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03-29-2011, 07:37 AM   #1
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Sigma 85mm F1.4, inconsistent AF?

Howdy Pentaxians,
I bought the Sigma 85 1.4 a week ago for my K7. I am aware of a lot of happy Siggy 85 owners, Canikon inclusive. I did formal testing (that is: test chart, tripod, mirror up, IR remote, etc.) and found this 1 major problem. With a lot of trials, I came up with a -5 microfocus adjustment for the lens.

The AF is rather inconsistent, considering normal use. What I mean is, it has 3 different behaviors:
(assuming subject is like 2-5 meters away, and remember, this is with -5 microfocus adjustment)
1. If AF starts from behind-subject (what I mean is, say I twisted the focus ring towards infinity before AF), the AF always locks on correctly.
2. If AF starts from very close to subject (say, the lens was already prefocused on the subject from a previous AF), the AF would lock on about 50% of the times. The other 50%, it locks on in front of the subject.
3. If AF starts from front-of subject (say I twisted the focus ring towards the minimum focus distance before AF), the AF always locks on somewhere in front of the subject (front focus). The distance would be similar to behavior 2, when it front focuses.

Here's what adds to the complication. As I add or subtract MF adjustments, the whole behavior shifts by that much, front or back depending on how you adjusted MF. Now the difference in the behaviors brings about miss focuses of a factor similar to as if I had done a 5 to 7 MF adjustment.

Also, to those interested, I did find that the AF does FF and BF depending on subject distance, noticable at F1.4, but probably ignorable at F2.0. And, I did not notice any FF or BF with change in aperture. So, this is a big win for Sigma. Or maybe it's to do with the optics of any 85mm compared to 50mm.

As a result, my pictures come out with a 1:3 to 1:7 hit:miss ratio. This is awful Especially considering the DOF is so thin for those OOF parts of the subject and also because I know other lenses (Sigma 50 1.4, Pentax 55 1.4) were a lot more consistent. And of course for the almost $1K price tag!

Question to forum:
So, my question to the forum members is if anybody knows what is causing this, or if anybody else has experienced the same thing with the Sigma 85 1.4. I'm definitely dissatisfied with the behavior and will exchange (BH has a good policy)

I have had a Sigma 50mm F1.4 before, for a short while. But, I returned it because it did BF and FF too much depending on aperture and subject distance, which I put forward to the forum in this post. Also, I was not too fond of the perspective, although I will have to get one for those 50mm shots. But, later

But what I have noticed as a difference between the Sigma HSM and Pentax SDM is that the SDM is very sensitive to slight changes in the subject distance, while the HSM does not decide to reevaluate until the subject distance changes enough to notice the clear difference, given the thin DOF at 1.4. Maybe this is what is showing up in my copy, only quite exaggerated.

Cheers,
Anil


Last edited by icypepsi; 03-29-2011 at 07:46 AM.
03-29-2011, 08:39 AM   #2
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QuoteOriginally posted by icypepsi Quote
Howdy Pentaxians,
I bought the Sigma 85 1.4 a week ago for my K7. I am aware of a lot of happy Siggy 85 owners, Canikon inclusive. I did formal testing (that is: test chart, tripod, mirror up, IR remote, etc.) and found this 1 major problem. With a lot of trials, I came up with a -5 microfocus adjustment for the lens.

The AF is rather inconsistent, considering normal use. What I mean is, it has 3 different behaviors:
(assuming subject is like 2-5 meters away, and remember, this is with -5 microfocus adjustment)
1. If AF starts from behind-subject (what I mean is, say I twisted the focus ring towards infinity before AF), the AF always locks on correctly.
2. If AF starts from very close to subject (say, the lens was already prefocused on the subject from a previous AF), the AF would lock on about 50% of the times. The other 50%, it locks on in front of the subject.
3. If AF starts from front-of subject (say I twisted the focus ring towards the minimum focus distance before AF), the AF always locks on somewhere in front of the subject (front focus). The distance would be similar to behavior 2, when it front focuses.

Here's what adds to the complication. As I add or subtract MF adjustments, the whole behavior shifts by that much, front or back depending on how you adjusted MF. Now the difference in the behaviors brings about miss focuses of a factor similar to as if I had done a 5 to 7 MF adjustment.

