Luminous Landscape Forum
Equipment & Techniques => Medium Format / Film / Digital Backs – and Large Sensor Photography => Topic started by: VinceGalloro on April 14, 2010, 01:28:17 pm
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Hello. Reading here about the Pentax 645D, I was struck by the minimum ISO of the camera being 200. As the lengthy, informative interview that was published on Luminous Landscape made clear, Pentax aimed this camera squarely at landscape shooters. Why isn't there a lower native ISO option than 200? It can get down to ISO 100 equivalent, but still, why not ISO 50? The D3X has native ISO 100, and ISO 50 equivalent, but again, I wonder why it doesn't go even lower, to a native ISO 50 and then extended ISOs below that.
I can guess why a camera that aims to give much higher usable ISOs (and not designed with landscape shooters in mind, at least not primarily), like the D3/D3s, would bottom out at ISO 200 -- I can imagine that a sensor that is usable at those sky-high ISOs just can't be made any less sensitive than ISO 200. But can sensors for cameras that are not seeking to push the limits on the high end instead push the limits on the low end?
I'm wondering if there is a technical reason that sensors can't be made to native ISO 50, or maybe even ISO 25. Or maybe that, while they can be made to that spec, doing so makes too much of a tradeoff w/r/t other features that photographers want in a sensor.
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I'm wondering if there is a technical reason that sensors can't be made to native ISO 50, or maybe even ISO 25. Or maybe that, while they can be made to that spec, doing so makes too much of a tradeoff w/r/t other features that photographers want in a sensor.
I've owned several older Leaf backs that start off at 25 and 50...
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Hi,
It's called quantum efficiency. A sensor captures something like a 80% of the photons falling on it. There are two ways of reducing ISO:
Leaving out the micro, lenses, gives about one stop.
Putting an ND filter in the front of the sensor
Essentially there is zero benefit of keeping sensor sensivity down. You can actually achieve the same thing by adding an ND filter in front of the lens. In some light conditions you may be able to overexpose, something Leica calls "pulling" on the S2.
Most MFDBs don't have microlenses.
This is really a question of technology moving forward. Digital sensor technology is quite sensitive to light, so base ISO tends to be pretty high. Why would a camera maker "cripple" the high ISO performance of a camera when you can achieve the exactly same effect with a cheap peace of ND glass in front of the lens?
Best regards
Erik
Hello. Reading here about the Pentax 645D, I was struck by the minimum ISO of the camera being 200. As the lengthy, informative interview that was published on Luminous Landscape made clear, Pentax aimed this camera squarely at landscape shooters. Why isn't there a lower native ISO option than 200? It can get down to ISO 100 equivalent, but still, why not ISO 50? The D3X has native ISO 100, and ISO 50 equivalent, but again, I wonder why it doesn't go even lower, to a native ISO 50 and then extended ISOs below that.
I can guess why a camera that aims to give much higher usable ISOs (and not designed with landscape shooters in mind, at least not primarily), like the D3/D3s, would bottom out at ISO 200 -- I can imagine that a sensor that is usable at those sky-high ISOs just can't be made any less sensitive than ISO 200. But can sensors for cameras that are not seeking to push the limits on the high end instead push the limits on the low end?
I'm wondering if there is a technical reason that sensors can't be made to native ISO 50, or maybe even ISO 25. Or maybe that, while they can be made to that spec, doing so makes too much of a tradeoff w/r/t other features that photographers want in a sensor.
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Hi,
It's called quantum efficiency. A sensor captures something like a 80% of the photons falling on it. There are two ways of reducing ISO:
Leaving out the micro, lenses, gives about one stop.
Putting an ND filter in the front of the sensor
Essentially there is zero benefit of keeping sensor sensivity down. You can actually achieve the same thing by adding an ND filter in front of the lens. In some light conditions you may be able to overexpose, something Leica calls "pulling" on the S2.
