CI-TECH---XF-FocusTrimming

The ability to tune your camera specifically to your lenses has been around for sometime, not only on Canon & Nikon DSLR’s but also on medium format bodies like the Phase One 645DF+

Phase One IQ3 100 & XF Camera: Extreme capability, when used optimally.

Phase One IQ3 100 & XF Camera: Extreme capability, when used optimally.

The modular design of Phase One cameras and digital backs introduces some variance with where the exact sensor plane of focus is and rather than tweaking those physical distances with shims as thin as .01mm like on an Alpa tech camera, a user definable compensation is factored via electronics.

.02mm Shim

.02mm Shim to tune ALPA tech cameras

In the DF+, focus trim was available through Custom Function #20, but it was a single setting that would apply to any lens attached to the camera. Certainly useful when the camera was consistently back focusing with any glass attached to it, but the single setting had its limitations.

The XF has upped that game by tracking every lens focal length attached to the camera, and in the case of the Schneider Kreuznach ‘Blue Ring’ lenses, each and every serial number is recorded as a unique trim value so multiple copies of the same focal length will have their own perfect calibration.

xf-with-prism-viewfinder-and-full-blue-ring-lens-line

It has been my experience, however, that the proper trim value overall tends to be a relationship more about a focal length of any copy of a lens to your specific XF body and digital back combination.

The variance between the body and the digital back mounting along with the physicality of the auto focus system mounting within the camera itself tends to be the variables you’re correcting for and not as much the specific copy of your lens, although there will definitely be a trim difference between lenses. More like %70 body-DB relationship / 30% body-lens relationship for any given focus trim setting.

Depending on that overall relationship and on a specific XF body, I may only have to trim a legacy 80LS a few digits while I trim a new 80LS Blue Ring (with tighter manufacturing tolerances) to a higher trim level on the same body.  Not an indication that the Blue Ring is outside of tolerance, but that the XF/Digital Back needed compensation that the older lens made up for arbitrarily.

150LS-2.8_BlueLine

Schneider Kreuznach 150mm 2.8 LS Blue Ring

This leads to a relative clustering of trim values for all the lenses in your kit. I’ve found that it’s likely that the second third and fourth lenses in your kit will fall into the same range of trim on that body and those same lenses will likely fall into a different range on a different body but stay relatively clustered again.

Advanced users have been using focus trim to program offset values to shift focus forward and back so that critical focus can be achieved even in extreme focus and recompose scenarios.

I have not seen an XF yet that didn’t benefit greatly from the procedure of focus trim and that 4 out of 5 times I’m entering negative trim values to correct for some level of back focusing. My preference is to evaluate images shot at a medium distance, set trim values there and then test against near and distant values to see if that trim setting holds. This is the quickest route to a perfectly trimmed camera.

Target Selection:
-Flat, flat to camera, well lit, detailed target 10-20’ away depending on focal length, or a LensAlign Focus Calibration set, although the LensAlign brings the target much closer to the camera to be able to fill the spot sensor markings in the viewfinder and I’ve found tends to not lend to the most accurate focus trim values for all distances.

The completely flat and detailed portion of the target should entirely fill the focus point indicator in the viewfinder. If not using the LensAlign system, best shot in an environment that has other detail front and back (like a brick wall hallway with good texture) so it can be determined if focus is falling in front or in back of the target and that 1/3 of the focus falls in front of the focus spot and 2/3rds behind.

I’ve Frankenstein’d a target that has both a large flat area to let the sensor focus on, as well as a the Lens Align Long Ruler to better evaluate which direction the trim settings need to go.

Step 1: Setup

-Camera locked down on tripod

-XF set to Average focus (Only use Spot if your target isn’t large enough for the reticle)

XF-FocusScreen

XF-FocusScreen_Marked

-Autofocus Mode – Continuous

-If Shooting from the Camera Autofocus set to Rear Button / Shutter – 1/2 press autofocus turned off

01_XF_ControlSetup

Recommended Workflow: Shooting from Capture One 10, you can make use of the Autofocus button in the Camera Focus Tab (preferred, since you don’t have to touch the camera to focus or clear the focus point, and the focus trim value adjustment selection stays on screen, so you don’t have to re-navigate to it) 

C1-10_CameraFocus

-Base/Low ISO for best file clarity.

