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01-12-2015, 07:16 PM   #1
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I feel that my DA 28-45 should be sharper

So I took delivery of my new DA645 28-45 yesterday but after giving it a run on my 645Z I was a little disappointed at the sharpness of the lens. I mean its sharp but no way is it 6K sharp... I wanted to get some opinions from you guys, am I expecting too much out of it or should I return it post hast..

Here is a link to a raw file, if anyone has the time could you please give it a look over.. I used live view at 100% to focus as well as mirror lock up and remote trigger

http://www.mediafire.com/view/56ucvvq9xigmpqs/2015_01_13_LuckyBay-009.PEF


Last edited by gary alan; 01-12-2015 at 07:22 PM.
01-12-2015, 08:37 PM   #2
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That looks a bit softer than it ought to be, but it seems the focus was on the foreground rather than the background. It also looks like you used F22, which should start showing diffraction. F11-16 is probably a safer bet.

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01-12-2015, 09:12 PM   #3
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Downloaded it and ran it through LR. I looks sharp at the point of focus, which appears to be the seaweed in the foreground. It's sharp up through the barnacles eight or ten feet out. This all crisped-up nicely when sharpened properly. The boulder and background are outside the zone of focus.

I'd say the resolution out towards the edges looks pretty good, too. None of that mushing one sees on lesser wides.

You have to remember that with a super wide-angle lens, details in the middle to far range are simply too small to be rendered sharply. They are smaller than the resolution of the camera. Moreover, you are going to start getting a bit of diffraction at f22. I sense it in the detail here.

This kind of shot is really the hardest thing to do in MF. The focal lengths prevent us from getting enough DOF at critical apertures, while we lack tilt to get everything in focus. And the resolution is so merciless on error or deficiency. You've set up a bit of a torture test here. I don't thing the lens has underperformed under the circumstances.

Try it at f8 or f11 with a less demanding DOF situation.

- N.
01-12-2015, 09:38 PM   #4
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QuoteOriginally posted by ndevlin Quote
Downloaded it and ran it through LR. I looks sharp at the point of focus, which appears to be the seaweed in the foreground. It's sharp up through the barnacles eight or ten feet out. This all crisped-up nicely when sharpened properly. The boulder and background are outside the zone of focus.

I'd say the resolution out towards the edges looks pretty good, too. None of that mushing one sees on lesser wides.

You have to remember that with a super wide-angle lens, details in the middle to far range are simply too small to be rendered sharply. They are smaller than the resolution of the camera. Moreover, you are going to start getting a bit of diffraction at f22. I sense it in the detail here.

This kind of shot is really the hardest thing to do in MF. The focal lengths prevent us from getting enough DOF at critical apertures, while we lack tilt to get everything in focus. And the resolution is so merciless on error or deficiency. You've set up a bit of a torture test here. I don't thing the lens has underperformed under the circumstances.

Try it at f8 or f11 with a less demanding DOF situation.

- N.
Thanks for the taking the time, that makes perfect sense to me and it was kind of the answer I hoping for. I am new to medium format and I guess I am still working through it. I really love the colour rendition and the edge to edge consistancy of medium format so far and have zero regrets. I used the 645z for a family shoot last week and the skin tones were just beautiful, nothing like I have seen on my d800 or my previous 5D mkii, even with there flagship lenses.

Your comment about small details getting rendered sharply on a super wide angle did come to mind because I have experienced that previously on my d800 with its 36MP sensor but I thought it was a shortcoming of the lens I was using. The 28-45 being designed specifically for the 51MP sensor I guess I figured that limitation would be overcome but I guess not.

01-13-2015, 03:06 AM   #5
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When I focus landscape I use stopped down manual focus. I hold the power toggle switch to "preview" so that it stops down, then zoom to 16x and focus manually while checking back and forth between fore and background until I get it right.

I do get sharp distant details but it takes a little effort and is rewarding.

The lens can definitely resolve detail.
01-13-2015, 03:23 AM   #6
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Yeah, I agree with Nick, there doesn't seem to be a point critical sharpness anywhere because of diffraction softening, I've seen sharper images from this lens wide open. Just going by pixel pitch at 51MP and having shot a chart between f/11 to f/22, I can say that you can get good results up to f/16, but f/22 is just terrible on all the lenses I have tested, assuming your criteria is pixel sharpness and not print sharpness.

The kind of image you shot is in the realm of tech cams and tilt-shift lenses, features that are missing from the Pentax 645 system, at least until they design a TS of their own. It would have been better if you stopped down to around f/13 and and tilted the plane of focus, but that can't be done on the 645Z yet. Even so, this image looks good enough to be printed 20" along it's width at least.
01-13-2015, 03:31 AM   #7
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QuoteOriginally posted by 2351HD Quote

The lens can definitely resolve detail.
Oh absolutely, I guess though on the wider vista type scenes there is only so many pixels to go around making the shot sometimes appear lacking in detail. I have since taken a few close up macro type shots of some fabrics and am very happy, was even expecting to see some moire in a few of them but nope, just beautiful edge to edge detail throughout..
Here is a small section of one the shots, cant complain here..
Attached Images
 
01-13-2015, 05:49 AM   #8
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Fwiw, I've been similarly frustrated on similar shots on comparable cameras (I've never had the 28-45). This is just a hard shot to make happen. The other thing is that DOF with a 51MP digital camera is not your daddy's DOF. Things that used to looks sharp to us on film will be palpably not 100% crisp at 100% pixel view in digital. The DOF was the same with film, of course, but the film was way more forgiving of imperfection.