I agree with Erik that quantum efficiency is a desirable attribute and the resulting increase in ISO is an asset and not a liability in most cases. Another way to lower the effective ISO of a sensor would be to increase the full well capacity so that more electrons could be collected. As Roger Clark (http://www.clarkvision.com/articles/digital.sensor.performance.summary/#full_well) points out, "As a pixel holds more electrons, the charge density increases. There are finite upper limits to the charge density of electron storage". Full well capacity is basically related to pixel area, and for a given quantum efficiency, the number of electrons collected is also related to pixel area. For example, the Nikon D3 sensor is generally well regarded, but as Roger's Figure 1 shows, its full well is no greater than the smaller pixel Canon 5D Mark 2, and there would be some room for improvement with the D3 full well.
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I absolutely agree with Bill, good point.
What I intended to say that relatively high sensitivity is an inherent property of the process and there is little technical merit to decrease ISO by artificial means so I don't really see it happening. Doubling the full well capacity would essentially decrease ISO, at least in terms of exposing to the right. On the other hand pixels tend to shrink and having more pixels has some merits so I don't think we are going to see a big raise in well capacity.
in MFDBs the premium sensors are essentially nearly full frame 645 and going to having like 6 my (micron) pitch, so I don't see them increase well capacity either. One of the reasons MFDBs have low ISOs is that they don't have microlenses, mostly. The Leica S2 has microlenses and a base sensivity of 160 ISO, but has an option to "pull" ISO to 80. Pulling ISO could be achieved by "exposing to the right" under certain conditions.
The simplest way to add low ISO capability would probably to have an optional replacement for the front assembly of the sensor having an ND-filter like it was done on the Mamiya ZD, which had an optional OLP (Optical Low Pass) filter. This would be very much doable, at least if enough people would be willing to pay for it.
Best regards
Erik
I agree with Erik that quantum efficiency is a desirable attribute and the resulting increase in ISO is an asset and not a liability in most cases. Another way to lower the effective ISO of a sensor would be to increase the full well capacity so that more electrons could be collected. As Roger Clark (http://www.clarkvision.com/articles/digital.sensor.performance.summary/#full_well) points out, "As a pixel holds more electrons, the charge density increases. There are finite upper limits to the charge density of electron storage". Full well capacity is basically related to pixel area, and for a given quantum efficiency, the number of electrons collected is also related to pixel area. For example, the Nikon D3 sensor is generally well regarded, but as Roger's Figure 1 shows, its full well is no greater than the smaller pixel Canon 5D Mark 2, and there would be some room for improvement with the D3 full well.
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Hello. Reading here about the Pentax 645D, I was struck by the minimum ISO of the camera being 200. As the lengthy, informative interview that was published on Luminous Landscape made clear, Pentax aimed this camera squarely at landscape shooters. Why isn't there a lower native ISO option than 200? It can get down to ISO 100 equivalent, but still, why not ISO 50? The D3X has native ISO 100, and ISO 50 equivalent, but again, I wonder why it doesn't go even lower, to a native ISO 50 and then extended ISOs below that.
I can guess why a camera that aims to give much higher usable ISOs (and not designed with landscape shooters in mind, at least not primarily), like the D3/D3s, would bottom out at ISO 200 -- I can imagine that a sensor that is usable at those sky-high ISOs just can't be made any less sensitive than ISO 200. But can sensors for cameras that are not seeking to push the limits on the high end instead push the limits on the low end?
I'm wondering if there is a technical reason that sensors can't be made to native ISO 50, or maybe even ISO 25. Or maybe that, while they can be made to that spec, doing so makes too much of a tradeoff w/r/t other features that photographers want in a sensor.
Vince,
I shoot landscapes and portraits as an advanced amateur and use nearly exclusively ISO 50 & 100. On rare occasions do I use ISO 200 or 400. That applies to film and digital alike. Simply, ISO 200 as base ISO would not be acceptable to me.
For digital I use Leaf Aptus 65 with base ISO 50. Simply it gives the optimum image quality. Higher ISO also with digital result in more contrast, and by pushing away from base ISO it results in noise. Now, for main steam amateur shooters it may perhaps not matter, but for someone that is very serious in photography it does.