Also, to those interested, I did find that the AF does FF and BF depending on subject distance, noticable at F1.4, but probably ignorable at F2.0. And, I did not notice any FF or BF with change in aperture. So, this is a big win for Sigma. Or maybe it's to do with the optics of any 85mm compared to 50mm.

As a result, my pictures come out with a 1:3 to 1:7 hit:miss ratio. This is awful Especially considering the DOF is so thin for those OOF parts of the subject and also because I know other lenses (Sigma 50 1.4, Pentax 55 1.4) were a lot more consistent. And of course for the almost $1K price tag!

Question to forum:
So, my question to the forum members is if anybody knows what is causing this, or if anybody else has experienced the same thing with the Sigma 85 1.4. I'm definitely dissatisfied with the behavior and will exchange (BH has a good policy)

I have had a Sigma 50mm F1.4 before, for a short while. But, I returned it because it did BF and FF too much depending on aperture and subject distance, which I put forward to the forum in this post. Also, I was not too fond of the perspective, although I will have to get one for those 50mm shots. But, later

But what I have noticed as a difference between the Sigma HSM and Pentax SDM is that the SDM is very sensitive to slight changes in the subject distance, while the HSM does not decide to reevaluate until the subject distance changes enough to notice the clear difference, given the thin DOF at 1.4. Maybe this is what is showing up in my copy, only quite exaggerated.

Cheers,
Anil
highlighted part could be the most obvious cause. but anyway, if you can still replace the lens, please do so. it doesn't hurt to see if there is any difference.
03-29-2011, 09:25 AM   #3
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QuoteOriginally posted by icypepsi Quote
Howdy Pentaxians,
I bought the Sigma 85 1.4 a week ago for my K7. I am aware of a lot of happy Siggy 85 owners, Canikon inclusive. I did formal testing (that is: test chart, tripod, mirror up, IR remote, etc.) and found this 1 major problem. With a lot of trials, I came up with a -5 microfocus adjustment for the lens.

The AF is rather inconsistent, considering normal use. What I mean is, it has 3 different behaviors:
(assuming subject is like 2-5 meters away, and remember, this is with -5 microfocus adjustment)
1. If AF starts from behind-subject (what I mean is, say I twisted the focus ring towards infinity before AF), the AF always locks on correctly.
2. If AF starts from very close to subject (say, the lens was already prefocused on the subject from a previous AF), the AF would lock on about 50% of the times. The other 50%, it locks on in front of the subject.
3. If AF starts from front-of subject (say I twisted the focus ring towards the minimum focus distance before AF), the AF always locks on somewhere in front of the subject (front focus). The distance would be similar to behavior 2, when it front focuses.

Here's what adds to the complication. As I add or subtract MF adjustments, the whole behavior shifts by that much, front or back depending on how you adjusted MF. Now the difference in the behaviors brings about miss focuses of a factor similar to as if I had done a 5 to 7 MF adjustment.

Also, to those interested, I did find that the AF does FF and BF depending on subject distance, noticable at F1.4, but probably ignorable at F2.0. And, I did not notice any FF or BF with change in aperture. So, this is a big win for Sigma. Or maybe it's to do with the optics of any 85mm compared to 50mm.

As a result, my pictures come out with a 1:3 to 1:7 hit:miss ratio. This is awful Especially considering the DOF is so thin for those OOF parts of the subject and also because I know other lenses (Sigma 50 1.4, Pentax 55 1.4) were a lot more consistent. And of course for the almost $1K price tag!

Question to forum:
So, my question to the forum members is if anybody knows what is causing this, or if anybody else has experienced the same thing with the Sigma 85 1.4. I'm definitely dissatisfied with the behavior and will exchange (BH has a good policy)

I have had a Sigma 50mm F1.4 before, for a short while. But, I returned it because it did BF and FF too much depending on aperture and subject distance, which I put forward to the forum in this post. Also, I was not too fond of the perspective, although I will have to get one for those 50mm shots. But, later

But what I have noticed as a difference between the Sigma HSM and Pentax SDM is that the SDM is very sensitive to slight changes in the subject distance, while the HSM does not decide to reevaluate until the subject distance changes enough to notice the clear difference, given the thin DOF at 1.4. Maybe this is what is showing up in my copy, only quite exaggerated.

