Pentax 645Z review

[Hans Kruse]

I have just read the review and was pleased to see a comprehensive and detailed review resulting from real experience and use of the camera. Especially I appreciate the comments on ETTR which are often neglected in reviews and happy to see that  Pentax has at least made a practical solution to avoid the need for bracketing. Neither Canon or Nikon has done that and I have the Canon 5D III and the Nikon D810. So to handle really high DR scenes without HDR blending true ETTR is essential as is written in the review.

There is one error: The size of the Pentax sensor is as mentioned 1.7x larger than 35mm full frame, but the difference between 35mm full frame and APS-C is even larger. It's 2.25x for Nikon and 2.56x for Canon. The difference between 35mm FF and 645 FF is 2.5x. And between 645Z and 645 FF as in Phase One IQ260 and IQ280 the sensor is 1.5x larger. So going from APS-C Canon to FF is about the same step as going from 35mm FF til 645 FF.

One could argue that the difference between 645Z and 35mm FF as in e.g. Nikon D810 is not that big. The comment on cropping 35mm 3:2 aspect ratio to 4:3 aspect ratio is a fair comment if this is common for the photographer. If this is the case then the area ratio is larger than 1.7x (1.66x) and becomes 1.87x. Although I like this review it would have been stronger for those interested in the real difference between e.g. D810 and 645Z by comparison shooting between the two. But I know this is a lot to ask.

I was surprised to see to see f/22 used that much and accepted. Lloyd Chambers at http://diglloyd.com/ has shot a series of comparison shots from f/2.8 up to f/22. And at f/22 details get really lost, f/16 is better, but really details start to get lost at around f/8. It's similar to 35mm FF where I find f/16 ok when needed with proper sharpening in Lightroom but f/22 is not.

So thanks for the review. All in all a good review!

[Telecaster]

Showing overexposure zebras or blinkies in live view is a terrific feature. Sony's A7(r) displays zebras in its EVF. It also lets you adjust the threshold, useful for optimizing exposure for video as well as stills. For me this alone wipes out mirror-based TTL viewing. I simply don't under/over-expose with the A7r.

Regarding aperture choice: if f/22 is the aperture I need to get the DOF I want, then f/22 is what I use. It makes no sense to choose a larger aperture for the sake of maximizing resolution in some areas of a photo if that results in undesired softness elsewhere. With the 645D I use f/16 a lot with the 35mm FA lens, and have used f/22 too. Results are fine & dandy.

-Dave-

[michael]

Well, I enjoy Lloyd's site, but I don't take his word as gospel.

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
 

[michael]

Telecaster....

We must have posted at the same moment.

Agree 100%...obviously. Too many people become afraid of the diffraction boogyman. I'll take the DOF I want and need over a bit of diffraction lose any day of the week.

Michael

[Robert-Peter Westphal]

Hello,

in your review you judge the dynamic range of the sensor by looking at the bright and the dark parts of the image in Lightroom. As far as I know, one of the biggies of the latest process version of Lightroom is that Lr does an automatic optimization on raws shadows and highlights without showing it as a slider position other than the neutral point.
And, if I understood Jeff's words right, it depends on the image and no to the type of camera, so you will never see a complete us handled image in Lightroom.

Please, correct me if I'm wrong, but to me a judging on the dynamic range is pretty difficult using a raw file in Lightroom.

Nevertheless, I really enjoyed reading this review and I really appreciate this type of reviews which give us your personal feelings on a product's quality than showing curves and data !


Best wishes Robert

[Hans Kruse]

Showing overexposure zebras or blinkies in live view is a terrific feature. Sony's A7(r) displays zebras in its EVF. It also lets you adjust the threshold, useful for optimizing exposure for video as well as stills. For me this alone wipes out mirror-based TTL viewing. I simply don't under/over-expose with the A7r.

