When your camera’s perception of where a lens is sharp, is a tad off.

 

Co-written with my good friend Claus Møller, whom I spend countless hours diving and taking photos with.

 

Not all lenses are created equal.

Moreover, most certainly, is the lens mount and the camera bayonet alignment not perfect. This result in slight variations in where the actual focus point is, differing from where the camera believes the focus point is. Micro adjust your camera In order to get the most out of your lens. Every maker of hi-end DSLRs acknowledges this by providing auto-focus adjustment capabilities right in their camera’s menu systems. On SLT cameras, it is especially easy to perform this action, while it is easy to see the effect of your micro adjustment. I know that professionals spend focus on this area to a great extent, but oddly I see many photo enthusiasts spending 1000 of dollars on camera equipment, and lenses, and not focusing on how their lenses performs on their cameras. Generally micro Adjustments will have the greatest benefit for lenses with fast apertures (f/2.8 and wider), because the thin depth of field at wide apertures makes even small focus errors more evident.

 

Should I worry about damage to my equipment? Or is there special considerations.

No, there is no chances for damage to your photo equipment. The only fear is that you, if doing a bad job, can make your photos worse than they was to begin with. In any case, you can just remove the micro adjustment and be where you took off.

Pay attention to your lens type. Micro adjustment works well with primes and high-end zooms. Lower end zooms with variable apertures and long focal ranges generally will have multiple defects, and calibrating for a front focus at 135mm might cause the lens to back focus at 28mm. So test your lens at both focus length, allowing you to make the compromise performing optimal at the both focus points. Alternatively, you might take the attitude to optimize for the focus length where you expect to use the lens the most.

 

How do I determine if I need micro Adjustment?

If you have noticed, that your auto-focus is not where you expect it to be, maybe it is slightly in front or behind of where you told your camera to focus. On the Sony Alpha A99V (SLT) is it so easy to go through this procedure, that I just took my lenses through the test setup. Out of my 9 lenses, 8 needed the adjustments. Sony A99V can hold adjustments at up to 30 lenses.

 

In the example below, the red arrow points where we told the camera to focus and the green arrow points where the lens is actually in focus. This exercise aims to align these two points.

 

Prerequisities

To perform this operation you need

  1. A laptop with a focus Calibration Pattern and you need to make the screen display this on max.
  2. A tripod
  3. Set your Sony Alpha A99V to Spot Focus (page 95).
  4. Set your Sony Alpha A99V Peak colour to red (page 102).


  5. Locate the micro adjustment menu in your Sony Alpha A99V (page 101).


     

     

 

How to set up your test bench.

We need to be placing our camera in precise 45-degree angle to the monitor. The monitor has to be upright at 90 degrees. The distance between the monitor and the camera should be approximately 25 times the focal length of the lens (e.g. 85mm x 25 = 2.1 m = 7 feet). Anywhere within 5-50x focal length will work. Using the distance of 25x focal length will make you independent of sensor size.



Procedure.

  1. Load the focus Calibration Pattern on your monitor
  2. Set your camera on a tripod as close to a monitor as it can possibly focus
  3. Focus as close as possible
  4. Set minimum aperture
  5. Repeat until alignment of the focus line and red block. Do check more than once, that you get consistent results.
    1. Set your camera to auto focus-single AF-S
    2. Focus on the focus line at the monitor
    3. Set your camera to MF
    4. Magnify your focus area at the bottom of the test sheet (showing the squares and the focus line)
    5. See where the focus is located (marked with red) compared to where your focus line is. IF the red block IS on top of your focus line, then all is well, if it is in front of your focus line, then you need to add to the adjustment setting; if it is behind the focus line, you need to subtract. The amount is countable from squares on the test sheet

 



 

4 thoughts on “When your camera’s perception of where a lens is sharp, is a tad off.”

  1. Remember to write down your lens microfocus number in case your camera is reset. Then you dont have to start all over again

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