Cheers,
Anil
All the C & N users I've heard from love the 85 1.4, especially its AF performance. You have 2 choices:

1) try another lens
2) Get your money back

* If you really want the lens, you'll try another copy--I sure would, an B & H willl be glad to assist you.*
03-29-2011, 09:28 AM   #4
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Are there happy Sigma 85 1.4 users on K7 or any Pentax body?

QuoteOriginally posted by Pentaxor Quote
highlighted part could be the most obvious cause. but anyway, if you can still replace the lens, please do so. it doesn't hurt to see if there is any difference.
QuoteOriginally posted by Jewelltrail Quote
All the C & N users I've heard from love the 85 1.4, especially its AF performance. You have 2 choices:

1) try another lens
2) Get your money back

* If you really want the lens, you'll try another copy--I sure would, an B & H willl be glad to assist you.*
Absolutely, guys. I'm really swaying towards that possibility of me having a bad lens copy. Or else, why would there be so many happy owners? Are they all dumb? Some of them are even professionals.

At one corner, the question I always ask is "is it my K7 ?"!!! Could it be? But then, the AF algorithm is the same that all K7 owners have... which, Sigma reverse engineered. What's different with Sigma is that they have different algorithms for Pentax, Canon and Nikon. So it should be bad for all Pentax users.. if it is. Or at least all K7 users.. if it is. Are there happy Sigma 85 users on K7?? Please show up.. please show up.. please show up..

Or could it be my AF sensor? I remember only using the center one for the tests. Let me do more tests today evening. But even so, my other lenses behaved fine. So maybe it's not even my K7 copy.

So you see what I'm saying about the Sigma copy being bad? I'll only know after the exchange, tomorrow. Man, this waiting can really kill!


Last edited by icypepsi; 03-29-2011 at 09:33 AM.
03-29-2011, 11:00 AM   #5
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QuoteOriginally posted by icypepsi Quote
Absolutely, guys. I'm really swaying towards that possibility of me having a bad lens copy. Or else, why would there be so many happy owners? Are they all dumb? Some of them are even professionals.

At one corner, the question I always ask is "is it my K7 ?"!!! Could it be? But then, the AF algorithm is the same that all K7 owners have... which, Sigma reverse engineered. What's different with Sigma is that they have different algorithms for Pentax, Canon and Nikon. So it should be bad for all Pentax users.. if it is. Or at least all K7 users.. if it is. Are there happy Sigma 85 users on K7?? Please show up.. please show up.. please show up..

Or could it be my AF sensor? I remember only using the center one for the tests. Let me do more tests today evening. But even so, my other lenses behaved fine. So maybe it's not even my K7 copy.

So you see what I'm saying about the Sigma copy being bad? I'll only know after the exchange, tomorrow. Man, this waiting can really kill!
unfortunately not me. my recent financial situation has kept me from spending too much cash nowadays.
03-29-2011, 11:02 AM   #6
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send it back, it's easier than having days of headache
03-29-2011, 11:02 AM   #7
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QuoteOriginally posted by Pentaxor Quote
unfortunately not me. my recent financial situation has kept me from spending too much cash nowadays.
Why does that sound familiar to me?!!
03-30-2011, 07:14 AM   #8
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QuoteOriginally posted by icypepsi Quote
But what I have noticed as a difference between the Sigma HSM and Pentax SDM is that the SDM is very sensitive to slight changes in the subject distance, while the HSM does not decide to reevaluate until the subject distance changes enough to notice the clear difference, given the thin DOF at 1.4.
Note that the camera does the AF. The lens merely provides the image and enacts the commands from the camera. In that sense, there is no difference between SDM and HSM.

It might be the case that your lens copy has an optical problem that makes it hard for the K-7 to lock focus. It might be that your K-7 has a slight problem.

Does your K-7 behave properly with other very fast lenses?

Do you have any test shots? Can't wait to see the first Sigma 85/1.4 vs FA 77/1.8 comparison.

