Pentax 645Z review

[Hans Kruse]

What this entire conversation appears to miss, is that the reason we are stopping down is not to push our little photons through tiny, tight little holes, but because the subject of the photograph will otherwise not be in focus.

If key components of the subject are not sharp, the photograph is often pointless in landscape work. The selection of aperture is not a function of anything other than a desire to actually create the desired image.  What resolution is obtained is a consequence of that choice, and irrelevant if the image is not satisfactorily captured at all.

- N.

For me at least this is implicit in the discussion. To get a large enough DOF can be achieved (as you know) in different means, but the cost of stopping down to f/22 was under debate and I think by now all should be in agreement that the cost is considerable in terms detail rendering. There are many things that can be said about how to avoid f/22. My personal approach is to use live view in such situations to get the optimal balance of where DOF is placed. I would typically shoot this on a tripod and I would also bracket the aperture and then judge in post processing which aperture with proper sharpening settings is the most pleasing picture. I seldomly use focus stacking. I have found that I can usually do my compositions in such a way that f/16 will be enough with the careful adjustment of focus. My default aperture is f/8 and f/11 for landscapes. I have used tilt and shift lenses but hardly do this any more.

If the details are rendered as mush I don't think is is irrelevant if the aperture was f/32 and the resolution was reduced a lot. In such a case one would be much better off either choosing a slightly different composition not needing f/32 or use focus stacking and manual blending if need be. In any case this is the decision of the artist and in my view this is not the discussion. The discussion is about facts.

[michael]

What more needs to be said? In my world, reality trumps theory.



In other words, I do what it takes to get the shot that I want and don't worry about not doing the theoretically correct thing.

Michael

[michael]

I'd like to elaborate on the above....

If one is photographing 2 dimensional test charts, then of course f/5.6 would produce superior results. This would be the case for "flatlanders as well"

But in the three dimensional world that we inhabit DOF is a real concern, especially when shooting with larger format sensors. So, like everything in photography one must make trade off decisions. I choose DOF over minimizing diffraction. Why? Because it produces what are to my eye aesthetically superior images.

There really is no debate.

Michael

[tsjanik]

Reading the review and Michael's comments in this thread, I found the following statements from him concerning DR and diffraction.

From this thread:

".......................I have tested the 645z extensively in this regard and for my purposes diffraction doesn't start to show so that it's a concern until f/22. Much of my shooting is at f/16 and I am completely satisfied with the results. If I was super anal retentive I'd shoot at f/8 or f/11, but I'm not. :-)

Michael"

From the review:

".......................... If the ISO hits 12,800 a bit of noise reduction is needed, but otherwise there's hardly any concern about noise, and dynamic range holds quite well up to about ISO 6,400." 

I don't see a denial of the effects of diffraction or reduced DR with high ISO in these statements, but rather that he finds the images acceptable despite those limitations.  I do see in the posts of this thread a rather rude insistence that Michael, by being satisfied using high ISO and f/16, is denying these effects.

Tom

[bjanes]

What more needs to be said? In my world, reality trumps theory.
In other words, I do what it takes to get the shot that I want and don't worry about not doing the theoretically correct thing.
Michael

Theory does encompass your macro situation, where image detail is determined by the opposing effects of diffraction and defocus. Both of these effects are well characterized by theory. Interested readers can refer to this article on Wikipedia. In a macro situation, depth field is very shallow and defocus is the limiting factor. In many landscape situations, diffraction would be the limiting factor. This assumes that other aberrations are well controlled. If you repeated your test in a landscape situation where there are no significant foreground elements, the results would be different. In both cases the laws of physics are not violated.

Bill

[Bart_van_der_Wolf]

I do see in the posts of this thread a rather rude insistence that Michael, by being satisfied using high ISO and f/16, is denying these effects.

Hi Tom,

That's not what the comments were about, IMHO.

