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Do I Need to Calibrate my CLE's Rangefinder Patch?
Old 02-09-2017   #1
intangiblethings
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Do I Need to Calibrate my CLE's Rangefinder Patch?

My patches on my CLE don't align perfectly. That's not really the issue but how can I determine if this is having an effect on hitting focus?

i.e. I have a Canon 50mm f/1.4 LTM and sometimes shooting portraits, I'd like to be confident I'm nailing focus.

Does the fact the patches don't line up yield a high(er) margin of error, especially wide open and near minimum focusing distance?

Or is it focus shift I'm seeing?

SIDENOTE:

How to determine focus shift vs. rangefinder patch issues?

Thanks!
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Old 02-09-2017   #2
intangiblethings
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I should add as well, I have a Voigtlander 75mm f/1.8 and I wonder what impact imperfectly aligned patches may have on focusing.

Thanks!
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Old 02-09-2017   #3
Fixcinater
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Do you mean that when you focus to a measured distance (say, 10ft), the rangefinder is not horizontally aligned? Or do you mean vertically mis-aligned as it seems you are alluding to?

You can determine by putting ground glass or substitute on the focus rails with the door open and the camera on a tripod (or resting securely on a table if tripod is not available and confirming that when you focus to your 10ft distance (check closer focus points too, just saying 10ft for simplicities' sake) that everything is showing 10ft. Lens should indicate 10ft on focus scale, rangefinder should be aligned.

Vertical and horizontal adjustments on most cameras are made separately.
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Old 02-09-2017   #4
Sarcophilus Harrisii
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Focus shift and RF calibration aren't quite the same issue. Eg you can have a RF perfectly calibrated that is spot on for a lens that is wide open. But the focus shift when the lens is stopped down is not a RF error, rather an optical characteristic of the lens. Of course you might possibly be inclined to try to optimise the RF adjustment for a particular f stop or set of f stops but that's another matter. You'll need to do as previously suggested and use a ground glass to work out what the lens is actually doing. Make sure the lens is correctly set for whatever register a CLE uses, see if the RF calibrates to the same focus point and take things from there.
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Old 02-09-2017   #5
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Focus shift is a result of lens design so it is unlikely that only your copy of the Canon 50/1.4 LTM would suffer from it. I've not read of others complaing of focus shift re: this particular lens. If you were using the 50/1.5 instead then that lens uses a Sonnar design which will focus shift (as Sonnars do).
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Old 02-09-2017   #6
Huss
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Quote:
Originally Posted by intangiblethings View Post
My patches on my CLE don't align perfectly. That's not really the issue but how can I determine if this is having an effect on hitting focus?
Shoot a roll of film and see.
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Old 02-09-2017   #7
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Quote:
Originally Posted by Huss View Post
Shoot a roll of film and see.
And take notes.

Write down what you are focussing on - from the distance, down to the near focus limit.Good distance objects include the moon, or the furthest object you can see near the horizon (or try both).

I have a bench with slats that i use for the near focus test - camera at one end.
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Old 02-10-2017   #8
intangiblethings
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Thanks for the replies.

Essentially I'm trying to isolate:

1. User error (missed focus)
2. Vertical patch misalignment (or does it have no bearing on focus)?
3. Focus shift (something that I didn't fully understand but you guys have explained)

I'll shoot a roll and make some notes. But I suspect that if #2 has no bearing on accuracy of focus, then it is #1.

Thanks for all your help.
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Old 02-10-2017   #9
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The vertical misalignment will have no bearing on the focus but there may be a horizontal misalignment - these are only obvious by their effect on focus.

So ideally, notes would include intended focus point plus estimated (or directly measured) distance, as well as what the lens marks indicate (these in themselves may not be correct), then when you are comparing the results you can see what the focus WAS on (this is where a slatted background at near distance is helpful - marked distances from the film plane also mean you don't have to recheck the measures.)

While this type of photography is not at all useful for impressing friends, it certainly aids getting the focus sorted, which in the end makes impressing people easier :-)

PS if you want to check for focus shift you can do so, but really that is a later exercise. You want the lens as open as possible - low numbers/wide open aperture - for the initial testing.
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