03-30-2011, 09:33 AM   #9
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QuoteQuote:
Class A: Can't wait to see the first Sigma 85/1.4 vs FA 77/1.8 comparison.
Agreed!
03-30-2011, 09:33 AM   #10
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QuoteOriginally posted by Class A Quote
Note that the camera does the AF. The lens merely provides the image and enacts the commands from the camera. In that sense, there is no difference between SDM and HSM.

It might be the case that your lens copy has an optical problem that makes it hard for the K-7 to lock focus. It might be that your K-7 has a slight problem.

Does your K-7 behave properly with other very fast lenses?

Do you have any test shots? Can't wait to see the first Sigma 85/1.4 vs FA 77/1.8 comparison.
Thanks for the info. Yes, my K7 showed consistency when I used the Sigma 50 1.4 and DA 55 1.4. However, with those very fast lenses, I also noticed the phenomenon where focus shifts based on subject distance and aperture. I discussed my findings in this thread.
So I'm aware of that focus shift thing and I'm not complaining about that here for the 85 1.4. At least, that would have been predictable and explainable. But what is happening with me is something different. Seems like the AF is "stuck" towards the minimum focus (near focus) side whenever it has to focus onto a subject that is further away from what it finished off on the previous AF . Though it is predictable this way, I am unable to set any camera parameter (like microfocus adj.) to counter this. It is impossible to tell before an re-focus whether the subj has gone back a little, for things to mis-focus, esp, given the thin DOF. Imagine my frustration when doing AF-C!!

Going to get the exchange this evening. Otherwise, I like the lens and I need the fast aperture and longer than 50/55mm FL

Last edited by icypepsi; 03-30-2011 at 09:52 AM.
03-30-2011, 01:01 PM   #11
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Looks like you just got a bad copy, Dude. Sigma's been having q.c. issues lately and the 85 is included. What you describe, simply shouldn't happen. I don't know what the defective rate is for the Pentax versions of these lenses, but be happy it's not mounted to a Canon. The canon people are having all kinds of problems, maybe 4 or 5 out of 10 using this lens. I just recently acquired this lens myself, tested it for about 20 minutes or so, and found no issues at all. I did notice that it tends to fine adjust the focus LESS than some of my other lenses as you make fine changes in distance, but this could also be due to my lack of recomposing the shot as well. For the most part it was accurate and spot on most of the time, even in dim light. Good luck with your resolution
03-30-2011, 06:08 PM   #12
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QuoteOriginally posted by icypepsi Quote
So I'm aware of that focus shift thing and I'm not complaining about that here for the 85 1.4.
Good to hear that it doesn't have a focus shift issue.

QuoteOriginally posted by icypepsi Quote
At least, that would have been predictable and explainable. But what is happening with me is something different. Seems like the AF is "stuck" towards the minimum focus (near focus) side whenever it has to focus onto a subject that is further away from what it finished off on the previous AF.
The camera either
  1. thinks it has obtained focus sufficiently
  2. gave up after having tried to obtain better focus
Case 2 should be detectable by observing some micro hunting. Case 1 could mean that the slightly OOF is already sharp enough for the camera, or (more likely) that the AF module gets a slightly different view on the scene. The latter case would require a recalibration of the lens.


QuoteOriginally posted by outsider Quote
Sigma's been having q.c. issues lately and the 85 is included.
On what basis can you claim a general "QC issue"?

QuoteOriginally posted by outsider Quote
What you describe, simply shouldn't happen.
I agree that ideally it shouldn't happen but the reality is that you get lenses like that from all manufacturers.

A forum member went through five DA* 55/1.4 copies and couldn't get one that didn't focus erratically. BTW, he also used a K-7 and "erratic focusing" seems to describe the problem of the OP well. Maybe the camera plays a part in this too?

Glad that the Sigma 85/1.4 works well for you. Are you planning to post sample shots? Would be interesting.
03-31-2011, 09:54 AM   #13
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Got the second copy

Well, B&H was glad to give me the second copy. Too bad you cannot test a F1.4 lens without a tripod. So have to do a formal test, maybe tonight (by the time I reach back home and finish spending time with my baby, the day's 24hrs are usually up!)