All Leaf and Phase One digital backs have base ISO at 50 or less (25), only the new Aptus-II 8 & 10 models have higher, at ISO 80.
Perhaps Pentax tried to make the sensor cheaper in order to compete with Nikon & Canon? I do not know. However, there are quality refurbished Leaf and Phase-One digital backs available for good prices from Leaf and Phase One agents and under warranty. Those are also very tried and reliable products that are capable of exceptional image quality.
As some replies already indicate, in this forum it is popular to argue technology as in the lines of Nikon, Canon and the like. For optimum highest image quality it takes low ISO with a medium format digital back and this is one important reason to why people use them. Perhaps some will argue my post. I will ignore that. Simply it is tiring and waste of my time argue with folks who simply will not see. If you have any more questions, please feel free to drop me a private message instead.
Regards
Anders
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I'm wondering if there is a technical reason that sensors can't be made to native ISO 50, or maybe even ISO 25. Or maybe that, while they can be made to that spec, doing so makes too much of a tradeoff w/r/t other features that photographers want in a sensor.
Hi Vince,
IMHO it's important to understand that silicon based sensors have an inherent sensitivity to various wavelengths of light, and that sensitivity is not that much different between sources. There can however be several design compromises that will reduce that inherent sensitivity. Examples of such sensitivity reducing compromises are the signal connection architecture to off-load the signal to other places which reduce the effective light sensitive surface area, and/or color filters with certain transparency characteristics. Some designs are more efficient in avoiding the loss of quantum efficiency, e.g. back illumination to avoid obstruction from connection gates.
In addition, there is the matter of definition of ISO. If one adopts a Saturation (clipping) based definition, like in 'expose-to-the-right' (ETTR), then the capacity to collect the energy of a large numbers of photons will influence the amount of exposure needed to reach that saturation level. In other words, sensels with large capacity wells or capacitance, will have a lower equivalent ISO. That has nothing to do with sensitivity of silicon.
So ultimately, it's the combination of design characteristics and per sensel surface area that will determine the ISO. Those characteristics also define things like color accuracy, dynamic range, color uniformity, etc., i.e. other aspects of image quality (which can be one reason to want low ISO capability).
The question thus becomes, why does one want low ISO? Is it for quality reasons, or does one need a low efficiency sensor design for the purpose of allowing low ISO capability (e.g. in bright lighting conditions)? One may hope it's the quality aspect that prevails, since Neutral Density filters can come a long way in reducing the scene brightness (although unfortunately also the viewfinder).
One trend to keep a critical eye out for is increasing the transparency of the CFA filter structure, since that may negatively impact color accuracy, i.e. the capability to successfully recombine RGGB filtered sensels into RGB pixels. The quest for high ISO performance may lead to poorer color quality.
Cheers,
Bart
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I shoot landscapes and portraits as an advanced amateur and use nearly exclusively ISO 50 & 100. On rare occasions do I use ISO 200 or 400. That applies to film and digital alike. Simply, ISO 200 as base ISO would not be acceptable to me.
For digital I use Leaf Aptus 65 with base ISO 50. Simply it gives the optimum image quality. Higher ISO also with digital result in more contrast, and by pushing away from base ISO it results in noise. Now, for main steam amateur shooters it may perhaps not matter, but for someone that is very serious in photography it does.
There is no doubt that shooting at base ISO will give the best quality, but your implication that a higher base ISO per se degrades image quality is unfounded. Could you please elaborate and post references?
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Hi,
Just a few points. It seems that the base ISO for the Kodak CCD used in the Leica S2 and the Pentxa is about 160. At least the Leica uses micro lenses. It's reasonable that a microlens free design, like most MFDBs would have something like a sto less speed. There may also be differences in the CGA.
