href=\"index.php?act=findpost&pid=103251\"][{POST_SNAPBACK}][/a]
Yes, but that is up till now: I was speculating about the future, and one of the dominant MF sensor makers, Kodak, has just moved interline CCD into territory previously monopolized by FF CCD. OK, that is still CCD not CMOS! I can see Live View (remotely on a computer monitor?) being useful with MF studio work, and then FF CCD is not an option.
« Last Edit: February 26, 2007, 12:44:44 pm by BJL »
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bjanes

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« Reply #83 on: February 26, 2007, 01:08:41 pm »

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I don't think it's really an issue of how much "information" is in the stop; the real issue is where your signal is, relative to the noises.  If you use the full top stop, read noise, relative to signal is only half what it would be if you exposed 1 stop lower, and shot noise (relative to signal), is only 71%.  The noises are far more limiting, in practice, than "numbers of values" are.
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Many exponents of exposing to the right use the "information" in the stop as justification for the procedure, but I agree that the real justification is in the signal to noise ratio. The eye can only perceive a limited number of levels within the range of an f/stop.

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As far as log output is concerned (I think you probably really mean gamma-adjusted; 0 has no log), the real issue is the read noise, and having a gamma-adjusted output from an ADC is not going to reduce the signal-to-read noise ratios, and the diodes or transistors used would probably add more noise of their own.
[a href=\"index.php?act=findpost&pid=103244\"][{POST_SNAPBACK}][/a]

Log ADCs are widely used in voice communications.

From [a href=\"http://en.wikipedia.org/wiki/Analog-to-digital_converter]Wikipedia[/url]

"For example, a voice signal has a Laplacian distribution. This means that the region around the lowest levels, near 0, carries more information than the regions with higher amplitudes. Because of this, logarithmic ADCs are very common in voice communication systems to increase the dynamic range of the representable values while retaining fine-granular fidelity in the low-amplitude region."

Such ADCs can not encode a value of zero, just as the progression of luminance's in the steps of the zone system can never represent 0: each step is half the preceeding. and true black is never reached.

Bill
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jani

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« Reply #84 on: February 26, 2007, 02:57:02 pm »

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That's a good point, but CMOS has its limitations also as described here.  With deep submicron fabrication techniques, CMOS sensors develop problems in the analog portion of the chip. Below 0.25 μm supply voltages drop from 5 volt levels, imposing constraints on dynamic range. Below 0.35 μm, linearity of the transistor performance suffers.
This is hardly a surprise. Because the gate width and distance between paths is smaller, you either need exotic materials where electrons won't leap across the gaps too often, or you'll need to reduce the core voltage of the circuit (conveniently combined with materials we might have thought were "exotic" a couple of decades ago).

A fundamental problem in circuit design today is the increased risk of errors, and the chip designers are performing miracles in assuring us that CPUs actually do what we expect them to, instead of behaving erratically.

So why not just keep the larger circuits with the higher voltage?

Well, higher voltage generally means a greater power consumption.

While I'm not familiar with the particular of the CMOS designs used by Canon and Sony (the Canon white paper isn't really detailed enough), it is conceivable that you could make a hybrid circuit in different processes for different tasks, but that is so complicated that I expect ongoing advances in "standard" CMOS engineering to be better, at least in the short term.

But that's just speculation, of course, and I'm not even in that particular industry.
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Ray

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« Reply #85 on: February 27, 2007, 08:34:30 pm »

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You amplify the signal from the photosite, just as Dolby, tape bias and RIAA bias (for vinyl) amplify high frequency parts of the signal from the microphone. In each case, it is for protection against noise arising at later stages, not for reducing "shot noise" in the original detected signal.

[a href=\"index.php?act=findpost&pid=103239\"][{POST_SNAPBACK}][/a]

Agreed! There's some general principle that is vaguely similar here, but the application is quite different. As I understand it, Dolby is amplifying only those frequencies in the original signal that are in the same domain as the tape hiss generated on playback. After amplification and recording on the tape, the signal is brought back down to its original level (otherwise the music would sound odd) and in the process of which the tape hiss is consequently also reduced.

