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Focal7175
Tinkerer
Username: Focal7175
Post Number: 7
Registered: 08-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, May 06, 2007 - 07:48 pm: | 
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I recently purchased a Fujica ST-801 from keh.com
I've run a couple rolls of B&W film through the camera and in nearly every frame of both rolls, the right-most portion of the frame (i.e. the portion of the frame that is closest to the next, numerically higher frame) exhibits an area of greater density (i.e. an area darker on the negative) than the remainder of the frame.
Here are additional details...
- The darker area is very definitely rectangular in shape (i.e. comprised of four 90 degree angles and the opposite sides are equal in length - just like we learned in geometry class).
- The darker area encompasses the width of the frame - but does not extend outside it (i.e. the area occupied by the sprocket holes is clear as we would expect)
- The shutter speeds used to expose these frames were all faster than the x-sync speed of the shutter (1/60sec). I know that because I used a 135mm lens to take them and I would never use a shutter speed slower than 1/125sec with a lens of this focal length, as it would invite camera shake. I believe that about 90% of the exposures were taken at 1/250sec, 1/500 sec, and 1/1000 sec.
- The affected area seems to occupy between 0.2mm - 2 or 3mm in length. In other words, the length of the rectangle of greater exposure is not uniform from frame to frame.
- The last fraction of travel of the film winding mechanism is a bit rough in that it requires a bit more torque on the winder.
- The spaces between the frames seem to be uniform in the developed rolls. There is a slight variation between them but nothing unusual for a camera with a manual film-crank to advance the film.
- This really doesn't seem to be a film defect or an issue with film development. I've developed about 350 rolls of B&W film and never seen anything like it. Moreover, the two rolls of film were different makes (Kodak Tri-X and Ilford HP5+) and were processed at different times by myself.
I'm uploading 2 negative scans to illustrate the problem.
-"A" is a frame where the additional exposure on the right-hand edge affects a relatively wide portion of the frame
-"B" shows a frame where the additional exposure on the right-hand edge affects a relatively narrow portion of the frame
Any thoughts? I suspect that the trailing edge of the shutter is decelerating too slowly at the end of its travel as it closes...leading to the rectangular area of greater density.
Thanks!
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Anirban
Tinkerer
Username: Anirban
Post Number: 15
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, May 06, 2007 - 09:03 pm: |
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Hi!
I think your suspicion is well-placed: this could be caused by the first shutter curtain slowing down towards the end of its travel, but the second curtain maintains its speed, resulting in underexposure towards the end of the travel (left side of the frame if you open the back of the camera).
If I remember correctly, the shutter speed adjustments in the 801 need removal of the top cover.
www.pentax-manuals.com has the repair manual. If you decide to do-it-yourself, you should proceed with care, as any tweaking of shutter travel speeds might need to recalibrate all shutter speeds.
Anirban |
Ethostech
Tinkerer
Username: Ethostech
Post Number: 66
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, May 09, 2007 - 10:07 pm: |
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This is not a gospel definitive answer to your query. I do not have an 801 i my collection and have not done surgery on that specific model. BUT - I can tell you that all other Fujica SLR models have electronically-controlled shutters and there was an endemic flaw in Fujifilm's choice control capacitors. Read on.
On all the other models, removal of the baseplate reveals a hard double-sided pcb to the underside of which is to be found a small electrolytic polarised capacitor of value 47microfarads at 6.3v. . Electrolytics dry out and should never have been used. A tantalum substitute is the way to go.
Whenever I have desoldered and removed the electrolytics, one of the legs has simply dropped off - indicating the component was physically and electrically dead. The cameras alwways came back to life when the capacitor was replaced with new (and I used tantalums instead of electro's).
The smaller tantalums on that pcb control the second curtain delays - but they are custom values as determined by factory tests and such odd values are not commercially available.
However - given that tantalums are virtually indestructable I removed each one at a time using solderwick and cleaned up the solderpoints of the pcb. On all five of my Fujica SLR restorations, the shutter speeds and 2nd curtain delays then came good.
This for whatever it is worth to you. |
Donnie_strickland
Tinkerer
Username: Donnie_strickland
Post Number: 22
Registered: 09-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, May 11, 2007 - 08:28 am: |
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The 801 has a mechanical shutter. A repair manual is here, if you haven't seen it already:
http://www.pentax-manuals.com/fujica/fujica.htm
Look under "M42 bodies", click on the 801, and scroll to the bottom of the page to see the manual link. |
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