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Polymerase
Tinkerer
Username: Polymerase
Post Number: 1
Registered: 01-2012
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 19, 2012 - 07:03 pm: | 
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Hey Folks!
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.
Cheers,
Andrew |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 1172
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 19, 2012 - 09:18 pm: |
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It sounds like the focusing helical has been separated for service, and reassembled on the wrong turn of the thread. But I have never worked on this particular lens, so I can't give you specifics for disassembly and correction. |
Polymerase
Tinkerer
Username: Polymerase
Post Number: 2
Registered: 01-2012
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, January 19, 2012 - 11:51 pm: |
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Rick, thanks for the thought. Sadly, I'm suspecting more and more that it's not a mechanical issue and is more likely a mount problem or a problem with one of the lens elements possibly being somehow inverted? After taking the lens apart again, I found that the helical 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.. 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. I added 10 new photos to my flickr set. They show all of the innards of this lens assembly.
Obviously, this is driving me slightly crazy. All of your help is greatly appreciated. Please keep the ideas flowing! |
Polymerase
Tinkerer
Username: Polymerase
Post Number: 3
Registered: 01-2012
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, January 21, 2012 - 03:19 am: |
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I'm still missing/overlooking something very simple... the lens continues to have the same focusing issue.
To anyone that's curious, this discussion has evolved at APUG:
http://www.apug.org/forums/forum51/100834-cant-inf-focus-hasselblad-distagon-40m m-f-4-c-lens-thoughts.html
Thanks again for your help! |
Brcamera
Tinkerer
Username: Brcamera
Post Number: 146
Registered: 08-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, January 21, 2012 - 04:49 am: |
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At this point, I would want to eliminate the possibility of the mount or helical causing the focus issue. Normally, I would put the lens on the autocollimator for image examination. A much more simplified test would be to hold the lens up to a ground glass and see if you can get infinity focus at a distant target. You can also examine image quality and instantly tell if the problem is optical (which I believe it is in this case) or mechanical.
Bill |
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