Lens calibration...again?!

Hey guys, been a while since I posted in here. I have a quick question; I bought a 70-200 maybe a year back from now and when I first got it, it needed to be sent in to get calibrated since it was back-focusing. I got it back 5-6 weeks later and it was amazing! Took very sharp images like this:

HOSTED PHOTO
please log in to view hosted photos in full size.

HOSTED PHOTO
please log in to view hosted photos in full size.

Are you sure the problem wasn't low contrast, white snow? Try your lens on another body.

It doesn't really look like they are backfocusing, to me. Keep in mind, that there is more DOF behind the focus point than in front. That is the way it should be.

One can argue that if they focused a touch more forward, it would be better, but they look fine to me.

Thanks for the quick replies guys. Well I dont know if its back-focusing but they just seem way softer than they should. Here is another example.

Test Image on Object
Of course the focal point was on the type on the cup.

Yes, you should Google "hyperfocal distance" and get up to speed on that.

When focused precisely on an object, about 2/3 of the apparent depth of field will fall behind it, about 1/3 in front of it. This is an approximation, but it's always the case, with every lens.

Looking at your images, I'd say your focus appears right on. The way DOF falls might give you the impression it's back focusing, but I don't think it is.

In light of the way DOF works, I've often wondered if it wouldn't be best to actually have a lens set to slightly front focus.

I imagine Canon service techs practically go nuts dealing with people photographing test charts and sending their lenses in for calibration. Maybe that's why the mid-level camera models are all now getting lens calibration built in, so people can adjust their own and give the techs a break.

bohdank wrote in post #6872343
It doesn't really look like they are backfocusing, to me. Keep in mind, that there is more DOF behind the focus point than in front. That is the way it should be....

Both shots sure look like it's back focusing to me. Looks like the focal plane is set somewhere between 4mm and 6mm.

I don't think Canon techs mind each person giving them $150 to do absolutely nothing per lens. lol.

Thanks for the reassurance. I guess I got scared when I called the camera store and they mentioned how it probably got out of wack due to expansion and contraction in the cold weather.

gjl711 wrote in post #6872660
Both shots sure look like it's back focusing to me. Looks like the focal plane is set somewhere between 4mm and 6mm.

Thats what I was thinking. But if you look at the object test I did, it doesnt look like any portion of the image is in focus and the overall lens is soft.

Just out of curiosity, is the 70-200 the IS version?

gjl711 wrote in post #6872678
Just out of curiosity, is the 70-200 the IS version?

Oh no, its non IS but those were taken with a tripod and I used a remote.

gjl711 wrote in post #6872660
Both shots sure look like it's back focusing to me. Looks like the focal plane is set somewhere between 4mm and 6mm.

Shooting paper at MFD has only so much value.

I can put my Tamron 28/75 through the same test and it will focus perfectly every time. Use it in the field and the focusing is sometimes erratic. So much so it is with Tamron at the moment getting looked at. I'm pretty sure part of the problem is not focusing on something with enough contrast at times but it still has a problem. Maybe the focus gearing is loose (it's not USM).

The charts you posted... there is nothing wrong with the focus, imo, under the test conditions. It does not mean that the lens doesn't have a focus problem at infinity or other distances.

I took a shot of a Christmas tree with my 85/1.8 this afternoon under natural light (it's next to a window) OOF.... not enough contrast. Makes sense.

I'm coming to the conclusion that what you focus on has a real bearing on the success of the focusing system. When I was "stupid" everything seemed to be in focus.....lol