-Vibration Delay ON

-Aperture set to maximum open* / Zooms set to longest focal length  (*You will likely experience the phenomena of Focus Shift when trimming the 35mm, 45mm, and 55mm lenses.  If you intend to shoot the lens wide open, then trim there, otherwise, since those lenses are typically operated at closer to f8, trim there to make sure the window of depth of field is appropriately set. In practice, when I trim a those lenses, I’ll first trim at wide open to set the general reality for the lens, then stop down and trim again.  The focus trim number tends to go further in the direction you moving.)

-Ideal environment is tethered to workstation running Capture One where you can evaluate the images at 100%-400% on screen at the moment you capture them.

Step 2: Establish the Focus Baseline for the lens manually (optional)

– Clutch hard setting on lens to Manual Focus

– Utilizing Live View at 100% (on DB or preferably Computer) manually focus and capture image to create a focus reference. (Easiest on CMOS technology backs, CCD owners may prefer to skip this step and move on to Step #3)

FocusTrimBaseline

-Spin focus away from reference mark, clutch lens back to Autofocus.

Step 3: Establish the Autofocus Baseline for the lens

-Autofocus on target, and hold down on the autofocus button for a second or two to make sure that the XF has settled and is no longer correcting.  In Capture One, you will see the focus arrows settle on either side of the AF button.

-Capture Image

-Between captures, tap the triple left or right manual motor engagement mark in Capture One to rotate the focus away from where the autofocus settled on the previous exposure.

Step 4: Test your Focus Trim Test Environment

Repeat Step #3 2-3 times to make sure the focus is landing in exactly the same spot every time with no other changes. If you see changes between the shots, make sure that the focus reticle fully falls within the boundaries of your target and that the target is exactly square to camera.

-Determine at 100%-200% on screen whether focus is in front or in back of target.

Step 5: Gross Focus Trim

-Go to XF menu from lower silver button on top of XF, navigate to Capture Setup—>Focus Trim and adjust by 100 in the direction observed between the reference image and the first autofocus image. Negative 100 if the autofocus falls in back of the target, Positive 100 if the focus falls in front of the target. (Some will recommend moving in 25 step increments but I’ve routinely applied focus trim values above 100 and so would rather risk overshooting my value and drawing back, than moving forward in too small of an increment and making the process that much longer.)

03_XF_FocusTrim-100

– Drop your hand or a card in front of the camera and engage autofocus to reset it from its last engagement, then autofocus on the target again.

– Continue previous two steps shot to shot, adjusting by 100 until you clearly go past the target in the direction you had been adjusting.

04_XF_FocusTrim-200

Step 6: Fine Focus Trim

– Find the two 100-increment shots that show the range of appropriate focus that the lens should fall into

– Shoot an increment of Focus Trim change at values of 20 in between those two points.

05_XF_FocusTrim-180
06_XF_FocusTrim-160

– Evaluate images one at a time or shoot 5 in a row, although if shooting the bracket to evaluate, it helps to use a scribble pad that has your frame number and your trim value. (Capture One currently doesn’t display the focus trim value attached to any given image, although this has been requested as a feature)

Step 7: Refined Focus Trim

-Find the 20 increment shots that show best focus and change the value by 10’s and then 5’s until you settle on the perfect focus.

07_XF_FocusTrim-170
08_XF_FocusTrim-165

Step 8: Confirm trim value with target closer and farther than initial distance

-Consider again as you do this the rules of depth of field. Make sure that the focus trim you’re accepting isn’t too far on either side of 1/3rd into the focused scene. (it’s possible to set the trim too far to the back and still have your 2-dimensional target in focus)

Step 9: Repeat the process for each lens in your kit

I have found that 80% of lenses fall into the -200 to +150 range, while some have been outside of the -350 mark. (total scale 2000, -1000 —> +1000 in 5 increments)  

Edit 7/14/17: I recently spotted a rare white-unicorn 80mm on a new XF, IQ3-100 system that needed zero trim.  First time ever.

%d bloggers like this: