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08-03-2014, 06:32 AM   #1
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Why no sensitive K-3s?

If the Sensor in the 645z is capable of 51 MP and exceptional high ISO performance, why isn't there a 24 Mp APS-c version of the sensor?
It would seem that such a sensor would knock the sox of the D4s or A7s with equivalent low light performance, while having 50% more resolution, and give us birders the best of both worlds. APS-c reach and FF low light performance.

Come on Sony, cut those wafers into smaller sizes....

08-03-2014, 06:48 AM   #2
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But noo, if you cut the wafer, it will immediately become noisier and lose DR
08-03-2014, 06:50 AM   #3
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The image sensor in the 645Z has about 3.8 times the area of APS-C sensors, but only 2.125 times the number of photosites. So, for a given area, the Z sensor has fewer, larger photosites (~35.5k sites/mm^2 vs. 65.6k sites/mm^2), and these larger photosites help with low light performance.

If you made an APS-C sensor with the pixel density of the Z's sensor you'd end up with a 13MP sensor.
08-03-2014, 07:13 AM   #4
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I bet a APS-C sensor cut from 645Z would perform similar to K-5/K-3 in high ISO noise performance and DR.
645Z has almost 4x the sensor area as APS-C, so it should have about 2 stops advantage because of sensor area.
Which also might explain why 645Z has highest ISO of 204K, while K-5/K-3 have 51K.

08-03-2014, 07:14 AM   #5
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Huh? Where is anybody drawing the conclusion that the 645z has better equivalent high iso performance than the k3? Did I miss something?
08-03-2014, 07:22 AM   #6
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QuoteOriginally posted by ElJamoquio Quote
Huh? Where is anybody drawing the conclusion that the 645z has better equivalent high iso performance than the k3? Did I miss something?
All the reviews, the images at Imaging Resources photos etc. come on ElJay, get with the program.

QuoteQuote:
The image sensor in the 645Z has about 3.8 times the area of APS-C sensors, but only 2.125 times the number of photosites. So, for a given area, the Z sensor has fewer, larger photosites (~35.5k sites/mm^2 vs. 65.6k sites/mm^2), and these larger photosites help with low light performance.

If you made an APS-C sensor with the pixel density of the Z's sensor you'd end up with a 13MP sensor.
The Sony A7s is 12 Mp, I'll take it.

---------- Post added 08-03-14 at 10:27 AM ----------

QuoteQuote:
I bet a APS-C sensor cut from 645Z would perform similar to K-5/K-3 in high ISO noise performance and DR.
645Z has almost 4x the sensor area as APS-C, so it should have about 2 stops advantage because of sensor area.
Which also might explain why 645Z has highest ISO of 204K, while K-5/K-3 have 51K.
Or perhaps it's a backlit sensor that achieves a more efficient photo receptor with a smaller footprint on the surface of the sensor. Look up "Sony backlit sensor" to see what I'm talking about. The assumption that there are going to be no improvements in technology beyond the K-3 sensor is not accurate. Sensors continue to improve and according to rumour, if Canon ever gets their organic sensors out, are about to be blown through the roof.

Last edited by normhead; 08-03-2014 at 07:45 AM.
08-03-2014, 07:29 AM   #7
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QuoteOriginally posted by aremmes Quote
The image sensor in the 645Z has about 3.8 times the area of APS-C sensors, but only 2.125 times the number of photosites. So, for a given area, the Z sensor has fewer, larger photosites (~35.5k sites/mm^2 vs. 65.6k sites/mm^2), and these larger photosites help with low light performance.

If you made an APS-C sensor with the pixel density of the Z's sensor you'd end up with a 13MP sensor.
Just to re-enforce your argument, using pixel size or pitch, you have the following:
  • Pentax K100D - 7.87 micron
  • Pentax K10D - 6.07 micron
  • Pentax 645D - 5.9 microns
  • Pentax 645Z - 5.3 microns
  • Nikon D800/e - 4.88 microns
  • Pentax K5/II/IIs/30/50/500/-01 - 4.75 microns
  • Pentax K3 - 3.9 microns
  • Pentax Q - 1.5 microns
Looking at the 645Z, D800 and the K5 family. Their pixel size are all within 8% of each other, however they represent 3 very different sensor sizes. The D800 is twice as large as the K5 family (in physical sensor size), and the 645Z is 60% larger than the D800. The all have excellent high ISO (signal to noise) and resolution. For what its worth, they are essentially the same pixels, just placed on larger sensors.

