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Author Topic: DXOmark ranks DB image quality well below DSLR!  (Read 32392 times)
ThierryH
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« Reply #180 on: May 24, 2009, 06:56:36 AM »
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Gabor,

we understand each other, when speaking about that.

To add to your remark: yes, the eMotion backs are "pushing", as do other backs from other manufacturers: that is not a secret, and never was ever lied on concerning this. Now, coming to the naming of a pushed file: how would you call it?: +1 for ISO 200?, +2 for ISO 400?, etc ...? This has been explained many times, on different forums, without making a secret out of it.

But I guess that is not really relevant. What is relevant is the final image quality, and in this respect, I would not believe that a photographer would use higeher ISOs less when having the quality he wants.

Anyway, it is a long road between telling a lie and what is described here.

Best regards,
Thierry

Quote from: Panopeeper
Thierry, forget about the term used by Plekto, let's deal only with the factual background.

The eMotion 54 LV is said to have ISO up to 400, according to you in an earlier post. However, the fact is, that the e54 does not have different ISOs at all; ISO 100 and above are plain underexposures, and the so-called ISO is nothing more than metadata telling to the raw processor to boost the intensity. Many customers (I dare say the vast majority of the customers) don't know this. Don't you think that if they knew this, they would be more conservative in their using of ISO 100 and above?
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ejmartin
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« Reply #181 on: May 24, 2009, 07:33:44 AM »
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Quote from: Panopeeper
But they don't record any (except for the D300). Did you think I asked specifically the Nikons by chance?

Are you sure about this?  Bill Claff's Nefutil program
http://home.comcast.net/~NikonD70/Download...til/NefUtil.htm
uses the masked pixels to evaluate read noise.  He reports results from many Nikons at
http://home.comcast.net/~NikonD70/Investig...acteristics.htm
in the column labelled "NP" (for Nikon Proprietary).

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I find this not reliable enough even with the latter method, particularly with 12bit depth. A small difference in the "read noise" causes a large difference in the engineering DR.

You need images taken specifically for this purpose, with a sufficient amount of data near black (but not clipped) in order for the method to be accurate.  Analyzing web-posted RAW files is not up to the task.
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emil
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« Reply #182 on: May 24, 2009, 10:58:17 AM »
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Quote from: ejmartin
Are you sure about this?  Bill Claff's Nefutil program
http://home.comcast.net/~NikonD70/Download...til/NefUtil.htm
uses the masked pixels to evaluate read noise
How do you think Rawnalyze could display an image without my knowing about the masked pixels?

D40, D50, D70, D3X: none.

The D60 and the D80 have four rows and two columns of masked pixels; they are useless for measuring noise (the standard deviation varies between the channels for example from 1.23 to 1.95 in the same image - this in the numerical range 0-4095).

The D100 has two dirty columns; the D200 has four, the D2X eight.

The D3 has two rows, but the standard deviations between the channels are 70% apart.

If Claff uses those pixels for measurement, he can save the bandwidth.

Only the D300's 32 columns are suitable for this purpose.
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Gabor
Plekto
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« Reply #183 on: May 24, 2009, 12:40:01 PM »
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Quote from: Panopeeper
Keep in eye, that DSLR manufacturers are doing the same, with the same success. Read the diverse forums and see, how many owners believe to shoot with ISO 6400 and above with the 5D2, 12800 and 25600 with the D3, etc., while they are in fact only underexposing.

That was also (or at least I thought it was obvious) my point.  They *all* lie and fudge their data.  Some more than others, of course.  But when you see glitches in the data or things that stand out badly, well, you know something is wrong.  What that is, I'm making no judgment on(and not trying to start some quasi-religious war here about DBs vs DSLRs).   A good example of this in a DSLR would be how the A900 has "issues" with NR not really being off when it says it is.  So it does happen to DSLRs as well.  

Oh - and the link I posted was for a specific model that I happened to run across.  Could have been any manufacturer, really.
« Last Edit: May 24, 2009, 12:40:18 PM by Plekto » Logged
paratom
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« Reply #184 on: May 25, 2009, 05:01:55 AM »
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Quote from: Panopeeper
Thierry, forget about the term used by Plekto, let's deal only with the factual background.

