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Hasselblad Vacuum backs - magazines for roll-films 220

Presently is coming, what I mentioned in the initial part of the "Technique" section. I am going to disclose one of many secrets leading to the exceptional brilliance results when you are working with the medium format equipment using roll films.

As you can guess or even know - digital chips are definitely not my cup of tea. This has many reasons. For me crucial are:

1. The global marketing lobby does not intent to grant the production and sale of the full-frame chips for the medium format cameras - especially not for the format of 6x6 cm (55 x 55 mm), although these were developed and tested long time ago.

2.
The effective color resolution of the largest and commercially available digital back is 39/4 for blue and red, and 39/2 for green color = approximately 11 megapixels. The results of this nasty interpolation is disastrous moire and false colors along the high contrast lines and affecting objects of the size or width less than 2 image pixels. This issue can be solved by either the availability of a correctly working Foveon type chip (separate-color-sensitive elements are placed below each other) or, let's say, 1.5 or more times better physical resolution of the current digital back than the maximal resolution of the used lens. By the way, for example, we can eliminate a possibility of a small white spot being projected on the green pixel only, rendering such spot as green instead of white.

3. The dust and other crap on the chip or protective filter encasing real chip. This cannot be probably called the other way than "a product of global imbecility". It would not be a complicated design problem to insert this or any other protective filter closely behind the lens in front of the folding mirror. The crap coming inside the body would settle on the "front" filter in longer distance from the chip, from where it could not be displayed in the final image as hardly retouchable large dark "pancakes", disturbing especially on smooth areas. This is a flagrant example of the human idiotism, stupidity and ignorance.

4. Difficulties with battery charging outdoors and unpredictable behavior in the frosty or humid environment.

5. And finally perhaps the worst - the absence of the film grain, causing the flat up to nearly "plastics" appearance of the photographs, that are not powerful "to pull in" you into the action and leave you unemotional.

The most of us, who uses the medium format roll-film cameras, face difficulties with the correct focusing, especially in case of the small or zero stopping down (full-aperture shooting). The people that do not understand real fundamentals usually attribute the cause of the soft and uneven sharpness to the poor-quality optics. If they are in the picture, they are fallen to the situation when in the case of more than 5 minute lag between the single exposures, they are doomed to sacrifice next two frames to avoid the worst.

The common deviation from the ideal focal plane immediately after the 120 film rewind (pull on the camera) is usually around 0.2 mm and it increases over time by more than 0.5 mm and this is without speculating about extreme conditions as high humidity or temperatures well below freezing point - under these conditions it is "fuck it all :-).
This issue is well demonstrated by the Zeiss study - the Document is available for download here:

In simplified way, it can be stated that: "average error" of roll film 120 with the underlay paper base is typically in the magnitude of 350 microns (0.35 mm) and for roll film 220 (without the paper base) it is about 200 microns (0.2 mm). My own measurements correspond very well with another study, available for download here:

Based on this knowledge, it is very hard to understand why roll films 220 are not used exclusively, when if compared to 120 films it has a lot of advantages and almost double precision of the film position, because it is not forced away by the absolutely needless underlying paper. Thanks to ignorance and pointless fear of the "reflexes from the film pressure plate", scratches, or light intrusion during the film exchange, the 220 roll film is difficult to buy on the European market at all. Nevertheless, this material itself does not solve the problem, but only reduces it a little bit. However, it is essential material for the operation of the underpressure magazines (backs) as described hereinafter.

Underpressure magazines are commonly used (or rather were used) in conjunction with special bodies for aerial photography - these were usually stationary-mounted monsters weighing tens of kilograms. Only Contax manufactured vacuum film holders equipped by a mini (piezo) suction pump installed directly in the Roll Film Insert (inner part of the film magazine). Their functionality was quite questionable and its serviceability was reduced only to short exposures. On the Internet, I have also found several hopeless attempts of the manufactures or end-users from the astronomical branch, whose work was totally destroyed by the incurvation of the film surface during long exposures. Over again, this equipment was imperfect and quite expensive monsters with the vacuum air pump weighing more than one kilogram and operational only for a few hours on one charge.