Regarding aperture choice: if f/22 is the aperture I need to get the DOF I want, then f/22 is what I use. It makes no sense to choose a larger aperture for the sake of maximizing resolution in some areas of a photo if that results in undesired softness elsewhere. With the 645D I use f/16 a lot with the 35mm FA lens, and have used f/22 too. Results are fine & dandy.

-Dave-

Regarding DOF shooting 35mm I never need to stop down to f/22. I do use f/16 when needed. Careful focusing and check of DOF can avoid excessive stopping down which does harm IQ. If course and I did intend to say there never would be a need to stop down to f/22, but it is not without cost in IQ.

[Hans Kruse]

Well, I enjoy Lloyd's site, but I don't take his word as gospel.

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
 

Diffraction starts way before f/22. The questions is what is acceptable and what is not. If you are happy with f/22 that is fine, but to say there is no degradation is simply wrong.

[michael]

Please note what I wrote... For my purposes it isn't an issue. I know when diffraction starts, i just prefer having more DOF to the small quality loss of a smaller aperture.

Michael

[Mark Ransom]

I think you have a minor error in the review. When comparing sensor sizes, you seem to use the ratio of the areas for the 645z to FF but the ratio of the linear dimensions for FF to APS-C. The ratio of areas for FF to APS-C would be in the range of 2.25 to 2.56.

This is just a nit, I enjoyed the review overall.

Edit: I see Hans Kruse has already made the same point, sorry for being redundant.

[ErikKaffehr]

Hi,

My solid opinion, being analytic, is that the better lenses perform best at f/8 or below. Stopping down to f/16 on my P45+ largely eliminates colour aliasing, a good thing, but also a sure indication of sharpness loss.

My take may also be that if we buy MFD for sharpness, that advantage will be reduced/lost with stopping down to much, so I am reluctant to go below f/11 - f/16.



The example above is a Sonnar 150/4 on Hasselblad 555/P45+, near axis, but laws of physics are same for all lenses and all sensors.

In this case stopping down to f/16 corresponds to loosing like 16 MPixels of 52, 36 MP resolution remaining.

But, some lenses need to be stopped down to f/11 for optimum sharpness. I sometimes take a few pictures with different focus and blend, that often works reasonable well.

Best regards
Erik

Diffraction starts way before f/22. The questions is what is acceptable and what is not. If you are happy with f/22 that is fine, but to say there is no degradation is simply wrong.

[laughingbear]

In this case stopping down to f/16 corresponds to loosing like 16 MPixels of 52, 36 MP resolution remaining.

Loosing MP by stopping down the lens? I lack the knowledge to be able to follow this Eric. I was under the impression that stopping down introduces lack of sharpness/diffraction, but I never would have concluded that this equals loss in MP.

 

[michael]

Erik,

With a due respect, but I believe that you (and many others) overstate the issue of diffraction losses at small apertures, especially with medium format.

Somewhat frustrated with this debate, after breakfast this morning I did a quick test, just to post here.



This is the set up, taken with the Pentax 645z and Pentax 120mm Macro, a lens of undisputed high resolution.

I did a series of exposures, keeping the ISO the same and simply varying the shutter speed relative to the aperture. The range was f/5.6, f/8, f/11, f/16, f/22, and f/32.



F/5.6



f/22

As I suspected, f/5.6 and f/8 were indistinguishable. F/11 was minutely less crisp and f/22 a bit more so. f/32 was noticeably softer.

The point though, is that a small increase in the amount of sharpening used is all that's need to bring the f/22 shot to the point that it's almost indistinguishable at 100% on screen, and completely indistinguishable in a 16X20" print.

So, while I have no problem with theory, I am much more interested in practice, and as I've written for years, make your own tests before believe so-called experts (including me).

The secret to making the f/22 shot look almost the same as the one at f/5.6 was simply a bit of extra sharpening. Nothing more.

By the way, I wrote about this back in 2002, in the film days, and the same thing applied then. http://www.luminous-landscape.com/essays/stop-d.shtml. Stop worrying and keep shoot!

