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Author Topic: Guidance on buying a digital back for 500CM  (Read 26788 times)
Dave Gurtcheff
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« Reply #20 on: July 02, 2010, 03:27:07 PM »
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I do not undserstand why manual focus would work with film, and be a problem with digital. Isn't depth of field at a given f stop with a given lens independent of what the light hits? (film or sensor). I have a serious interest in this issue of MF digital manual focus. I have 4 beautiful manual focus Pentax 645 lenses, and I had fully intended getting the new 645D as soon as it is available in the US. Am I going to find the lenses are unuseable from a practical point of view? Pentax says all their legacy lenses, both AF & MF will work. Any help/advise?
Thanks in advance
Dave Gurtcheff
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VanKou
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« Reply #21 on: July 02, 2010, 06:29:15 PM »
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Quote from: fredjeang
John,

I will add another perspective to your statement. Not that I'm saying that you are wrong but I have a slightly different experience.
Don't know if this is a 500's exacerbate issue that's involved.

When I first hanged the Contax and focus manually, my rate of well-focussed frames was extremely low, as you point.
Then I started to examinate the files and realised that the manual errors where always similar and start to apply little corrections in the field.
Using a reduced range of focals, you finally get used of, let's call it a sort of 6th sense and your brain automatically "understand" the idiosyncracy of one particular gear.

What you point is also true in FF 35mm if you use manual focus, but it is magnified in MF.

I completly agree that there is a big difference between film age, digital does not forgive.
But if an AF can get the correct point, is that correct point exists and can be trained.

IMO, not contradicting your experience on that matter, I think that most of the time, (or we are in times when) taking this training into account and
accepting a learning curve is what is also missing.

Many times I just want to focus quickly on a part of the frame that I just feel more "creative" and if I had to relly on any AF, I just miss the shot on moving objects.
So, yes, manual focussing is more complicated in digiland, but like it or not you have to train this sort of 6th sense (don't know how to call it).

If not then you are just chained to the machine. Because let's say you focus first AF then reframe very quickly. You will have to apply anyway a little correction manually.
If you don't train yourself in manual focussing, the way you will apply this correction will be hazardous.
That's also the case with any dslr.

You can not relly on the viewfinder really, but you end to learn in what sense the viewfinder is fooling you.

I also use a lot MLU on field and that also makes differences.

Again, I'm not contradicting your point and your experience, but adding a "yes but" that IMO has to be taken into consideration.

All I can tell you is that having taken the time to deal with that (insisting on focussing manually despite the issues), my rate of
well focussed images has increased dramatically on moving subjects, and I feel more free to frame and choose my focus point by myself.

Cheers.

Edit: Mr Reichmann pointed in some articles that when it comes to the P65 sort of backs, forget about brain training for focussing. I've never tryied such a back and I suppose it is logical.
But he also stressed that this not relly only on the AF but all the elements on the chain: tripod, MLU, exposure, lightning...
It happens that the AF of manual focussing has been correct but one element of that list where missing.


I use a 553ELX with an Imacon 584C multishot back and I shoot fashion and beauty mostly in a studio.  

Focusing was a big problem at the beginning but after making sure that my modeling lights were the strongest possible and I had the brightest screen to focus (I paid $300 for it on ebay) and after I get used to doing it, now, a year later my keepers are above 95%.  I actually started shooting at f/4 and results are pretty good.  As far as people are concerned, you got to make sure that there is a bright catch light on the model (or person) so that you can focus accurately.