The 645Z is closer to the K10D in pixel size than it is to the K3. However, to get the larger pixel size you give up resolution and roll back to CCD - in order to get the largest possible pixels.

08-03-2014, 07:39 AM   #8
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MP are irrelevant in terms of light gathering, it's just splitting your water into more buckets. If you zoom in to 1:1 it looks bad with more MP but if you zoom out to the entire picture (and/or apply noise reduction) it looks the same.

I suspect the 645Z is merely on-par with the SNR of the K-3 or A7s at equivalent ISO.

---------- Post added 08-03-14 at 07:42 AM ----------

QuoteOriginally posted by normhead Quote
All the reviews, the images at Imaging Resources photos etc. come on ElJay, get with the program.
Imaging resource? Yeah, get with the program.

If you have pics to share, say the K-3 at ISO1600 and the 645Z at actual ISO6400, comparing noise and color depth, I'd be more than willing to eyeball them. Thus far I haven't seen anything that shows the 645Z as a game changer, but at that price point you never know what they've been up to.

08-03-2014, 07:51 AM   #9
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QuoteOriginally posted by ElJamoquio Quote
MP are irrelevant in terms of light gathering, it's just splitting your water into more buckets. If you zoom in to 1:1 it looks bad with more MP but if you zoom out to the entire picture (and/or apply noise reduction) it looks the same.

I suspect the 645Z is merely on-par with the SNR of the K-3 or A7s at equivalent ISO.

---------- Post added 08-03-14 at 07:42 AM ----------



Imaging resource? Yeah, get with the program.Pentax 645Z First Impressions Review

If you have pics to share, say the K-3 at ISO1600 and the 645Z at actual ISO6400, comparing noise and color depth, I'd be more than willing to eyeball them. Thus far I haven't seen anything that shows the 645Z as a game changer, but at that price point you never know what they've been up to.

From this site...Luminous Landscape
QuoteQuote:
We'll start this section with with a flat statement – The Pentax 645D may well have the best high ISO performance of any camera to date (including the Sony A7s), and with little doubt has the lowest noise high ISO performance of any medium format camera, including as best we can tell that of the Phase One and Hasselblads that use the same sensor.
Make sure you scroll down to see the 6400 ISO pixel peeping images.. they are at least as good as an 800 ISO K-3 images, better for noise.

Last edited by normhead; 08-03-2014 at 07:57 AM.
08-03-2014, 08:19 AM   #10
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QuoteOriginally posted by normhead Quote
From this site...Luminous Landscape


Make sure you scroll down to see the 6400 ISO pixel peeping images.. they are at least as good as an 800 ISO K-3 images, better for noise.
I draw no conclusions from those images other than the 645Z produces good images at ISO 6400.

The K-3 is also produces good images at ISO1600.

I think we don't have enough data to say that the 645Z is any better or worse than the K-3 at equivalent settings. I think we'll have enough data very soon, as Pentaxians purchase the 645Z.

I hope it's better, but again, don't have enough data to say so yet.
08-03-2014, 08:24 AM   #11
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QuoteOriginally posted by ElJamoquio Quote
I draw no conclusions from those images other than the 645Z produces good images at ISO 6400.

The K-3 is also produces good images at ISO1600.

I think we don't have enough data to say that the 645Z is any better or worse than the K-3 at equivalent settings. I think we'll have enough data very soon, as Pentaxians purchase the 645Z.

I hope it's better, but again, don't have enough data to say so yet.
Yes, but the guy who used the camera at LL does.... his findings are admittedly preliminary.. but I completely disagree that you could reproduce his images at 6400 with a K-3. I'd shoot a few examples, but my K-3 seems to be a little noisier than most so, while I could sort of prove the point, it would be pretty much propaganda.
08-03-2014, 09:59 AM   #12
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QuoteOriginally posted by aremmes Quote
The image sensor in the 645Z has about 3.8 times the area of APS-C sensors, but only 2.125 times the number of photosites. So, for a given area, the Z sensor has fewer, larger photosites (~35.5k sites/mm^2 vs. 65.6k sites/mm^2), and these larger photosites help with low light performance.

