I have a Zeiss Super Ikonta IV. Everything works except the meter but that's not a problem. I have a Gossen meter that does the job.

After shooting a few rolls I have noticed that the focus isn't always sharp. Sometimes it's blurry around the edges.

I've been reading up and have found a couple of things that could give an answer but I'm looking for some confirmation.

I read that you should not wind the film to the next frame until just before you plan to take a picture. If you close or open the bellows too fast, you create a vacuum that pulls the film out of the focal plane. Advancing the film AFTER you open the bellows puts tension on the film which ensures it lies flat in the gate.

I'm not 100% convinced of that but it's easy enough to prove or disprove by experimentation. I'm running through a roll of film, right now, to test the theory.

I also read that the rangefinder mechanism needs to be calibrated from time to time. It's easy enough to send it in for a CLA but I would, of course, like to avoid spending money unless it is necessary. (The camera is near mint. Probably only had a couple of rolls through it in its lifetime before I inherited it.)

I'm pretty sure that the lens board is opening all the way and locking fully into position. The struts move smoothly and the bellows are in good condition.

Strangely enough, the focus seems to be more out of calibration when set closer to infinity. That's sort of counter intuitive. Isn't it? You'd think focus is less critical when the lens is at infinity. Wouldn't you?

I don't rule out the possibility that the problem lies, not in the camera, but in the idiot behind the camera.

Rangefinder focusing just seems a bit finicky to me. You really have to pay attention and focus very carefully. I also have the bad habit of focusing then moving slightly before taking the shot. It's stupid but it's something I have always done, subconsciously, ever since I was a kid. I just have to buckle down and pay attention. Most of the time I can deal with it but, on a camera like this, my bad habits might be making the problem worse.

So... Is it the camera? Is it me? Or, is this just par for the course with a folding rangefinder camera?