I love the quality I am getting out my back.  You can underexpose by up to 2-3 stops and still pull shadow detail without any noise.  The colors and the detail are great

Evangelos
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K.C.
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« Reply #22 on: July 02, 2010, 08:57:57 PM »
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Quote from: VanKou
I use a 553ELX with an Imacon 584C multishot back and I shoot fashion and beauty mostly in a studio.
Not likely to be found on ebay for the $2700 the OP wishes to spend.
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John R Smith
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« Reply #23 on: July 03, 2010, 02:06:00 AM »
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Quote from: Dave Gurtcheff
I do not undserstand why manual focus would work with film, and be a problem with digital. Isn't depth of field at a given f stop with a given lens independent of what the light hits? (film or sensor). I have a serious interest in this issue of MF digital manual focus. I have 4 beautiful manual focus Pentax 645 lenses, and I had fully intended getting the new 645D as soon as it is available in the US. Am I going to find the lenses are unuseable from a practical point of view? Pentax says all their legacy lenses, both AF & MF will work. Any help/advise?
Thanks in advance
Dave Gurtcheff

Until you have actually experienced this for yourself, it is very hard to believe. And only those who have shot film for years on a particular camera/lens combination and then put a digital back on the same camera will have encountered it. But the fact is that your effective and usable depth of field appears to simply evaporate into thin air with a MF DB. And your ability to focus accurately seems to vanish along with it.

As you and the OP point out, DOF is DOF. The laws of physics are immutable and apply equally to whatever emulsion or medium the light from the lens falls on at the point of the focal plane. However, there seem to be other factors at work. All of us here, as photographers, have a highly developed sensitivity to focus and sharpness in a print. Much more so than non-photographers. In fact, rather similar to musicians who develop a refined sensitivity to pitch and can instantly tell when one of a group of instruments is out of tune.

There is actually no such thing as DOF. There is only one plane of focus in any photograph where the subject is perfectly sharp, a plane which has no physical depth. Everything else is out of focus to a greater or lesser degree. What happens is that the grain of film masks this. All film has some grain, and it covers the whole of the image, unlike digital noise. If you can imagine printing a photograph through ever coarser litho screens, then what you will observe is that the apparent depth of field increases because your ability to judge sharpness is progressively impaired by the screen. The sharp and soft parts become more equal, as resolution is diminished by breaking the image down into coarser chunks of information. (For an extreme example of this, walk up close to a big billboard poster. Can you tell any longer which parts of the image are in or out of focus? Or where the DOF begins and ends?)

Film grain works in the same way as the litho screen. We don't really see it most of the time (except perhaps in skies) but it is all pervading, and has the effect of expanding the area of apparent sharpness, which is what we call DOF. With a digital back of say 39 MP on a MF camera, grain suddenly ceases to exist for all practical purposes at low ISO. There is the granularity of the sensor photosites, of course, but the demosaic algorithms are designed to process this out and interpolation ensures that we never see it.

With (effectively) no grain, we can see for the first time exactly where true focus is. Without the screening effect of grain, the sharp parts of the image appear sharper and the soft parts appear softer. It is rather like going from ISO 400 film on MF to ISO 25 on a 10x8 view camera. And we find, to our horror and dismay, that what was good enough in terms of focus and DOF for film falls far short on a high-end digital back.

John
« Last Edit: July 04, 2010, 05:27:35 AM by John R Smith » Logged

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Rob C
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« Reply #24 on: July 03, 2010, 03:18:02 AM »
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Well John, I've pondered this focus probem for quite some time, and though I do think I had the reason understood, I had never really articulated it to myself in quite those terms. Thanks for giving me the mental short cut!

Regarding the 'blads, all my lenses were of the silver school and yes, I rmember how painful the fingers felt after a long studio session with any of those lenses! Not only the lenses, but also the filmwind knob can be a source of sore fingers after a long session. And yet, the machine was a beautiful camera to use.

Another writer mentions the trick of focussing on a brilliant highlight: that was one of the side-benefits of the era of large junk-jewellery when the model could just put her hand on her waist, chest, face or wherever and you got those points of sharpness glowing at you off the reflected modelling light. However, it isn't just the stiffness of the lenses but the relatively small maximum apertures that caused hassle with the Hassel - just too much dof in front of the lens and too little certainty in the dim screen.