Another issue, it seems, with older MFDBs that the higher ISO settings were not achieved using variable pre amplifiers but fixed preamps and tagging the file with higher ISO also called "fake ISOs", these factors could at least in part explain why MFDBs work best at low ISOs. The few MFDBs that sport microlenses also tend to have about twice the ISO compared with the microlens free designs.
Best regards
Erik
There is no doubt that shooting at base ISO will give the best quality, but your implication that a higher base ISO per se degrades image quality is unfounded. Could you please elaborate and post references?
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There is no doubt that shooting at base ISO will give the best quality, but your implication that a higher base ISO per se degrades image quality is unfounded. Could you please elaborate and post references?
Obviously a comparison test will be done, but by definition 200 iso will have more noise than 100 iso or lower. Unless somehow they are using a sensor that has the sensitivity of 200 iso with the same amount or lack of noise as 100 iso.
I think it makes more sense that they are using cheaper sensors, but I have no idea for sure.
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IMHO it's important to understand that silicon based sensors have an inherent sensitivity to various wavelengths of light, and that sensitivity is not that much different between sources. There can however be several design compromises that will reduce that inherent sensitivity. Examples of such sensitivity reducing compromises are the signal connection architecture to off-load the signal to other places which reduce the effective light sensitive surface area, and/or color filters with certain transparency characteristics. Some designs are more efficient in avoiding the loss of quantum efficiency, e.g. back illumination to avoid obstruction from connection gates.
One trend to keep a critical eye out for is increasing the transparency of the CFA filter structure, since that may negatively impact color accuracy, i.e. the capability to successfully recombine RGGB filtered sensels into RGB pixels. The quest for high ISO performance may lead to poorer color quality.
Bart,
Thanks for adding your insights to the discussion. One example of compromises in CFA filter characteristics is discussed on the DXO (http://www.dxomark.com/index.php/eng/Insights/Canon-500D-T1i-vs.-Nikon-D5000/Color-blindness-sensor-quality) comparison of the Canon EOS 500D and the Nikon D5000. The former camera tries to push up the global sensitivity of the sensor by applying a less selective filter, requiring higher color matrix coefficients which push up color noise. The Canon has higher resolution with smaller pixels, likely leading to this compromise in an effort to maintain sensitivity.
Bill
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Hello. Reading here about the Pentax 645D, I was struck by the minimum ISO of the camera being 200. As the lengthy, informative interview that was published on Luminous Landscape made clear, Pentax aimed this camera squarely at landscape shooters. Why isn't there a lower native ISO option than 200? It can get down to ISO 100 equivalent, but still, why not ISO 50? The D3X has native ISO 100, and ISO 50 equivalent, but again, I wonder why it doesn't go even lower, to a native ISO 50 and then extended ISOs below that.
I can guess why a camera that aims to give much higher usable ISOs (and not designed with landscape shooters in mind, at least not primarily), like the D3/D3s, would bottom out at ISO 200 -- I can imagine that a sensor that is usable at those sky-high ISOs just can't be made any less sensitive than ISO 200. But can sensors for cameras that are not seeking to push the limits on the high end instead push the limits on the low end?
I'm wondering if there is a technical reason that sensors can't be made to native ISO 50, or maybe even ISO 25. Or maybe that, while they can be made to that spec, doing so makes too much of a tradeoff w/r/t other features that photographers want in a sensor.
http://www.leaf-photography.com/news_0410_js.asp (http://www.leaf-photography.com/news_0410_js.asp)
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Obviously a comparison test will be done, but by definition 200 iso will have more noise than 100 iso or lower. Unless somehow they are using a sensor that has the sensitivity of 200 iso with the same amount or lack of noise as 100 iso.
I think it makes more sense that they are using cheaper sensors, but I have no idea for sure.
