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Archive 2013 · Sigma 35mm f/1.4 DG HSM - AF
  
 
Yakim Peled
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p.10 #1 · p.10 #1 · Sigma 35mm f/1.4 DG HSM - AF


I admire you. I think I'd crack at this stage.

Happy shooting,
Yakim.



Jan 30, 2013 at 10:37 AM
sfcyclist
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p.10 #2 · p.10 #2 · Sigma 35mm f/1.4 DG HSM - AF


Interesting poll.. at least it's feedback based on user's experience.

I like the fact that you added that detail in the "no" response. Perhaps also add, if no, do you have any focus issues with Canon's lenses?



Jan 30, 2013 at 05:46 PM
badlydrawnboy
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p.10 #3 · p.10 #3 · Sigma 35mm f/1.4 DG HSM - AF


Yakim Peled wrote:
I admire you. I think I'd crack at this stage.

Happy shooting,
Yakim.


Ha ha. I'm close to cracking, but the moments of brilliance were sufficient to keep me at it.

I've also discovered that it doesn't focus properly from far distances, say 15 feet. Right now it is nailing focus with a +9 MFA between MFD and about 6-8 feet.

I am considering keeping it because I shoot at these distances perhaps 90% of the time with a 35mm lens. I'm also at least curious whether Sigma may be able to fix this behavior. I've heard people say they've had similar issues with the Sigma 50/1.4 that were resolved by sending it for calibration.



Jan 30, 2013 at 06:28 PM
snapsy
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p.10 #4 · p.10 #4 · Sigma 35mm f/1.4 DG HSM - AF


badlydrawnboy wrote:
I've also discovered that it doesn't focus properly from far distances, say 15 feet. Right now it is nailing focus with a +9 MFA between MFD and about 6-8 feet.


Have you tried tuning it for far distances? My experience with many large-aperture primes is that if I tune for the usual 25x or 50x focal length distances it wont focus well at further distances, but if I tune at further distances the lenses still focus fine at near distances.



Jan 30, 2013 at 06:32 PM
badlydrawnboy
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p.10 #5 · p.10 #5 · Sigma 35mm f/1.4 DG HSM - AF


snapsy wrote:
Have you tried tuning it for far distances? My experience with many large-aperture primes is that if I tune for the usual 25x or 50x focal length distances it wont focus well at further distances, but if I tune at further distances the lenses still focus fine at near distances.


What distance do you tune at?



Jan 30, 2013 at 07:14 PM
newone757
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p.10 #6 · p.10 #6 · Sigma 35mm f/1.4 DG HSM - AF


So happy my copy is spot on. No MA on this old 5D body


Feb 05, 2013 at 04:22 AM
Fred Miranda
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p.10 #7 · p.10 #7 · Sigma 35mm f/1.4 DG HSM - AF


badlydrawnboy wrote:
Ha ha. I'm close to cracking, but the moments of brilliance were sufficient to keep me at it.

I've also discovered that it doesn't focus properly from far distances, say 15 feet. Right now it is nailing focus with a +9 MFA between MFD and about 6-8 feet.

I am considering keeping it because I shoot at these distances perhaps 90% of the time with a 35mm lens. I'm also at least curious whether Sigma may be able to fix this behavior. I've heard people say they've had similar issues with the Sigma 50/1.4 that were resolved by sending it for
...Show more

Same here... +7 AF tune value for the Sigma 35mm f/1.4. It nails focus from MFD until about 9-10 feet. After that, the target gets slightly out of focus...Beyond 15 feet, target is no longer in focus. If I AF tune it at 15-20 feet, it works well for that range but images at MFD are no longer as sharp.
On the Canon 35mm f/2 IS, I needed +2 AF tune and this setting works great for MFD and long distances...I guess with some lenses, we need to AF tune for the distance range we use the most.



Feb 06, 2013 at 06:28 PM
badlydrawnboy
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p.10 #8 · p.10 #8 · Sigma 35mm f/1.4 DG HSM - AF


Fred Miranda wrote:
Same here... +7 AF tune value for the Sigma 35mm f/1.4. It nails focus from MFD until about 9-10 feet. After that, the target gets slightly out of focus...Beyond 15 feet, target is no longer in focus. If I AF tune it at 15-20 feet, it works well for that range but images at MFD are no longer as sharp.
On the Canon 35mm f/2 IS, I needed +2 AF tune and this setting works great for MFD and long distances...I guess with some lenses, we need to AF tune for the distance range we use the most.


I'm relieved I wasn't the only one. I tried 2 copies and had the same problem. I finally gave up.

Fred: since you have the 35/2 IS and the Sigma, how much sharper is the Sigma @f/2?

I've decided to just cover the 35mm with my 24-70 II for now, and pick up a 50L. Later if I need a faster 35 I'll consider the 35/2 IS or the 35L. I had the 35L before and was perfectly satisfied with it.