If one were to apply such a principle to the digital camera, the equivalent Dolby NR system would be looking at low level signals in an exposure at base ISO, amplifying only the low level signals from wells that generate a charge below a certain threshold. The fact that the voltages from only certain photosites had been amplified would be stored in temporary memory. Before recording the RAW file to flash card, such signals would be restored to their proper level, with consequent reduction of shadow noise.

Such an image at base ISO would then have similar low noise (with same exposure) as we see at high ISO, and at full ETTR exposure, at base ISO, dynamic range would be much expanded.
« Last Edit: February 27, 2007, 08:41:55 pm by Ray »
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Ray

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« Reply #86 on: February 28, 2007, 12:10:02 am »

I'm going to amplify on this basic principle with a few demonstration shots. (Howard, do not criticise these images on the basis that they are processed for exhibition).

The dynamic range of DSLRs has been increased by the concept of ETTR (expose to the right). The DR of current DSLRs is now roughly equivalent that of to color film, but not as great as the best B&W film.

From previous comments, I know BJL thinks the DR of current DSLRs is sufficient.

The following images will show that it's not sufficient.

Whilst trekking recently in Nepal, I took a few shots to demonstrate the tremendous (monetary) value of accommodation, even though it was very poor by western standards. The following shots of hotel accommodation in the middle of the Nepalese hinterland, demonstrate the value you get for $6 a night with ensuite.

I tried to capture the 'room with a view' concept in the following shots.

Of course the DR of my 5D was not up to the task, as can be seen in the following shot.

[attachment=1940:attachment]

So what happens if I try my best to bring out the shadow detail?

[attachment=1941:attachment]

Well, clearly, that's an absolutely hopless shot. Nothing there that's interesting.

Supposing I take a shot that's right for the room.

[attachment=1942:attachment]

As you can see, I've lost the view.

Okay, so I blend 2 different exposures (as it so happens the differnece between an ISO 1600 exposure and an ISO 100 exposure.)

This is what I get.

[attachment=1943:attachment]

Whilst we're on the subject, here's the view from the ensuite. Blended images of course, but not a perfect blend. This would need some work before exhibition.  

[attachment=1944:attachment]

Notice what a meticulously tidy person I am   .
« Last Edit: February 28, 2007, 12:17:21 am by Ray »
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bjanes

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« Reply #87 on: February 28, 2007, 08:57:33 am »

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I'm going to amplify on this basic principle with a few demonstration shots. (Howard, do not criticise these images on the basis that they are processed for exhibition).

The dynamic range of DSLRs has been increased by the concept of ETTR (expose to the right). The DR of current DSLRs is now roughly equivalent that of to color film, but not as great as the best B&W film.
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Ray,

I commend you on your digital blending, but disagree with your comparison of the dynamic range of digital (with a high end camera) to color film.

[a href=\"http://www.clarkvision.com/imagedetail/dynamicrange2/index.html]Roger Clark[/url] has done a detailed comparison of the dynamic range of a Canon 1D M2 with Fuji Velvia slide film and Kodak Gold 200 consumer negative film. Roger's test target had a metered luminance ratio of 1500:1, or about 10.6 f/stops.

The dynamic range of the digital was much better than the slide film and considerably better than the negative film. His transfer curves (figures 8a and 8b) are very instructive. Film, especially negative film, has high noise in the shadows, and this limits the floor of the dynamic range, where noise obscures useful shadow information.

As anyone who has used high speed color film and digital at high ISO knows, the advantage of digital is even more marked at high ISO, although this was not tested by Roger in that experiment.

Roger's experiment has been criticized in its use of a Polaroid Sprintscan 4000 in the tests. This scanner does not have the highest DMax, but Roger states that it was capable of capturing visible detail in the slides and negatives.