But, accepting all of this argument about the differences between a sensor and film, I still believe that it all comes down to the same thing: on a given size of print, either film or digi look much the same and it's at 100% where the nonsense begins. I do not buy that your 10ins x 12ins print is going to look any less accurate from digital than from film. The 'masking' effect of film probably only comes into effect at the point of magnification where grain on a print becomes noticeable - prior to that magnification I imagine both media give the same degree of perceived focus accuracy. Like anything, when you take things to extremes they tend to fall down. Possibly like discussions on this very topic!

If I might divert the topic to one side for a sec - I have been looking through some early-80s magazines I'm weeding out in an effort to tidy up my life, and it is amazing to see how many double-page shots were used (French PHOTO) where by today's standards, they are mush! I can't say for sure if I thought them poor at the time, but as I bought the mag for many years, I must have thought them acceptable; I guess we do have rose-tinteds about past technology...

; - )

Rob C
« Last Edit: July 03, 2010, 03:19:14 AM by Rob C » Logged

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« Reply #25 on: July 03, 2010, 04:05:58 AM »
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Quote from: John R Smith
All of the V-System 500 series cameras were manufactured to the same (very high) tolerances. The same collimation tools are used to set them all up. You won't get a better result from a 503CW than a 500C just because of the age difference per se.

John,

In fairness I do not know a fact answer on the above. Same time in all respect but I find difficult to buy what you claim with it. It seems illogical that a 500C made in 1957 had same fabrication tolerances as a 503CW made today. Likewise it does not appear sense that they have used exact same machinery and fabrication tolerances over all these years without improvements.

Further, specifically regarding focus exactness; for film it was adequate with tolerances of film flatness of 0.2mm, while for digital a common tolerance is 0.02mm. That is ten times more exact. What I refer is not the DOF that is critical but the depth of focus, which is on the camera side of the lens. Thus, since newer Hassy 500 series are also made for digital backs, one would expect that they were made to stricter fabrication and adjustment tolerances.

I would also assume they improved on groundglass over the years which ought to help. As example, for 4x5 I use the Maxwell screen and it made world of different in focus.

---

At current I am reading up on the Hassy all out of curiousity because I find a camera with groundglass folding viewer interesting as compared to staring down pipe of my Mamiya 645 system. Thus it would be interesting to read comment if someone have had extensive experience on use of high res digital back on a newer Hassy V camera. I know it is outside O.P. but any info is much appreciated.

Regards
Anders
« Last Edit: July 03, 2010, 04:09:05 AM by Anders_HK » Logged
John R Smith
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« Reply #26 on: July 03, 2010, 05:59:40 AM »
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Quote from: Anders_HK
John,

In fairness I do not know a fact answer on the above. Same time in all respect but I find difficult to buy what you claim with it. It seems illogical that a 500C made in 1957 had same fabrication tolerances as a 503CW made today. Likewise it does not appear sense that they have used exact same machinery and fabrication tolerances over all these years without improvements.

Further, specifically regarding focus exactness; for film it was adequate with tolerances of film flatness of 0.2mm, while for digital a common tolerance is 0.02mm. That is ten times more exact. What I refer is not the DOF that is critical but the depth of focus, which is on the camera side of the lens. Thus, since newer Hassy 500 series are also made for digital backs, one would expect that they were made to stricter fabrication and adjustment tolerances.

I would also assume they improved on groundglass over the years which ought to help. As example, for 4x5 I use the Maxwell screen and it made world of different in focus.

Anders

Only someone from the factory in Sweden could answer this for sure. It may be, that the recent 503 which was sold as a set with the CFV back as part of the package was indeed set up to higher tolerances with the included sensor. But I somehow doubt it. All the 500 (and 2000 and 200) series cameras are set up with exactly the same lens mount to film plane geometry. They have to be, because you can use the oldest lens on the newest cameras and the newest lens on the oldest cameras. And all the film magazines are totally interchangeable, right back to 1957. To make this possible, the tolerances in manufacture have to be very tight indeed. One of the ways in which this was done is that the camera itself is a seperate body within an outer shell. The inner body can be removed for CLA without disturbing any of the crucial mounting points between lens and film plane, mirror and focus screen, and these planes of reference are protected from wear or damage by the rugged outer shell.

