Hasselblad 500 c/m focus issue

Discussion in 'Medium Format' started by cameracravings, May 30, 2018.

  1. Hi I just joined the forum in hopes that someone really can help me with advice so that I can put my Hasselbad 500c/m back in service :smile: My Hassy was taking perfect, sharp photos and then one day something happened and it started taking very out-of-focus photos. I don't have the 'Hasselblad' tools and I don't have the money to service it. So I have to do it myself using regular tools that I have. If I fail the first time, I will just keep coming at it.

    Some time ago I had to put away my Hasselblad 500c/m until I can afford to repair it because it developed focus problem. The last roll of film I shot was out of focus pretty bad. Today I tried to evaluate the scope of the problem. I mounted Polaroid back and used ground glass pressed against picture plane of the Polaroid back and a magnifier glass to compare focus through waist-level finder vs. through the lens. For this used 50mm f/4, 80mm f/2.8 and 150mm f/4 Zeiss lenses.

    20180529_224923-1.jpg 20180529_224036-1.jpg 20180529_223916-1.jpg
    While all lenses showed good focus at infinity (except for 80mm which came up short) they all performed differently at the close distance of approximately 1.5-1.7 meters. 150mm showed the least discrepancy, and the 50mm showed the most discrepancy. Photos show my blue marker markings labeled 'W' for the viewfinder and 'L' for through-the-lens. Please note that my markings have no relation to the distance scale of the lenses.

    I set the camera on a tripod and only changed the lenses. For each lens, I first established sharp focus through the viewfinder and then checked it through the lens. I found that the camera was back-focusing through the lens. I think this suggests that the flange to the ground glass distance (viewfinder) is shorter than the flange focal distance. I thought it is probably not the mirror / deteriorated mirror cushion issue, for, if the mirror sogged, the flange to ground glass distance would be longer, right?

    At this point, I only know that the camera's focal distance is adjusted by moving the chassis against the outer body shell.

    Next, I decided to check the camera's flange focal distance using depth gage with the wide base. I do realize that my method may be fundamentally flawed as I was not entirely sure what points I should measure to and from. So I would welcome any suggestions on this!

    I mounted a lens and placed calibrated depth gauge with the wide base on the picture frame of the open Polaroid back, and measured the distance to the back side of the mounted lens. Here's what I measured:
    top left corner 2.8" or 71.12mm
    top right corner 2.797" or 71.04mm
    bottom left corner 2.797" or 71.04mm
    bottom right corner 2.796" or 71.03mm

    I know that the flange focal distance for Hasselblad 500c/m is 71.4mm +- 0.03mm, so my camera is outside the tolerances by at least 0.3mm. Does this agree with my camera back-focusing through the lens? Can this error dramatically affect focus at close distance and be less noticeable at infinity? If not, then I should probably check camera back. ANY SUGGESTIONS TO IMPROVE MY MEASUREMENT? Once I am able to verify my measurements I will start figuring out how to adjust the camera.

    Thanks, everybody for your input! Really appreciate it!

    Alex
     
  2. I forgot to mention instant film back that I have is NPC Polaroid back.
     
  3. Also I am a little confused about flange focal distance for 500c/m -- I believe it to be 71.4mm but some of the sources on the internet report it to be 74.9mm. I guess the latter is wrong.
     
  4. I can't think of anything which would affect the flange to film plane distance, other than dropping the camera and bending the lens mount. That would not happen without your knowledge.

    In terms of conventional focusing, the length of the optical path is paramount, and can only be measured with special fixtures. It is more likely that this distance has changed, either by wear on the mirror linkages and stops, or by the focusing screen. Make sure that the focusing screen is not upside down. The grid marks, prism, etc, would be facing the lens, not the eye. If the mirror position is off, there will be a shift in focus between the top and bottom of the screen. A newspaper taped to the wall and careful leveling (paralleling) would provide an easy test setup.

    Another problem is focusing on the correct plane of the screen. Acute-Matte screens are too transparent for accurate confusing, in order to be as bright as possible. Make sure your eye is focused precisely on the screen grid or other features, If you relax your eye, there is a tendency to focus through the screen on a virtual image, which will result in rear-focus from correct plane.
     
    cameracravings likes this.
  5. Thanks Ed I will try your suggestions! Don't remember dropping my camera. It's been sitting in my closet for 5 years though -- can't remember too well what happened 5 years ago. The screen is placed correctly prism facing the lens. Now, I have a question about your comments on focusing -- Ok so when I am focusing I should make sure I am mentally aware of the visible properties of the focusing screen such as the grid etc and make sure I am factoring them in when focusing? Thanks
     
  6. When I removed focusing screen I noticed that the mirror in the up position has uneven spacing on the sides. While on the left side (top picture) the space is even, on the right side (bottom picture) I notice that the space is wider towards the back and narrower towards the front of the camera. And I guess mirror damper is shot too!