The eMotion 54 LV is said to have ISO up to 400, according to you in an earlier post. However, the fact is, that the e54 does not have different ISOs at all; ISO 100 and above are plain underexposures, and the so-called ISO is nothing more than metadata telling to the raw processor to boost the intensity. Many customers (I dare say the vast majority of the customers) don't know this. Don't you think that if they knew this, they would be more conservative in their using of ISO 100 and above?

Isnt it more important how the result looks like vs how it is produced (in hardware vs in software)?
For me 50 and 100 ISO look fine, 200 ok, 400 not really great.
I rather use my eyes than technical explanation. I wouldnt call that"lying" if ISO differences are generated in software.
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ejmartin
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« Reply #185 on: May 25, 2009, 08:46:10 AM »
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Quote from: Plekto
I think it really comes down to the fact that a lot of people were lied to by the DB makers for years(eg - fake ISOs above ~400) and don't want to deal with the results of the bit camera makers' DSLRs.  It's not like Sony is a tiny company, after all.  One would expect the giants to eventually overtake the small DB makers or come very close - and for less cost, too.  If for no other reason than market share and advertising, which allows them to sell 10x as many units.

This happens in every case.  Take the Audi R8.  It's a mainstream auto maker that suddenly has a car that's nipping at the heels of the Ferrari and similar boutique cars.  Well, it's not too surprising if you think about just their R&D budget and number of employees.

Dx0 is good for at least that much in any case, because it clearly shows glitches and lying.  For example:

http://www.dxomark.com/index.php/eng/Image...se-One/P45-Plus
Click on the ISO Sensitivity tab.  Whatever their testing methods, there plainly is something the maker isn't telling us going on.

I wouldn't call software implementation of ISO "lying".  

The only reason to have hardware ISO gain is if the dynamic range of the electronics downstream of the sensor in the imaging pipeline is smaller than the DR of the sensor itself.  Then it is that electronics that limits the DR of the camera, and one is forced to choose what portion of the sensor DR is digitized and stored in the RAW data.  This is the way it works in DSLR's, especially CMOS, where the sensor has about 14 stops of DR in many current models but the camera only delivers about 11-12.  Then it makes sense to have variable hardware gain ISO.

If on the other hand one is using sufficiently clean electronics that the entire DR of the sensor is digitized with ample bit depth, there is absolutely no reason why one needs to use separate hardware gains for each ISO; the entire DR that the sensor is capable of is already captured, so one is not going to get anything more than that by changing the gain in the hardware.  Higher ISO is underexposing the sensor no matter what, in the sense that the max signal falls far below the well capacity of the photosites.  If the DR of the ADC sufficiently exceeds the DR of the sensor, it is irrelevant whether the amplification of that low signal is done in the analog or the digital domain.  In fact, it is better to do it in the digital domain, since one isn't throwing away highlight information that the sensor captured by amplifying it beyond the range of the ADC, which is what hardware-based higher ISO gain does.

If MFDB manufacturers are using sufficiently high quality components that they don't need to use hardware based ISO gain, good for them; it means that they are getting the most out of their sensor.  It looks like this is the case with the P45+ above ISO 100, based on the link to DxO.  I wish Canon/Nikon would do the same, then they could unlock the 14 stops of DR that their sensors seem to be capable of, and that their amplifier/ADC's can't so far deliver.
« Last Edit: May 25, 2009, 08:50:26 AM by ejmartin » Logged

emil
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« Reply #186 on: May 26, 2009, 12:18:58 AM »
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Quote from: ejmartin
If on the other hand one is using sufficiently clean electronics that the entire DR of the sensor is digitized with ample bit depth, there is absolutely no reason why one needs to use separate hardware gains for each ISO; the entire DR that the sensor is capable of is already captured, so one is not going to get anything more than that by changing the gain in the hardware.  Higher ISO is underexposing the sensor no matter what, in the sense that the max signal falls far below the well capacity of the photosites.  If the DR of the ADC sufficiently exceeds the DR of the sensor, it is irrelevant whether the amplification of that low signal is done in the analog or the digital domain.  In fact, it is better to do it in the digital domain, since one isn't throwing away highlight information that the sensor captured by amplifying it beyond the range of the ADC, which is what hardware-based higher ISO gain does.