For what it is worth, my observation through purchasing and using a great deal of 'Blad V-system gear is that quality of design and manufacture actually declined over the years. The early magazines are better made and finished than the later ones, for example, and that goes for a lot of the rest of the range. A great deal was re-designed, simplified and cheapened as time went on. And I say this from the perspective of having dismantled and serviced most of my kit. I sold and traded all my later V-system gear for the older original versions over time because of this.

The focus screens were indeed improved over the years. Hasselblad eventually went to Minolta for the Acute-Matte screens, which are an essential upgrade for any 500 - I have three, and they are light years ahead of the old standard screens.

The problems I have had with my old 500 kit are nothing to do with manufacturing tolerance, I am sure. I can shoot off a tripod with my ancient 120mm S-Planar on the most critical of still-life subjects and get razor-sharp results. It is out in the field where you can't spend half an hour setting up each shot that the snags arise.

John
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« Reply #27 on: July 03, 2010, 07:49:55 AM »
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Quote from: John R Smith
Anders

Only someone from the factory in Sweden could answer this for sure. It may be, that the recent 503 which was sold as a set with the CFV back as part of the package was indeed set up to higher tolerances with the included sensor. But I somehow doubt it. All the 500 (and 2000 and 200) series cameras are set up with exactly the same lens mount to film plane geometry. They have to be, because you can use the oldest lens on the newest cameras and the newest lens on the oldest cameras. And all the film magazines are totally interchangeable, right back to 1957. To make this possible, the tolerances in manufacture have to be very tight indeed. One of the ways in which this was done is that the camera itself is a seperate body within an outer shell. The inner body can be removed for CLA without disturbing any of the crucial mounting points between lens and film plane, mirror and focus screen, and these planes of reference are protected from wear or damage by the rugged outer shell.

For what it is worth, my observation through purchasing and using a great deal of 'Blad V-system gear is that quality of design and manufacture actually declined over the years. The early magazines are better made and finished than the later ones, for example, and that goes for a lot of the rest of the range. A great deal was re-designed, simplified and cheapened as time went on. And I say this from the perspective of having dismantled and serviced most of my kit. I sold and traded all my later V-system gear for the older original versions over time because of this.

The focus screens were indeed improved over the years. Hasselblad eventually went to Minolta for the Acute-Matte screens, which are an essential upgrade for any 500 - I have three, and they are light years ahead of the old standard screens.

The problems I have had with my old 500 kit are nothing to do with manufacturing tolerance, I am sure. I can shoot off a tripod with my ancient 120mm S-Planar on the most critical of still-life subjects and get razor-sharp results. It is out in the field where you can't spend half an hour setting up each shot that the snags arise.

John

John,

I have written Hasselblad in Goteborg, Sweden to ask them - in Swedish. By the way Goteborg is my hometown of birth and where I grew up, which is an interesting spice to my curiosity about the Hasselblad V!

Basically if I interpret what you have written above, your above post highlight (apart from focus screen);

1. System dimensions / standard for critical dimensions of the system.

2. Fabrication and adjustment tolerances.

3. Changes in materials and assembly of other than the above.


Of the above three, 1 is mandatory, while 2 is critical for digital, and 3 will not effect the photos.

I will post their reply, assuming I will receive it.

Regards
Anders
« Last Edit: July 03, 2010, 07:50:35 AM by Anders_HK » Logged
John R Smith
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« Reply #28 on: July 03, 2010, 01:01:20 PM »
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Anders

The reply from Hasselblad will certainly be very interesting. I look forward to it.

