Hasselblad Adjustment "Tweaking"

Discussion in 'Medium Format' started by henry_finley|1, Aug 30, 2014.

  1. This is meant to be something of a treatise, inviting all respondents and opinions on "tweaking", or making small customized adjustments on so called "factory perfect" adjustments on the Hasselblad equipment, to achieve perfection within a particular owner's personal equipment array.
    Speaking of several pieces I have at hand are a 553ELX and the 80mm T* lens I will be using on it. I've made some on-film focus tests, viewfinder focus tests, and engraved lens scale tests, as well as dial caliper checks. Nothing is adding up perfectly. The body is very close to correct on the mike measurements, film, and finder checks, but it could be a bit better. First let me say that the C's, CM's, ELM's are worthless due to thier mirror pad problems, so I'll concentrate on the aforementioned pieces.
    I have my T* lens at hand, but I also have 2 of the older chrome barrel 80's that have NEVER been tampered with. You can tell by looking for scratches on the screw that holds the scale on. This is an easy screw to chew up with even the best of tools. The 2 chrome lenses are 1/16' off to the left on one, and 1/16' off to the right on the other. So much for factory perfect. To achieve this 3 foot test, I've had to put 3 little pieces of masking tape under the mirror hold-down pawls (for now). Without this tape, the lenses focus more like 2'10 or 11 inches on the scale.
    So I have a choice of "tweaking" the 4 focus screen pegs, or the 2 mirror pawls to get the perfect 3' on scale, and on screen. I'll leave this discussion here as I'm off to go to town 10 miles up the road where I can set up to test on the town water tower (infinity testing).
    But I'll lay the question out there: what is your opinion of small non-laboratory adjustment "tweaking"?
  2. The 4 pegs on the focus screen should be adjusted for accurate infinity focus with any lens installed.
    The mirror pegs should be adjusted for even focus across the the focus screen with the camera perfectly perpendicular and square to a high resolution, flat test target. The EIA_Resolution_Chart_1956 or similar should show if the mirror is out of alignment https://www.google.com/search?q=optical+test+targets (click on the images to see the target.

    If the lens scale are off so be it. Lens are rarely their marked focal length. They can vary .01mm to 3mm either side of the marked focal length. The difference in marked to actual focal length is more apparent at close focus distances than infinity.

