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Archive 2013 · Sigma 35mm f/1.4 DG HSM - AF
  
 
Bruce Sawle
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p.4 #1 · Sigma 35mm f/1.4 DG HSM - AF


Got mine this evening and mounted it on my new 5d MK III. Shooting around the house the AF seems dead on. I will play a bit more this weekend and report back.


Jan 10, 2013 at 04:50 AM
umihoshijima
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p.4 #2 · Sigma 35mm f/1.4 DG HSM - AF


A lot of people here report focus issues outside of MA range. I'm sure that if bodies didn't come with MA, the poll would be shifted significantly towards "doesn't autofocus well". I'm still tempted to play Sigma roulette, I guess I'll think about itů


Jan 10, 2013 at 06:55 AM
Lasse Eriksson
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p.4 #3 · Sigma 35mm f/1.4 DG HSM - AF


umihoshijima wrote:
A lot of people here report focus issues outside of MA range. I'm sure that if bodies didn't come with MA, the poll would be shifted significantly towards "doesn't autofocus well". I'm still tempted to play Sigma roulette, I guess I'll think about itů


And how many of those 9 votes that report back/front focus have done a test that where not so good?
And how many was it the camera and not the lens that had focus problems?
And how many did vote that didn't even own the lens?

Nearly every Canon lens also need MA in the camera so there is no difference in that. Every Canon lens that I own have some MA



Jan 10, 2013 at 11:36 AM
river rover
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p.4 #4 · Sigma 35mm f/1.4 DG HSM - AF


Accepting the possibility there might be some Focus issues, (mine seems to hit most times, even at 1.4 but on occasion I'll get a WTF shot) How much of this is going to be mitigated by the USB dock? Isn't this the sort of issue it was made for?


Jan 10, 2013 at 12:30 PM
snapsy
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p.4 #5 · Sigma 35mm f/1.4 DG HSM - AF


river rover wrote:
Accepting the possibility there might be some Focus issues, (mine seems to hit most times, even at 1.4 but on occasion I'll get a WTF shot) How much of this is going to be mitigated by the USB dock? Isn't this the sort of issue it was made for?


It doesn't appear the dock will allow for adjustments that would affect AF tuning. From http://www.sigmaphoto.com/shop/sigma-usb-dock:

Focus Settings:
4 Categories of customization for fixed focal length.
16 Categories of customization for zoom lenses (4 options for focal length) x (4 options for shooting distance).

Sports Line:
AF Speed: 3 adjustment modes.
Focus Limiter: Customize auto focus range.
OS: 3 adjustment modes.



Jan 10, 2013 at 12:39 PM
river rover
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p.4 #6 · Sigma 35mm f/1.4 DG HSM - AF


Not sure I follow. What is meant by 4 options for shooting distance?



Jan 10, 2013 at 12:42 PM
goosemang
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p.4 #7 · Sigma 35mm f/1.4 DG HSM - AF


it says

"to update firmware and other parameters such as focus, and for the Sports category: Autofocus speeds, focus limiters, and optical stabilization functionality"

which, to me, means you can adjust focus.



Jan 10, 2013 at 01:57 PM
SeverianTL
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p.4 #8 · Sigma 35mm f/1.4 DG HSM - AF


goosemang wrote:
it says

"to update firmware and other parameters such as focus, and for the Sports category: Autofocus speeds, focus limiters, and optical stabilization functionality"

which, to me, means you can adjust focus.


Screen shot from somewhere on the web (I forget where):







Jan 10, 2013 at 03:30 PM
Shield
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p.4 #9 · Sigma 35mm f/1.4 DG HSM - AF


I'm curious if anyone with a 5d3 has tested their copy and require 0 MFA. Anyone?


Jan 10, 2013 at 07:38 PM
Bruce Sawle
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p.4 #10 · Sigma 35mm f/1.4 DG HSM - AF


Shield wrote:
I'm curious if anyone with a 5d3 has tested their copy and require 0 MFA. Anyone?


As of now after a day with the lens mine does not appear to need any MFA. I am going to run a few more test over the weekend before I can say for certain.



Jan 10, 2013 at 08:18 PM
 

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Lord Gnome
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p.4 #11 · Sigma 35mm f/1.4 DG HSM - AF


As far as I can tell mine doesn't need any MFA either (on a 5D3). I should say that this is my second copy, the first having faulty AF (variable front focus). I'm very happy with it and the fact that I have not been motivated to experiment with MFA says something.


Jan 10, 2013 at 09:13 PM
Shield
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p.4 #12 · Sigma 35mm f/1.4 DG HSM - AF


Well #2 has arrived. Will report in later.


Jan 10, 2013 at 09:49 PM
Shield
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p.4 #13 · Sigma 35mm f/1.4 DG HSM - AF


Well #2 arrived. This one needs a +14 but it's much better than the first. This one doesn't backfocus up close, and I tried several different distances and got a 100% hit rate (not keeper rate mind you - these are boring pics).

All in all I'm happy now. Ridiculously sharp lens in the center wide open.



Jan 11, 2013 at 02:10 AM
dennisgibson
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p.4 #14 · Sigma 35mm f/1.4 DG HSM - AF


nice to hear Shield! I love mine.


Jan 11, 2013 at 02:46 AM
RCicala
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p.4 #15 · Sigma 35mm f/1.4 DG HSM - AF


One thing that hasn't been mentioned is we're still a month away from Sigma's AF correction widget, which this lens is designed to use. I haven't gotten one yet, but I've been able to get some background. Unlike camera MA adjustment, the Sigma will give us a lot more options.

