focus problem with 500cm

Discussion in 'Medium Format' started by demet, Mar 13, 2018.

  1. Hi all, I recently put the first rolls through a 500cm that I have had for a few years but never used as lens was jammed. Sent it to David Odess in the fall and had the body and 50mm lens serviced. First rolls just back and every image is out of focus. I was fairly careful with focusing, using the magnifier in the hood and rolling in and out of focus to get it as spot on as possible. I was shooting wide open at 3.5 and subject was generally fairly close in the 5-10 foot range. So yes, shallow DOF but no way I missed focus on every shot of four rolls.

    And in almost all the images I can see that the actual focus was about 1-2 feet behind my intended point, and it looks quite sharp there.

    And ideas about what might be causing this? I elected not to have the back serviced, so that might be it, although it winds and functions normally. The plate behind the film is springy and evenly so.

    Thanks in advance for any insight!
     
  2. Focusing screens on the 500cm are not easily changed. The screen height may be misadjusted. When you focus, make sure your eye is focused on the screen. Grid marks help. The screens are rather transparent, so there is a tendency to relax your eye and focus on a virtual image genuine the screen.

    If the mirror stops are not set properly, the image will be OOF, but also offset.
     
    Last edited: Mar 14, 2018
  3. When I look through the focusing hood the image is clear and I see no ghost image or anything that I could be mistakenly focusing on. It seems actually very easy to focus!

    I just tried to focus on a house across the street and at infinity I don't think it is focused properly... Not sure what that says and I'll try to test more, but any help still appreciated. I'm thinking of running a test roll through it, and using both the 60mm that I have been using, and also my 80mm to see if the lens is creating the problem.

     
    Ed_Ingold likes this.
  4. Perhaps a stupidly obvious question-but are you getting the film tucked behind the "tab" when you load the magazines?
     
    Ed_Ingold likes this.
  5. Is your focusing screen in correctly? Perhaps upside down?
     
  6. Ed_Ingold wasn't referring to you focusing on an obvious "ghost" image: he was referring to an odd waist-level-finder quirk where your eye accidentally focuses on the aerial image of the scene instead of on the actual screen. This is really hard to explain, but you have to sort of train your eye to focus on the screen surface image and not the scene itself as it floats just underneath. This quirk is more of a problem with the ultra-bright Acute Matte screens, the older darker ground glass screens tend to lead your eye more towards the proper image plane. The issue is much less likely to occur with screens that have a split image rangefinder: the rangefinder will almost always indicate correct focus, overriding eye errors. One reason Hasselblad began bundling split image screens with later cameras.

    Shooting another test roll with the second lens will narrow the possibilities down considerably: if you have the same misfocus issue with both lenses, the problem is in the body or possibly your eye focusing incorrectly below the screen. If the second lens gives sharp results, the problem may lie in the first lens (or you're getting better at finding the focus plane: maybe a third roll would be the tie breaker). But first, heed what oldwino prompted: check your focus screen to make sure it isn't upside down (corner feet facing up). The shiny side of the screen with continuous smooth bezel frame should face up. You'd be amazed how often that turns out to be the glitch: we get distracted and drop it in wrong after cleaning.

    You didn't specify exactly how old your 500cm is, or exactly how long it had been sitting since you last used it. After some years, esp in storage, these cameras can develop an issue with the mirror that causes a repeatable misfocus error very similar to your description. There are three little foam pads sandwiched between the mirror glass and metal plate it sits on, that act as both shock absorbers and positioners for mirror alignment. If the foam decays to goo and/or dust, it will throw off the mirror position and induce a permanent focusing error. Usually a tech like David Odess would notice this and ask if you want it fixed, but it is possible he overlooked it: perhaps you should email him and ask if he checked for it. Replacing the rotted pads requires significant work and expense: when it happened to my Hasselblad 500EL/M, I thought it more cost effective to just sell it for scrap and buy a used, newer 500EL/X.

