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David Lewalski
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 05, 2006 - 12:32 pm: | 
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I recently purchased a Mamiya 6 medium format rangefinder and a 50MM wide angle lens from two different sellers online. My problem is this- the images are not sharp.I guess you could say they're barely acceptable sharpness at certain aperatures.Nowhere neer what I would expect from a lens of this quality. I first thought that I might need to calibrate the rangefinder, but after doing research on the web, I don't think this is my problem because fine tuning the RF calibration is not that critical for a wide angle lens. I wondering about the lens working distance. Since this camera has a retractable lens housing, and a variable 120/220 film pressure plate, could the distance from the rear lens element to the film plane be off? How could I test or measure this? |
Jan Dvorak
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, April 05, 2006 - 06:43 pm: |
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David,
Do you have access to a ground glass? Place a piece of ground glass on the film rails, making sure that it is sitting where the film would be positioned and the matte side is facing the lens. Best would be having a ground glass sized a few milimeters larger than the film gate opening and doing the test with the camera mounted on a tripod.
Set the shutter to 'B' and leave it opened using a locking cable release. With the lens fully open, examine the image on the ground glass with a magnifier. Is it sharp? Does it correspond to the rangefinder at different distances?
This is where I would start my diagnostics.
Good luck,
Jan |
RJ
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, April 06, 2006 - 01:35 pm: |
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To add to Jan's comment, try typing in google:
"collimation test camera"
This will help deal with the concern you have. The simplest method has been described with semi-translucent sellotape (sticky tape in other countries) with an X in pencil scored across the sellotape between the film gates of the film chamber. It is very hard to discern accuracy using an unaided visual method - one of the links details using an SLR + a camera (Mamiya on tripod will do) focussing onto the sellotape against a window. It'll take some time however will clarify collimation issues.
I wonder if camera shake or film flatness might be worth thoroughly excluding first. Having used a Mamiya 6 on assignment, I found that I was suffering from more camera shake than a 6x6cm SLR with mirror lock-up. The excessive finger weight tripping the shutter from a vertical position isn't something I'm very good at - you might find that a horizontal shutter trigger is easier to stabilise. I don't know if other Mamiya 6 users have this problem, however if you're migrating from 35mm, then camera shake is much harder to contend with in 6x6cm format.
Similarly, if the 120/220 plate is reversed for the wrong type of film, then film flatness will be an issue. The Mamiya 6 is very taut with 120 roll film.
Another point which perhaps is irrelevant is whether there is any factor in image degradation at the post-exposure stage. You've not mentioned if you shoot on slides, negatives, or are viewing unsharp images in print. Overseas, I've found scanned 120 roll film sharpness to be mostly abysmal compared to 35mm lab scans - this may be possible due to the higher throughput of 35mm film or film-scanner flatness issues where 120 roll film is supplied in a cellophane sleeve about 1 metre long.
Not sure if any of those thoughts are useful, but good luck in any case. |
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