If you made an APS-C sensor with the pixel density of the Z's sensor you'd end up with a 13MP sensor.


As far as im concerned this is absolutely on the money and well said.


But there are I think 3 factors affecting noise in sensors.


1 is the photosite size


2 is the basic chip construction CMOS or CCD (or indeed foveon) which affects the signal to noise ratio and quality of the image.


3 is the age of the chip. - Old chips were much noisier. look at the 2 megapixel chips with large photosites they were much noisier, iso 800 on those old 2001 sensors was often noisier than iso 64,000 is on some sensors today.


In other words you cannot directly compare a range of cameras simply on photosite size (and a photosite is 1/9th of a pixel) it depends as well on basic construction and also age of design of the sensor. Comparing sensors by photosite size alone leads to confused and misleading results in noise comparisons.
08-03-2014, 10:15 AM   #13
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Photosite size doesn't have an influence on picture noise. You're zoomed out too far for it to matter.
08-03-2014, 11:15 AM   #14
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QuoteOriginally posted by ElJamoquio Quote
Photosite size doesn't have an influence on picture noise. You're zoomed out too far for it to matter.

I disagree


Photosite size is a big factor.


The size of the photosites determines the light gathering capacity of the photosites. If the photosites are tiny and the sensor is therefore a high resolution sensor, which is what that's saying put slightly differently, the photons gathered by each photosite is therefore less, and the signal from each photosite, is therefore reduced and is lower.


The signal must then be amplified more to provide a coherent image because its weaker, the signal to noise ratio then changes because the greater magnification of the poorer signal amplifies the background noise as well, and more amplified noise is therefore generated. therefore the image carries more noise.


This surely is already well established.


Small photosites = less signal
less signal = more amplification
more amplification = more amplified noise
more amplified noise = poor signal to noise ratio
poor signal to noise ratio = more obvious noise in the image.


This is one reason why Full Frame sensors tend to have lower noise characteristics than smaller sensors, the photosites are bigger, they gather more photons, the signal is stronger and needs less amplification, the background noise doesn't get amplified as much and the noise is lower.


If you have a photosite twice the size it gather 4 times the photons and the background noise stays much the same, the signal is 4 times stronger and the signal to noise ratio is 4 times better, you then have much less noise in the image, due entirely to changing the photosite size and nothing else.


With real world losses, the truth is the difference isn't so pronounced as the raw figures would suggest but none the less noise is better controlled with larger photosites.
08-03-2014, 11:42 AM   #15
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@Imageman... Just two comments, basically, as I've seen where these discussions have gone before!* In connection with pixel site size, I've seen the term "well depth" used, which relates as well to the matter of pixel site saturation. You can make up ground on full frame cameras with a K3 simply by giving your sensor more exposure. The IBIS of the K3 is a big plus in this regard, something I still think goes underappreciated. This works up to a point (and in a practical way, I think); but eventually the saturation issue becomes critical [n.b., El Jam-o]. Hence, well depth is a very descriptive term.

The second thing is the matter of amplication you've raised, which I also think goes underappreciated and somewhat misunderstood in all the talk, talk, talk about sensors. You also need to understand that the quantum level efficiency and overall capacity of a sensor's photosites for resolving at some signal to noise ratio are *accompanied* by the noise factor of the amplification circuit itself (and its power supply), some part of which can be improved by technology (or spending more money on its implementation), and some part of which is inherent to its nature -- much like an antenna feed RF amplifier, or a common audio amplifier. Here's where a good deal of the noise gets generated, irrespective of the assumed quality of the sensor at the photo site level. A low input level signal to this amplifier naturally puts the focus on the chip's amplifier noise by way of the relative balance of noise contributing factors... and this is what you notice subjectively. Is Pentax doing a better job with this aspect of things in the 645z compared to competitors?

* Addendum, 8-5-14: Ha, ha, I called it! 😉

Last edited by Kayaker-J; 08-05-2014 at 03:01 AM.
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