[TDvN57]

I'd like to share my experience with the 645z and using it in high ISO situations. Hopefully others can build upon this and move the capabilities of this system even further forward. The methods I have found are also not the only way to do get good quality pictures from high ISO shots.

Personally I recommend for the best performance from the camera to use it at its native ISO of 100. For a technical reference of which elements degrade with a higher ISO it may be best to look at DXOMARK's testing of the sensor. Link: Pentax 645Z - DXOMARK

On a practical note, I hardly ever find the opportunity to use the camera at ISO 100 and almost always are somewhat higher. My rationale is that yes, the quality degrades, but the end result is still acceptable to me for the intended end purpose. If it is a snapshot of our cats, I am willing to tolerate a lot of image degradation, because it is about the memory and the moment I capture. If for a critical picture I intend to print, then I want the absolute best the camera can produce. I am sure I am echoing the approach of many others. Nothing new here.

Originally I used the ISO series of pictures taken by the PF team doing the 645z review here on PentaxForums. Link: Pentax 645Z - Pentax Medium Format DSLRs - Pentax Camera Reviews and Specifications From these pictures I created an adaptive preset for noise cancelling that I loaded into the startup of ACR. I always found it to be lacking in achieving the same results as they achieved in the review.

Building upon that I took my own series of pictures at different ISO settings, which I knew would closer match my own "style" and created an adaptive preset from that in ACR. Since then I can get fairly close to an acceptable picture with a reasonably high ISO which may require some minor tweaking.

I found that the first visible degradations that become difficult to recover are the small details, particularly hair. The same with dynamic range and color tones. That makes white balance an important ally in "recovering" some colors. I also use shallow depth of field to hide the extent of poor detail definition at high ISO. Usually under exposing makes matters worse, meaning a picture under exposed at ISO 12k is worse than a picture well exposed at ISO 18k or perhaps even 25k.

Below are samples of one picture's editing path. I regard this as an extreme example which does not represent the same extent of correction needed for a picture at a more reasonable ISO 6400.

Sample picture: 645z + P67 55-100mm, ISO 25k and -1 exposure bias. Needless to say it does help to have a sharp lens if you plan to shoot high ISO. I did not plan at taking the picture at -1, it was a setting from during the day which I forgot to change back.

#1 Original with no settings and the adaptive noise preset cancelled.

#2 With adaptive presets enabled and with editing.

#3 Screen shot of ACR edit "Detail". The noise cancelling is from the adaptive preset. I sometimes tweak it as needed.

#4 is a screen shot of the "Sharpening" Mask with the Alt Key held down. I first aim for sharpening the eyes, then the details, in this case hair in the focus DoF area.

#5 is a screen shot of the "Basic" section. The White balance helps to get the whole colour scheme out of the yellows, for the rest I try to be light handed on the sliders as far as colour is concerned. Also prefer no Vibrance or Saturation added. When it comes to Texture I prefer to go directly to between +50 and +70 and the Clarity to -20. It does not work in all cases but I was surprised to see how much it changed the sharpness. In some cases it totally spoils the image and then of course I back down. For the Dehaze I normally leave it on zero, although in this case it did add a bit of needed contrast.

In this instance I did not have an opportunity to add more light and had the option to take the "home" memory shot or not. For me it is acceptable for that purpose. I managed to recover some sharpness especially in the areas where the human eye will be drawn towards, i.e. the cat's eyes and whiskers. The rest of the cat's hair is mottled together which then blurs as it fades out of the depth of field, giving the impression of a sharp picture taken at ISO 25k at -1 exposure bias. In theory the sharpness could have been better at ISO 50k at an exposure bias of +/-0.

I am also willing to share the RAW files and the adaptive preset if someone would like to "take it apart". All I ask in return is to share your comments, findings and improvements.

The big why? I am doing this because I believe that more modern cameras are incorporating AI based algorithms to artificially enhance their products beyond the original abilities. If we share skills and build upon the experiences of others than we can extend the practical capabilities of systems we already invested in. Human Intelligence (HI) is still superior to the artificial version, just slower, yet more accurate.

Note: In the interest of keeping it short I may have left out some details, please feel free to ask questions, comment, critique, disagree or agree if you wish.

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[DonV]

Thanks for the post.
Looks like it is tough or at least time consuming to improve on #2.

[RICHARD L.]

Beautiful image ! That P67 55-100 mm zoom sure delivers.

Regards

[Ed Hurst]

Beautiful image ! That P67 55-100 mm zoom sure delivers.

Regards

Certainly does. I use mine extensively with a 100MP camera and it seems to me to be up to the job. As ever, its focusing is fussy and you have to be extremely precise to get the best from the lens, even stopped down. I set the camera up on a tripod and use live view at maximum magnification to preset it. With that kind of care, it's razor sharp.

[TDvN57]

Certainly does. I use mine extensively with a 100MP camera and it seems to me to be up to the job. As ever, its focusing is fussy and you have to be extremely precise to get the best from the lens, even stopped down. I set the camera up on a tripod and use live view at maximum magnification to preset it. With that kind of care, it's razor sharp.

I agree with you on the focus difficulties. Up to 10m distance it is relatively easy to focus, but from there onwards the focus throw is very small making objects further away difficult to focus without live view as you describe.

I bought a second copy of this lens to use on the 645z with the Pentax P67-P645 adapter, and found the same as with my first copy, that it cannot accurately focus on objects far away, say two or three kilometers distance.

With the 67-645 adapter ground down by about 1mm I get focus to slightly beyond infinity which enables me to accurately focus on distant objects (with live view). The ground down adapter does not seem to affect near focus, since the lens still will focus to objects at +/-57cm measured from the sensor marker on the camera. Defies logic, but I suppose some things in life just need to be accepted. :-)

Beautiful image ! That P67 55-100 mm zoom sure delivers.

Regards

I really like this lens (P67 55-100), together with the P67 165mm f2.8 and the P645 80-160mm.

Thanks for the post.
Looks like it is tough or at least time consuming to improve on #2.

I am sure there are more tricks in the book that I still need to discover. Although so far I think I can somewhat extend the 645z's capabilities to match what the new toys deliver, without any extra cost.

Playing around with these settings and reading up on how voltage data from sensors are converted to pixel data I came to the realization that there is a large vacuum of information we don't have and probably will never have, that allows manufacturers to tweak and enhance images before the data is written to a RAW file.

[RICHARD L.]

You know, another great zoom is the P67 90-180 mm f/5.6. Moreover, its sharpness peaks at only f/8. Tripod almost necessary for critical focusing.

[TDvN57]

You know, another great zoom is the P67 90-180 mm f/5.6. Moreover, its sharpness peaks at only f/8. Tripod almost necessary for critical focusing.

Thank you for the info and suggestion Richard. I'll add that to my GAS list when the bug bites next time. :-)

[RICHARD L.]

I paid my like-new copy only 265 US$ on eBay Japan. A little heavy and in need of a tripod but a yet unknown treasure, for sure ! Below, compared to an FA 80-160 mm f/4.5.

Regards