For most normal photography, noise is determined by shot noise and read noise added in quadrature. Shot noise is determined by the number of photons that are collected and has little to do with the ISO. Except for the deep shadows, shot noise predominates with all decent digital sensors. Read noise at low ISO for many DSLRs is actually larger than at higher ISOs due to limitations in the analog to digital converter at the high readout rates required for high frame rates. This limits the dynamic range at low ISO. For an example, look at the DR for the Nikon D3 on the DXO (http://www.dxomark.com/index.php/eng/Image-Quality-Database/Nikon/D3) site. The DR vs ISO curve flattens below ISO 800 due to ADC and electronics limitations. I wouldn't say that Nikon is using a cheap ADC, but rather they accept higher read noise for a fast frame rate.
Comparison tests have been done by DXO. For example, the SNR (screen) of the D3x is 39 dB at an effective base ISO of 78 and that of the Phase One P65+ is 39.2 dB at an effective base ISO of 44. If one compares the print SNRs, the P65+ has an advantage of 48 dB as compared to the D3x SNR of 43.9. This is due to the fact that the P65+ has a larger total sensor area and collects more photons and not due to the difference in ISOs.
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by definition 200 iso will have more noise than 100 iso or lower. Unless somehow they are using a sensor that has the sensitivity of 200 iso with the same amount or lack of noise as 100 iso.
Not "by definition" at all when comparing different sensors or films. The latter is exactly the point: the base ISO of sensors increases in newer models mostly because of improved sensitivity, due to improvements in microlenses (gapless is the latest trend) and lower dark noise (improved amplifier designs), so that S/N ratio at base ISO is the same or better.
I would be wiling to bet that the IQ at base ISO is consistently improving in rational IQ comparisons (like viewing images at equal size) along with the increases in base ISO. In particular when the base ISO increase comes from adding microlenses in sensors like that of the Leica S2 and Pentax 645D.
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Not "by definition" at all when comparing different sensors or films. The latter is exactly the point: the base ISO of sensors increases in newer models mostly because of improved sensitivity, due to improvements in microlenses (gapless is the latest trend) and lower dark noise (improved amplifier designs), so that S/N ratio at base ISO is the same or better.
I would be wiling to bet that the IQ at base ISO is consistently improving in rational IQ comparisons (like viewing images at equal size) along with the increases in base ISO. In particular when the base ISO increase comes from adding microlenses in sensors like that of the Leica S2 and Pentax 645D.
Adding microlenses or having more noise than with base iso 100. either way, the IQ suffers
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Adding microlenses or having more noise than with base iso 100. either way, the IQ suffers
Hi Jonathan,
IQ doesn't necessarily suffer from the use of micro-lenses, in fact it can improve the quantum efficiency and reduce light fall-off, which in turn boosts base ISO requiring lower amplification and thus noise. Perhaps you are referring to something else?
Cheers,
Bart
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Hi,
It is not my opinion that micro lenses affect IQ negatively. The effect they have is mainly that photons that would normally be lost are detected. On the other hand, micro lenses will increase the fill factor and thus reduce aliasing artifacts. The very same effects may reduce perceived resolution.
My understanding is that micro lenses play well with telecentric lens designs like DSLR/MF wide angles, but less so with more symmetric wide angle designs or shifted lenses.
Best regards
Erik
Adding microlenses or having more noise than with base iso 100. either way, the IQ suffers
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Adding microlenses or having more noise than with base iso 100. either way, the IQ suffers
Why, apart from special cases like tilt-shift lenses? Adding micro-lenses mainly means that the sensor gathers light faster from the same scene, so each photo-site gets about as much light at the new base ISO of 200 with micro-lenses as it would at the old base ISO of 100 without micro-lenses. Same signal, same S/N ratio, but with options like less motion blur and/or more DOF depending on whether one increases shutter speed or f-stop.
And most recent DSLR base ISO increases are in sensor product lines that already had micro-lenses, through improving the micro-lenses to gap-less designs and such. Where is the worse noise and IQ there?
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Why, apart from special cases like tilt-shift lenses? Adding micro-lenses mainly means that the sensor gathers light faster from the same scene, so each photo-site gets about as much light at the new base ISO of 200 with micro-lenses as it would at the old base ISO of 100 without micro-lenses. Same signal, same S/N ratio, but with options like less motion blur and/or more DOF depending on whether one increases shutter speed or f-stop.