Michael

UPDATE: My apologies. I mistakenly posted the f/5.6 shot twice. The correct f/22 shot is now there. Same difference.

[tsjanik]

Michael:

Point well made.  By the way, what construction products do you serve with fruit?   
Tom

[buckshot]

Nice write up Michael - really enjoyed it, looks like a great camera at a sensible price point.

Having just watched the 'Mirrorless Revolution' video (again, very informative - especially for someone like me who's been ignorant of everything other than 35mm and MF) it would be interesting to hear the opinions of you both on the state of MF in general. To me that whole segment seems to be desperately trying to figure out where it's going - Pentax serve up the 645Z for less than $10k, Hasselblad may well be opening up their 'H' system again, and have pitched the new CFV-50c at ~$15k, while Phase One appear to be doing pretty much nothing (publicly). Strange times.

Jim

[Bart_van_der_Wolf]

Please note what I wrote... For my purposes it isn't an issue. I know when diffraction starts, i just prefer having more DOF to the small quality loss of a smaller aperture.

Hi Michael,

That's fine if one does know what diffraction does with one's particular lens and sensor. I agree that in case of a (creative) trade-off one chooses the best option, even if it hurts the technical quality. However, others should be aware that from f/18 and narrower, effective resolution is reduced below maximum. Also high contrast detail will be unrecoverably lost, even deconvolution sharpening cannot restore it.

At f/22, 'only' some 80% of the maximum attainable resolution is left for restoration (similar to a low contrast 33 MP quality), and even then the amplitude of low contrast micro detail that could theoretically be resolved is reduced so much that it will be hard to see, because diffraction has the effect of a low rate AA-filter. That will effectively pull a 'veil of dullness' over the entire image.

Depending on subject matter, that creates a serious hit on image quality and will require superior quality postprocessing like deconvolution sharpening to restore a little detail from the drabness (and deconvolution sharpening, like with FocusMagic, does improve the quality of the detail that is left in such images).

Only when the creative options demand it, e.g. to achieve a very strongly composed image with important OOF detail contribution to the scene, or a unique event, will the trade-off for smaller apertures than f/18 be a good trade-off. One can boost the 'look' of such diffraction affected images with very specialized software like Topaz Clarity, to counteract some of the lost liveliness, and use Topaz Detail to trick our eyes in to seeing more detail than there actually is. That will work best on low noise images, because serious adjustments to tonality will be required.

I would personally be very careful, and avoid anything narrower than f/16, even with a very good lens, unless absolutely unavoidable. At f/18 the resolution is reduced to virtually zero at the Nyquist frequency, all aliasing is practically eliminated on the 645Z due to diffraction blur, which may be a justification to use such a narrow aperture (e.g. as an additional shot to repair aliasing artifacts with).

Of course this restriction can be relaxed a bit for small  output sizes, but then it would also be adequate to use any of most other smaller cameras with lower resolution. An image from the 645Z deserves/demands large output sizes.

Cheers,
Bart

[bjanes]

Loosing MP by stopping down the lens? I lack the knowledge to be able to follow this Eric. I was under the impression that stopping down introduces lack of sharpness/diffraction, but I never would have concluded that this equals loss in MP.

 

Have a look at Figure 3 in the excellent article by Rubén Osuna and Efraín García posted on LuLa. Megapixel equivalents vary more than you might think according to the wave length of the light used for imaging. These figures are for green light (λ = 550 nM) and a 36x48 mm medium format sensor:

f/5.6 = 120 MP
f/8 = 31 MP
f/11 = 31 MP
f/16 = 15 MP
f/22 = 8 MP

According to these figures, using f/22 on your MFDB reduces it to the resolution of an iPhone. Of course, the SNR of the MFDB would be much higher. That said, excellent images may be obtained from an iPhone as long as the viewing size is kept relatively small.

Bill

[ErikKaffehr]

Hi,

Sorry, I see a lot of loss of IQ at f/22, this is my test (actual pixel crops):

http://echophoto.dnsalias.net/ekr/Articles/Aliasing2/Dollars.jpg


The image below is probably downscaled, so link above is a better reference.