Feb 06, 2013 at 06:33 PM
Rickuz
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p.10 #9 · p.10 #9 · Sigma 35mm f/1.4 DG HSM - AF


Fred Miranda wrote:
Same here... +7 AF tune value for the Sigma 35mm f/1.4. It nails focus from MFD until about 9-10 feet. After that, the target gets slightly out of focus...Beyond 15 feet, target is no longer in focus. If I AF tune it at 15-20 feet, it works well for that range but images at MFD are no longer as sharp.
On the Canon 35mm f/2 IS, I needed +2 AF tune and this setting works great for MFD and long distances...I guess with some lenses, we need to AF tune for the distance range we use the most.


With some Sigma lenses, yes.

This is exactly the problem I had with my Sigma 85 f/1.4. I tried two different copies, and both had the same issue. I even sent one to Sigma for calibration. They said that they had fixed the lens, but they really didn't. It came back with the same "distance based AF issues".

I've never had this problem with my lenses from Canon.

Sigma really needs to deal with this mess. It is getting old.

I really want Sigma's lenses to work. The IQ is superb when they hit, but the AF issues kills all the fun.



Feb 06, 2013 at 06:58 PM
snapsy
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p.10 #10 · p.10 #10 · Sigma 35mm f/1.4 DG HSM - AF


Fred Miranda wrote:
Same here... +7 AF tune value for the Sigma 35mm f/1.4. It nails focus from MFD until about 9-10 feet. After that, the target gets slightly out of focus...Beyond 15 feet, target is no longer in focus. If I AF tune it at 15-20 feet, it works well for that range but images at MFD are no longer as sharp.
On the Canon 35mm f/2 IS, I needed +2 AF tune and this setting works great for MFD and long distances...I guess with some lenses, we need to AF tune for the distance range we use the most.


On my 5DM3+Sigma 35mm f/1.4, I just tuned at +6 at 5 feet and +5 at 25 feet...so essentially identical irrespective of focus distance. And I measured spherical aberration on the lens at almost nil. I wonder how sample variation could influence distance-specific focus performance...I'm thinking it might be from imperfectly centered elements, which I'm theorizing could cause the focal point on the imaging plane to change depending on where the moveable (focusable) lens element is positioned relative to the other elements. Since the split light beams used in phase AF are split on the mirror from light entering at opposite sides of the lens, if the lens is decentered then the baseline phase differential will be off, similar to how its off in lenses that suffer from spherical aberration but in this case due to asymmetry. Some possible support for this theory could be found in Roger's article here.



Feb 06, 2013 at 09:36 PM
 

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RCicala
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p.10 #11 · p.10 #11 · Sigma 35mm f/1.4 DG HSM - AF


I think that decentering could possibly affect things, but in my experience decentered lenses affect autofocus accuracy rather randomly. I've seen cases where a lens simply misses more, but more specifically have seen zooms that are decentered in a focusing group so that they look good at one focusing distance but are decentered at another. These tended to miss focus randomly at the bad distance, but didn't exhibit the behavior described.

Here is another thought:

Phase is 'semi closed loop' and more accurate at saying '12 more feet over there' than 'here we are'. (Contrast detection is more accurate at saying 'here we are' and not at all accurate at saying even what direction to go in. Phase is more like a GPS, triangulating two different points and extrapolating where it should go. As it gets very close, the range of error is increasing. So it takes a couple of readings on the way to where it's going, but it's final 'here we are' is not accurate like contrast detection would be.

Each lens has a slightly different motor (we know they are calibrated for voltage and frequency in firmware), slightly different resistance to movement, etc. The resistance and movement are not linear, they vary according to a mathematical curve at different distances.

If the numbers for the lens are off slightly in firmware, it could affect it more at different distances.




Feb 07, 2013 at 12:19 PM
snapsy
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p.10 #12 · p.10 #12 · Sigma 35mm f/1.4 DG HSM - AF


RCicala wrote:
I think that decentering could possibly affect things, but in my experience decentered lenses affect autofocus accuracy rather randomly. I've seen cases where a lens simply misses more, but more specifically have seen zooms that are decentered in a focusing group so that they look good at one focusing distance but are decentered at another. These tended to miss focus randomly at the bad distance, but didn't exhibit the behavior described.

Here is another thought:

Phase is 'semi closed loop' and more accurate at saying '12 more feet over there' than 'here we are'. (Contrast detection is more accurate at saying
...Show more

Hey Roger. That's plausible as well, thanks. I think there's an easy way to see which theory might be correct here. For the Sigma copies that need focus-distance specific AF tune values like Fred's, if they're able to arrive at the correct at-distance AF tune value by using my dot-tuning technique then that would indicate the lens motor has no influence on the issue and that it is entirely an optical phenomena. Fred and others, can you give it a try?



