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11-27-2010, 07:03 AM   #16
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I don't disagree with this, but really the only reason to consider the cost and hassle of MF is IQ. To get IQ that beats the D3x (it's nearest downward competitor), a lot of stars need to align. Focussing is one of them.

An article on "MF - Is it worth it?" is brewing in my mind. There's obviously no universally applicable "yes" / "no" answer, but the many photographers never really even ask the question the right way.

While there are good reasons to chose Pentax over the other MF systems if you are getting into MF presently, I wouldn't suggest anyone switch to the 645D from another comparable MF system right now. It might be a much better camera, but they will sell as many as they can make for months to come, so let others suffer the agony of early adoption (such as in my case, sending the camera back for mechanical repair, along with a brace of lenses to calibrate to the camera, assuming they can do that).

Cheers,

- N.

11-27-2010, 08:20 AM   #17
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QuoteOriginally posted by paratom Quote
But you a re probably right that I shall wait - specially it concerns me if some people might have AF issues. I have learned that accurate focus is really critical to take advantage of the bigger sensor.
Tom
Although AF absolutely should work without "issues" I cannot imagine why anyone would use it except for moving subjects. For landscapes, which is the camera main target market, hyperfocal focusing is the name of the game and AF is just in the way here. The focusing screen is good enough for precise manual focusing.
11-27-2010, 03:23 PM   #18
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QuoteOriginally posted by Pål Jensen Quote
Although AF absolutely should work without "issues" I cannot imagine why anyone would use it except for moving subjects. For landscapes, which is the camera main target market, hyperfocal focusing is the name of the game and AF is just in the way here. The focusing screen is good enough for precise manual focusing.
I will probably wait a little longer. However I find MF also nice for shooting portrait images and even images of my kid (I like the skin tones and tonality I get with MF) and for this AF doesnt hurt.
However I am concerned with the comments about AF calibtration (my M9 with 5 lenses is on a trip to Leica for calibration right now). I would like to see and be sure that the AF is really reliable. Speed is not as much an issue as accurancy for me.
11-27-2010, 03:47 PM   #19
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I doubt any AF system on the planet will give 100% accurate focus at the pixel peeping level of a 40mp camera. I believe the error margin in the system is too large for that. AF detection systems provides a ballpark figure of absolute focus and the error margins is usually covered by DOF. In addition, theres the tolerances in the implementation of the AF system (mirror box, sensor placement and alignment, AF sensor placement) and then there's the lenses... Again, for best results, AF is best when it can do a better job than yourself; that is how it is with most auto features on our cameras...

11-28-2010, 02:00 AM   #20
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QuoteOriginally posted by Pål Jensen Quote
I doubt any AF system on the planet will give 100% accurate focus at the pixel peeping level of a 40mp camera. I believe the error margin in the system is too large for that. AF detection systems provides a ballpark figure of absolute focus and the error margins is usually covered by DOF. In addition, theres the tolerances in the implementation of the AF system (mirror box, sensor placement and alignment, AF sensor placement) and then there's the lenses... Again, for best results, AF is best when it can do a better job than yourself; that is how it is with most auto features on our cameras...
I am afraid that I might agree with you . On the other side my Nikon AF is more accurate than my eye.
11-28-2010, 09:31 AM   #21
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QuoteOriginally posted by Pål Jensen Quote
Although AF absolutely should work without "issues" I cannot imagine why anyone would use it except for moving subjects. For landscapes, which is the camera main target market, hyperfocal focusing is the name of the game and AF is just in the way here. The focusing screen is good enough for precise manual focusing.
I wish you were right, but my experience says otherwise. Forget everything you know about hyperfocal in film when dealing with digital. I don't find the focussing screen good enough. It's damn hard to use, frankly. I'm thinking of buying the focus magnifier for just this reason.

- N.
11-28-2010, 10:03 AM   #22
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QuoteOriginally posted by ndevlin Quote
... I don't find the focusing screen good enough. It's damn hard to use, frankly. I'm thinking of buying the focus magnifier for just this reason.
I use a focus magnifier on my K20D for exactly this reason. The magnifier remains attached to the camera. It flips down for focusing and flips up for framing. It makes quite a difference. Small focusing errors are visible when viewed under magnification. Of course this also requires that the focusing screen be adjusted accurately (and that you use a good quality ground-glass screen). For most of their cameras, Pentax sells shims in various sizes that can be used to fine-tune the focusing screen. I'm not sure how the screen is adjusted on the 645D, but I would think that the professional support offered by Pentax for the 645D should include this adjustment.