As an aside - if indeed the tolerance for digital sensor focal plane is 0.02mm (and Joseph Holmes says something like the same thing) then I really can't believe that any MF camera with a removable back can be within that tolerance. Just the mere fact of being able to remove and replace the back would mean that you could never achieve such close measurements, as even the slightest wear in the mount would throw it off. Just the expansion of the body between winter and summer temperatures would be more than that. Surely only a fully integrated camera could be so precise? However Phase or anyone else does it, I would be pretty certain that no 500 series Hasselblad could get close to 0.02mm, whatever the back. Well, I bet mine aren't, that's for sure  

John
« Last Edit: July 03, 2010, 02:47:05 PM by John R Smith » Logged

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Dave Gurtcheff
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« Reply #29 on: July 03, 2010, 03:33:01 PM »
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Quote from: John R Smith
Until you have actually experienced this for yourself, it is very hard to believe. And only those who have shot film for years on a particular camera/lens combination and then put a digital back on the same camera will have encountered it. But the fact is that your effective and usable depth of field appears to simply evaporate into thin air with a MF DB. And your ability to focus accurately seems to vanish along with it.

As you and the OP point out, DOF is DOF. The laws of physics are immutable and apply equally to whatever emulsion or medium the light from the lens falls on at the point of the focal plane. However, there seem to be other factors at work. All of us here, as photographers, have a highly developed sensitivity to focus and sharpness in a print. Much more so than non-photographers. In fact, rather similar to musicians who develop a refined sensitivity to pitch and can instantly tell when one of a group of instruments is out of tune.

There is actually no such thing as DOF. There is only one plane of focus in any photograph where the subject is perfectly sharp, a plane which has no physical depth. Everything else is out of focus to a greater or lesser degree. What happens is that the grain of film masks this. All film has some grain, and it covers the whole of the image, unlike digital noise. If you can imagine printing a photograph through ever coarser litho screens, then what you will observe is that the apparent depth of field increases because your ability to judge sharpness is progressively impaired by the screen. The sharp and soft parts become more equal, as resolution is diminished by breaking the image down into coarser chunks of information.

Film grain works in the same way as the litho screen. We don't really see it most of the time (except perhaps in skies) but it is all pervading, and has the effect of expanding the area of apparent sharpness, which is what we call DOF. With a digital back of say 39 MP on a MF camera, grain suddenly ceases to exist for all practical purposes at low ISO. There is the granularity of the sensor photosites, of course, but the demosaic algorithms are designed to process this out and interpolation ensures that we never see it.

With (effectively) no grain, we can see for the first time exactly where true focus is. Without the screening effect of grain, the sharp parts of the image appear sharper and the soft parts appear softer. It is rather like going from ISO 400 film on MF to ISO 25 on a 10x8 view camera. And we find, to our horror and dismay, that what was good enough in terms of focus and DOF for film falls far short on a high-end digital back.

John
John: Thanks for the quite thorough explanation. This does not bode well for my planned Pentax 645D body to use with my four manual focus Pentax 645 lenses (45mm, 55mm, 75mm & 80~160 zoom). My intended use is ONLY lanscape/seascape, where I would use my present method of shooting, namely f11 or 16, focused (manually or AF) on some object about one third into the scene. It works perfectly with manual & AF lenses with Full Frame 1DSIII and Alpha 900. Also, I wonder out loud if the Pentax lenses might use an electronic in-focuse light/beep when using MF Pentax lenses (the MF lenses do have contacts on the lens mount). I suspect I will hold off on a 645D purchase, until someone has had a chance to review the performance with MF lenses (I suspect sooner or later, someone will make some tests/trials and report back)
Thanks again for taking the time to explain
Dave
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John R Smith
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« Reply #30 on: July 03, 2010, 04:02:11 PM »
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Dave

There was a little write-up in our Amateur Photographer journal this week by Damien Demolder, who has handled and taken some shots with the new Pentax. One of the things he mentioned was how good the viewfinder and focusing screen was. If the prism has a good magnification, and the screen is indeed very good, you may find that manual focus is perfectly OK using your existing lenses. There will still be less subjective DOF than with film, but if your focus is good, half the battle is won. This is a 2010 camera, after all, and my 'Blads are the 1957 version.