The A77 image is included as a reference, as far as I recall it was shot using same (or similar) lens at similar shooting position.

It is a myth that MF would be less prone to diffraction than smaller formats. It may be almst true that you loose less with "fat pixels" but the P645Z has relatively small pixels, smaller than a 24 MP (FF) DSLR but larger than a 36 MP (FF) DSLR.

BTW, I am he guy who says that there is no significant difference between P45+ and 24 MP DSLRs in A2-prints. I may need to revise that statement a bit, or may be not.

Best regards
Erik

Erik,

With a due respect, but I believe that you (and many others) overstate the issue of diffraction losses at small apertures, especially with medium format.

Somewhat frustrated with this debate, after breakfast this morning I did a quick test, just to post here.



This is the set up, taken with the Pentax 645z and Pentax 120mm Macro, a lens of undisputed high resolution.

I did a series of exposures, keeping the ISO the same and simply varying the shutter speed relative to the aperture. The range was f/5.6, f/8, f/11, f/16, f/22, and f/32.



F/5.6



f/22

As I suspected, f/5.6 and f/8 were indistinguishable. F/11 was minutely less crisp and f/22 a bit more so. f/32 was noticeably softer.

The point though, is that a small increase in the amount of sharpening used is all that's need to bring the f/22 shot to the point that it's almost indistinguishable at 100% on screen, and completely indistinguishable in a 16X20" print.

So, while I have no problem with theory, I am much more interested in practice, and as I've written for years, make your own tests before believe so-called experts (including me).

The secret to making the f/22 shot look almost the same as the one at f/5.6 was simply a bit of extra sharpening. Nothing more.

By the way, I wrote about this back in 2002, in the film days, and the same thing applied then. http://www.luminous-landscape.com/essays/stop-d.shtml. Stop worrying and keep shoot!

Michael

UPDATE: My apologies. I mistakenly posted the f/5.6 shot twice. The correct f/22 shot is now there. Same difference.

[bjanes]

Hi,

My solid opinion, being analytic, is that the better lenses perform best at f/8 or below. Stopping down to f/16 on my P45+ largely eliminates colour aliasing, a good thing, but also a sure indication of sharpness loss.

My take may also be that if we buy MFD for sharpness, that advantage will be reduced/lost with stopping down to much, so I am reluctant to go below f/11 - f/16.



The example above is a Sonnar 150/4 on Hasselblad 555/P45+, near axis, but laws of physics are same for all lenses and all sensors.

In this case stopping down to f/16 corresponds to loosing like 16 MPixels of 52, 36 MP resolution remaining.

But, some lenses need to be stopped down to f/11 for optimum sharpness. I sometimes take a few pictures with different focus and blend, that often works reasonable well.

Best regards
Erik

Erik,

My results with the Nikon D800e with the Zeiss 135 mm/f2 ApoSonnar confirm your observations. Here are my results using Bart's test target. For those not familiar with the target, the 92 pixel circle indicates the Nyquist limit. The images were rendered by ACR and no sharpening was used.

Maximum resolution is at f/4 as determined by Imatest analysis of the slanted edges of the target. Resolution extends to the Nyquist limit and alaising is clearly present.



At f/16, the resolution extends nearly to Nyquist and alaising is nearly gone. Deconvolution can restore some lost detail.



At f/22 there is severe loss of resolution and there is nothing to recover near Nyquist.



Here are the Imatest results:



Bill

[michael]

So there we have it. The experts on both sides have spoken.

Now people just have to decide if they want to do real-world photography or test chart photography.

Michael

[ErikKaffehr]

Hi,

Could it be that that the guys doing chart photography can do real world photography on a shoestring just by making the best use of the equipment they choose to afford?

An interesting question, sort off…

Best regards
Erik

So there we have it. The experts on both sides have spoken.

Now people just have to decide if they want to do real-world photography or test chart photography.

Michael