The larger viewfinder of the 645D should aid in focusing, but this is likely offset by the fact you need to focus much more accurately (given the higher resolution and narrower depth of field). Even with a crop-sensor DSLR, I have been surprised to find that very small improvements in focusing accuracy yield large improvements in sharpness when images are viewed at 100 percent. Focusing accuracy must be even more important when trying to squeeze all the benefits out of medium-format digital.

Dan
11-29-2010, 01:40 AM   #23
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Mmmh, I have to say the Hy6 viewfinder is so bright and nice (at least when you use fast lenses with f2.0 or f2.8) that manual focus works pretty good.

Are you suggesting the Pentax 645D is not so great regarding manual focus/viewfinder?
QuoteOriginally posted by Dan Quote
I use a focus magnifier on my K20D for exactly this reason. The magnifier remains attached to the camera. It flips down for focusing and flips up for framing. It makes quite a difference. Small focusing errors are visible when viewed under magnification. Of course this also requires that the focusing screen be adjusted accurately (and that you use a good quality ground-glass screen). For most of their cameras, Pentax sells shims in various sizes that can be used to fine-tune the focusing screen. I'm not sure how the screen is adjusted on the 645D, but I would think that the professional support offered by Pentax for the 645D should include this adjustment.

The larger viewfinder of the 645D should aid in focusing, but this is likely offset by the fact you need to focus much more accurately (given the higher resolution and narrower depth of field). Even with a crop-sensor DSLR, I have been surprised to find that very small improvements in focusing accuracy yield large improvements in sharpness when images are viewed at 100 percent. Focusing accuracy must be even more important when trying to squeeze all the benefits out of medium-format digital.

Dan


11-29-2010, 04:10 AM   #24
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QuoteOriginally posted by paratom Quote
Are you suggesting the Pentax 645D is not so great regarding manual focus / viewfinder?

No pentax DSLR viewfinder ideal for manual focusing, but then again neither are my Canon or Nikon bodies. Granted, my Canon 1DsMKII and Nikon D3s are full frame cameras and have bigger viewfinders but manually focusing an f/1.2 lens isn't easy without some form of electronic/focusing screen confirmation. The focusing screens you typically find on DSLR cameras today are designed to transmit more light than they used to, the drawback to that is they don't have enough "snap" and make it difficult to see whether the subject is focus or not.
11-29-2010, 04:55 AM   #25
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I have a 645D, a 5Dii, a 1DSii and a couple of 67ii's. All fitted with the default screens (so please interpret my comments with that in mind - I don't know if other screens might change my conclusions). From my own experience, the 645D has a better viewfinder all around than either of the Canons and can certainly be manually focused more easily (including with the variety of 67 lenses I am using). However, the 67ii finder is superior and easier to use with manual focusing.
11-29-2010, 07:25 AM   #26
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Dear All:

Given the tolerances of sensors it's easy to see the need for focus accuracy in terms of best image quality, especially when large prints are made. In my mind there is no pretty good when it comes to focus. It's either right or it's not.

Digitalis points out the difficulty getting a dslr into focus at times. Disconcerting news for the perfectionist.

From what I've read it seems that auto focus is a hit or miss proposition on mfdslr and manual focus is required. Since there's no penalty with multiple exposures and there's software available why doesn't focus blending or focus bracketing solve the focus problem? That's given that there isn't another fly in the ointment, as in lens performance, operator error, sensor mis- alignment....etc.

I've seen critical focus errors over and over again with medium format.

Oh well, tough love.

Claude Fiddler
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11-29-2010, 11:51 AM   #27
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@ paratom:

im german, owned a 645D since 2 Weeks, email me and you can get my phone number so we can have a talk about the Camera ;-))

for the rest: i have NO, absolut no focus issues with my example, the matte screen is nearly so good as the screen from the 67II. I only miss the miroprismfield, but if we all howling a lot, maybe Pentax is willing to here us ??

Focussing manuell an with AF give always the same focusspoint, so i realy like the Camera.

And i work most of the time not in the studio, my prefer workplace is an military training area, now we have -4°C, mud, snow, bad dull light and all the happiness you can have between tanks and weapons and soldiers ,-))
11-29-2010, 02:10 PM   #28
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QuoteOriginally posted by Frank Michael Quote
@ paratom:

im german, owned a 645D since 2 Weeks, email me and you can get my phone number so we can have a talk about the Camera ;-))

for the rest: i have NO, absolut no focus issues with my example, the matte screen is nearly so good as the screen from the 67II. I only miss the miroprismfield, but if we all howling a lot, maybe Pentax is willing to here us ??