And most recent DSLR base ISO increases are in sensor product lines that already had micro-lenses, through improving the micro-lenses to gap-less designs and such. Where is the worse noise and IQ there?
Microlenses soften the image. I'm more interested in tack sharp images than better noise reduction at iso 200
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Microlenses soften the image. I'm more interested in tack sharp images than better noise reduction at iso 200
Microlenses do not soften the image, other than by potentially reducing aliasing, and thus modifying the MTF.
Perhaps you are confusing them with an anti-aliasing filter, AKA optical low-pass filter (OLPF)?
Cheers,
Bart
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Microlenses do not soften the image, other than by potentially reducing aliasing, and thus modifying the MTF.
Perhaps you are confusing them with an anti-aliasing filter, AKA optical low-pass filter (OLPF)?
Cheers,
Bart
You are correct. I mostly use a view camera for my work, so I did confuse the two. My brain has been trained to hate microlenses. I also have no use for ISO over 100, unless I was to capture aerial landscapes.
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You are correct. I mostly use a view camera for my work, so I did confuse the two. My brain has been trained to hate microlenses. I also have no use for ISO over 100, unless I was to capture aerial landscapes.
Is there something about ISO100 that your brain has been trained to love? Or is this based on experience with film and earlier generations of digital sensors? Perhaps you need long exposure times for some aspect of your work?
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Is there something about ISO100 that your brain has been trained to love? Or is this based on experience with film and earlier generations of digital sensors? Perhaps you need long exposure times for some aspect of your work?
I'm always working with a tripod, mirror up, cable release, longer exposures than average. I actually shoot at ISO 50 with my H DB. I don't need to use anything faster. I have it easier than most. I'm sure there are a good deal of photographers like me. To have a camera that's base ISO is 200 is just silly. Is Pentax noise reduction at ISO 200 as good as Hasselblad or Phase ISO 100? I have no idea. It really doesn't make much sense that Pentax doesn't have base ISO 100. From the Landscape or Architectural photographer's point of view, it's a turn off. I can understand the appeal of high ISO for handheld photography. I'm sure the Pentax is geared toward this type of photographer specifically.
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Hi,
Low ISO gives normally the best quality, simply by collecting more photons. The best Signal Noise Ration (SNR) is always achieved exposing so the the pixels are near saturation (full well capacity) for the highlights. DR generally increases with exposure.
The DxO-measurements illustrate this quite handily:
[attachment=21514:Screen_s...37.09_AM.png]
Note the "hump" at 800 and 1600 ISO on the Phase One P65+, that is the effect of Sensor+ technology.
All three cameras achieve maximum SNR at minimum ISO and the SNR diminishes with similar slope for increasing ISO. The Nikon D3X has about one stop advantage which is consistent with it having micro lenses. This comparison is per pixel. The MFDBs have about twice the number of pixels and this would give an advantage in similarly sized prints:
[attachment=21515:Screen_s...54.54_AM.png]
Note also that in the normalized print size view the Sensor+ hump disappears.
The DxO measurements only measure sensor data and the SNR is just one of their measurements. Their measurements only relate to sensor data. Vendor software may have access to more data like individual camera calibration data so it may achieve better results.
Best regards
Erik
Is there something about ISO100 that your brain has been trained to love? Or is this based on experience with film and earlier generations of digital sensors? Perhaps you need long exposure times for some aspect of your work?
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I'm always working with a tripod, mirror up, cable release, longer exposures than average. I actually shoot at ISO 50 with my H DB. I don't need to use anything faster. I have it easier than most. I'm sure there are a good deal of photographers like me. To have a camera that's base ISO is 200 is just silly. Is Pentax noise reduction at ISO 200 as good as Hasselblad or Phase ISO 100? I have no idea. It really doesn't make much sense that Pentax doesn't have base ISO 100. From the Landscape or Architectural photographer's point of view, it's a turn off. I can understand the appeal of high ISO for handheld photography. I'm sure the Pentax is geared toward this type of photographer specifically.
