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Bessa RF calibration: off at infinity, ok at film plane
Old 08-29-2018   #1
Takkun
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Bessa RF calibration: off at infinity, ok at film plane

Hi all,

I just got my R3a back from our host and head bartender for a RF touchup this weekend. Picked up a brick of HP5 and went out shooting: my RFs have been out of commission for a couple years (just didn't have the time to send everything in), and it's good to be back shooting.

I was out photographing some of our forests of cranes here in Seattle and noticed the focus patch was coming up short at infinity. At first I was a bit alarmed, since the two lenses I was working with had been collimated relatively recently, and one had a year-and-a-half turnaround time with DAG. My first assumption was that they'd come out of alignment again.

Got home, swapped out for my CV lenses and went up on the roof: same deal. Thoughts turned to the RF coming out of adjustment just days after getting back. I don't baby my camera, but it does live in a case, and Stephen packed it well.

After finishing off the roll, I tried to get a better look at the film plane through a ground glass swiped off my Nikon and a jewelers loupe. Set up the camera on a tripod about 4' from a computer screen with some large type displayed in a word processor.

As far as my admittedly poor eyes can tell, the RF is coincident with the image on the film plane at close distances with all my lenses, from a 25/4 to a 90/2.8. Which is good, since that's where critical focus happens. But at infinity, things still don't line up and Im out of focus lever travel—but it still looks okay on the ground glass. Haven't developed/scanned the test roll yet.

Unsure what to do here: to put up with it and stop with my slight compulsive tendencies (I've been up doing this testing for 4 hours now), or is this actually an issue to pursue?
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Old 08-29-2018   #2
d.dulin
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I’ve noticed both my rangefinders m4-2 and CL are off at infinity, with lens at infinity the patch is slightly over. Opposite direction from your problem but similar. I don’t have any actual m-mount lenses all are adapter LTM with Leitz adapters. I’ve always just assumed it was an issue because of this.
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Old 08-29-2018   #3
CameraQuest
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When checking a RF for "infinity"
focus on something a mile or farther away.

Stephen
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Old 08-29-2018   #4
Dante_Stella
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If the linearity adjustment is correct, the RF being "past" infinity means front-focusing and stopping short means back focusing. But if the linearity is anything but perfect, or it's not adjustable, you can live with misalignment at a mile (because you don't really need an RF to tell you something is at infinity) if it means better focus at a meter. And a lot of times, DOF sucks up the difference in focusing at far objects.
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Old 08-29-2018   #5
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Quote:
Originally Posted by CameraQuest View Post
When checking a RF for "infinity"
focus on something a mile or farther away.

Stephen

This is probably my problem
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Old 08-29-2018   #6
Sarcophilus Harrisii
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Do you get a clear view of the moon from your house? On a clear night it’s a good target. Whilst not actually at infinity, it’s a pretty good start.
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Old 09-08-2018   #7
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Not much luck on the moon, since we're back to rain here in Seattle. I do, however, live in a tall building and have a sliver of a view of downtown a few miles away.

My test roll showed the focus pretty close for 50 and under, but off enough to notice with the 90.

Regardless, I think the issue resolved itself: the lens release needed a little exercising, and it seems lenses weren't seating all the way.

On the other hand, the retaining screw on the eyepiece has gone missing...
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Old 12-17-2018   #8
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A little late, but for the future...have a look at http://rick_oleson.tripod.com/index-123.html

When travelling with my Bessa III I have a small piece of paper with two marks corresponding to the RF base length.

For checking close distances I use the laser pointer method:
Focus the RF patch on a subject while the camera is on a tripod. Then shine a laser pointer light through the viewfinder and see if there is only one dot on the subject. If there are two, the rangefinder needs calibration. This also works well for helping with critical focusing.
I find this works better than ground glass, and you can do that while the film is in.
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Old 12-17-2018   #9
Sarcophilus Harrisii
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Quote:
Originally Posted by Peter_S View Post
A little late, but for the future...have a look at http://rick_oleson.tripod.com/index-123.html

When travelling with my Bessa III I have a small piece of paper with two marks corresponding to the RF base length.

For checking close distances I use the laser pointer method:
Focus the RF patch on a subject while the camera is on a tripod. Then shine a laser pointer light through the viewfinder and see if there is only one dot on the subject. If there are two, the rangefinder needs calibration. This also works well for helping with critical focusing.
I find this works better than ground glass, and you can do that while the film is in.
You are conflating two different processes. A ground glass is used to check the focus of the lens at the film plane. Not to check the rangefinder calibration.
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