Consistency and Inconsistency
Here at Cameracal we have over the years built up a considerable data on the most consistent and inconsistent lenses (we are still in the process of looking to publish this database sometime in the near future) as in those that not only need calibration (because of lens optic displacement) but also the typical values needed to correct the front / back focus issue.
So here's an insight to one of the most common lenses we are asked to calibration
Canon EF 100-400mm F4.5 – 5.6 USM II
We literally see 3-4 of these a week and over the last 3 years we have calibrated hundreds of examples. Over this time (and number of examples we see) we have been able to build a pretty good picture of the values needed to correct these lenses.The calibration software we use here at Cameracal (Reikan’s Focal) has a handy feature often overlooked by users, the ability to check your calculated calibration results with other users. One stipulation when using Focal is that an internet connection is required, this is required for licensing and reporting, each time you conduct a calibration your results are forwarded to Reikan’s servers, this facility also allows you to check your results against other users.We have as mentioned, built up our own database, so much so that we are often able to predict what the required results will be before the calibration process (hence consistency).
So back to the lens in question..Virtually every example of this lens we see falls within the following category, and 99% of the time exactly these values, so what are they? 100mm end = -4 (the lens back focuses) 400mm end = +4 (the lens front focuses) . So what is the point of this, where are we going with this you may ask? Well recently we had another example of this lens to be calibrated to two different bodies, in this case a 7D MK 2 and a 5D MK IV
Lenses Must Be Calibrated to Both Camera Bodies
One question we often get asked (and is going to feature in our comprehensive FAQ section on our new website coming soon) is “If I have two camera bodies, do I have to calibrate the lens to both bodies, should they not be the same?" The answer is a categorical yes! You should consider calibrating the lens to each body and not use calibration figures from one body on another. This is due to the fact that rarely do two separate bodies return the same figures, one factor that often is different is the amount of displacement of the AF modules in the camera body. This is why it is not unusual to see two entirely different sets of results from two bodies. Hence why when you calibrate one lens to a body, the corresponding results ensure that the lens and body are “perfectly” matched.
Can I not use the figures from one body as a starting point on another body you may ask?
Yes, but again this does not take into account the possible displacement of the AF sensor in the second body. So this is where the inconstancy comes in but also the consistency. Inconsistency 100mm = +6 on both bodies 400mm = +5 on one body, +6 on the other.
Consistency, with the exception of the 5D Mk IV giving a variation of 1* micro adjustment both bodies where the same. This however was not just a one off, we calibrated 5 other lenses, and all were identical on both bodies which means the placement of the AF sensors were either perfectly seated or out by exactly the same amount*
Note this variation of 1 micro adjustment could well have been caused by minute changes in the test conditions / operation of the software, the latter being the probable cause as we calibrate under consistent conditions, this was most likely the reason as all the other lenses on both bodies were identical.So there we have it, the FIRST lens we have seen in over 3 years needing a totally different value at both ends and especially at 100mm as in a positive value as opposed to a negative value..