Help with Graflex Top Mounted RF Calibration

[NortheastPhotographic]

Hi!
I recently purchased a Graflex kit with a Rollei 150/2.8 in barrel projection lens mounted to it from Catlabs. I'm wondering about the RF, and if there is something wrong. Here is what is happening.

1. I open the camera and set the bed to infinity. The RF also seems to indicate infinity. I slide the front standard to correct focus, using a loupe on the GG, and lock it down.

2. I pick a target 50ft away and focus to that target using the RF. Suddenly, using a loupe I confirm that my image is defocused. So I think, maybe the inf target was too faint, and adjust my calibration at this new distance using the RF and the GG.

3. I pick a target 4ft away and focus using the RF. I then confirm using the GG and find that the target is defocused. Without changing the front standard position from the 50ft calibration, I check infinity, and find that it too is still defocused.

So it seems like I can calibrate the front standard & bed position to be acceptable for one range, but not another. Is this normal for this RF? Is it only good for specific distances? The guy from Catlabs did mention that I need to separately set the bed-stop levers for infinity and close. I was a little confused about this because I thought focus should be uniform from infinity once calibrated...maybe I'm wrong.

Any help you can provide would be appreciated!

 

[Dan Fromm]

Which cam is in the RF?

 

[shutterfinger]

The Graphic rangefinder uses cams machined to match the focal length of the lens. The graphic rangefinder is calibrated at infinity, the cam takes care of the closer distances.
This service manual covers setting up of the rangefinder: http://www.southbristolviews.com/pics/Graphic/manual-pdf/servicemanual.pdf
This is a list of cams made by Graflex for the Graphic rangefinder: http://www.graflex.org/speed-graphic/top-rangefinder-cams.html

 

[NortheastPhotographic]

I think I found my problem. I'm assuming this guy is labeled 127mm because it's for a 127mm lens?

 

[shutterfinger]

I'm assuming this guy is labeled 127mm because it's for a 127mm lens?

Correct.
Years ago I developed a procedure for making a cam from scratch for the Super Graphic https://graflex.org/helpboard/viewtopic.php?t=4653
Lens are rarely their marked focal length, they can be ,1mm to 3mm either side of the marked focal length. The greater the difference in actual focal length of the lens and the cam in use the greater the error at distances. A .1mm difference will be off at 3 or 4 feet while a 3mm or more difference will be noticed at 10 feet or more.
Find a 127mm lens, common, should be around $100 in working shutter, focus the lens at 100ft, 50ft, 25ft, 15ft, 10ft, 8ft, 6, and each foot closer until the cam travel is reached measuring the cam height at each distance, calculate the ratio of bed travel to cam movement.
Take the new lens and set to infinity with the RF at infinity then how far the rails have to move to achieve the same distance focus as measured until the travel of the cam has been reached in forward rail movement.
Cut a piece of aluminum or brass the same length and thickness as the factory cam, infinity height on the right, the focused distances height moving to the left using the travel ratio to determine the exact position then test against the lens.
You should now have a cam that matches the lens if all measurements were correct. The factory cam is nickel plated brass. I think the hole is for weight reduction but may be for ease of removal but not absolutely necessary.

 

[Sirius Glass]

See the articles in www.graflex.org

 

[NortheastPhotographic]

Ok I installed a 152mm cam. I noticed that the RF seems to stop working after about 20ft. Is that normal for the 152mm cam? Should i be able to RF focus closer?

 

[shutterfinger]

I noticed that the RF seems to stop working after about 20ft. Is that normal for the 152mm cam? Should i be able to RF focus closer?

Check the position of the cam at 20 feet, if the cam is at or near the end or it the bed actuator is no longer contacting the plunger and the plunger is fully extended (about 1 to 1/1/4 inches) then the limit of the rangefinder has been reached.

 

[mshchem]

The cams were matched to a specific lens by Graflex. Just using the correct focal length cam doesn't insure it will work with all lenses of that focal length. I have a top rangefinder Pacemaker w/135 Xenar, rangefinder is clear and very accurate. I tend to shoot 400 speed film. so in bright sunlight I am at f16, everything is sharp. These are GREAT cameras.
Best Mike

 

[shutterfinger]

90mm lens RF close focus to about 3 feet, 135mm to about 6 feet, 152mm to about 12 feet. A projection lens may have different characteristics than taking lens.

The cam is moved by balls and spacers in the tube and can become sticky with age. There are 42 to 45 balls and spacers inside the tube + 2 plungers and the cap at the bed. Assembly is plunger, ball, spacer, ball, spacer until all are installed then the lower plunger and the cap.
Best to remove the cam and tube from the camera if cleaning is needed.
https://graflex.org/helpboard/viewtopic.php?t=4952