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Gear Talk => Lenses => Topic started by: Ewinter on May 14, 2013, 06:22:20 PM

Title: +18 AFMA out of the box....return?
Post by: Ewinter on May 14, 2013, 06:22:20 PM
Hi all,
I got bored of waiting for a siggy 50 'A' so I bit and bought the canon 50mm 1.4 as I didn't want focus issues.
Lawl.
I've got it and it seemed really soft, and tried an afma.
It's at +18.
My question is : AFMA is supposed to be for dealing with tolerances and mishaps in the field. I know i'm not going to get a perfect 0, but if say, it gets knocked +3, i'm going to have a 1.4 I can't use.
Do I take it back or send it to CPS under warranty?
Title: Re: +18 AFMA out of the box....return?
Post by: neuroanatomist on May 14, 2013, 06:25:34 PM
I'd do one or the other. If you just bought it, I'd exchange it.
Title: Re: +18 AFMA out of the box....return?
Post by: Ewinter on May 14, 2013, 06:26:51 PM
Got it today.
The thing is, I have no guarantee another won't be the same. And it's not a usual item at the store, so it's probably a delay of equal time either way.

Or, do I get the store to send it to CPS for me?
Title: Re: +18 AFMA out of the box....return?
Post by: brad-man on May 14, 2013, 07:21:28 PM
If you get another that requires that much correction, you should probably send both the lens and the camera to Canon.
Title: Re: +18 AFMA out of the box....return?
Post by: Luke on May 14, 2013, 07:29:30 PM
Yeah, send it back..
That's what my Sigma was before I took it and the body in to Sigma :)
Title: Re: +18 AFMA out of the box....return?
Post by: Mt Spokane Photography on May 14, 2013, 07:33:15 PM
My 35mmL was +2 on my 5D MK II and +14 on my 1D MK III.  I sent it to CPS and they calibrated the lens to their reference 1D MK III and its been nearly right on for every camera since then, including another 5D MK II, two 5D MK III's, and a 1D MK IV.
 
I think having CPS calibrate it is your best bet.
Title: Re: +18 AFMA out of the box....return?
Post by: R1-7D on May 16, 2013, 06:18:10 PM
I just bought the 50mm f/1.4 yesterday and calibrated it. I got 11+.

Think I should try for a different copy of the lens too?
Title: Re: +18 AFMA out of the box....return?
Post by: killswitch on May 16, 2013, 07:09:43 PM
I recently bought a used 16-3L II and it seemed soft at first. After a quick AFMA, Focal suggested +12/13 on both ends. It was tested under very good lighting conditions(+15EV) and on a stable tripod. That AFMA made it a lot better though. But do these extreme values imply something is seriously wrong with the lens and need to be checked/calibrated?
Title: Re: +18 AFMA out of the box....return?
Post by: jdramirez on May 16, 2013, 07:41:36 PM
I recently bought a used 16-3L II and it seemed soft at first. After a quick AFMA, Focal suggested +12/13 on both ends. It was tested under very good lighting conditions(+15EV) and on a stable tripod. That AFMA made it a lot better though. But do these extreme values imply something is seriously wrong with the lens and need to be checked/calibrated?

 if I sell a lens, I  don't want someone with an xti  complaining I sold them a bad lens because they can't do afma. 
Title: Re: +18 AFMA out of the box....return?
Post by: victorwol on May 16, 2013, 08:04:07 PM
I recently bought a used 16-3L II and it seemed soft at first. After a quick AFMA, Focal suggested +12/13 on both ends. It was tested under very good lighting conditions(+15EV) and on a stable tripod. That AFMA made it a lot better though. But do these extreme values imply something is seriously wrong with the lens and need to be checked/calibrated?

 if I sell a lens, I  don't want someone with an xti  complaining I sold them a bad lens because they can't do afma.

Very good point..... Return it.
Title: Re: +18 AFMA out of the box....return?
Post by: R1-7D on May 16, 2013, 10:48:58 PM
So you guys are saying that if there's a big adjustment to the afma that a lens should be returned until one is found that doesn't require as much of an adjustment?
Title: Re: +18 AFMA out of the box....return?
Post by: neuroanatomist on May 16, 2013, 10:52:21 PM
There's no problem with a big adjustment, per se, as long as it's 20 units or less.  The problem is when you change upi your gear.  If your lens needs +18 on your current body, what if you get a new body that is off in the same direction - now, 20 units of adjustment isn't enough.
Title: Re: +18 AFMA out of the box....return?
Post by: jdramirez on May 16, 2013, 11:57:51 PM
I'm not really an AFMA expert, but the problem is as such.

lens is -15 and the body is +4 making the total adjustment 19 notches till AF is perfect.

Then you get a new body and the same lens.  The lens is still at -15, but the new body is at +9, so now you are at 24 notches till perfect. 

And if I'm wrong, please feel free to correct me out there.

So it is really about the lens, because let's say your body is +15 and your lens is +13, then you only have 2 in total difference.  So when you sell it to someone without AFMA, their body is -10 and the lens is +13 for a total difference of 23... which could be a real problem. 