Bill
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Ray

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« Reply #88 on: February 28, 2007, 09:42:32 am »

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I commend you on your digital blending, but disagree with your comparison of the dynamic range of digital (with a high end camera) to color film.
[a href=\"index.php?act=findpost&pid=103743\"][{POST_SNAPBACK}][/a]

Bill, I see once again you are using Roger Clark as an appeal to authority   .

I should have been more explicit. I meant that DSLRs have about the same dynamic range as color negative film; more than slide film but less than B&W film. My understanding is, the DR of slide film ranges from 4-6 stops, that of color film 7-9 stops and B&W film 9-11 stops.

I notice that Roger Clark used Royal Gold 200 in his tests. I don't know if this film has a reputation for a particularly high DR or just an average DR for an ISO 200 film. I get the impression that slow films would tend to have a better DR. However, I would not dispute that a modern DSLR has a higher DR than the average slide film. Nor would I dispute that that modern DSLRs do better than film in general at high ISO.

Extracting the full dynamic range from some negatives is a real challenge for both the scanner and the operator. Shadows on negative film can look so transparent one sometimes wonders if there's anything there at all. Yet with a scanner like the Nikon 8000ED which has analog gain, one can get surprising results by setting the gain to its minimum value (which reduces the time of the scan), then doing a second scan with a higher gain setting for the denser parts of the negative, then blend the 2 images.
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Ray

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« Reply #89 on: February 28, 2007, 10:50:38 am »

Having attempted a google search on the dynamic range of color negative film, I'm beginning to have doubts if any DSLR can match the DR of color film.

There's a dynamic range test of Fuji Real 100 by someone at the University of Melbourne who gives it a theoretical DR of 15 stops. There's always going to be a subjective element as to just how useful the information might be in a particular stop at the extremes of the range. Some sources quote a theoretical DR of 20 stops for (presumably the best) color films. Digital sensors also have a theoretical DR, sometimes quoted by the manufacturer, but I've never seen figures as high as 15 stops.

The link to this experiment is http://www.path.unimelb.edu.au/~bernardk/t...hdri/index.html
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BJL

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« Reply #90 on: February 28, 2007, 11:04:59 am »

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Agreed! There's some general principle that is vaguely similar here, but the application is quite different.
[a href=\"index.php?act=findpost&pid=103623\"][{POST_SNAPBACK}][/a]
The big difference is that Dolby and tape bias are trying to reduce high frequency noise (tape hiss) without increasing the total "bandwidth" used, so only high frequencies get extra amplification at the recording end, and extra de-amplification" at play-back, reducing the high frequency hiss. For digital photography, I envision simply amplifying everything enough to rise above the level of subsequent noise sources. The main barrier to this as far as I can tell is the dynamic range of the A/D convertor.
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bjanes

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« Reply #91 on: February 28, 2007, 11:08:39 am »

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Bill, I see once again you are using Roger Clark as an appeal to authority   .

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If you look at Roger's [a href=\"http://www.clarkvision.com/rnc/index.html]biography[/url], it is indeed impressive, but I am appealing to Roger's data, not his eminence as a scientist.  That is the beauty of the scientific method: it is based on data, not eminence. Roger's experimental setup is relatively simple, and his experiments could be replicated by any decent photographer. If you don't want to pay for ImagesPlus for analysis of linear raw data, you can use the freeware Iris software.

As you may recall, two of your Aussie countrymen won the Nobel prize in Medicine or Physiology for discovering that stomach ulcers are often caused by a bacterial infection rather than primarily by oversecretion of acid. This theory was ridiculed by many "experts" who had made their name and often fortunes from the acid theory.

"The greatest obstacle to knowledge is not ignorance, it is the illusion of knowledge", quote from Marshall's Nobel lecture, 2005. I think that this quotation also applies to photography: we must often adjust certain preconceived notions put forth by "experts". Perhaps Marshall's Aussie tendency of not bowing to dogma was instrumental in his (and his colleague's, Dr. Warren) discovery.