If MFDB manufacturers are using sufficiently high quality components that they don't need to use hardware based ISO gain, good for them; it means that they are getting the most out of their sensor.  It looks like this is the case with the P45+ above ISO 100, based on the link to DxO.  I wish Canon/Nikon would do the same, then they could unlock the 14 stops of DR that their sensors seem to be capable of, and that their amplifier/ADC's can't so far deliver.

That's an excellent point to make, Emil. However, the DXO results would suggest that neither the P45+ nor the P65+ is using sufficiently clean electronics to match the lower loss of DR, as ISO is increased, that is apparent with the D3X. How do you get the impression that this is not the case?

For example, at base ISO, the D3x has a full stop better DR than both the P45+ and P65+ (slightly more than a full stop, but let's not quibble).

At ISO 800, the D3X has a full 2.5 stops greater DR than the P45+. Nikon's analog, pre-A/D boost, is having the desired effect.

Here's the DXOmark link to the graphs I'm looking at.

http://www.dxomark.com/index.php/eng/Image...d3)/Phase%20One

Edit:I forgot to mention for the benefit of those who never get past the single figure "Overview". Click on the 'Dynamic Range' heading.
« Last Edit: May 26, 2009, 12:25:06 AM by Ray » Logged
ejmartin
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« Reply #187 on: May 26, 2009, 09:42:47 AM »
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Quote from: Ray
That's an excellent point to make, Emil. However, the DXO results would suggest that neither the P45+ nor the P65+ is using sufficiently clean electronics to match the lower loss of DR, as ISO is increased, that is apparent with the D3X. How do you get the impression that this is not the case?

For example, at base ISO, the D3x has a full stop better DR than both the P45+ and P65+ (slightly more than a full stop, but let's not quibble).

At ISO 800, the D3X has a full 2.5 stops greater DR than the P45+. Nikon's analog, pre-A/D boost, is having the desired effect.

Here's the DXOmark link to the graphs I'm looking at.

http://www.dxomark.com/index.php/eng/Image...d3)/Phase%20One

Edit:I forgot to mention for the benefit of those who never get past the single figure "Overview". Click on the 'Dynamic Range' heading.

I didn't say their DR was better at base ISO, I simply said that they are getting close to the full DR of the sensor they are using.

The ISO chart indicates that there is no analog gain for the P45+ beyond ISO 100; that is what the flat ISO graph means.  The P65+ ISO rises from 100 to 3200, indicating that it does have hardware gains for each of these ISO's.  So let's concentrate on the P45+.  

DxO had a choice to make in reporting the DR of the P45+: Do they report the actual DR, max signal level over read noise?  This does not change when the "ISO" is set above 100, since the ISO is metadata and the same analog gain as ISO 100 is used.  However, a photographer would typically double the ISO to 200 when the ambient illumination level drops by two, so middle gray is going to be located at half the RAW level for a typical ISO 200 exposure compared to a typical ISO 100 exposure.  The engineering DR at ISO 200 is the same, but only by virtue of there being an extra stop of highlight headroom above middle gray of typical exposures; the amount of "footroom" in shadows below middle gray drops by a stop.  In other words, what changes is the typical placement of middle gray in the available DR.  So DxO could report the engineering DR, but that would be misleading for photographic purposes, so I think they decided in circumstances where the ISO is done in software to simply lower the graphed DR value by one stop for every stop increase in ISO above the highest hardware-based ISO.

Now, the CCD in the P45+ is a 12-bit device.  The DR of the P45+ at base ISO is quite close to 12 stops.  This says that they are getting just about everything out of the sensor that could be got, and therefore there is no reason to have hardware gain.  I'm not sure what bit depth of ADC they are using, though the output files are 16-bit, they may be oversampling the DR to eliminate quantization error, which would become more apparent as the RAW values are multiplied digitally to generate "higher ISO" if they didn't have enough bit depth.