For many years I was shattered by the feeling of despair, that the focal plane is randomly set by the film and magazine themselves instead of myself. The eight-thousand-meter mountains expeditions with Hasselblad camera have "enlightened" me enough, because despite of high stopping down (typically 11 to 22), the center area of the picture was generally razor-sharp only the third frame from the series which came after the longer time after previous shooting. Night exposures were much bigger lottery. Some years ago, I obtained very "stiff" A12 (120) magazine which could hold the film tightened in place quite reliably for several tens of seconds after rewinding, but all at the cost of too high mechanical stress affecting the body. The necessity to sacrifice two frames before the next exposition still persisted. I "fluctuated" within the film position tolerance of 150 microns, that was more than great outcome taking into account this prevailing hardship and I could even afford to set the aperture between 4 - 5.6. Another disillusion came when I have acquired Superachromat lenses, having - by the matter of physical principle - the focal plane tolerance approximately three times lower than the ordinary lenses of comparable parameters and additionally (it concerns especially corners) are the sharpest at full-aperture. The similar features apply to a new super-sharp Distagon 4/40 IF. Zeiss calls it "digital lens", probably because it cannot "catch up" its own quality on uneven film surface. As I discovered by many tests and measurements during the calibration of the bodies and lenses, the tolerance of the focal plane (presumable layer thickness, inside of which we cannot recognize any decrease of the sharpness) of "common" Zeiss lens type Sonnar 4/150 or Planar 2.8/80 at full-aperture, lies within 100 to 120 microns (at the most +/- 50 to 60 microns off the ideal focal plane). This tolerance of Superachromat lenses abruptly decreases to mere 40 microns. As for common lenses, it is caused mainly by the residual chromatic aberration which paradoxically creates an additional contrast before and behind the ideal focal plane by the projection of blue-green and red contours, whereas Superachromats, fully optically corrected between 400 and 1000 nm do not create these aberration images. This character was clearly demonstrated by the story, when the strong gust of wind on Bolivian Altiplano knocked down my tripod with Hasselblad 501CM with mounted Sonnar 5.6/250. As I found out later, this accident caused a flexure of the bayonet mount sideways about nearly 100 microns (the lens survived well). The test slides under the same conditions with Sonnar 5.6/250 mounted on this body were still usable, while the slides exposed by the Superachromat 5.6/250 showed the left and right part of the picture visibly blurred toward the edges .

After these experience I felt myself in a tight corner, or more specifically - buried deep in the shit for good. The only option that has been left was a tabular digital back that I scorn due to reasons hereinbefore..........

I have contemplated already earlier about making the underpressure magazine myself
. But after disassembling and analyzing Hasselblad magazine A24, I was horrified after findings of what everything I must alter and mainly I also saw an unsurpassable obstacle in the final system calibration. There is no "substance" between the surface of contact of the magazine and film guiding ledges for milling or grinding. It looks like sophisticated brain-teaser firmly riveted with no chance to make any adjustments. The final calibration was at last "in the sign of pounding out and pressing out"of film guiding ledges. Last 20 microns I scraped off by the steel triangular scraper. By the estimate, the "cross" calibration of one magazine with three bodies (cameras) represented 100 - 200 hours of incredibly intensive and concentrated work. Previous calibration of all my 501CM and 503 CW bodies was naturally necessary. I decreased a default manufacturing tolerance of 60 microns between the bayonet mount and rear "magazine mounting plate" down to 5 microns. An adjustment of four times claimed Zeiss Tele Superachromat 5.6/350 worth more then EUR 8000 was an individual procedure. (I plan another article about this :-).

It was essential to drill holes of 0.6 mm in diameter into the film pressure plate:

Partly processed pressure plate


Follows grinding, polishing and flattening:

Final look of the eloxal-coated pressure plate in the finalized magazine


A duralumin tray is screwed on and glued to the rear side. A flat stainless-steel spring must be reshaped according to the duralumin tray. The spring also serves to hold down the film during its loading into the magazine:

Rear view at the tray:

The duralumin tray with the reshaped stainless-steel spring


Detail:

Lateral detail of the tray and pressure plate


During many hours lasting hardening of Seamgrip glue, the whole system must be continually calibrated by underlaying (inserting) centesimal ultra-thin steel sheets and tuning of draught and pressure screws located at the rear side of the tray. It is not a job for weak nerves. I have completed the rebuilding of 3 magazines within the tolerance of 8 microns on the plate. An inner part of the original magazine had to be milled down for 2 mm and the complete interior mechanics readjusted. The plate-tray sandwich is connected by three millimeter thick silicon tube with the light-tight and air-tight "pipeline" mounted to the inner part of the magazine:

Rear view of the inner part of the magazine – air conducting tube is sealed by the glue and paint.