Your goal, and that of many others as you say, is obviously the absolute lowest possible noise (highest SNR). You can achieve this if you can shoot 50, based on Erik's examples. My question went towards why you picked 100 as acceptable and 200 not.
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Hi,
My view is simply that you want to absorb as many photons in the sensor as possible. That is always achieved by maximum exposure. You want to do that without clipping non-specular highlights, that's called expose to the right.
One interesting observation may be that on both the Nikon D3X and the Phase One P65+ the two lowest ISO are in reality identical.
[attachment=21516:Screen_s...34.54_AM.png]
The noise plots on DxO are based on real ISO.
[attachment=21517:Screen_s...54.54_AM.png]
The two lowest ISOs are plotted as a single point in the figure above. What this says is that ISO 50 and ISO 100 on the P65+ give the exactly same results if you expose to the right! The software may do different tricks based on ISO, however.
It strikes me how similar the sensors are. Other parameters tested by DxO show larger differences.
BR
Erik
Your goal, and that of many others as you say, is obviously the absolute lowest possible noise (highest SNR). You can achieve this if you can shoot 50, based on Erik's examples. My question went towards why you picked 100 as acceptable and 200 not.
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Low ISO gives normally the best quality, simply by collecting more photons.
True when comparing different ISO settings on the same sensor; not true when comparing different sensors of different QE. For example, adding or improving the efficiency of microlenses over the same basic photosite design with the same full well capacity will increase the base ISO but, by the definition of base ISO, exposing each of these different sensor versions at base ISO and at shutter speeds adjusted in proportion to the ISO speed difference will collect equal numbers of photons: roughly, photosites at metered mid-tones will get about 1/10 of full well capacity.
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So if one makes the "perfect" exposure based on the desired image, and this does not take advantage of the whole range of the sensor (by not exposing to the right) has one lost a significant part of the advantage of the low ISO at 50 or 100? A shot exposed to the right at 200 ISO and darkened in PP may well be "cleaner" than one exposed correctly at ISO 100, might it not? I would be more inclined to focus on exposing to the right all the time if I wanted maximum DR and "clean" images, no matter what ISO. Is this what is commonly done by those who prefer using the lowest ISO possible?
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Hi,
One interesting observation may be that on both the Nikon D3X and the Phase One P65+ the two lowest ISO are in reality identical.
The noise plots on DxO are based on real ISO.
The two lowest ISOs are plotted as a single point in the figure above. What this says is that ISO 50 and ISO 100 on the P65+ give the exactly same results if you expose to the right! The software may do different tricks based on ISO, however.
It strikes me how similar the sensors are. Other parameters tested by DxO show larger differences.
BR
Erik
Erik,
As you note, the lowest ISO with the D3x is merely overexposure. If one keeps the f/stop and shutter speed the same, the raw files are identical. This shows that the electronic amplification has not changed and one is merely overexposing and losing "highlight protection". Nikon allows 0.5 EV headroom for "highlight protection", so many times one can get away with this overexposure.
Bill
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Your goal, and that of many others as you say, is obviously the absolute lowest possible noise (highest SNR). You can achieve this if you can shoot 50, based on Erik's examples. My question went towards why you picked 100 as acceptable and 200 not.
The noise level is visible at 200 on the H3DII. I dont have any reason to shoot that fast, at least yet. Phocus does a great job removing noise, but since I dont need to shoot at 200, why even bother if there are no benefits to my work?
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As for your comment that ISO 50 or 100 being "best" for a landscape shooter, can you please explain why you feel it would be any better than 200 or 400 if all these ISO settings generated identical noise and identical DR; IOW if all generated identical final images from a purely technical standpoint?