Now, the D3x is another story.  The sensor has more DR than the camera is delivering, and so it makes sense to have hardware based ISO gain.  Here's how it works for my Canon 1D3:



Here I have plotted the S/N as a function of absolute exposure, for various ISO.  At the upper end of exposure, each stop increase in ISO pushes another stop of sensor data past the range of the ADC, and so a stop of highlights is lost.  But because the amplifier isn't clean enough at low ISO, increasing the ISO gain boosts the signal relative to the amplifier/ADC noise, and so shadow S/N improves with increasing ISO up to about ISO 800, and a bit more at ISO 1600 (I didn't plot the ISO 3200 curve since it lies on top of the ISO 1600 curve, apart from an extra lost stop of highlights).  Thus the DR curve of the 1D3 is relatively flat from ISO 100-400, because although each bump in ISO drops a stop of highlights, the decrease in amplifier/ADC noise relative to signal adds back in almost a full stop at the shadow end.  If the amplifier/ADC noise were less than the noise of the photosite array, then the latter noise would dominate, it would be amplified as much as the signal with increasing ISO; shadow S/N would not improve with increasing ISO, and DR would drop in proportion to ISO when using analog gain.  And then there would be no point to having analog ISO gain; simply have an ADC with sufficient bit depth, and do ISO in software.  You're not going to get less noise than the photosites themselves are generating, so why throw away potentially useful highlight data by having variable ISO gain in hardware?

Note that if the amplifier/ADC were less noisy than the photosite array, the S/N curve would be the envelope of all the above S/N plots -- that is, it would look like the ISO 1600 curve at low exposure, and the ISO 100 curve at high exposure.  The full DR would be about 14 stops.  I did a little analysis and simulation of what the images from such a camera could look like:

http://theory.uchicago.edu/~ejm/pix/20d/te.../noise-p3a.html
« Last Edit: May 26, 2009, 10:09:41 AM by ejmartin » Logged

emil
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« Reply #188 on: May 27, 2009, 05:14:43 AM »
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Quote from: ejmartin
I didn't say their DR was better at base ISO, I simply said that they are getting close to the full DR of the sensor they are using.

Emil,
That's right. You didn't. The reason I mentioned the better DR of the D3X at base ISO is, despite the P45+ and P65+ having better quality components to process the signal from the sensor, and therefore not needing the analog boost prior to A/D conversion which Nikon and Canon employ, the D3X still has that full stop DR advantage at base ISO and a full 2.5 stops DR advantage at ISO 800.

Reading your explanation, I get the impression that it would be possible for Nikon in a future upgrade to the D3X, to use more expensive, more robust, heavier duty and lower noise A/D converters and other components in the processing chain, to produce a DR result which would be 2.5 stops greater than the P45+ at base ISO as well as at ISO 800.  (Although, after the furore regarding the price of the D3X, Nikon might be having second thoughts about an even more expensive upgrdade employing more expensive components. That's unfortunate for Nikon users I guess, but serves them right   )

Can you confirm that this is essentially what you are saying? Because, if you are, that's quite amazing.
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ejmartin
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« Reply #189 on: May 27, 2009, 08:48:33 AM »
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Quote from: Ray
Emil,

Reading your explanation, I get the impression that it would be possible for Nikon in a future upgrade to the D3X, to use more expensive, more robust, heavier duty and lower noise A/D converters and other components in the processing chain, to produce a DR result which would be 2.5 stops greater than the P45+ at base ISO as well as at ISO 800.  (Although, after the furore regarding the price of the D3X, Nikon might be having second thoughts about an even more expensive upgrdade employing more expensive components. That's unfortunate for Nikon users I guess, but serves them right   )

Can you confirm that this is essentially what you are saying? Because, if you are, that's quite amazing.


The sensor photosites can't know what amplification of their signal is going to be performed downstream, therefore their contribution to the noise is independent of ISO.  The read noise has to be at least as large as the photosite noise, so an upper bound on the photosite noise is the lowest read noise, which when referred to photoelectron equivalents occurs at high ISO (typically 3-5 electrons, depending on the model).  So if the manufacturer were able to maintain that read noise at low ISO, the ISO 100 DR would be four stops more than the ISO 1600 DR, assuming that the well capacity is not exceeded at RAW saturation at ISO 100 (full well is slightly below RAW saturation on Canons at ISO 100, so one wouldn't quite get four stops, more like 3.8-3.9).  The extra stops come from the highlight end because the hardware ISO gain at ISO 1600 pushes four stops of highlight data, which would be captured at ISO 100, past the saturation point of the ADC.

Instead, low ISO read noise is about 15-25 electrons in current models, losing well over two stops of the DR that the sensor is recording.  The inferred DR of the sensor obtained by dividing the full well at ISO 100 by the read noise at high ISO is what Roger Clark calls "sensor DR" (as opposed to camera DR).  You can find some data on his website clarkvision.com.