Focussing manuell an with AF give always the same focusspoint, so i realy like the Camera.

And i work most of the time not in the studio, my prefer workplace is an military training area, now we have -4°C, mud, snow, bad dull light and all the happiness you can have between tanks and weapons and soldiers ,-))
Does Pentax offer a focusing screen perhaps optimized for manual focus lenses? Thanks
Dave
11-29-2010, 05:47 PM   #29
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Hi Nick,

This point about tolerances cannot be over emphasized, and it is equally true for film. I recently adapted 120, 180 and 300 Carl Zeiss Jena lenses for my Pentax 67II, which in all cases requires the manufacture of spacers to fit between the lenses and the new 67 mounts. A friend recommended a tolerance of 0.010mm or 10 microns in the thickness of the spacer over its entire (mounting) surface. At first, I doubted this requirement, but prototype manufacture and testing indicated it was indeed true. This requirement turned the fabrication of the spacers into a rather formidible task, requiring multiple repetition of the surface finishing step with excessive measurement of thickness using very precise measurement tools.

So yes, for "perfect" picture quality, the lens, the mount and the sensor must all be aligned within tolerance. The fact that "the 75mm lens did just fine" tends to implicate the lens, rather than the mount or the sensor, but only after one could verify with absolute certainty that the camera and the wall were correctly aligned.

Best, Alan

QuoteOriginally posted by ndevlin Quote
Thanks for the kind words, glad you enjoyed the write-up.

While I originally blamed sensor-angle, we have added an addendum to the article in which we posit that internal misalignment of the sensor or lens plane is a more likely culprit.

The more I think about this, the more likely I feel that this is the explanation, perhaps operating in conjunction with a failure to achieve perpendicularity to the wall (not a real concern in the real world).

On further reflection, I think it is likeliest that the lens is to blame, at least on my camera, since the fixed 75mm did just fine.

I'm going to reshoot this later this week, with a different camera along as well, just to mess around with this issue.

What this illustrates, however, is just how tight tolerances have to be in the digital world for 'ultimate' image quality to be realized.

Hopefully, however, our article also made it clear that the difference between "ultimate IQ" and what you actually get in a print is so minor to as to make little practical difference in most real-world applications.

Cheers!

- N.
11-29-2010, 08:20 PM   #30
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QuoteOriginally posted by ndevlin Quote
While I originally blamed sensor-angle, we have added an addendum to the article in which we posit that internal misalignment of the sensor or lens plane is a more likely culprit.
Frankly I'm amazed that you don't really know what happened, yet you give Pentax some homework to do at the end of your article.
It all begins to make sense, and it all delivers a message to the other camera manufacturers to get their act together: in this pricing stratosphere, there's no excuse for not going the whole nine yards on technical excellence.
What if it turns out that Pentax is not to blame? Wouldn't that be mighty embarrassing?

QuoteOriginally posted by ndevlin Quote
Forget everything you know about hyperfocal in film when dealing with digital.
Hmmh, perhaps you want to write to all the DOF calculator websites that they have to change their software. Well, perhaps not.

In your article you also write
While DOF should cover off an minor angularity on the plane of focus at these focal lengths at this distance, it has been suggested that DOF with digital is not the same in practice as with film.
The idea that the notions of DOF and hyperfocal focusing change with digital photography is simply crazy.

Do you know the definition of DOF? Do you know that it includes a definition of acceptable sharpness that a) differs among manufacturers and b) certainly isn't based on the assumption of pixel-peeping at 100% crops?

Did you use a mirror to align the camera to the wall? That the wall should be within the DOF will not guarantee that it will stay sharp across the image. Only one infinitely thin plane is in exact focus, everything else behind or in front of it is out of focus. What is still acceptably sharp depends on the enlargement and the viewing distance. You certainly cannot expect pixel-to-pixel sharpness in 100% crops even if something is within the DOF.

Maybe the one Pentax lens has an issue after all, but I'm quite amazed what you are writing about digital DOF and hyperfocal focusing, and that you are happy to give Pentax some quality assurance homework without having any solid results yet.

QuoteOriginally posted by ndevlin Quote
... so let others suffer the agony of early adoption...
Agony?
Even if you personally had tough luck, why should someone else too and where is the "agony"?
Come on.

Last edited by Class A; 11-29-2010 at 08:26 PM.
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