John
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Dave Gurtcheff
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« Reply #31 on: July 03, 2010, 04:42:03 PM »
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Quote from: John R Smith
Dave

There was a little write-up in our Amateur Photographer journal this week by Damien Demolder, who has handled and taken some shots with the new Pentax. One of the things he mentioned was how good the viewfinder and focusing screen was. If the prism has a good magnification, and the screen is indeed very good, you may find that manual focus is perfectly OK using your existing lenses. There will still be less subjective DOF than with film, but if your focus is good, half the battle is won. This is a 2010 camera, after all, and my 'Blads are the 1957 version.

John
Thanks again John. Naive question: lately I have made some really wonderous blow ups to 20"x30" using A900 files, and using "Exposure" or "Filmpack" and emulating Fuji Velvia, complete with grain. Would this help the "focus issue" because of lack of film grain?
Thanks again
Dave
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« Reply #32 on: July 03, 2010, 07:32:08 PM »
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Quote from: John R Smith
Anders

The reply from Hasselblad will certainly be very interesting. I look forward to it.

As an aside - if indeed the tolerance for digital sensor focal plane is 0.02mm (and Joseph Holmes says something like the same thing) then I really can't believe that any MF camera with a removable back can be within that tolerance. Just the mere fact of being able to remove and replace the back would mean that you could never achieve such close measurements, as even the slightest wear in the mount would throw it off. Just the expansion of the body between winter and summer temperatures would be more than that. Surely only a fully integrated camera could be so precise? However Phase or anyone else does it, I would be pretty certain that no 500 series Hasselblad could get close to 0.02mm, whatever the back. Well, I bet mine aren't, that's for sure  

John

John,

Actually it is not as difficult as you outline. The camera and lens can be built to the old 0.2mm tolerance but lens need perfect adjusted to be parallel to mounting plane for back. Then there need to be certain exactness in focus chain. As of course optic members in lens need be mounted parallel too.

Hassy V lenses start from 40mm (not counting fisheye), and have respectable distance from sensor. That makes relative ease. Compare this to Scheider 24mm Digitar XL large format lens which have only sits with flange ca 24mm from sensor and has thus 0.3mm total focus travel from 5m distance to infinity. That makes more difficult. Longer lenses is more simple I guess, because depth of focus is larger - if I got it all right. Thus important is really mounting of lens parallel to back.

I hope Hassy replies, I think interesting.

Regards
Anders
« Last Edit: July 03, 2010, 07:39:55 PM by Anders_HK » Logged
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« Reply #33 on: July 03, 2010, 07:55:02 PM »
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Quote from: John R Smith
Anders

The reply from Hasselblad will certainly be very interesting. I look forward to it.

As an aside - if indeed the tolerance for digital sensor focal plane is 0.02mm (and Joseph Holmes says something like the same thing) then I really can't believe that any MF camera with a removable back can be within that tolerance. Just the mere fact of being able to remove and replace the back would mean that you could never achieve such close measurements, as even the slightest wear in the mount would throw it off. Just the expansion of the body between winter and summer temperatures would be more than that. Surely only a fully integrated camera could be so precise? However Phase or anyone else does it, I would be pretty certain that no 500 series Hasselblad could get close to 0.02mm, whatever the back. Well, I bet mine aren't, that's for sure  

John

For what it is worth, the need for a very accurate positioning of sensor vs lens mount was cited by Pentax as a major reason why they decided to go the integrated route with the 645D.

The fact that Leica took the same design decision with the S2 makes me think that it does indeed make sense.

I had interesting conversation with Nikon engineers a few years back who were focusing on improving all the aspects of the imaging chain at the same time:
- sensor
- physical positioning
- accuracy of AF
- ...

The weakest part basically defines image quality.

