QL 1.7 rangefinder caibration issue

[Dave Krueger]

I have an old Canonet QL 1.7 in very good condition. The range finder is calibrated fine at infinity, but when focused close up (40" or so), it turns out that the film plane is actually focused slightly closer. In other words, at f/1.7, focusing on something 40" away using the rangefinder will result in a sharp image of something about 38" away. I verified this with actual film as well as putting frosted tape across the film plane as a ground glass.

Infinity focus seems to be ok.

Is this within tolerance for this camera or is something out of wack? And, if it is out of wack, how do I get it back into wack. I'd really like to be able to trust the rangefinder close up with the lens wide open.

Any suggestions would be appreciated.

-Dave

 

[Dave Krueger]

At that distance, and f-stop, two inches is pretty damn close to perfect on the RF. I doubt you can get it much better.

Maybe so, but that's the difference between having someone's ears in focus instead of their eyes.

I was thinking there might be some other calibration for close focus.

-Dave

 

[BrianShaw]

Don't shoot wide open and it will never be a problem!

 

[Dave Krueger]

If you can recalibrate it, recalibrate it for the close focus. Infinity focus is not so picky because if you are shooting at infinity you are probably outside and have a lot of light thus more margin for error. My 2 cents.

I tried that, but then the range finder is way off (in terms of the alignment of the split images) when I'm looking through the viewfinder at far away objects with the distance set to infinity.

 

[Dave Krueger]

Don't shoot wide open and it will never be a problem!

Haha! It's very possible the camera has been ths way since we bought it new. Most of the time we would have the lens stopped down enough to where we wouldn't notice it in our 4x6 snapshots (which is basically all we did with it) and any time when it was noticable, we probably would have assumed we focused wrong.

But, one of the more attractive features of the camera is the fast lens. I'm wondering if this level of error is normal for these cameras. If I shoot someone's face, focusing on their eyes, with the lens wide open, it would be quite apparent in an 8x10 that the eyes are out of focus.

 

[anirbax]

Hi Dave,
At 40" and with a circle of confusion of 0.03mm, the DoF is around 2.4", thanks to the 40mm focal length. The error you mention probably even won't show up on prints bigger than 4x6.

 

[Dave Krueger]

Hi Dave,
At 40" and with a circle of confusion of 0.03mm, the DoF is around 2.4", thanks to the 40mm focal length. The error you mention probably even won't show up on prints bigger than 4x6.

It was noticeable looking at the negative through an 8x loop, so I'm guessing it's going to be apparent in prints. But, I didn't actually make any prints, so I'm guessing that it will be visible.

I have to admit I never thought to run the numbers to see what the DOF would actually be.

 

[ruben]

I calibrated two of them some days ago and as you, couldn't conciliate between the minimum distance and infinity.

But then I calibrated them for 1 meter and get pretty acceptable results at infinity.

Cheers,
Ruben

PS to Brian: you forgot to add a smile at your post.

 

[BrianShaw]

PS to Brian: you forgot to add a smile at your post.

Actually, Ruben, I think I was being serious that time. 😱

Didn't the message come through as friendly even though it may not have been the most technical of solutions? 😀

 

[Dave Krueger]

I calibrated two of them some days ago and as you, couldn't conciliate between the minimum distance and infinity.

But then I calibrated them for 1 meter and get pretty acceptable results at infinity.

I hadn't thought of that. I will go back and check my test film. I took pictures at several different distances. Maybe it's only at the closest focus points where it gets out of sync with the rangefinder...

It's not out of the question to compensate when I'm using it at close range by focusing on a point that is slightly beyond the plane that I want to be in focus. I was just hoping there would be some simple means of adjusting both ends of the scale.

I will fool around with it and see if it will calibrate between infinity and something greater than the minimum focus point.

-Dave

 

[ruben]

In fact, by my limited experience, the calibration screw range of the QL is rather crude, as I speculate there must be some common point of agreement between infinity and 0.8m. The problem is that reaching this infinitesimal point, with the screw limitations provided by the QL, requires more than our bare hand and a screwdriver.

 

[Dave Krueger]

In fact, by my limited experience, the calibration screw range of the QL is rather crude, as I speculate there must be some common point of agreement between infinity and 0.8m. The problem is that reaching this infinitesimal point, with the screw limitations provided by the QL, requires more than our bare hand and a screwdriver.

At one point I adjusted the screw to make the rangefinder correct for close focusing. I used frosted tape at the film plane as a ground glass. Unfortunately, it was then way off when set to infinity.

I looked at the negatives again last night and it looked like the focus at the film plane was a little closer (about 1.5 inches) than the range finder indicated for distances of 3-5 feet, but beyond that I think I would actually have to print the negatives to see where it's focusing. My 8X loop just isn't good enough to detect tiny differences in sharpnss.