Welcome to the pleasure and the pain of MFD. There's a reason some people drive themselves to madness and bankruptcy with tech cam systems for landscape work. :-)

- N.

01-13-2015, 08:02 AM   #9
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For situations where getting enough DOF with full sharpness through the frame and where the scene isn't overly complicated and the light isn't changing to quickly I typically focus bracket at about f/13, sometimes f/16 if it has objects really close to the lens and I also want infinity focus. Use live view on the 645Z or on the 645D I would make a guess and then review the files for sharpness...find your two focus points (infinity should be near the middle of the infinity sign). Make sure you remember those points, then go ahead and focus bracket.


In Camera RAW I make my global adjustments, open both files in Photoshop, then create layers from the background. Drop one file on top of the other, then select both layers and go to Edit--> Auto Align Layers. You can then have PS "Auto Blend Layers" ...choose the option for focus bracketing. Or if it's a scene where you have moving objects, like waves, that may throw off the auto blend you can manually blend the layers using the erase tool.


It takes a while to learn the technique, but if you're an obsessive pixel peeper and plan to make large prints like I do, then it's the way to go!

---------- Post added 01-13-15 at 09:04 AM ----------

I just got my 28-45 last week and have done some shooting with it. I find it sharper than both my 35mm A and 25mm D FA and am very happy with it since it drastically reduces my lens swapping in the field. The only thing is that star bursts aren't rendered as beautifully as with the 35mm A, but I can live with that. I may end up selling the other two lenses, since I see myself using them much less now.
01-13-2015, 11:13 AM   #10
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Agree that attempting deep DOF shots affects sharpness due to diffraction. However this is classic reason why many of us own two or three formats. You might want to investigate a 4x5. With 20 square inches of film, an f/32 or f/45 shot will still look very sharp at large size prints. If most of your work requires deep DOF, the larger format is something to consider.
01-13-2015, 11:29 AM   #11
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QuoteOriginally posted by desertscape Quote
Agree that attempting deep DOF shots affects sharpness due to diffraction. However this is classic reason why many of us own two or three formats. You might want to investigate a 4x5. With 20 square inches of film, an f/32 or f/45 shot will still look very sharp at large size prints. If most of your work requires deep DOF, the larger format is something to consider.

Plus you can focus on a plane by tilting
01-13-2015, 11:58 AM   #12
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QuoteOriginally posted by ndevlin Quote
The other thing is that DOF with a 51MP digital camera is not your daddy's DOF. Things that used to looks sharp to us on film will be palpably not 100% crisp at 100% pixel view in digital. The DOF was the same with film, of course, but the film was way more forgiving of imperfection.
Most people I know pin this phenomenon on two factors:
1. Film captures the image plane over its entire thickness, increasing apparant DOF. Film is around 0.05-0.14mm thick, and it takes 0.1mm or less to lose critical focus on digital, so you can see how this may not be a trivial concept at all.
2. Film gradually loses contrast as it approaches it's resolution limit, while sensors maintain over 95% contrast until they hit their limit, making the effects of diffraction much more apparant and detrimental to image quality.

Last edited by Kolor-Pikker; 01-14-2015 at 05:02 AM.
01-13-2015, 03:48 PM   #13
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QuoteOriginally posted by Kolor-Pikker Quote
Most people I know pin this phenomenon on two factors:
Regarding film thickness-- an example is Velvia 50 in 120 or 220 size-- It is 98 microns or about 1/10 of a mm thick. Sheet film being nearly twice as thick.
When a lens is stopped down, not only does the depth increase in front of the diaphragm but it does also behind it. That translates to an increased depth of focus; one that is way thicker than the media used. The media thickness is of no consequence in this case.
01-13-2015, 11:09 PM   #14
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QuoteOriginally posted by desertscape Quote
Regarding film thickness-- an example is Velvia 50 in 120 or 220 size-- It is 98 microns or about 1/10 of a mm thick. Sheet film being nearly twice as thick.
Hmm, that's much thinner than I got from searching around online, is there a definitive list of slide and transparency film thicknesses?

Edit: apparantly the US has a measurement called Mil that's a 1/1000th of an inch, it seems easy to confuse for the verbose shorthand of millimeter since both are pronounced "mil" and that it's used nowhere else but for wire diameter in the states. I fixed my earlier post to reflect this.

Last edited by Kolor-Pikker; 01-14-2015 at 05:10 AM.
01-13-2015, 11:50 PM   #15
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If you used f22 as I have read, yes, you are getting refraction issues, the lest best sharpness is around f11, and I have actually compared it to the 25mm and the 28-45 is way sharper from full open to f22.
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