Calibrating lens to camera .. have you done it and does it really work ?

Started Jan 20, 2013 | Questions thread
MOD Victor Engel Forum Pro • Posts: 18,347
Re: Calibrating lens to camera .. have you done it and does it really work ?

HEWCanon wrote:

Calibrating lens to camera .. Is this really a useful thing to do .. ?? .. Please read to the end .. I would be interested in hearing from photographers who have done that and noticed an improvement .. Please let me know your experiences ..

I will start out by stating that I have not done this myself, so take what I say with a grain of salt.

If pictures from your camera, lens or combination are lacking proper focus, it may be that camera, lens, or both are causing front or back focusing.

Or there could be an operator error of some sort.

Common sense dictates making sure that any focusing problems are investigated to make sure that it is well and truly a problem that requires at least fine tuning, or if more serious sending the camera or lens back for servicing or exchange.

Rumours about quality control for cameras and lenses indicate they would pass the test as long as any focusing variations fall within the depth of field at a given focal length, aperture and focal distance.

It is more than just rumor. This has been confirmed by people who should know. One of the potential issues is that even if the camera and lens are both within spec, the combination might not be, if they are both out in the opposite direction. This is why Canon, for example, frequently suggests sending in camera and all lenses in when there is a focus issue.

All said .. if you find that your lens is either front or back focusing enough at a given focal length, aperture and distance (usually longest focal length in zoom, wide open, and at the minimal focusing distance as DOF is shallowest) then fine-tuning or micro-adjustment is going to be helpful.

From several resources on the internet I gathered the following, and others may differ;

  1. Calibrate a zoom using the longest focal length (the tele end of the zoom range)
  2. Use the maximum aperture (wide open)
  3. Use 25-50x focal length in mm as testing distance between camera and target
  4. Use tripod, mirror-up and remote shutter release
  5. If you print your own target sheet, do it on inkjet and not laser
  6. Do 3 shots per adjustment
  7. Do +/- adjustments and keep doing this until you narrow down your adjustment
  8. Use JPEG’s or RAW without any adjustments
  9. Use a standard target (DataColor© SpyderLensCal© or Michael Tapes Design© LensAlign©)
  10. Use computer software (Michael Tapes Design© FocusTune© or Reikan© FoCal©) to decide the best adjustment value

Before addressing these issues individually, I will suggest one general guideline that I think trumps most of them. If you have a specific project ahead, calibrate using settings similar to what will be used in the project.

1. What is the rationale?

2. This guideline will fail with certain lenses, most notoriously, the Canon 50mm f/1.4 lens. That is because the plane of best focus varies with aperture. Use the aperture that will be used in the project. If you will be shooting wide open, do so for the test. If you will be stopping down, stop down for the test. The camera will be use the same aperture when autofocusing, so this is actually quite important if you use lenses such as the one just mentioned.

3. Again, use what will be used in the project. This general guide strives to be generic and is appropriate if you don't know what you'll be shooting.

5. I'd be interested in the rationale for this one. I can't see it making a bit of difference.

6-7. Some suggest racking out before AF-ing, then racking in before AF-ing for separate shots. The camera/lens are doing different things but should have the same result. Others suggest repeated focus presses to ensure a good lock.

8. No such thing. <grin>

9. It's sometimes recommended to use a flat piece of newsprint.

10. I've always thought the camera should have a function to automatically calibrate. It should simply alternate between contrast and phase detection focusing methods in order to calibrate the latter using the former.

Remember that only one sample of a certain lens can be registered in the camera at any one time, and that the adjustment is saved in the camera. Also, if all the lenses register the same result, it is probably the camera body that needs to be adjusted for all the lenses.

I have to say that I have not tried this complete setup myself yet .. but tried the cheap way .. using a printed focus target sheet on a wall and also tried it on a floor or table with camera at 45 degrees, and I failed on both occasions to achieve a result that would produce better focused and sharper photos in real life after the calibration. I went out with my camera and shot handheld and on tripod real life shots with and without calibration and I have to say I have not seen an improvement .. so maybe the cheap way is not valid or reliable and maybe the more methodical way stated above would be more useful ..

The target should NOT be at 45 degrees to the camera. The portion covering the view by the focus sensor should be orthogonal to the camera. Parts of the target outside of this focus sensor view can be at 45 degrees to facilitate ascertaining where the focus was, but the focus sensor needs an unambiguous target, so it must be parallel to the sensor.

I would be interested in hearing from photographers who have done that and noticed an improvement .. So please let me know your experiences before I go out to buy all this kit!!

The only issue I ever had was with a fantastic plastic 50mm lens I bought. After two exchanges at the local store, they finally would not accept a third. So I wound up sending my equipment to Canon. It came back with no improvement, so I sent it in again. After the third trip, it performed well without even a hint of the typical fantastic plastic focus chatter that is fairly common. It's spot on now, and I'm happy.

I also do a fair bit of live view focusing and manual focusing, neither of which benefits from these procedures.

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Victor Engel

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