Well this seems like a daunting task ! but probably one that will make the auto focus accuracy extremely good right across the focal length range so its worth persevering with I think.
The Sigma has the ability to be programmed at 16 yep 16 points across its focal range, unlike a Canon zoom lens which can only be micro adjusted at its shortest and longest focal lengths, the Sigma can be adjusted 150, 250, 400 and 600mm.
Not satisfied with that Sigma have gone one step further and allow you to adjust the auto focus accuracy at 4 distances to subject at each of the four focal lengths.
However in order to make any custom adjustments you first need to purchase the Sigma USB Dock (£40) my first thoughts were, this really in my opinion should come with the lens and not be sold as an accessory ! upon reflection I would assume that not everyone will use it.
You also need to download the software
Sigma Optimisation Pro from the
Sigma Website
Once installed you then have the ability to customise the lens parameters, update firmware as and when updates are available all in all its a pretty nifty bit of kit, as always improvements could be made.
The first improvement I would like to see is the ability to save a customised profile to disc for later use, this would then allow you to create profiles for each camera body you use the lens with, as it stands if you adjust AFMA for the main camera body that the lens will be used with when you come to switch it to another camera body all the AF settings you have programmed in will not be accurate as no two camera bodies are alike.
This issue must be an easy fix as the first thing that happens when you connect the USB Dock to the lens and PC is it checks for the firmware version of both dock and lens and then reads the current configuration from the lens, which creates a temp .bin file on disc, that's as far as I have looked, someone with a bit more coding knowledge may well be able to knock up a routine that can save this .bin file and give it a meaningful name for later use, if that would work I don't know.
So how to go about adjusting AFMA, as far as I see it there are two options
- you either take the test shot analyse it, remove the lens connect it to the dock and pc make the adjustment via the software put the lens back on the camera and take another shot and repeat above for each adjustment for all 16 points !
- Use the camera bodies AF adjustment write down all the settings and apply them all in one go.
Both of these methods have issues, the first you will be forever taking the lens off and back on of the camera this seems to me like a lot of messing about and a very long drawn out process !
The second does the Canon AF adjustment scale directly match the Sigma AF adjustment scale, both have the same range of plus or minus 20 ?
Main Menu View
Auto Focus Adjustment View
If it does happy days I will email Sigma support to see if they know the answer to that one.
Well that's answered that one the man from Sigma he say "no"
"It does not relate to the Canon scale in any way. If
needed please input small values to see the difference and adjust accordingly."
Oh well at least that has cleared that one up !!
So today I thought I would have a little bash at seeing how good the focus is out the box, I have only tested @ 3m distance to subject and f6.3 or wide open for this lens :
@ 600mm I found the focus to be pretty much smack on
600mm
Using my home made focus chart it is clear that the red text is pin sharp and the 2 and 4 are pretty equal as you move away from the centre line, no adjustment required here.
@400mm it looks to me like there is a slight back focus the red text is still sharp but as you look at the scale above and below the centre line 2,4, 6 above look a little sharper then 2,4,6 below
400mm
@250mm again this is clearly back focusing the red text is still pretty sharp but looking at the scales the above scale is way sharper then the scale below
250mm
Finally @150mm this one looks a bit soft all over (but that is probably my fault) but still seems to be exhibiting some back focus
150mm
So what I will do next just for the sake of it is repeat this test and adjust using the Canon adjustment and then again using the Sigma adjustment to see if there is any comparison.
I have read up on this in some forums and it appears that for Nikon cameras the ratio is 2 to 1, 2 steps on the Sigma scale equate to 1 step on the Nikon scale.
I havent found this information online for Canon yet.
But that's a job for tomorrow !!