In principle, pushing an underexposed ISO 1600 exposure by 3 stops in post, should under normal conditions give better image quality (lower noise, more highlight headroom, better Dynamic Range) compared to an ISO 12800 shot. If this turns out differently with the 645Z because of High ISO noise reduction before writing the Raw data, then that's very interesting. Maybe it's even the start of a new trend.

Also, On a sensor with a 5.3 micron sensel pitch f/16 offers a much more solid basis for (capture) sharpening than f/22. Maybe this Raw data is also cooked, already somewhat diffraction 'corrected', which would make the differences smaller. If that's so, then it's another interesting observation by Michael if he picked that up without laboratory testing.

Also not challenged is Michael's creative choice for f/22 instead of something else, although the creative difference between f/16 (or f/18) and f/22 is relatively small for non-macro shots, especially in a viewfinder or Live View. So maybe in the longer run he will develop a preference for f/18 if a lot of DOF is required and large output is the goal? Focus stacking at the optimum aperture is also an option if technical quality is high on the list of choices.

Frankly, I see no rudeness, just honest concerns about how some people could potentially blindly follow Michael's ISO 12800 and f/22 remarks, without knowing Michael's creative options that led him to choose such settings, and being unaware of the trade-offs involved. No rudeness, but an exchange of info, an attempt to understand.

I for one, am intrigued by some of Michael's observations and look forward to someone doing a more technical test that will reveal what's going on under the hood of the 645Z. I'm sure Hasselblad and Phase One would also like to know.

Cheers,
Bart

[ErikKaffehr]

Hi,

I don't think that tone in these postings were bad.

Regarding the ISO thing I feel that it is good that we have a high ISO capable sensor that still leaves reasonable DR when 6 stops underexposed, weather or not it is achieved with manipulation of raw data.

Regarding diffraction I am pretty sure that the stuff Bart, Bill, Hans and I discuss is for real, but it is also possible that stopping down to far is not the ethernal sin we may pretend. Tim Parkin has posted an article discussing this and indicating that f/22 is still a decent aperture, when used with adequate sharpening.

On the other hand, I am in doubt if a Pentax 645Z used at f/22 and 12800 ISO will yield superior results to an A7r ord D810 at f/16 and ISO 6400. So shooting small aperture and high ISO may negate the benefits of the larger format.

Best regards
Erik

Ps. Tim's article is here: http://www.onlandscape.co.uk/2012/07/diffraction-limited/

He is quite critical of this article published here: http://www.luminous-landscape.com/pages.php/tutorials/resolution.shtml

Reading the review and Michael's comments in this thread, I found the following statements from him concerning DR and diffraction.

From this thread:

".......................I have tested the 645z extensively in this regard and for my purposes diffraction doesn't start to show so that it's a concern until f/22. Much of my shooting is at f/16 and I am completely satisfied with the results. If I was super anal retentive I'd shoot at f/8 or f/11, but I'm not. :-)

Michael"

From the review:

".......................... If the ISO hits 12,800 a bit of noise reduction is needed, but otherwise there's hardly any concern about noise, and dynamic range holds quite well up to about ISO 6,400."  

I don't see a denial of the effects of diffraction or reduced DR with high ISO in these statements, but rather that he finds the images acceptable despite those limitations.  I do see in the posts of this thread a rather rude insistence that Michael, by being satisfied using high ISO and f/16, is denying these effects.

Tom

[tsjanik]

Sorry Bart* I don't agree.  A polite, informative discussion concerning whether the use of high apertures and ISO on a camera like the 645Z is wise or if it reduces the output to a point and shoot could have occurred, instead Michael is accused of denying facts which, as far I can tell, he has not.

I am not referring to all the responses, but the ones that were confrontational in nature.

Tom


* and Erik, I didn't see your post.

[Hans Kruse]

I opened this thread by saying it was a good review but there were a few things that were not (factually) correct:

Larger Sensor

Some people may quibble about 51MP not being that much larger than 36MP. Well, they're off the mark, because the combination of larger sensels and more sensor surface real estate does add up to an appreciable advantage over 36MP. This size sensor is about 1.7X larger than full frame, which is an even greater ratio increase over APS-C's 1.5X or 1.6X difference from full frame 35mm.