    Other possibilities would include the entire inner body/outer body alignment being a bit off (Odess can check that with a jig), or a film loading snafu (as ben_hutcherson suggested). I'd be very surprised if it was an optical problem in the lens: the 60mm is normally razor sharp, and David Odess has specifically told me he does not disassemble element groups when servicing lenses. An optical issue bad enough to throw off focus would be bad enough to see in the viewfinder (or if you looked thru the lens glass with a flashlight).
     
  7. Thanks for your reply orsetto, and everyone.

    I have tried to find this ghost image, or anything like it, and I cannot. The focusing screen looks even and 'flat', and focusing with the magnifier seems easy. I have a memory of the 'dual/ghost' image thing from other waist level cameras I have used in the past, but I can find nothing like it with this one.

    I did check the position of the screen and it is installed correctly, by David Odess I guess.

    I purchased the camera aprox. 2 years ago and promptly got a lens jammed on it. I couldn't unjam it using the little screw inside and so it sat for quite awhile until I had the money to send it to David Odess. I got it back from him in late November and these are the first rolls through it. Other then that I do not know the history of the camera although I don't think any of it matches.

    I have been in touch with David Odess and will shoot a test roll following his instructions to narrow it down to the lens or body. (BTW I do know about getting the film under the tab when loading.)

    Thanks again for the feedback. I actually wish it was my eyes/focusing ability, but the results are very consistent and it's hard for me to believe I could miss every shot!

    Best
    demet
     
  8. What is this "ghost" image. I said nothing of the kind. Aerial images* are real, in spite of the alternate designation of "virtual image."

    Acute-Matte screens are brighter than older screens, which means they don't have a clearly defined image plane. To use them correctly, you must deliberately focus your eye on markings in the screen, even the Fresnel pattern in lieu of grid marks.

    A "chimney" finder makes this much easier, since it has fairly high power (4.5x), an eye cup, and focuses over a wide range on the screen itself. Prism finders have less power, but most have adjustable focus. If you use the hood magnifier (6x), hold it up to your eye rather than at waist level. If you try to hold the camera at waist level, Hollywood style, and focus, you are "waisting" your time.

    * Aerial image: When you use a compound microscope, the eyepiece focuses on the aerial (virtual) image projected by the objective. The same with a compound telescope. Everybody has done that. However the same principle applies to cameras. You can focus on an aerial image, and there are screens for microscopy and astronomy which facilitate this process. You move your eye from side to side until the image is stationary against a cross-hair in the clear field. (Stars are nearly invisible on a ground glass.) No parallax means you are focusing on the same plane as the film. MTF measurements are usually made using a virtual image rather than film or digital medium. When using so-called "bright" screens on an Hasselblad (including Acute-Matte), the correct technique is to make sure your eye is focused on the screen while you adjust the lens. This takes concentration and may be difficult if you wear (or should wear) corrective glasses.

    Failing this, your eye will often relax to a more comfortable position, which will result in focusing behind the desired subject. I suffered from the same back-focus issue until I realized I was using the camera incorrectly (and why).
     
  9. As I've said, this phenomenon Ed_Ingold and I were warning of is really difficult to explain because every descriptive term is misleading or confusing. Perhaps it will be clearer if I explicitly say we are NOT talking about something you can actually SEE, even if you looked for it? No secondary image, no "ghost". Everything looks perfectly normal when you peer thru the magnifier.

    Think of it this way: two identical "layers" of image are formed in the viewfinder. One is captured in the screen surface, and one is the aerial image SOURCE for the screen image. They are precisely aligned left to right and top to bottom, but at different DEPTHS: this can trick the eye into focusing on the wrong one, because the eye cannot perceive the two different depths: it just looks like a single coherent viewfinder image. For whatever reason, this particular issue is far more prevalent with Hasselblads than other waist-level cameras.

    As Ed_Ingold described in his reply above, with Hasselblads the eye has a tendency to lock on the aerial image layer: if you are unlucky enough to have the type of vision that consistently and naturally locks on this incorrect layer, your focus will consistently be off. The trick with Hasselblad is to train your eye to lock on the closer screen layer instead. Again, this is so difficult to explain in words because its an instinctive sensory thing you just eventually learn: you unconsciously make a habit of using the central cross lines inscribed on the screen as a touchstone, so that you're simultaneously keeping your eye locked on the physical screen surface while turning the focus ring on the lens.

