[jonny1986]

Here a little something I published today: DXO Shootout - Pentax 645D vs Hasselblad H3DII-39 vs Phase One P40+ - https://www.echenique.com/2010/10/25/dxo-shootout-pentax-645d-vs-hasselblad-...phase-one-p40/

The 645D does very well indeed!

in addition the high iso performance is obtained in 10 million pixel format...at high iso the file from pentax 645 resized to 10' million shoul dbe similar to a file from a d3 at 1600.

[etrigan63]

I agree. Also, the higher framerate of the P40+ is in Sensor+ mode which is 10 Mpx.

[Digitalis]

just a question has etrigan, did you test the long exposure capability on either camera. back when MF digital was in it's infancy it wasn't uncommon for the slowest shutter speed to be more than 1 second due to the heat the sensor would produce and we all know heat=noise.

has anyone tested the 645D with a REALLY long exposure?


I find it annoying that some people believe that 14bit Vs 16 bit is going to make a huge visible difference in their images, we all know photoshop renders them as 15bit+1unit which give us 32,769 levels to work with.

[etrigan63]

Long exposures are part of my test agenda for the 645D when I get my review unit in. (I am using positive thinking at this point). You are right about the heat issue but that also depends on who makes the sensor. Dalsa sensors have shorter long exposure times than Kodak sensors (which can go up to 30 min), the Dalsa's high ISO performance is better.

[jonny1986]

dalsa high iso beter?

pentax is a kodak and is performance at high iso is miles ahead every other back and even the phase plus tthat just use a resizing of the image at 10 million to have less noise....

for me pentax know how to do a processing engine thanks to his experience in dslr format. the others are far behind in processing incamera and even in building camera, apart hasselblad id say for some nice feature, but i have tried it at photokina and is really uncomfortable for long outdoor shooting and the button ergo is a pain.

[etrigan63]

Phase uses both Dalsa and Kodak sensors in their digital backs. The experience with that has been what I said: Dalsa has better high ISO and Kodak longer exposure times. I have not put the 645D through it's paces. Hopefully the combination of Kodak sensor and Pentax processing engine will give better results than other Kodak based units.

For the record on 14-bit vs 16-bit color:
The number of possible colors is calculated as 2 raised to the power of the bits of color, which yields the number of colors per channel (RGB). This result is cubed to express all possible combinations of R, G, & B.

14-bit color = (2^14)^3 colors = (16,384)^3 = 4,398,046,511,104 colors
16-bit color = (2^16)^3 colors = (65,536)^3 = 281,474,976,710,656 colors

[Digitalis]

The number of possible colors is calculated as 2 raised to the power of the bits of color

I was referring to levels and I corrected it in my earlier post.

[etrigan63]

Wasn't picking on you Digitalis, was making sure everyone was clear on the whole 14 bit vs 16 bit color issue. Final verdict: more crayons in the box.

Also, an earlier comment someone else made about Phase One Sensor+: no, it is not a file reduction technique. Sensor+ uses technology similar to the Very Large Array radio telescope to increase SNR by combining the signal from 4 pixels into one pixel (thus quartering the output file). You can read my report on it here.

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Last edited by etrigan63; 10-26-2010 at 07:12 AM.

[surfotog]

Since the subject of bit depth has been raised, can someone tell me how the Pentax is only 14 bit, while the Hasselblad using the same sensor is 16 bit? Isn't true bit depth determined at the sensor level?

The sensor in the Nikon D3x and Sony A900 share the same architecture. The Sony is 12 Bit, the Nikon is capable of 14 bit. I have read that Nikon acheives this by oversampling the data coming off the sensor, and converting to 14 bit, so it's not "true" 14 bit.

Many who use digital medium format have maintained that one of the reason for it's superior IQ is it's bit depth, which results in smoother tonality.
I'm NOT trying to stir a Hornet's nest here, simply trying to learn. Those who are more tech savvy please educate me. thanks.

Scott

[D W]

Since the subject of bit depth has been raised, can someone tell me how the Pentax is only 14 bit, while the Hasselblad using the same sensor is 16 bit? Isn't true bit depth determined at the sensor level?

The sensor in the Nikon D3x and Sony A900 share the same architecture. The Sony is 12 Bit, the Nikon is capable of 14 bit. I have read that Nikon acheives this by oversampling the data coming off the sensor, and converting to 14 bit, so it's not "true" 14 bit.

Many who use digital medium format have maintained that one of the reason for it's superior IQ is it's bit depth, which results in smoother tonality.
I'm NOT trying to stir a Hornet's nest here, simply trying to learn. Those who are more tech savvy please educate me. thanks.

Scott

My guess is the electronics/image processor was lifted from the K7. The controls had a K7 familiarity to it (for me).