In my article on noise that I linked to above, I proposed a scheme for recovering the extra DR.  I since found out that the idea is patented (one of the patent holders is the fellow who invented the active pixel sensor for CMOS).
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emil
BJL
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« Reply #190 on: May 27, 2009, 11:10:34 AM »
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Quote from: Ray
Reading your explanation, I get the impression that it would be possible for Nikon in a future upgrade to the D3X, to use more expensive, more robust, heavier duty and lower noise A/D converters and other components in the processing chain, to produce a DR result which would be 2.5 stops greater than the P45+ at base ISO as well as at ISO 800.

The D3X uses a Sony EXMOR sensor whose output is already digital, with ISO gain amplification and A/D conversion done on-chip at the bottom of each column of pixels. So if Nikon can do anything it is by helping Sony with its sensor designs, or moving to its own designs like that for the D700 and D3, which use off-chip A/D conversion. From what I have seen, reducing amplifier noise is likely to be the most important part of improving dark noise and DR, though the thousands of tiny 12-bit on-chip A/D convertors of EXMOR sensors could also be a significant limit.

(Aside: it seems likely to me that recent Canon CMOS sensors also apply ISO gain amplification as charge gain in the transfer of signal from photosite to column bottom, with the off-chip 14-bit A/D convertors unlikely to be a significant factor in DR. Emil Martin seems to believe that the A/D convertor is the main noise villain in Canon SLR's, but his evidence does does favor that hypotheses over my proposal about on-chip ISO gain amplifier noise. [Edit: Emil talks in this thread about combined amplifier/ADC noise, and I have no disagreement with that; his analysis both here and with the relationship between spatial resolution and DR is the best technical input we have in discussions like this.])

The idea of amp. noise as a major dark noise source can explain the slower degradation of DR and noise levels with increasing ISO speed with modern types of CMOS sensors than with CCD's, due to CMOS sensors applying gain earlier, and so better protecting the weaker signals at higher ISO from some noise sources, like noise during transportation across edge of the sensor.
« Last Edit: May 27, 2009, 11:17:54 AM by BJL » Logged
Panopeeper
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« Reply #191 on: May 27, 2009, 06:36:57 PM »
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Quote from: BJL
The D3X uses a Sony EXMOR sensor whose output is already digital, with ISO gain amplification and A/D conversion done on-chip at the bottom of each column of pixels
Is this the very same sensor, which is used in the Sony A900? If so, why does the A900 create only 12bit raw data, while the D3X creates 12 or 14bit?
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Gabor
Ray
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« Reply #192 on: May 27, 2009, 09:33:18 PM »
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Quote from: ejmartin
So if the manufacturer were able to maintain that read noise at low ISO, the ISO 100 DR would be four stops more than the ISO 1600 DR, assuming that the well capacity is not exceeded at RAW saturation at ISO 100 (full well is slightly below RAW saturation on Canons at ISO 100, so one wouldn't quite get four stops, more like 3.8-3.9).

Quote from: BJL
Emil Martin seems to believe that the A/D convertor is the main noise villain in Canon SLR's, but his evidence does does favor that hypotheses over my proposal about on-chip ISO gain amplifier noise. [Edit: Emil talks in this thread about combined amplifier/ADC noise, and I have no disagreement with that; his analysis both here and with the relationship between spatial resolution and DR is the best technical input we have in discussions like this.])

The idea of amp. noise as a major dark noise source can explain the slower degradation of DR and noise levels with increasing ISO speed with modern types of CMOS sensors than with CCD's, due to CMOS sensors applying gain earlier, and so better protecting the weaker signals at higher ISO from some noise sources, like noise during transportation across edge of the sensor.


The long an short of it appears to be that, with current Bayer-type CMOS sensors, we can expect only marginal improvements in high-ISO DR in subsequent models, but there's substantial scope for DR improvement at base ISO.

That the D3X has better DR than the P65+, even at 8x12 print size, is remarkable. But also remarkable is that the D3X has almost 2 stops better DR than the 5D2. If we can expect up to an additional 1.25 stops of DR at base ISO from future Nikon DSLRs, Canon will need to provide an additional 3 stops of DR at base ISO to catch up.