But, the first thing I noticed is that the lens side of the mount had a slight crescent etch on it, indicating it was previously used by somebody else. I told myself that I have to be considerate to B&H, because somebody like me would have returned it. But if they did because the lens had a major problem, I'll have to head back again. Won't get to know till I test it.

The other thing I noticed is that the focus ring was noticeably smoother than the 1st copy. So much that if you are somebody with an eye for detail, you will notice it. I was amazed. Same company, same product and so much of a difference? Are those parts hand made or what? I don't think so. While I know that the glass parts can be slightly different, the other mechanical parts (metal/plastic) must not be so much different, even with giving the manufacturing tolerances they must be within. Or maybe that was why the 1st copy was defective. Again, Won't get to know till I test it.

So, I mounted the 2nd copy and began clicking some shots indoors right there. It did show some BF/FF. Which is not a problem, coz the K7 can handle that. This, and some outside dusk shots with the downtown's neon lights and with me hand holding, I couldn't make sense of how much microfocus adj. had to be set. More shots indicated towards focus shift with subject distance. That's sad. But like I said, it's the characteristics of most very fast lenses and it is predictable.. so , handlable to an extent (here's where you gotta bite the bullet, though). At the moment, it looks like this Siggy behaved just like the Sigma 50mm 1.4 I tested before.

I think copy 1 was doing the Case 1 thing that Class A suggested. It never hunted too much. Right on target. But my copy 2 does hunting towards the end. Which I have read on forums about Pentax. I've seen other lenses do it on my K7 too. So I think it's a non issue. Case 2 is quite scary.

Class A, I deleted most of my test shots of copy 1 out of utter frustration. I'll post the few I have, later. It's quite obvious from them.

Well, I'll get back with the test results.

Last edited by icypepsi; 03-31-2011 at 10:01 AM.
03-31-2011, 04:14 PM   #14
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QuoteOriginally posted by icypepsi Quote
considerate to B&H, because somebody like me would have returned it. But if they did because the lens had a major problem, I'll have to head back again. Won't get to know till I test it.
AFAIK, B&H does send returned stuff back out in exchange for returns unless a customer tells them it's been returned because it was defective. Happened to one of my Tamron 28-75's (the guy smoked too so the box and lens had a smell)-: B&H let me return it at no charge (including shipping) though...

p.s., on your focus tests, be aware that Pentax's focus points are a *lot* larger than the little red indicators in the display, unlike Canikon systems. They also might be a little off center from the red dots on the display too. Won't matter as much w/ wide DOF, but w/ the 85/1.4's narrow DOF wide open, it may make a difference...
03-31-2011, 07:23 PM   #15
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QuoteOriginally posted by icypepsi Quote
But, the first thing I noticed is that the lens side of the mount had a slight crescent etch on it, indicating it was previously used by somebody else. I told myself that I have to be considerate to B&H, because somebody like me would have returned it.
B&H claim they don't send "open box" items to customers. According to their public statements they should have sold your copy as an "open box" item with a discount. If you decide to keep your copy, at least ask them for a discount. You paid full price for a brand new copy and don't need to accept a product someone else already marked or even dropped.

QuoteOriginally posted by icypepsi Quote
This, and some outside dusk shots with the downtown's neon lights and with me hand holding, I couldn't make sense of how much microfocus adj. had to be set.
Note that the K-7 is not perfect in compensating AF errors due to non-daylight lighting.

Before you draw final conclusions, make sure that you did some tests in non-dim daylight.

QuoteOriginally posted by icypepsi Quote
But my copy 2 does hunting towards the end. Which I have read on forums about Pentax. I've seen other lenses do it on my K7 too. So I think it's a non issue.
Yes, it is probably a non-issue. Maybe it even means that the lens is very sharp in that it the camera sees a point in doing further micro-adjusts. I don't really know.

QuoteOriginally posted by icypepsi Quote
Class A, I deleted most of my test shots of copy 1 out of utter frustration. I'll post the few I have, later.
OK, hope we can help.

Keeping my fingers crossed for you that you'll have a happy ending with this lens. I'd love to own a Sigma 85/1.4 myself one day.
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