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Rob
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 25, 2005 - 09:01 am: | 
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I have a Praktica Super TL that has a bit of a focus problem. The pictures I get are not too bad as far as the actual subject goes, but the subject is at the back of the "depth of field." Upon checking out the camera on a tripod, I've found the viewfinder sets the focus at 16 feet on a given target, yet the focus screen finds the target at 10 feet. It's not a big adjustment, but all the lenses I have do the same thing, not just one. Can the viewfinder be adjusted? |
Glenn Middleton
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, July 25, 2005 - 04:52 pm: |
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Are you saying that you placed a piece ground glass in the film plane and when you checked the focus on this and compared with normal focus on inbuilt screen there was difference of 6 ft on lens scale?Otherwise I do not understand how you checked the difference.
Pentaprism and view finder lens play no part in the process of focus except as a means of viewing the screen.It is the screen that must be correctly positioned in relation to mount and film plane.
Has this problem just appeared in an otherwise working camera? ie it has not had a screen replaced or mirror replaced.If answer is just appeared I suspect that the mirror is not returning to the correct position (angle in relation to screen).
The angle of mirror is important in ensuring that the distance from lens mount to film plane is equal to mount to focus screen distance.This is where your difference in focus is actually occurring I think.
If you know how to alter mirror rest angle,use the 'Second camera as substitute collimator' method to reset mirror.You will find reference to the method in the archive and also on Rick Olesen's site (see Bringing infinity indoors)
I do not know this camera well enough to know if it has any particular quirks in the focus department that could account for your problem. |
Rob
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 26, 2005 - 06:54 am: |
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Hi Glenn.
I used a piece of plexiglas with a strip of frosted tape set directly on the film rail, the tape on the rail side. It has taken decent, but not razor sharp photos in the past. |
Glenn Middleton
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, July 26, 2005 - 07:54 am: |
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Rob,
Your test confirms my original thought,the mirror is not at proper rest position.It has gone out of adjustment because something has worked loose or there is debris on/in the stop/rest.
I have no idea how the mirror is adjusted on this camera.From other postings there seems to be a number of Praktica experts on this forum,so I hope they will dive in and tell you how to adjust.
The aforementioned optical setup is quite simple,but if you get stuck on that I can talk you through.
Glenn |
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