Out of focus

[sscb1]

So I have a Canonet 28 that I purchased off ebay a while ago. It had some dirt particles between the lens elements, so I took it apart and cleaned it. I ran a roll of film through it and every shot was out of focus (I checked the negatives to rule out the photo lab). The range finder matches the markings on the lens barrel, so I'm guessing both the finder and the front element need adjusting.

Unfortunately the camera does not have a B or T function, so I don't know if or how I could use a piece of ground glass to find the proper focus. Any suggestions?

 

[Pinholemaster]

You should have left the particles alone within the lens. They would not harm your image unless there were lots of dirt.

Clearly you did not reassemble the lens correctly. Good luck.

 

[sscb1]

Thank you Pinholemaster, but what I really need is someone with a solution.

The only way that I can come up with is to make a bunch of test shots on film while incrementing the front element. Is there another way? How was the front element installed in the factory?

 

[John Koehrer]

Just guessing here, But it does sound like you got an element in backwards.
There's not a lot of adjusting available on the camera.

 

[sscb1]

I think that I might be using the wrong term. What I did was unscrew the front lens (maybe this is called a lens group?) without making a note of the exact position (I did not remove the glass from it's threaded brass holder). If the camera had a T setting, I would put a piece of ground glass across the film plane and twist the front lens until infinity is in focus, then attach the the focusing ring properly aligned at infinity. The problem is that the camera is only automatic and does not open the shutter for more then a fraction of a second.

 

[elekm]

Without a B or T setting and a slow speed of just 1/30, you'd have too figure out a way to block open the shutter.

A slightly difficult and time-consuming method would be to remove the lens, block the shutter open with a small piece of gaffer's tape (this tape doesn't leave behind residue), replace the lens, collimate for infinity, mark the position, remove the lens, remove the tape, replace the lens and then test.

The best method of collimating involves the use of an SLR and a telephoto lens. Here's my method of lens collimation.

 

[ic-racer]

Personally, I think a trial-and-error method with film will give the best results.

Put an index mark on the lens group ring and some tape on the lens barrel (or some way to keep track of where you are).

Rotate the lens a few millimeters of angular rotation as you shoot multiple frames of a distant scene with the rangefinder focused at infinity. Keep good records. Examine the negatives and pick the best one. Use the widest aperture. In the end, it will perhaps be better than when you started.