Any given camera manufacturer's 'base' ISO is usually the 'optimal' ISO as well, meaning best signal to noise ratio. So it may be the case for Pentax that ISO 200 generates the cleanest, highest DR file and therefore why that is it's base ISO. (We won't know until we actually get our hands on a raw file.) Some manufacturers expand ISO to generate lower ISO's than the base setting, but this usually trims DR to some measurable degree so is not advised for critical exposures, but it usually does not add to the base noise so may be desirable in some situations -- at least it's there as an option if wanted.
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As for your comment that ISO 50 or 100 being "best" for a landscape shooter, can you please explain why you feel it would be any better than 200 or 400 if all these ISO settings generated identical noise and identical DR; IOW if all generated identical final images from a purely technical standpoint?
Any given camera manufacturer's 'base' ISO is usually the 'optimal' ISO as well, meaning best signal to noise ratio. So it may be the case for Pentax that ISO 200 generates the cleanest, highest DR file and therefore why that is it's base ISO. (We won't know until we actually get our hands on a raw file.) Some manufacturers expand ISO to generate lower ISO's than the base setting, but this usually trims DR to some measurable degree so is not advised for critical exposures, but it usually does not add to the base noise so may be desirable in some situations -- at least it's there as an option if wanted.
If they generated the same image technically, it would be great to use ISO 400. ISO 100 wouldn't be better. Having the same image technically would just give more flexibility.
I'd like to know what the factors are behind a base ISO of 200. I don't know the technical details of it. Micro lenses cant be the only factor. If their ISO 200 is better than 100, would this be the first time this has happened?
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I'd like to know what the factors are behind a base ISO of 200. I don't know the technical details of it. Micro lenses cant be the only factor. If their ISO 200 is better than 100, would this be the first time this has happened?
Well first off, I think the root of the issue under discussion it this -- you have a pre-conception that ISO 200 on the Pentax is going to be inherently worse than ISO 50 or 100 on some other manufacturers digital back as respects noise and image quality. It may well be the case, but we simply won't know for certain until the camera is out and we can look at some raw files.
To answer your question of is this the first time. For ISO 200, possibly yes, but the Leica S2's native or base ISO is already at 160. As respects micro-lenses, they do increase the quantity of photons entering the site well, so it is likely to be a significant part of the higher base ISO. (Usually accounts for about a full stop.) As for where the rest is coming from, it could be a couple of things, but the most likely is probably newer sensor efficiency. Or possibly one of the newer style Bayer matrices with interspersed panchromatic or 'clear' cells --- basically because there is no color filter, there is no filter factor for some percentage of the sensor sites and hence the same base sensor ends up with a higher net sensitivity. So if those two technologies are combined on one sensor, it is not much of a stretch to envision netting a base ISO of 200 or even higher...
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I'd like to know what the factors are behind a base ISO of 200. I don't know the technical details of it. Micro lenses cant be the only factor.
It seems that with Kodak's medium format sensors, microlenses probably are the only factor, or close enough.
Compare the specs for the two new Kodak sensors, the 50MP KAF-50100 (http://www.kodak.com:80/global/plugins/acrobat/en/business/ISS/productsummary/FullFrame/KAF-50100ProductSummary.pdf) (without microlenses) and the 40 MP KAF-40000 (http://www.kodak.com:80/global/plugins/acrobat/en/business/ISS/productsummary/FullFrame/KAF-40000ProductSummary.pdf) (with microlenses), both using the same basic TrueSense 6.0 micron pixel design.
The former has quantum efficiencies in the three primary colors of 22%, 22%, 16%
The latter has quantum efficiencies in the three primary colors of 42%, 44%, 38%
All other per pixel specs are very similar.
That almost exact doubling of QE fits perfectly with a doubling of base ISO, and with the KAF-40000 offering almost exactly the same S/N performance at ISO 200 as the KAF-50000 does at ISO 100.
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I wanted to thank everyone who has posted in this discussion -- some of which, quite frankly, is over my head. Reading the discussion has helped me understand the choices made with products like the Pentax 645D, even if there is still some disagreement among those who posted here.