This is incorrect as the sensor area is 1.7x larger than 35mm FF, but the difference between 35mm FF and APS-C, which is for Canon 2.56 and for Nikon 2.25. The difference is more like the difference between 35mm FF and APS-H (which is 1.7x).

The ISO just was what ended up being needed, and as I've discovered with the Pentax 645z, anything up to and including ISO 3200 shows hardly any noise or reduction in dynamic range. from Michaels Phlog shooting the 645Z.

The noise is well suppressed in what I see shot at ISO 3200, but the dynamic range is reduced significantly compared to shooting at ISO 100. Since there are no DxO data for the 645Z yet, looking at the D800 or D810, at ISO 100 (print) the DR is just under 15 stops, at ISO 3200 the DR is 9.5 stops. This is good, but decreased about 5 stops as expected from ISO 100.

Though f/22 seems like it would be into diffraction, in fact I have found that with medium format (even the smaller size of the Pentax sensor) it really isn't apparent even at f/22.
and again from Michaels Phlog.

This has been discussed during this thread and no need to repeat it here.

If somebody finds it insulting or rude to point out these flaws, well then, what can I say? Certainly Michael has not bowed an inch 

But it does point out one fact: There is no point in commenting on reviews and other postings by Michael if there are factual errors to report. So I will not waste my time in the future to do that.

[ErikKaffehr]

Hi,

I think he bowed an imperial quibble, but probably not an imperial notch…

Just a point to make, Michael's reviews are subjective, he never said anything else. I have some respect for that, but it may not be the best base for purchase decisions. But I generally enjoy Michaels writings.

My own experience with my P45+ is closer to engineering stuff, like DxO-mark and Hasselblads own MTF data. A lot of myths and little reality. But I enjoy shooting with the stuff, and it can produce excellent results, at f/11 with the stars in proper alignment.

Best regards
Erik

If somebody finds it insulting or rude to point out these flaws, well then, what can I say? Certainly Michael has not bowed an inch 

[Rand47]

Good Lord.......  The sRGB / Adobe RGB color management thread must be contagious.   
We need some kind of cyber-disinfectant!

Rand

[michael]

After some 25 years online (remember CompuServe?), all I can say is that it doesn't matter what you say or write, it's what people think you've said or written that is their reality.

The end.

Michael

[Rand47]

After some 25 years online (remember CompuServe?), all I can say is that it doesn't matter what you say or write, it's what people think you've said or written that is their reality.

The end.

Michael

Quite right, Michael.  And in my experience, what they "think" you said is a horse that is already in their barn saddled up and ready to ride.  :-)

Rand

[Ray]

On the other hand, I am in doubt if a Pentax 645Z used at f/22 and 12800 ISO will yield superior results to an A7r ord D810 at f/16 and ISO 6400. So shooting small aperture and high ISO may negate the benefits of the larger format.

Hi Erik,
That's probably true. It would be interesting to see a comparison. However, hasn't it always been the case that the larger format tends to have an advantage mostly at a shallower DoF?

This also applies to the differences between the cropped format and full-frame 35mm. To get the equivalent DoF with full frame one has to stop down at least one stop. To get the equivalent shutter speed with full frame one has to raise ISO at least one stop. This effect tends to negate the advantages of full frame in terms of lower noise and higher resolution. It's usually unavoidable without employing focus stacking, except in specific circumstances when the desired DoF is so shallow that one has to use a very wide aperture with the cropped format lens, such as its maximum aperture of F1.4 or F2.8 which might be sub-optimal in terms of resolution.

In that situation, stopping down with the larger format might enable one to use a 'sharper' or optimal aperture, and if shutter speed is not a problem, there would be no need to raise ISO, in which case the larger format produces both higher resolution and lower noise.