    20180530_112023sss.jpg 20180530_112051sss.jpg
     
  7. It isn't that unusual for the mirror to sit unevenly in the up position. The Hasselblad myth is that they fell from the heavens as a completely ingenious flawless design, the Hasselblad reality is they contain a few questionable functional elements that are not nearly as refined as other aspects of the camera. The mirror geometry being the most obvious: it works and has proven reliable over the decades, but is notably cruder than many other aspects of the body mechanics. Vignetting wasn't the only reason Hasselblad eventually re-designed their mirror system.

    Your focusing issue is not something you'll be able to repair as a DIY project. Hasselblads are not DIY amenable, period: you wouldn't be the first photographer to discover this system will kill you with unexpected service costs (prices of bodies and lenses collapsed with the onset of digital, but required servicing became less available and ever more expensive). If you did not drop the camera or experience some other impact before the focus just suddenly drifted, the most likely cause is deterioration of the three foam pads sandwiched between the mirror and the metal plate it rides on. These pads function as both shock absorbers and positioning devices: depending on climate, after ten-fifteen-twenty years these pads rot into dust or goo, which throws the mirror viewing angle out of spec. The focusing error manifests most noticeably in the middle-close distance range (at least in my experience with a failed 500cm and 500elm). Replacing these pads will solve the problem, but requires fairly deep disassembly to get to them at a typical service fee of approx $200.

    I chose to replace my 500elm rather than have it repaired, since I could easily find a mint condition 500elx body (with improved mirror design) for about the same cost as the repair. My 500cm was serviced, because prices on manual wind replacement bodies have soared beyond all reason in the last couple years. Any random second-hand 500cm costs close to double the service fee, with no guarantee it won't soon need the same repair. Manual-wind Hasselblads with the improved mirror are priced in the stratosphere: you can't touch a 501cm or 503cw these days. Your best bet would be to contact factory-trained repair tech David Odess and see what he thinks: he is very cordial and helpful in making service decisions.
     
    cameracravings likes this.
  8. Hi thanks for your input! Unfortunately I don't like the way 500elx looks although it seems it has new mirror system, so I will need to fix my 500cm :) Do you know more about three foam pads between the mirror and its housing? Do you know the thickness? Thanks!
     
  9. Sorry, I don't know the exact measurements of the mirror pads, and that info doesn't seem to be in the service manual either. Parts like that were stock items repair shops used to just order in bulk from Hasselblad.

    Believe me when I tell you, I sympathize with your budget constraints tempting you to try self-repair. But its really not a good idea: the mirror mechanism is a goofy Rube Goldberg affair that is easy to misalign, and getting to it requires separating the inner and outer body shells along with other tricky shenanigans. Also, the precise cause of your focus issue might not be the mirror pads, it might be other parts of the mirror release system as Ed_Ingold suggested. Or a combination of factors.
     
  10. i have similar problem with my cameras, could you tell me how did you resolve the issue & what is actually causing the problem?
     
  11. With the preface that I absolutely DO NOT recommend the average Hasselblad owner do so, those who insist on attempting DIY replacement of mirror sandwich pads may find useful tips in the next-to-last post of this related thread:

    Hass 500C Mirror Pad Replacement Question

    Bear in mind, the OP never followed up with a report of whether his DIY efforts resulted in a complete fix of his focus issue (and/or if he got the camera back together in fully operational condition). Chances of separating and re-assembling the Hassy inner and outer shells without throwing something significantly off are about 50/50: either you'll totally get away with it, or you'll end up needing a tech with official, arcane Hassy tools to recalibrate the whole mess.

    If the focus goes out on your Hasselblad 500EL or ELM, junk it and replace with a newer 500ELX (or 553ELX) with redesigned mirror: this will usually be less expensive and more durable long-term than professional repair of EL/ELM. If the focus goes out on your 500c, 500cm, 501c or 503cx, the decision is more difficult. Professional repair cost of the manual wind bodies is still somewhat less than replacement cost of the same body, and manual wind bodies with the improved mirror (501cm and 503cw) still cost double or triple the price of earlier more-troublesome bodies. Budget and body preference would be the deciding factors.
     

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