So my presumption is that you want to make sure that you are identifying whether it is a combination of body + lens which is getting the high number or whether it is the lens itself.
Title: Re: +18 AFMA out of the box....return?
Post by: R1-7D on May 17, 2013, 12:23:47 AM
There's no problem with a big adjustment, per se, as long as it's 20 units or less.  The problem is when you change upi your gear.  If your lens needs +18 on your current body, what if you get a new body that is off in the same direction - now, 20 units of adjustment isn't enough.

Thank you and jdramirez for the reply! Makes sense.
Title: Re: +18 AFMA out of the box....return?
Post by: killswitch on May 17, 2013, 01:05:02 AM
I'm not really an AFMA expert, but the problem is as such.

lens is -15 and the body is +4 making the total adjustment 19 notches till AF is perfect.

Then you get a new body and the same lens.  The lens is still at -15, but the new body is at +9, so now you are at 24 notches till perfect. 

And if I'm wrong, please feel free to correct me out there.

So it is really about the lens, because let's say your body is +15 and your lens is +13, then you only have 2 in total difference.  So when you sell it to someone without AFMA, their body is -10 and the lens is +13 for a total difference of 23... which could be a real problem. 

So my presumption is that you want to make sure that you are identifying whether it is a combination of body + lens which is getting the high number or whether it is the lens itself.

Thanks jdramirez. Yeah, that made sense.
Title: Re: +18 AFMA out of the box....return?
Post by: cervantes on May 17, 2013, 01:52:28 AM
Sorry jdramirez, that doesn't really make sense to me.

AFMA is used to correct for manufacturing tolerances. Tolerance means that nothing can be made to an exact value but it can be made for sure within certain boundaries. Canon knows these boundaries for their lenses and cameras. I believe when they allow AFMA to be set from -20 to +20 it should be enough to correct worst case scenario. I don't know that for sure but it would be logical from my point of view.

E.g: The maximum amount a camera can be "off" would be +/-10 and the maximum amount a lens can be "off" would be +/-10 so a correction of +/-20 would be sufficient.

In this case the lens is probably off -9 and the body -9 (so they are both around their extremes) but you can correct it by using +18. Due to the known tolerances your next body will not be off more than -10 so correction should always be possible.

You - Ewinter - could test this by looking at the AFMA values of your other lenses. If you have a big enough amount of lenses you should see a tendency of AFMA values around +9 or at least they should be quite consistently >0. If you can't see this and the values are for example around -15 then there is probably something wrong with your lens.
Title: Re: +18 AFMA out of the box....return?
Post by: R1-7D on May 17, 2013, 05:09:36 AM
Well I just ran my 50mm f/1.4 through Focal Pro about eight times tonight. EV was 11. When Focal worked (it kept erroring out saying it could no longer find the target and then it prevented me from closing any of the app's windows) I got results from +10 to +15. When I got the +15 it said the fitment quality was poor. I got +10 with a "good" fitment quality, +12 with excellent, and twice +13 with excellent fitment quality and confidence rating. I set the lens to +13.

I don't know whether it is the new version of Focal or just this particular lens, but every other lens I have was much easier to calibrate...with no errors when using the program. Of course, f/2.8 is the fastest aperture of all my other lens, so perhaps having a two-stop aperture difference makes a difference to focus reliability on the target?

Anyways, I have tomorrow to return the lens before the long weekend here. I'm wondering if I should and get a different copy of it, or just keep playing with this current one. When I first brought it home it front-focused something fierce before I calibrated it. Now it is pretty good with focusing. I'm just getting a little anxious with all this camera and lens micro adjustment talk.

Advice? :-\
Title: Re: +18 AFMA out of the box....return?
Post by: neuroanatomist on May 17, 2013, 08:00:11 AM
Sorry jdramirez, that doesn't really make sense to me.

AFMA is used to correct for manufacturing tolerances. Tolerance means that nothing can be made to an exact value but it can be made for sure within certain boundaries. Canon knows these boundaries for their lenses and cameras. I believe when they allow AFMA to be set from -20 to +20 it should be enough to correct worst case scenario. I don't know that for sure but it would be logical from my point of view.

E.g: The maximum amount a camera can be "off" would be +/-10 and the maximum amount a lens can be "off" would be +/-10 so a correction of +/-20 would be sufficient.

In this case the lens is probably off -9 and the body -9 (so they are both around their extremes) but you can correct it by using +18. Due to the known tolerances your next body will not be off more than -10 so correction should always be possible.

That would be true if manufacturing process was perfect. It's not. Tolerances aren't absolute, to make them so would be prohibitively expensive.  A common manufacturing practice is 3σ, which basically means ~3 out of every 1000 products that leave the factory will not fall within the tolerance range.  Of course, if you get one of those you may not even notice it, but if you've got a lens on the other extreme, you might.  If you do notice it (in time), Canon will fix it under warranty - doing so is cheaper than tighter adherence to tolerances in manufacturing.