CAN'T INF FOCUS: Hasselblad Distagon 40mm f/4 "C" Lens, Thoughts??
I've got a headache of a focus problem that may be a simple fix. I'd love to hear your thoughts!
I recently purchased a Hasselblad Distagon 40mm f/4 "C" lens with a chrome barrel. I snagged it for about $400. That's a very good deal, but was already out of my budget b/c med school is expensive.. I can't afford to send it to an official hassy tech, but I regularly repair/restore old cameras to help pay rent and figure this lens can't possibly be that complicated.
That being said, I can't seem to figure it out...
Despite the focus ring marking 19 inches to 50ft then infinity, the lens has a max focusing distance of about 7ft, and minimum focusing distance of about 10 inches. While the macro is kinda neat, I mostly shoot landscapes and large interiors, so I need infinity focus.
I've tested this lens against my others on my 503CX body. This lens is the only one with a focusing issue, and it is reproducible every time I remove and re-mount the lens to the body (meaning the problem is consistent).
The shutter fires correctly at all speeds, and all glass elements are clear, except for the front element. The front element has a decent number of scratches and cleaning marks, but no chips, fungus, or haze. I strongly doubt the front element is contributing much to this focusing issue. As far as I can tell, all of the lens elements are aligned and correctly oriented. I even cleaned each one individually to make sure no sort of strange invisible coating was causing the issue.
I took the focusing ring off of the lens. I repositioned it on the barrel several times, each time setting the infinity at a different point. Unfortunately, the focus issue was identical every time I repositioned the focus ring, leading me to believe the problem lies elsewhere...
Here are some photos of the lens I quickly/haphazardly snapped via my cell while I was messing with it earlier today:
I'm sure the focusing problem is an easy fix involving something I've completely overlooked. I've never repaired a "C" lens before, and I don't have a service manual for anything earlier than the "CF" lenses, so I'm hoping you or someone else here can help me out.
Thank you for your time!! I look forward to your reply.
Put your glasses on. Can you see better now?
Probably a dumb question but: is there some sort of macro limiter? And is the flange to film distance the same for all the hassy bodies? And is there any sign of a different rear mount, i.e. was it adapted, perchance?
Just nutty thoughts....
Ah look at this, not the same lens but does it ring any bells?
This lens is visually distinctive by the appearance of the double blue
lines (also common to FE lenses) and by focus limiter knobs on each side
of the front of the lens barrel. These knobs are useful for certain
applications, such as sports photography, as they allow focus to be
restricted to a certain range and to stop at near and far points.
I'll second this. Lens helicoids have multiple threads, and you can pick the wrong point to start the threads. Depending on the whole focus system, this could lead to jamming or reaching certain limiting parts, or everything could seem normal except it is shifted 'in space.' Although this is a different focus system, here's a Minolta Autocord's focusing block showing the variety of possible steps to be off when re-threading- http://www.flickr.com/photos/1806725...57626869741228
Originally Posted by johnielvis
As to what it takes to get inside, and if it is worth even trying considering the risk, I can't help you. Unless I am prepared to lose a piece of equipment I don't poke around too much. And I consider the first time i go into a camera or shutter or lens, the most realistic thing I am doing is a dissection and autopsy, not a surgery from which the patient emerges alive.
Last edited by Dan Daniel; 01-19-2012 at 10:09 PM. Click to view previous post history.
Keith, sadly this lens has no limiters. And I've got other "C" lenses that work great on my 503CX. Good thoughts though!
John and Dan, I thought the same thing, but the helicoid seems to be a part of the barrel.. or at least I didn't see an easy way to alter its height. The other perplexing thing about the helicoid is that regardless of what point I screwed on the focus ring, the focus would still be off by the same amount. Also, the distance between the focus ring and the DOF scale when the ring is at infinity is correct. This all makes me think the helicoid might not be the issue.. :/
There are a few pictures of the focus assembly in the link I posted above. It's somewhat similar to the Minolta setup, but doesn't seem to be adjustable.
Thanks for your thoughts! Please keep em coming.
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Lens element turned around from prior tampering?
I have this but I think it applies to the later 40mm.
Last edited by ic-racer; 01-19-2012 at 10:14 PM. Click to view previous post history.
Well, all I can suggest is to compare your lens to another lens to see if the elements appear similar. Meaning if, for example, it is one single unit for focusing, the the rear element appears to be in the same spot in relation to the mounting flange. Do a search for images of your model? Hard to imagine how what appears to be a single unit in your snaps can focus at incorrect distances except by being mis-mounted, but there might be internal elements moving or such.
Most such lenses have multiple helicoids. I have re-assembled lenses for 35mm cameras where everything looks fine, markings fall into place, etc., but I have obviously mis-indexed something.
Or maybe the outer rings, with focus markings and such, have been re-assembled out of position?
This behaviour seems similar to what you would get if you used a very short extension tube, which makes me think there is something wrong with the mount.
“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2
I added 10 new photos to my flickr set. They show all of the innards of this lens assembly.
IC, thanks for the diagram. Sadly that is for a newer version of this lens and does not apply.
Dan, I'm suspecting more and more that it's not a mechanical issue and is more likely a problem with one of the lens elements possibly being somehow inverted? After taking the lens apart again, I found that the helicoid is locked in place by screws in a specific orientation, so the focus issue can't be due to a wrong turn. Regardless of where I attach the focus ring, and regardless of where the distance label is, the max and min focusing distance are still ~7 ft and 10 inches. Even if I screw the focus ring on in a way that lets me twist to the point of the ring being stopped by the VXM lever, the max focus is still ~7ft..
Matt, I completely agree. But there's nothing extending the barrel, no tube attached, and nothing seems to be missing.. A mount issue would make a lot of sense, but I stripped it down to essentially the chrome frame and didn't see anything out of the ordinary.. Maybe you can see something I'm missing (via my flickr link.)
Obviously, this is driving me slightly crazy. All of your help is greatly appreciated. Please keep the ideas flowing!
One thing I notice on the photos is scratch marks at the two spanner wrench holes on the back lens group. Not sure if that is from you or from a previous owner. If previous, it might give a hint as to where people have been mucking around? It's one thing I'll look for, signs of previous dismantling, etc. Maybe the helicoid, which appears locked, has been unlocked, rotated, then re-locked in the wrong orientation. Marks from set screws can hint at this, true 120 degree tapped holes allow for mistakes in re-assembly, etc. Study screw heads for signs of previous disassembly. Well, looks as if these are things you are comfortable with already. I don't know if David Odess (sp?) in Boston area is helpful, but maybe he has ideas.