One doesn't expect any camera to produce technically better images in all circumstances, unless one is comparing new technology with old technology. The 'best tool for the job' still applies. The main concern should be that the Pentax 645Z does not produce worse images at F22 than a 36mp D800E at F16, assuming general lens quality is comparable.

[bjanes]

Another quote from Michaels Phlog shooting with the 645Z is the following:

The ISO just was what ended up being needed, and as I've discovered with the Pentax 645z, anything up to and including ISO 3200 shows hardly any noise or reduction in dynamic range.


There is always a (significant) reduction in dynamic range when cranking up the ISO. Just look at DxO graphs for various sensors.

Quite true. For a so called ISO-less camera, one loses 1 stop of DR for each doubling of ISO. If the base ISO of the 645Z is 100 then ISO 3200 is five doublings or 5 stops less dynamic range. Quite a significant hit. This can be seen with the Nikon D800e and other cameras using the most advanced Sony sensors. Bill Claff has extensive DR data on many cameras and for the D800e, he reports the photographic DR at ISO 100 as 10.61 EV and the DR at ISO 3200 as 5.84 EV. The 645z has a larger and more recent Sony sensor and would likely have about 1 EV more DR than the D800e, but a similar trend would be expected. We will see when DXO tests the sensor.

Bill

[ErikKaffehr]

Hi,

Yes, that is what I expect.

On the other hand what Michael says is that DR at 3200 ISO was good enough.

When I was shooting Velvia I hade less than 5EV of DR, so I can see reason for that statement.

Best regards
Erik

Quite true. For a so called ISO-less camera, one loses 1 stop of DR for each doubling of ISO. If the base ISO of the 645Z is 100 then ISO 3200 is five doublings or 5 stops less dynamic range. Quite a significant hit. This can be seen with the Nikon D800e and other cameras using the most advanced Sony sensors. Bill Claff has extensive DR data on many cameras and for the D800e, he reports the photographic DR at ISO 100 as 10.61 EV and the DR at ISO 3200 as 5.84 EV. The 645z has a larger and more recent Sony sensor and would likely have about 1 EV more DR than the D800e, but a similar trend would be expected. We will see when DXO tests the sensor.

Bill

[Hans Kruse]

Hi,

Yes, that is what I expect.

On the other hand what Michael says is that DR at 3200 ISO was good enough.

When I was shooting Velvia I hade less than 5EV of DR, so I can see reason for that statement.

Best regards
Erik

Erik, this maybe what Michael thought he wrote but the actual text was as I quoted which is different (that there was hardly any reduction of DR). I cannot relate to what people think they wrote when they actually write somthing different. How can one discuss on that basis?

I have been writing online and in business for 25 years and this is not new at all, but I still find discussions where people try to change the subject when proven wrong is waste of time and I believe this will never change since this is so human.

[Bart_van_der_Wolf]

One doesn't expect any camera to produce technically better images in all circumstances, unless one is comparing new technology with old technology. The 'best tool for the job' still applies. The main concern should be that the Pentax 645Z does not produce worse images at F22 than a 36mp D800E at F16, assuming general lens quality is comparable.

That's correct, although I wouldn't call it a concern. While f/16 will allow the D800E/D810 (in principle, disregarding the lens) to resolve all the way to it's Nyquist frequency, despite diffraction. The fact that for larger output the resolution must be divided by the additional magnification requirement (divide by 32.8/24) for equal size output, will pretty much equalize the playing field.

The 645Z does have the advantage of a larger image magnification on sensor from a longer focal length. Larger magnification will boost the MTF for same sized subject detail. Add to that some Pentax secret sauce by writing somewhat 'pre-cooked' data to Raw, and one could anticipate somewhat better image quality for the 645Z. How much better, remains to be seen in a side-by-side shoot-off.