The air pipeline join into a brass / stainless-steel edged cone, on whose coupling connection is to be slipped on a silicon tube for the air suction:

Disconnected stainless-steel cone


A detail when connected:

The cone of the suction tube coupled into the brass socket in the magazine.


The magazine must be finally calibrated directly on the body against the bayonet mount:

Revision of the bayonet mount and the rear plate parallelism with the help of a special device


This is the most critical and the most infernal stage of the whole process - one inaccurate knock or spring compression of the film guiding ledges results in additional 5 hours of toil. The process gets so complex because not only the center and corners must be aligned within 10 microns (this strict tolerance was set by myself), but these film guiding ledges must also tight along their whole length within tolerance of 20 microns (not to allow false air blow in from aside). Approaching to the ideal situation required on the average 100 to 200 cycles of forming and measurements on the body. There are too many degrees of freedom for ordinary man to make it under makeshift conditions. I would probably never be able to finalize without my experience and qualification from the time of my youth, when I cut and polished aspherical surfaces of astronomical mirrors half meter in diameter within the accuracy of 1/16 of light wavelength. The film will be aligned as precisely as is the accuracy of the plate parallelism according to the bayonet mount level.

The under-pressure is easily achieved by "sucking" the tube kept for this purpose in the mouth.
By-passing of the false air around the film is practically near zero (approx. 10 to 30 cm3 per hour) therefore managing several minutes long exposures is without any difficulty. This vacuum air pump designed by myself is used during the long exposures (at night) or when I cannot stay for various reasons close to the camera:

Diaphragm vacuum air pump is switched on by the red button and the little ball serves as the vibration absorber (silencer)


The black rubber ball with hundreds of little (0.5 mm) holes made in six-millimeter silicon tube passing through it and filled with small pieces of the plastic foam serves as an absorber of vibrations generated by the micro vacuum air pump engine "Micro Diaphragm Gas Sampling Pump KNF NMP 09L":

Detail of the micro vacuum air pump with the diaphragm pumping engine


The under-pressure regulation is controlled by a 0.4mm hole with a 0.1mm wire in duralumin connection. Four AA-lithium batteries lasts 150 hours of the continuous operation (3V/40mA), hence practically one year of standard usage. The vacuum air pump including batteries weighs 120 grams and the vibration absorber weighs additional 30 grams - the total weight is 150 to 160 grams depending on the length of the silicone tube. It would be no problem to attach this gadget someways under or behind the magazine and synchronize its operation with the camera shutter. The under-pressure release necessary for the film rewind, enabled by the regulation hole in the duralumin connection (mentioned hereinbefore) takes effect within 0.3 seconds.

What about the conclusion? The development and production took half a year during which I could not engage myself in anything else. The reward for the successful accomplishment of this elaborateness is system which is about almost two digit positions more accurate, profoundly reliable and unparalleled in the whole world. Only now I can utilize full potential of the highest quality lenses, focus exactly and reliably just at the point I do want to and not to care about when I rewound the film for the last time. The biggest deviation from the ideal level, during mutual measurements from the corner to corner + center of 3 bodies and 3 magazines, amounts to 17 microns only (0.017mm). I have never dreamt about such results before - it has elevated myself to absolutely different level. I just hope that I will be able, within several years ahead, to buy 220 roll-films (Fuji Provia 100F and new Velvia RVP 50), hopefully somewhere in the world if not possible on the domestic market and that there will be a lab available that will be capable to develop 220 roll films with the use of E6 process at appropriate quality level.

 

Ladislav Kamarád - 19.2.2008 17:49:17 - Category »Technique - Viewed 707253x - Add new comment

Comments:

    1. from: Chris

      ...and that's what they call perfectionism
      great article, keep them coming please

      Reply to this comment20.2.2008 03:05:53
      1. Upon this comment from Chris dated 20.2.2008 03:05:53 responded: Monalisa

        Memberikan harga jasa seo murah kepada anda semua.