Bill
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Ray

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« Reply #92 on: February 28, 2007, 11:36:36 am »

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If you look at Roger's biography, it is indeed impressive, but I am appealing to Roger's data, not his eminence as a scientist. [a href=\"index.php?act=findpost&pid=103770\"][{POST_SNAPBACK}][/a]

Yes, I know you are, Bill. Just having a dig at you. Did you notice the smilie?

In these tests, Roger's data seems at odds with others and with my own experience. I don't know if it's due mainly to his choice of color negative film (Kodal Gold 200) or whether he could have done a better scanning job, or indeed whether he could have used a longer exposure. For best results with color negative film one also has to use a sort of ETTR principle. When I used to shoot with color negative film I often gave 1 to 1.5 EV greater than the exposure meter reading; that is for general scenes. Exposing similar scenes with my first DSLR, the D60, using the exposure meter without any compensation, would often result in irretrievably blown highlights, which I rarely experienced with color negative film despite giving a stop or 2 in excess of the meter reading.
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Ray

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« Reply #93 on: February 28, 2007, 11:49:13 am »

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For digital photography, I envision simply amplifying everything enough to rise above the level of subsequent noise sources. The main barrier to this as far as I can tell is the dynamic range of the A/D convertor.
[a href=\"index.php?act=findpost&pid=103769\"][{POST_SNAPBACK}][/a]

I'm not sure I understand why the dynamic range of the A/D converter should be a barrier. If all signals from all photosites are amplified by the same degree, the ratio between the lowest voltage and the highest voltage remains the same. However, the DR in the output should be greater because of improved shadow detail.
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CatOne

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« Reply #94 on: February 28, 2007, 11:55:15 am »

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Having attempted a google search on the dynamic range of color negative film, I'm beginning to have doubts if any DSLR can match the DR of color film.

There's a dynamic range test of Fuji Real 100 by someone at the University of Melbourne who gives it a theoretical DR of 15 stops. There's always going to be a subjective element as to just how useful the information might be in a particular stop at the extremes of the range. Some sources quote a theoretical DR of 20 stops for (presumably the best) color films. Digital sensors also have a theoretical DR, sometimes quoted by the manufacturer, but I've never seen figures as high as 15 stops.

The link to this experiment is http://www.path.unimelb.edu.au/~bernardk/t...hdri/index.html
[a href=\"index.php?act=findpost&pid=103765\"][{POST_SNAPBACK}][/a]

Let's be realistic here.  Who as an amateur or professional photographer actually has the tools to get 15 stops out of color negative film?  What sort of lab work would be necessary to do this?

Also, while digital sensors can give 10 stops (easy), or maybe 12 with RAW files, it is easy to in fact expand this range significantly in the situations where HDR processing is an option.

As a theoretical discussion, "# of stops" between color negatives and digital is a bit of a tired discussion... who actually shoots color negative film any more?  I mean, people shot slide film for years for landscape and its range is severely limited compared to negative film.
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jani

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« Reply #95 on: February 28, 2007, 01:24:36 pm »

With all this hooplah about the impressive dynamic range of today's DSLRs, it's rather interesting that Canon is one of the cooler "heads":

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The new CMOS sensor has been designed to
give greater depth to each pixel, allowing more
ample gradations, from highlighted to shadowed
portions of images. Each pixel can store more electric
charges, allowing a higher saturation point. As such,
the dynamic range of the CMOS sensor is on a par
with that of reversal film.
This is a full-frame 35mm high-resolution CMOS
sensor that performs on a par with 35mm film.

Yep, that's slide film, not negatives, and they probably mean colour film, not black and white.
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BJL

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« Reply #96 on: February 28, 2007, 01:52:18 pm »

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I'm not sure I understand why the dynamic range of the A/D converter should be a barrier.
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Because my idea is to amplify the signal enough to measure differences down to one electron, so as to read even he low signal levels relevant to high ISO exposures, and to do this all the time, even when there are brightly lit photosites giving near maximum electron count too. Then with a well capacity of, say, 50,000 (5D), the A/D needs to cover a range of signal levels from 1 to 50,000: a DR of 50,000:1, needing 16 bit accuracy. Currently, different ISO setting either cannot count up to full well capacity (high ISO) or do not count very low signals accurately (low ISO).
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bjanes

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« Reply #97 on: February 28, 2007, 03:40:57 pm »

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Yes, I know you are, Bill. Just having a dig at you. Did you notice the smilie?