Cheers,
Bernard
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« Reply #34 on: July 03, 2010, 09:50:47 PM »
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Quote from: Anders_HK
John,

Actually it is not as difficult as you outline. The camera and lens can be built to the old 0.2mm tolerance but lens need perfect adjusted to be parallel to mounting plane for back. Then there need to be certain exactness in focus chain. As of course optic members in lens need be mounted parallel too.

Hassy V lenses start from 40mm (not counting fisheye), and have respectable distance from sensor. That makes relative ease. Compare this to Scheider 24mm Digitar XL large format lens which have only sits with flange ca 24mm from sensor and has thus 0.3mm total focus travel from 5m distance to infinity. That makes more difficult. Longer lenses is more simple I guess, because depth of focus is larger - if I got it all right. Thus important is really mounting of lens parallel to back.

I hope Hassy replies, I think interesting.

Regards
Anders


I have four "V" bodies EL/M, 503CW, 203FE and SWC.  The EL/M is rarely used but using the other three, I think that my 40 year old SWC gives the best focus and perceived DOF with my  CFV back.  With SWC, the rear of the 38mm Biogon is ~25mm from the sensor.

Steve
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« Reply #35 on: July 04, 2010, 01:20:55 AM »
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Hi,

I agree with what John is saying, with some more comments.

The first issue is that there are two major differences between film and digital sensors regarding DOF. The first one is that film is not really fat and has also a significant thickness. What this essentially means that focus on film is less well defined than on a digital sensor. The other factor is that the digital image is often studied at very high resolution. In the film days I used a 15X loupe to check sharpness but I'm quite confident that 30X or 40X would be more adequate. In younger days I checked Kodakchrome slides on a Leitz microscope under 100X and 400X magnification. So the issues are:

- Film not necessary less incriminating than digital but the uncertainty of focus is larger
- We normally evaluate digital images under more discriminating conditions than we used to have with film

So DoF is actually the same on film and digital as long as you look at prints.

Let's look at things like this. The DoF scale on the lens barrel is normally based on a CoC (Circle of Confusion) of 0.066 mm (1/15 mm). If you regard a high resolution back, like the P65+ it will have a pixel pitch less than 6 micron (0.006) mm. This essentially means the normally used CoC would cover 11 pixels across or it would cover 97 pixels. So as long you look at the screen at 1:1 magnification the Circle of Confusion would be 11 pixels across. The situation would not be better if you scanned film at 4200 PPI. (Note: 1/15 mm is typically used for DoF calculations for MF film, 1/30 mm has been used in practice for 135 film.)  DoF scales are based on the assumption that we would look at small prints (like 5x7") and convenient viewing distance.

Normally, when I used film I would use the f/22 DoF markings when using f/8. Also consider that we loose sharpness due to diffraction when we stop down beyond f/8, my experience is that the loss of sharpness is acceptable until f/16 but sharpness really starts to drop beyond that. See it this way, f/22 turns your 40 MP back  into a 10 MP back.

I would recommend that you check out the following articles:

http://www.josephholmes.com/news-sharpmediumformat.html

http://www.josephholmes.com/news-medformatprecision.html

This lengthy thread started by 'Anders HK'
http://luminous-landscape.com/forum/index....&pid=153549

Some testing I have done:

http://echophoto.dnsalias.net/ekr/index.ph...-sony-alpha-900

http://echophoto.dnsalias.net/ekr/index.ph...ng-the-dof-trap

Best regards
Erik


Quote from: Dave Gurtcheff
John: Thanks for the quite thorough explanation. This does not bode well for my planned Pentax 645D body to use with my four manual focus Pentax 645 lenses (45mm, 55mm, 75mm & 80~160 zoom). My intended use is ONLY lanscape/seascape, where I would use my present method of shooting, namely f11 or 16, focused (manually or AF) on some object about one third into the scene. It works perfectly with manual & AF lenses with Full Frame 1DSIII and Alpha 900. Also, I wonder out loud if the Pentax lenses might use an electronic in-focuse light/beep when using MF Pentax lenses (the MF lenses do have contacts on the lens mount). I suspect I will hold off on a 645D purchase, until someone has had a chance to review the performance with MF lenses (I suspect sooner or later, someone will make some tests/trials and report back)
Thanks again for taking the time to explain
Dave
« Last Edit: July 04, 2010, 01:26:50 AM by ErikKaffehr » Logged