    Of course, this may not be your problem at all: it may be a physical misalignment in the lens, body or back. Since you're back in touch with David Odess, he'll help you sort it all out.

    This brings up another small but important potential glitch. Are you quite sure your Hasselblad is a 500cm? Does it actually read CM on the side plate? Or does it read 500C (without the M)? The C is older and has a non-removable screen (if you take the finder off, you'll see it has a black border frame which is secured with a screw at each corner). This screen was not intended to be changed: only reluctantly did Hasselblad offer optional screens for installation by factory-trained service centers. Getting the screen to precisely the correct height and skew to match the individual body/mirror alignment is rather tricky. In recent years especially, as used Hasselblads became more affordable to the masses, many 500c owners tried to change the screen themselves, which resulted in a ton of misaligned 500c bodies floating around eBay.

    If you do indeed have a 500CM (or late 500C with the same user-changeable screen), when you take off the finder you will notice the screen has a silver frame and is held in place by two small silver tabs on the right and left sides. push those tabs flush within their notches, turn the camera upside down, and the screen should fall out into your hand with a gentle shake. It can be cleaned or changed with another type of screen (split image, microprism, checker grid, etc). It goes back into the camera with the little raised corner feet facing down: align it in the finder well, it should drop in place with a gentle shake or slight push. When you slide the WLF back on, it will automatically close the two retaining tabs, securing the screen. If the finder does not slide back on easily, the screen is not completely seated: jiggle things a bit until it lies flat and the lille tabs can slide in place over it.

    Okay, so that essentially means this is a completely unknown new-to-you Hasselblad, and this is your first actual use of it. Doesn't matter how long you've owned it: if it jammed from the get-go, you never had a chance to test if it was in perfect working order to begin with. So, you're starting from scratch with an unknown body that could very well be completely whack (under-mirror pads decayed, mirror stop out of adjustment, inner body not aligned with outer shell to micron specs).

    One thing that people need to understand about techs like David Odess: they are human beings with limits, not clairvoyant "Hasselblad Whisperers". David is one (very talented) man with one workbench and a crushing backlog of clients: at some point he had to develop a realistic workflow to keep things moving. He will look into specific problems you complain of, and make sure certain standard adjustments that Hasselblad trained him to make on every camera are up to spec, but beyond that he may not always catch an optical issue issue like back focusing (because its time consuming and may not be obvious unless a roll of film is shot). He may not always spend time time checking arcane things like the mirror pads or ancient 500c fixed screen collimation if you haven't included focus issues in the list of problems you asked him to solve. And very occasionally, after he reassembles your camera to spec it may get knocked out of alignment again during return shipping.

    Hasselblads are tough, but not invincible hockey pucks like the Nikon F. In their heyday, they were used mostly by pros who had access to numerous local service shops that would CLA them on a yearly (sometimes even monthly) basis. It was not expected 40-50 years after leaving the factory they would have changed hands numerous times, shipped and reshipped to new owners with no servicing over decades, then subject to shipping long distances yet again to perhaps be opened for maintenance for the first time in 30 years. It is an unfortunate fact of Hasselblad life today that successful servicing will sometimes require more than one round trip to any particular tech. So keep the faith: David Odess will work with you to get everything buttoned up.

    Just as an aside, in my experience a Hasselblad body that jams a lens so badly that the screwdriver trick doesn't release it is a "Black Sheep" Hasselblad that may continue to act up intermittently even after expert servicing. Over the past 20 years I've been burned by a couple 500cm bodies that didn't "like" certain lenses: they would mount and work perfectly until I tried to remove them, at which point they'd completely jam within a microturn after pressing the mount release button. After spending a kings ransom having those bodies and lenses overhauled, the problem would return: some bodies are just a haunted PITA that will never work perfectly with every single lens out there. If your body ever locks up solid like that again with the same lens, I'd recommend getting another body instead.