[etrigan63]

Color depth is not directly controlled by the sensor per se, but by the Analog-to-Digital (A/D) converters attached to it. A camera sensor is, for intents and purposes, an array of photovoltaic cells that can only measure the luminosity at a give site. These photovoltaic cells directly translate brightness to electric current. The brighter the light, the more current is produced. A/D converters translate this current into a numerical value. The sensitivity to changes in voltage and the number of bits of output determines the number of levels of sensitivity for that particular pixel. On top of each pixel is a colored filter laid out in the Bayer Pattern (RGGB) and from there red, green, and blue values are derived and interpolated for each pixel. The only exceptions to this last bit are multishot systems from Hassy and Foveon sensors from Sigma. No color interpolation there.

In low light conditions the photocells produce weak current and the A/D converter have problems determining a reading. One then "cranks up the volume" by increasing the sensitivity of the A/D converters, but you increase the bad with the good and that translates into noise. The best A/D converters have high signal-to-noise ratios (SNR) which allows for cleaner high ISO shots. Phase One achieves this via pixel binning in hardware where the signal from four pixels is combined to increase the SNR and thus, high ISO performance.

The day they release the P80+ with Sensor+ you will see it crank out 20 Mpx high ISO in Sensor+ mode. Scary.

[jeffkrol]

Since the subject of bit depth has been raised, can someone tell me how the Pentax is only 14 bit, while the Hasselblad using the same sensor is 16 bit? Isn't true bit depth determined at the sensor level?

The sensor in the Nikon D3x and Sony A900 share the same architecture. The Sony is 12 Bit, the Nikon is capable of 14 bit. I have read that Nikon acheives this by oversampling the data coming off the sensor, and converting to 14 bit, so it's not "true" 14 bit.

Many who use digital medium format have maintained that one of the reason for it's superior IQ is it's bit depth, which results in smoother tonality.
I'm NOT trying to stir a Hornet's nest here, simply trying to learn. Those who are more tech savvy please educate me. thanks.

Scott

Actually this is a lot more complicated (in a simple manner) then that...
For a nice little synopsis:

Noise, Dynamic Range and Bit Depth in Digital SLRs

I suspect the MF "bit depth" advantage had to do more w/ higher quality electronics, huge sensors and the fact that due to noise, need for speed and cost smaller sensors did not use larger bit depth ADC's or sensor outputs..

Curiously, most 14-bit cameras on the market (as of this writing) do not merit 14-bit recording. The noise is more than four levels in 14-bit units on the Nikon D3/D300, Canon 1D3/1Ds3 and 40D. The additional two bits are randomly fluctuating, since the levels are randomly fluctuating by +/- four levels or more. Twelve bits are perfectly adequate to record the image data without any loss of image quality, for any of these cameras (though the D3 comes quite close to warranting a 13th bit). A somewhat different technology is employed in Fuji cameras, whereby there are two sets of pixels of differing sensitivity. Each type of pixel has less than 12 bits of dynamic range, but the total range spanned from the top end of the less sensitive pixel to the bottom end of the more sensitive pixel is more than 13 stops, and so 14-bit recording is warranted.

A qualification is in order here -- the Nikon D3 and D300 are both capable of recording in both 12-bit and 14-bit modes. The method of recording 14-bit files on the D300 is substantively different from that for recording 12-bit files; in particular, the frame rate slows by a factor 3-4. Reading out the sensor more slowly allows it to be read more accurately, and so there may indeed by a perceptible improvement in D300 14-bit files over D300 12-bit files (specifically, less read noise, including pattern noise). That does not, however, mean that the data need be recorded at 14-bit tonal depth -- the improvement in image quality comes from the slower readout, and because the noise is still more than four 14-bit levels, the image could still be recorded in 12-bit tonal depth and be indistinguishable from the 14-bit data it was derived from.

[etrigan63]

I was presenting a simplified explanation. We can drag this on for pages and pages of mind-numbing physics equations, but I fear for the sanity of rest of the gang.

[surfotog]

jeffkrol,

Thanks for that link, although I will have to digest it in small bites, or my aging brain will
explode ;~)

Carlos,
What I (and suspect others), are looking for, are comparative results in print. If you have the opportunity in your tests, try and compare some big ( 30" x40") prints. I'd be interestd in knowing if the theoretical advantage of greater bit depth is apparent in a real world print.

Scott

[det1rac]

Can anyone here who is/has tested the 645D comment on those comments?

For those who read their site, they're basically Leica users BUT from the samples i see here from users this particular statement from their brief use at Photokina has me shaking my head, i've always respected their knowledge but this just doesn't seem at all very unbiased?

Clicker,
DxO benchmarked the 645D so there is now a formal test published on the 645D's IQ:
https://www.pentaxforums.com/forums/pentax-medium-format-645-6x7-645d/119905-...ntax-645d.html