John R Smith
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« Reply #36 on: July 04, 2010, 01:59:38 AM »
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Quote from: vandevanterSH
I have four "V" bodies EL/M, 503CW, 203FE and SWC.  The EL/M is rarely used but using the other three, I think that my 40 year old SWC gives the best focus and perceived DOF with my  CFV back.  With SWC, the rear of the 38mm Biogon is ~25mm from the sensor.

Steve

That's interesting Steve, but the Biogon is noted as one of the best lenses Zeiss ever made. And you need to compare like with like, really - the SWC versus the 40mm on the 503. Also, which CFV back are you using? Because the SWC apparently has more issues on the 39 MP than on the 16 MP, which is what you would expect.

John
« Last Edit: July 04, 2010, 03:54:58 AM by John R Smith » Logged

Hasselblad 500 C/M, SWC and CFV-39 DB
and a case full of (very old) lenses and other bits
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« Reply #37 on: July 04, 2010, 04:14:00 AM »
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Digital on the 501 with a P20 can be easily summarised:


Henry Wadsworth Longfellow (1807-1882)


"And when she was good, she was very, very good,
But when she was bad she was horrid."

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Chris Livsey

http://www.flickr.com/photos/red_eyes_man/

It's not what you look at that matters, it's what you see.
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« Reply #38 on: July 04, 2010, 04:44:23 AM »
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Quote from: Dave Gurtcheff
Thanks again John. Naive question: lately I have made some really wonderous blow ups to 20"x30" using A900 files, and using "Exposure" or "Filmpack" and emulating Fuji Velvia, complete with grain. Would this help the "focus issue" because of lack of film grain?
Thanks again
Dave

It can, and does, Dave. You can make the experiment yourself using a very low ISO grainless digital file, and add progressively larger amounts of gaussian noise to it using PS. If you then print enlarged sections from the centre of the file, you will see an apparent increase in DOF as the "grain" gets larger and heavier. However, this is something I avoid, because one of the reasons for spending huge sums of money on a digital back was to get better IQ than film on MF, and rather more like the super-smooth tonality from a view camera. And when everything goes right, the 39 MP back delivers just that.

"And when she was good, she was very, very good,
But when she was bad she was horrid."

Nice one, Chris, that just about sums up a conclusion for this topic  

John
« Last Edit: July 04, 2010, 06:09:06 AM by John R Smith » Logged

Hasselblad 500 C/M, SWC and CFV-39 DB
and a case full of (very old) lenses and other bits
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« Reply #39 on: July 04, 2010, 12:02:02 PM »
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Quote from: John R Smith
That's interesting Steve, but the Biogon is noted as one of the best lenses Zeiss ever made. And you need to compare like with like, really - the SWC versus the 40mm on the 503. Also, which CFV back are you using? Because the SWC apparently has more issues on the 39 MP than on the 16 MP, which is what you would expect.

John

I agree...my response was more directed to the comment ".. and have respectable distance from sensor. That makes relative ease. Compare this to Scheider 24mm Digitar XL large format lens which have only sits with flange ca 24mm from sensor"..  

I'm just a hobbyist but in "controlled" situations, ie inside, D-40 flash, tripod etc., any "V" body + any lens + CFV produces repeatable, spectacular,  sharpness and "fall into the image" "apparent" DOF.  Out in the "wild" similar results are much less frequent and seem to be more "hit or miss".  At least my "inside" pictures reassures me that the basic camera/sensor geometry is OK. (I think)

steve
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