    Unlike simple user-error jams which are easily released with a screwdriver, these complex "not-your-fault" jams disrupt the entire timing chain in the body. The only way to release the lens form this type of jam is to remove the wormgear cover over the screw, and adjust the two hidden screws until the drive mechanism tension releases completely. If you get stuck with one of these "gotcha" bodies, like I did, you learn to perform this delicate surgery yourself a few times a year (otherwise it costs a hundred bucks for each jam at the repair shop). Nerve-wracking, to say the least: if it happens more than twice, ditch that body despite the financial cost.
     
    Last edited: Mar 17, 2018
  10. The CM screen is easily removed, fasten two tabs on either side of the screen. Press those tabs out of the way and the screen will drop out when inverted. Reattaching the viewfinder automatically returns those tabs to the locked position.

    Grid lines in genuine Hasselblad screens are embossed into the bottom layer of the screen, in the same plane as the ground surface. It is not ground in the same sense as on a view camera, rather composed of microscopic prisms to direct light toward the viewer. A Fresnel lens, sandwiched between the layers, directs light from the corners toward the center, so that the screen is uniformly illuminated.

    Because of the way the grid lines are formed, they are in the exact plane of desired focus. If you concentrate on those lines, your back-focus issue should go away.

    There is one other thing. The focusing screen rests on four flat screw heads, which can be adjusted (or mis-adusted) which keep the screen exactly at the right distance from the lens. It requires special tools and fixtures to make that adjustment. We're talking about thousandths of an inch.

    If Murphy's Law prevails, it is always the most expensive alternative at fault. However try the cheap way first. As I said, I had the same problem until I changed my focusing method.
     
  11. A classic Hasselblad "lens jam" occurs when the lens is accidentally tripped as it is being attached or removed. If the coupling between the body and lens is mostly engaged, you can use a screwdriver (very carefully) through the back of the camera to turn the shaft (it's slotted for that purpose) to re-cock the lens. A more serious jam occurs when the coupling is 90 degrees or more out of phase. Nothing will turn. The factory uses force to shear the pin holding the gears to the shaft, then repairs any damage that ensues.

    The right tool is a flat bladed screwdriver with a collar to keep in from slipping off the slotted shaft. If it's going to work, very little force is required. It's basically the same force required to re-cock the lens off the camera, about 270 degrees of turn, until you hear the latch click.

    Aside from carless operation (like changing your mind when the lens is half removed), the latch in the lens, shielded by a half-tube, that keeps the lens cocked can wear, making it easy to dislodge the shutter. That latch is ordinarily depressed by a pin in the camera mount just before the lens latches in place, but can be a hair trigger with wear or a weak spring. It's easy to repair if you act before the lens jams.
     
  12. This sounds suspiciously like the issue which Mr Odess just corrected for me last month. A 500 cm back focused by about 2 feet consistently with any lens.

    On sending Mr Odess the body I specifically mentioned this issue and also advised that the same lenses focused correctly on a different body.

    On the service invoice, which was billed at his regular CLA price for labor, he indicated that he had replaced the foam pads regulating mirror position and then adjusted the mirror position. Seems like a couple of other parts were replaced which did not relate to the original complaint.

    The camera looks and functions as new.

    As an aside, I'm 70 and have significantly less than perfect eyesight. I can't focus the camera with the standard screen configuration, Accute Matt or otherwise. With a split image screen however my hit rate is approaching 100%. It's not beyond the realm of possibility that you are not able to use a standard focusing screen.
     
  13. Thanks everybody for your feedback. I've come down with a nasty cold, so working on this has stalled, but hope to focus (pun intended) on it tomorrow. I'm open to the possibility that it's my eyesight which has been declining in recent years ;-/ But it just seems so... clear. The image is very clear and I've tried to find something else to focus on but cannot. I should say I definitely need the magnifier to be able to focus at all. I will try again tomorrow.
     

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