Cheers,
Bart

[Bart_van_der_Wolf]

Quite true. For a so called ISO-less camera, one loses 1 stop of DR for each doubling of ISO. If the base ISO of the 645Z is 100 then ISO 3200 is five doublings or 5 stops less dynamic range. Quite a significant hit. This can be seen with the Nikon D800e and other cameras using the most advanced Sony sensors. Bill Claff has extensive DR data on many cameras and for the D800e, he reports the photographic DR at ISO 100 as 10.61 EV and the DR at ISO 3200 as 5.84 EV. The 645z has a larger and more recent Sony sensor and would likely have about 1 EV more DR than the D800e, but a similar trend would be expected. We will see when DXO tests the sensor.

Hi Bill,

That's correct, although I do have a bit of a problem with Bill Claff's assumed acceptable shadow noise limit for the calculation of DR. The reason becomes clear with the Pentax 645Z for which we already know (from Phase One IQ250 samples) that it will probably best the engineering DR of the sensors used in the Nikon D800 series, by a small amount (maybe 14 stops in total). However, we do not know what the influence of noise reduction will be, which may be happening with the Pentax before Writing Raw, or by the use of dedicated software. I prefer to set my own lower limit of acceptable noise, after noise reduction. That's why I prefer pure Engineering DR numbers as an upper limit goal.

Michael reports very clean shadows at high ISO settings. That might add some low exposure region to the effective Dynamic Range that Bill Claff's previous measurements on other sensors would extrapolate to.

Cheers,
Bart

[Hans Kruse]

Regarding diffraction I am pretty sure that the stuff Bart, Bill, Hans and I discuss is for real, but it is also possible that stopping down to far is not the ethernal sin we may pretend. Tim Parkin has posted an article discussing this and indicating that f/22 is still a decent aperture, when used with adequate sharpening.

On the other hand, I am in doubt if a Pentax 645Z used at f/22 and 12800 ISO will yield superior results to an A7r ord D810 at f/16 and ISO 6400. So shooting small aperture and high ISO may negate the benefits of the larger format.

Best regards
Erik

Ps. Tim's article is here: http://www.onlandscape.co.uk/2012/07/diffraction-limited/

He is quite critical of this article published here: http://www.luminous-landscape.com/pages.php/tutorials/resolution.shtml

I do quote the tables from the article in LuLa in my workshops in order to say that there is a (severe) cost in fine details stopping down too much. So what I say is that although these numbers should not be taken as exact since they are dependent on the calculation parameters, it is is easy to see in test shots what the effect is. So I mention Lightroom sharpening to compensate for f/16 and beyond and also that the best thing to do is to take test shots with the given camera and lenses to see what is acceptable since every person has a different threshold for what is usable and acceptable (also related to print size). I also mention that often it is not needed to stop down as much if careful focusing adjustment is done using live view and possibly a slight composition change that still achieves the desired image but changes the DOF requirements just slightly. But if some feel f/22 is fine for them and it makes them work faster and don't like the live view adjustments then that is fine too. The key is to understand the consequence of the compromises. On 35mm I will stop down to f/16 when needed and change my standard sharpening parameters in Lightroom by increasing radius slightly and increase detail to 100. This helps to make the picture regain some of the crispness that it has lost at f/16 compared to e.g. f/8. For me it is not only about resolution but also about the look.

I do subscribe to the onlandscape monthly publications but have not seen this subject come up again. I do see many landscape photographers use f/22.

High resolution sensors on medium format does come at a collision with DOF in e.g. landscape shooting. I was instructor on two Phase One workshops last year and Phase One personel was very honest about this towards the participants. Basically saying that with large DOF the high resolution of the sensor could not be achieved, so if one wanted to have the full resolution in such shots then focus stacking was the recommended approach. I found this very good so that one can make the needed compromises with knowledge. I have shot many pictures at f/8 with the Phase One IQ160 I was using for a while and with very good resolution in all parts of the image. In some shots where I did not do aperture bracketing I found a lack of sharpness looking at 100% but downsized the picture was quite ok. The final is therefore: We all make mistakes even when knowing the facts