Set the aperture to wide open
Set the lens focusing to ~ (infinity)
Go outside your house, find a scene with a view to infinity (like the gate in the field opposite my house for instance) and set the centre of the frame to pick out a feature (like a wooden gate in the field)
Starting at the lenses ~ mark take a shot.
Move the focus to just off infinity (lets say 1mm off infinity for instance) Take a shot
Keep creeping the lens and taking shots, around five should do it.
Open the files in RAW software (Capture One is excellent for this as it allows you to see many files open at the same time)
Analysis -
If the adapter is the correct thickness the first shot taken at infinity will be in focus
Here\'s two obvious problems with this technique (and the reason I started this thread)
1: Some lenses exhibit focus-shift when stopped down. Since you would most likely be taking distance shots with a larger DOF, wouldn\'t it be safer to make your calibration at f/8?
-Or perhaps test at f/16 AND wide ope, and find the happy medium if they don\'t match?
2: You method only works if the lens is currently focussing PAST infinity. This is the only way you\'d know for sure that one of the 5 shots was actually in critical-focus. (I\'ll adopt Jim\'s term from now on)
As I wrote originally, let\'s say shot #1 was the crispest of the 5. How do you know that \"shot # 1/2\" would have been even better? (i.e., you still have a ways to go) The only way I can see this working is to first PURPOSELY thin the adapter or shim, so that maximum crispness is achieved within shots 2-4, then do the shimming until shot #1 matches the original best shot.
Set the aperture to wide open
Set the lens focusing to ~ (infinity)
Go outside your house, find a scene with a view to infinity (like the gate in the field opposite my house for instance) and set the centre of the frame to pick out a feature (like a wooden gate in the field)
Starting at the lenses ~ mark take a shot.
Move the focus to just off infinity (lets say 1mm off infinity for instance) Take a shot
Keep creeping the lens and taking shots, around five should do it.
Open the files in RAW software (Capture One is excellent for this as it allows you to see many files open at the same time)
Analysis -
If the adapter is the correct thickness the first shot taken at infinity will be in focus
Here\'s two obvious problems with this technique (and the reason I started this thread)
1: Some lenses exhibit focus-shift when stopped down. Since you would most likely be taking distance shots with a larger DOF, wouldn\'t it be safer to make your calibration at f/8?
-Or perhaps test at f/16 AND wide ope, and find the happy medium if they don\'t match?
2: You method only works if the lens is currently focussing PAST infinity. This is the only way you\'d know for sure that one of the 5 shots was actually in critical-focus. (I\'ll adopt Jim\'s term from now on)
As I wrote originally, let\'s say shot #1 was the crispest of the 5. How do you know that \"shot # 1/2\" would have been even better? The only way I can see this working (if your most is to first PURPOSELY thin the adapter or shim, so that maximum crispness is achieved within shots 2-4, then do the shimming until shot #1 matches the original best shot.
Oct 05, 2008 at 08:19 AM
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