Feb 07, 2013 at 03:32 PM
RCicala
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p.10 #13 · p.10 #13 · Sigma 35mm f/1.4 DG HSM - AF


Looking at what is going to be available on the Sigma Optimation Pro software, whatever the cause they plan on being able to adjust it, basically microfocus tuning at several different focusing distances. I'm not certain if this adjusts a look-up table or actually recalibrates the motor's electronics, but I suspect the lookup table from the little I've seen of the software.

On the other hand, both Canon and Nikon (at least) have several motor adjustments that are made when adjusting lenses for this problem. One is a mechanical spring resistor in the USM motor, the other two electronics I mentioned above.

When adjusting they set the spring tension manually (BTW - this is something that can un-adjust over time for those who find a lens doesn't AF as accurately as it once did), then the others are adjusted on a computer using factory software.



Feb 07, 2013 at 04:26 PM
geniousc
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p.10 #14 · p.10 #14 · Sigma 35mm f/1.4 DG HSM - AF


Roger,

No one has mentioned the possibilty of the camera bodies not focusing in a linear manner. What do you think of the possibilities of that happening? BTW, my Sigma focusng is perfect when calibrated at 20 feet right up to MFD wide open and all distances in between.

gene



Feb 07, 2013 at 04:45 PM
RCicala
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p.10 #15 · p.10 #15 · Sigma 35mm f/1.4 DG HSM - AF


Gene, that's absolutely possible I think, but should have a similar effect on all lenses.


Feb 07, 2013 at 05:27 PM
snapsy
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p.10 #16 · p.10 #16 · Sigma 35mm f/1.4 DG HSM - AF


RCicala wrote:
Looking at what is going to be available on the Sigma Optimation Pro software, whatever the cause they plan on being able to adjust it, basically microfocus tuning at several different focusing distances. I'm not certain if this adjusts a look-up table or actually recalibrates the motor's electronics, but I suspect the lookup table from the little I've seen of the software.

On the other hand, both Canon and Nikon (at least) have several motor adjustments that are made when adjusting lenses for this problem. One is a mechanical spring resistor in the USM motor, the other two electronics I
...Show more

I'm not sure how the Sigma adjustment might work. Each AF cycle involves a unique series of focus sensing+movement operations, depending on how far the focusable element is from its intended target. So trying to apply a fixed bias inside the lens based on either movement distance or element position might work for some AF cycles but not others.



Feb 07, 2013 at 05:27 PM
JPdeR
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p.10 #17 · p.10 #17 · Sigma 35mm f/1.4 DG HSM - AF


May I point out that in this discussion, the information that there are some people out there who do not have problems with their sigma 35 1.4 AF (or are not aware of them) does not mean that there, generally, is no problem with this lens' autofocus.

It reminds me of those people who respond to the question posted on the web "does anyone have tips for how to treat my splitting headache?" by saying "Hey, I have no headache at all!".

JP



Jul 30, 2013 at 10:56 AM
johnctharp
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p.10 #18 · p.10 #18 · Sigma 35mm f/1.4 DG HSM - AF


JPdeR wrote:
May I point out that in this discussion, the information that there are some people out there who do not have problems with their sigma 35 1.4 AF (or are not aware of them) does not mean that there, generally, is no problem with this lens' autofocus.

It reminds me of those people who respond to the question posted on the web "does anyone have tips for how to treat my splitting headache?" by saying "Hey, I have no headache at all!".

JP


Holy thread necro... but it's funny that I just read through this thread again last night. Note the ~25% of respondents that have focus issues with this lens (I didn't vote).



Jul 30, 2013 at 02:38 PM
jffielde
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p.10 #19 · p.10 #19 · Sigma 35mm f/1.4 DG HSM - AF


This was my first Sigma purchase and it was a mixture of awe and disappointment. I have yet to find a 35mm f/1.4 lens that satisfies me (the Nikon, Canon and Zeiss each have notable flaws). The IQ of the Sigma is fully satisfactory to me. It's brilliant. Unfortunately, the autofocus is simple unusable. I've even bought the dock as a bandaid - which helped, since now the inconsistency of the AF "averages" the right spot, which it didn't do before the dock. But it's just terribly inconsistent at middle to far distances (worse as gets farther away. I've resolved to use it as a manual lens only, since I tried the Zeiss 35mm f/1.4 which was MF only, and I think the Sigma is better. Still, I can't say that I'll every try another one.


Sep 26, 2013 at 07:33 PM
AGeoJO
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p.10 #20 · p.10 #20 · Sigma 35mm f/1.4 DG HSM - AF


Wow, I just saw Yakim's post on the top of this page....


Sep 26, 2013 at 07:43 PM
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