I kew there was something holding me back and preventing me from jumping in and buying a 5D2   . There's no doubt that the 5D2 is a significant improvement over the 5D, but there are too many issues which Canon haven't got right, including a less-than-stellar DR at base ISO, a rather limited autobracketing fuction, and a hobbled video capacity with limited manual control. There has to be something better on the horizon.

(Perhaps an additional 1.25 stops of DR for Nikon is unrealistic. If we make it an additional 1/2 a stop, Canon still needs an additional 2.25 stops to catch up.)
« Last Edit: May 27, 2009, 09:47:09 PM by Ray » Logged
Panopeeper
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« Reply #193 on: May 27, 2009, 09:46:05 PM »
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Quote from: Ray
a hobbled video capacity with limited manual control. There has to be something better on the horizon.
Like a firmware update, to be released on 2009-06-02?
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Gabor
Ray
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« Reply #194 on: May 27, 2009, 09:50:01 PM »
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Quote from: Panopeeper
Like a firmware update, to be released on 2009-06-02?

That's news to me. What are the details?

I see. Dpreview, as usual, have the details. That's certainly good news. All we need now is an enhanced autobracketing feature that enables more than 3 shots, a greater range than +/- 2 stops, and the facility to autobracket ISO in manual mode. A faster frame rate would be useful too.
« Last Edit: May 27, 2009, 10:00:15 PM by Ray » Logged
Panopeeper
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« Reply #195 on: May 27, 2009, 10:03:58 PM »
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Quote from: Ray
That's news to me
Really? Your complaints were decisive in the development.

Quote
What are the details?

http://luminous-landscape.com/forum/index....showtopic=35059
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Gabor
Ray
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« Reply #196 on: May 27, 2009, 10:16:38 PM »
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Quote from: Panopeeper
Really? Your complaints were decisive in the development.

I certainly hope so   . If the Aussie dollar keeps rising, I might eventually buy a 5D2, if nothing better appears on the market before my next photographic trip. A good video capability will be very useful to capture authentic folk dancing in the villages of Nepal, in the evenings when lighting is not so good.

I'm a bit worried about that rather poor DR at base ISO, though. I might have to take my D700 along as well.
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Panopeeper
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« Reply #197 on: May 27, 2009, 10:31:13 PM »
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Quote from: Ray
I'm a bit worried about that rather poor DR at base ISO, though. I might have to take my D700 along as well.
How do you see the DR of your 5D?
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Gabor
Ray
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« Reply #198 on: May 28, 2009, 01:20:04 AM »
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Quote from: Panopeeper
How do you see the DR of your 5D?

Even worse, but I've moved on from the 5D. On a future photographic trip when weight is a consideration, I'll be carrying the 50D and the D700. I'd like to be able to 'get by' with just the 5D2, if I were to buy one. But I'm concerned there would be too many disadvantages compared with the 50D/D700 combination.

First, for long telephoto purposes, the 5D2 is hardly better than the 20D.

Secondly, there's no Canon lens on a par with the Nikkor 14-24.

Thirdly, neither the autobracketing flexibility of the 5D2 nor the frame rate is on a par with those of the D700.

Fourthly, whilst the DR at base ISO is not significantly worse than that of the D700, I'd be a bit concerned about the waterproofing issue with the 5D2 that became apparent on Michael's recent Antarctic trip.

It's a difficult decision with a lot of compromises and trade-offs.
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billthecat
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« Reply #199 on: May 28, 2009, 04:15:25 AM »
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I ran a little test between the ZD back and my 5D2. The DR looked similar. The 5D2 noise down deep showed up as expected, but the ZD also got messy when bringing up the shadows. I used Lightroom for processing the RAW files of each camera. I used a hot light and used many exposures, but kept exposures bellow a second as the ZD gets messy quickly on long exposures. ZD ISO 50 and 5D2 ISO 100.

In my personal experience I tend to like the ZD when DR is important. It appears that the ZD doesn't have a DR advantage from this one test. I assume that the ZD has image quality advantages over the 5D2 that has made it feel like it has better DR to me.

Note: DXO rates the DR of the 5D2 a tad higher than the ZD. From photos I have taken I felt like the DR was much higher in the ZD.

Bill
« Last Edit: May 28, 2009, 05:01:20 AM by billthecat » Logged
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