Sigma 18-35mm f/1.8 DC HSM Art + 7D Mark 2

“ Hi Zsolt,

FoCal can be used with the Sigma Dock. Easiest way to think of it is this (I have simplified it a little) the normal camera/lens calibration is a fine tune setting held in the camera and FoCal can be used to work out the best value for this setting. With the Sigma Dock you now have a lot more points of adjustment and they must be set inside the lens rather than inside the camera.

To get an idea of what is involved take a look at this as an example of a user calibrating his Sigma lens with the help of FoCal, www.dpreview.com/forums/thread/3809354 and the related thread linked by tektrader where they talk in more detail about the steps.

We don't have an official written down procedure or tutorial video (yet!) but from what we understand FoCal can be useful for Sigma lens calibration. We'll need to do our own tests and more research using multiple different Sigma lenses before we'll have an official procedure that we guarantee will work in all cases.

You have a couple of options for the nearer distances, FoCal generally expects the target to take up between 20%-90% of the vertical frame, that way when you run target setup and select validate target you see the 'green tick'. With all the near distances you might find a the standard target works fine for this (or possibly re-print smaller as needed to ensure that it still fits inside the 90% with the closest distance).

With further distances and indeed with the 'infinity' setting it's unlikely you can print a FoCal target large enough for this calibration. The "infinity question" as I'm calling it is an interesting one(!)

I think the best way round is to find a natural or environmental target and use that instead. So turn off the function where FoCal expects a target ("Preferences" > "Tests" you can tell FoCal not to look for the specific target design at all by setting "Target Validation" to "No Target Validation").

A 'natural target' would be anything with high contrast edges in both the vertical and horizontal axis. Perhaps a large road sign with text on it, or a high rise apartment block that has strong defined lines (say window frames).

This is the approach we've come up with as a suggestion for now, one of the things we want to do is provide more information to users and this will be happening soon.

Essentially the expected process would be the calibrate (using FoCal) the lens at a specific distance (as given by Sigma in their user interface) and then try to dial out that adjustment such that the AFMA ends up at 0 and the adjustment is entered instead within the Sigma Dock settings.

It's hopeful (and there is some evidence to suggest) that once a relationship is found between AFMA / camera fine tune value and Sigma Dock calibration units that relationship holds true for further adjustments on that same lens.

Best Regards,
Dave „

“ Yep, the conversion between 'camera AF units' and 'Sigma Dock AF units' does seem to vary :) „

“ Quindi consigli la scelta? Io vorrei sostituire il 15-85 con 18-35 e 50 stm. „