    The only question here is did Hasselblad optically measure each lens and make a focusing scale for them or did they make a nominal focal length scale and use it for all lens?
    1% tolerance of 80mm is .8mm; 80mm±.8=79.2mm to 80.8mm. Your lens could be as much as 1.5% of nominal.
  3. malfunction, please delete
  4. Thank you Charles. But I'm of a mind that fooling with the 4 screen pegs might be foolhardy. Anytime you upset known factory adjustments with no proper equipment to put it back is dangerous. Those are non-moving parts that have no chance of wear-related changes. Whereas the mirror mechanism and its stops and hold-down fingers DO have opportunity to get out of adjustment. I'm talking about extremely small increments of adjustment. I'm still thinking the 2 mirror hold down pawls might be the best way to go. We KNOW the lenses are factory unchanged, we ASSUME the screen pegs have not changed. The chassis length has not changed. That must mean mirror. has changed a hair. It is the most punished part in the equation. That's my train of thought. Keep in mind the error I want to perfect is already extremely small, compared to the GIGANTIC errors in all the non-gliding mirror earlier cameras with the stupid foam pads under the mirror.
  5. I would print out one of the test patterns even if you have to poster/multipage it, fasten it flat against a wall then set up the camera with the film plane square to it then check the focus screen with a loupe.
    While I haven't worked on a medium format SLR. the mirror in large format SLR's has little effect on the focus unless its off 1 degree or more in its angle. to the ground glass/view screen. The view screen is adjusted on the LF SLR's, formats 2x3 aka 6cm x 9xm, 3x4, and 4x5.
    I realize that the error you are talking about is minor, about 30" arc to 1' arc (turn) of the stop screws.
  6. Mirror position generally affects where the center of focus is on the view screen or whether the focus is good in the center and off in the top/bottom edges of the frame. If the mirror position is causing distance scale errors then it would be consistent with all lens and focused distances.
    You may be experiencing the effects of wear in the lens focusing mechanism.
  7. So far, the error seems to be somewhere around 1/2 inch of 3 feet. But I've set up Kalart rangefinders on Speed Graphics more accurate than what I'm seeing Hasselblad is capable of. I even successfully calibrated 2 Rapid Omegas better than what I see out of Hasselblads. Try your hand at calibrating a Rapid Omega 200 rangefinder. That's the toughest of the tough.
    As far as Hasselblads, you can't even find any 2 film backs, or for that matter, any 2 corners of the same back that agree on a dial caliper. I don't think a Hasselblad CAN be calibrated to perfection. Or at least if so, the lenses and backs can't interchange among bodies and hold that perfection.
    I'm about of the mind that at one point you have to realize that it can only be so good, and that Hasselblads aren't made by God after all.
  8. I thought "God" used no tolerances so his stuff is anything goes.
    I set up SLR's for the central portion of the view screen/ ground glass. Film plane tolerance on 2x3 is .007 inch, the thickness of thick base sheet film. 120 film runs .0035 to .0045 inch thick so if the distance error is not greater you probably won't notice the difference.
    Kalarts and Hugo Meyer RF's aren't that difficult unless they are dirty.
  9. For setting up a view ground glass/view screen/mirror in a camera body I make a temporary ground glass to fit the film guide rails of a roll film holder for the format and adjust the mirror/ground glass to match the film plane ground glass. As long as the surface of the film is in tolerance when loaded in its holder I have no further concerns with it.
    I cut a piece of regular 1/8 inch thick window/picture frame glass to just fit in the guides as film will and put strips of Scotch Magic Transparent Tape across one side without overlapping then put the tape side toward the lens. With the camera level and the test target/infinity target critically focused I adjust the view screen/ view ground glass to match the film plane gg.
    You can also measure from the target to the film plane to check the positioning/reading of distance scales.
  10. In doing Hass, I go for the customary chassis length bit--I forget this minute--I think it's 71.40mm. Then I put some scrap film in a back and wind to 1 and use the depth gauge portion of my dial caliper to measure to the film. It is with that you realize how much variation there is from the lens flange-to-film with these backs. It's all over the place, even among center and corners of the same back. Anyway after I've struggled to compromise, I use shims, paper, whatever; to stand off a piece of Rolleiflex ground glass from the camera rear opening, so I can do infinity testing on a tripod. I use a KNOWN UNTAMPERED 80mm to focus by under the dark cloth. It's extremely tedious, but after a while you "get to know" the situation. Then I move on to see if the focus screen in the Hass agrees with everything. I believe after hour and hours of this tedium, I've set the camera up as well as a Hasselblad tech in New York who didn't sleep well the night before. They have jillions of dollars worth of jigs and equipment, but that stuff varies too, I'm sure.
    Anyway, the film tests come next. I use a tape measure and a grain focuser on the film. Of course I have to use 25A filters or whatever so I can do all film tests wide open.
  11. All this said. since it only took 3 pieces of masking tape under the mirror hold-down pawls on this 503LX Gliding mirror camera, my best bet would be to simply turn those adjustment screws a hair, just to keep the microprism from "shimmering" at infinity, on this particular job, and leave the GG pegs alone. If your film is sharp at infinity, 6 feet and 3 feet, and the microprism isn't "shimmering", then you should be in good shape. At least I believe so.
  12. Henry,
    I do feel that you are approaching this in the wrong way, you just cannot assume that a piece of equipment that has no marks on it can be correctly aligned/focussed, especially a chrome lens from the 1960s. All the Hasselblad modules are set to the same specs so that there should be no ‘individual tweaking’ necessary, the variation you are seeing is down to wear and tear and that is what a CLA is for, to correct all those errors. What I would strongly suggest is that you get one of the most fundamental pieces of camera workshop equipment that I frankly feel that you cannot do without. Namely an Autocollimator, you will be able to ACCURATELY set the lens focus without any doubt whatsoever at a flange to image plane distance of your choice, you can also use the same device to align parts of the camera assembly, you can even check that the film gate is in the right place.
    The Hasselblad camera is basically a camera the same as any other and obeys all the same rules of engineering and optical design, the only difference is the modular design and all those components must agree to a common standard. That is the reason for all the special tools, and this is why I encouraged you to gain experience with simpler cameras with less variables, not suggesting in any way that you were unskilled or unable but because you would quickly gain the experience that would take you to the where you wanted to go.
    This may be a poor analogy but if you were a musician and wanted to build your first instrument would you start with a grand piano?
  13. Thanks Douglas. I'm afraid income prohibits. I felt lucky to have temporary possession of a friend's 2 80mm's that I expertly deemed untampered. And they were so close together at the 3 foot mark that the proved to be the best standard I would ever have available in my income class. So I calibrated my homemade 80mm T* by them using my 503 ELX as the "collimator". I was fortunate to have answered an APUG "free" thread and ended up with this camera. All I had up till then was an assortment of the C and EL class, which are overpriced box cameras now. I wouldn't give a dime for a trainload of them off ebay, because every one of them need mirror pads. Those paperweights can't focus withing 7 inches of 5 feet.
    Now I have something that gets me between 1/4 and 1/2 inch of 3 feet. Maybe only 1/4 inch. And infinity is only an f stop away from perfect. I frankly don't think a Hasselblad was ever better than that when new. I'm a man who has worked on Kowa Super 66's, and they had some pretty good engineering in some things. Their mirror mechanism was certainly smarter. But their shutter cock drove me nuts. If it weren't for the way the Kowa shutter was cocked, I'd be using them now. But they were dependent on a single little piece of flat spring steel away from failure.
    Speaking of my consternation with some Hasselblad engineering, why did the only put 3 pads under the mirror, and not 1 under all four corners? That doesn't make a lick of sense. There's no way of keeping the mirror up against the frame up at the hinge with just 1 pad in the center.

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