In these tests, Roger's data seems at odds with others and with my own experience. I don't know if it's due mainly to his choice of color negative film (Kodal Gold 200) or whether he could have done a better scanning job, or indeed whether he could have used a longer exposure. For best results with color negative film one also has to use a sort of ETTR principle. When I used to shoot with color negative film I often gave 1 to 1.5 EV greater than the exposure meter reading; that is for general scenes. Exposing similar scenes with my first DSLR, the D60, using the exposure meter without any compensation, would often result in irretrievably blown highlights, which I rarely experienced with color negative film despite giving a stop or 2 in excess of the meter reading.
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In his experiments Roger did expose the medium to saturation, effectively exposing to the right. His saturation exposure for the negative film was +1 EV, which is less than I would have imagined, but that is what he got with the Kodak Gold 200. That film is no longer made, but in the [a href=\"http://www.kodak.com/global/en/professional/support/techPubs/e4040/e4040.pdf]data sheets[/url] for Kodak's newest Portra professional films, I note that the characteristic curve is linear up to a DMax of about 2.0 for green light; there is no shoulder.

When I used to scan film, I always preferred transparency film (Velvia, Provia, Kodachrome) to negative film, since I always found the grain to be excessive with negative film.

Bill
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Ray

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« Reply #98 on: February 28, 2007, 06:51:20 pm »

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Let's be realistic here.  Who as an amateur or professional photographer actually has the tools to get 15 stops out of color negative film?  What sort of lab work would be necessary to do this?

Also, while digital sensors can give 10 stops (easy), or maybe 12 with RAW files, it is easy to in fact expand this range significantly in the situations where HDR processing is an option.

As a theoretical discussion, "# of stops" between color negatives and digital is a bit of a tired discussion... who actually shoots color negative film any more?  I mean, people shot slide film for years for landscape and its range is severely limited compared to negative film.
[a href=\"index.php?act=findpost&pid=103777\"][{POST_SNAPBACK}][/a]

You've missed the point, CatOne. I'm not recommending a return to color negative film. I'm just replying to Bill's refutation of my statement that I believed current DSLRs have around the same DR capability as color negative film. Bill, quoting his favourite authority, Roger Clark, claims this is not so.

It's not entirely a dead issue. There appear to be still some photographers shooting film because they believe, rightly or wrongly, that negative film gives them wider latitude and DR (according to a google search).
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Ray

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« Reply #99 on: February 28, 2007, 07:10:26 pm »

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Because my idea is to amplify the signal enough to measure differences down to one electron, so as to read even he low signal levels relevant to high ISO exposures, and to do this all the time, even when there are brightly lit photosites giving near maximum electron count too. Then with a well capacity of, say, 50,000 (5D), the A/D needs to cover a range of signal levels from 1 to 50,000: a DR of 50,000:1, needing 16 bit accuracy. Currently, different ISO setting either cannot count up to full well capacity (high ISO) or do not count very low signals accurately (low ISO).
[a href=\"index.php?act=findpost&pid=103803\"][{POST_SNAPBACK}][/a]

Fair enough! I imagine it's always better to have a greater DR capability in the components than may be actually required in practice.

I'd be happy if the quality of the lowest 2 stops or so was just improved to the point one could use them. I suspect the problem has more to do with miniaturising components that can handle the amplified voltages from photosites with a full charge. If this indeed is the problem, then selective amplification of just the low signals from certain sites might be a way around this. On the other hand, this approach would require more circuitry on the sensor and less room for the photodiode. We're between a rock and a hard place here.
« Last Edit: February 28, 2007, 07:13:16 pm by Ray »
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