I don't want to write a book, but some things to consider:

1) Focus groups don't move linearly. Moving from 4 to 8 feet may be 800 steps, from 8 to 12 650 steps, from 12 to 16 414 steps. You can actually see how nonlinear it is by following the path of the AF helicoids.
2) Ultrasonic focus motors estimate how far they're moving for a given current burst. There are tension adjustment rings in them that, even when properly calibrated, still have a 'range of acceptable' movement per current.
3) The mechanical resistance of the lens changes at different focal distances and is slightly different for each lens.
4) The in-camera algorithms in a Canon camera are not designed for the motor, focusing rings, and distances in a Sigma lens. Third-party lenses 'borrow' the best-fit algorithm from an existing Canon lens, the chip in the third-party lens is converting that instruction.

So it makes sense that some copies may AF accurately at certain distances but not at others. They may have slightly tighter collars in the helicoids (those only come in 2 or 3 sizes, so in some lenses they're slightly more resistant than others because of a snugger fit). Or that AF motor my be moving fewer or more steps than the current tells it to.The resistance to movement is different at different portions of the focusing curve.

You also have to consider that the motor - focusing system of a third-party lens has to be able to mimic the motors Canon uses and the motors Nikon uses (which are very different, trust me, I take them apart for a living). That has to complicate things further. For example, the Canon 35 L has some 3200 steps of focus but the Nikon a very different amount (don't have the exact number). The Sigma insides has to be able to do either one depending on which mount (and electronics) are attached to it.

Unlike MFA, the Sigma lens programming thing will let us set adjustment at 4 to 16 focus distances if I read correctly, calibrate the actual motor function to the algorithms, etc. I think it will also allow us to compensate for focus shift at different apertures. It will be a much more powerful tool than what we get with the cameras MFA.

Will it work better? I don't have a clue. But it certainly seems possible. In fact, now that I see a little bit about the tool it seems amazing that third-party lenses could work without it.

I've spent the last 2 months reading more stuff about how phase detection AF works than I ever, ever wanted to. Everything from patents to academic journals to white papers. The more I read, the more amazed I am that it ever works at all.

Edited on Jan 11, 2013 at 03:25 AM · View previous versions



Jan 11, 2013 at 03:03 AM
snapsy
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p.4 #16 · Sigma 35mm f/1.4 DG HSM - AF


I'd be curious to see how a lens-based AF adjust mechanism would actually work. Based on experiments I've done on Nikon cameras, the camera's AF adjust value feeds a bias into the input side of the PDAF system, adjusting how the camera evaluates the split beam in determining whether focus has been obtained, whereas most believe AF adjust is an output bias that gets added to the "move focus to here" command. An "output bias" wouldn't work since a single AF acquisition involves multiple evaluation/move commands, so the biases would stack and compound - this is why I'm curious as to how a lens-based AF mechanism would work, even one which provides for different adjustment values based on focus distance.


Jan 11, 2013 at 03:17 AM
badlydrawnboy
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p.4 #17 · Sigma 35mm f/1.4 DG HSM - AF


I'm encouraged by the Sigma widget, but it sounds complicated!


Jan 11, 2013 at 03:23 AM
Lars Johnsson
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p.4 #18 · Sigma 35mm f/1.4 DG HSM - AF


RCicala wrote:
One thing that hasn't been mentioned is we're still a month away from Sigma's AF correction widget, which this lens is designed to use. I haven't gotten one yet, but I've been able to get some background. Unlike camera MA adjustment, the Sigma will give us a lot more options.

I don't want to write a book, but some things to consider:

1) Focus groups don't move linearly. Moving from 4 to 8 feet may be 800 steps, from 8 to 12 650 steps, from 12 to 16 414 steps. You can actually see how nonlinear it is by following the
...Show more

Roger, thanks for the good info



Jan 11, 2013 at 04:47 AM
Invertalon
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p.4 #19 · Sigma 35mm f/1.4 DG HSM - AF


Having used the Sigma 35 with my 5D3 the past week with hundreds if not thousands of shots on my vacation.

Mine requires 0 MA outdoors in natural light. Near to far, focus is spot on and accurate as can be. Add any MA at all and the image gets softer. 0 is perfect at all distances from MFD to infinity.

Indoors I run into some issues. I ran FoCal multiple times are various distances before my trip using 1000W halogen lighting... It constantly gave me +9 over and over again. I noticed indoors with certain lighting, it does require that +9 to be sharp. Having it set at 0 MA looks terrible and severely front focused. But outdoors, +9 looks terrible.

Not sure what causes this behavior... I have confirmed this behavior doing tests plenty of times now, and I can 100% confirm it is happpening. But indoors in natural light, 0 is perfect. Only with artificial light does it *sometimes* not work and require the +9 to be sharp. Distance does not change this. It is constant throughout at any distance.

Outdoors, +9 has no chance at all of working... It is simply soft always. Indoors, 0 works sometimes and other times there is no way. It really has something to do with types of light. Just not sure which or how, though.

I may exchange my lens with another, but performance has been downright spectacular as long as I change the MA value as need be. Indoors, sometimes, I need to switch to +9.... Otherwise, it stays on 0 the other 90% of the time and performs perfectly at any distance. Extremely consistant.

Anybody know what would cause this behavior? Does it sound like a lens or body issue? My 5D3 was with Canon weeks ago for a check/clean, and months prior as well so it has been checked and all that routinely. Roger, any help here with your lens knowledge? What could cause this behavior? I would love to hear from you!

Lens performs so dang good other than this little quirk. Just tying to figure out if exchanging lenses will fix this problem and risk worse performing lens... It really is blowing me away with its performance honestly. I have owned the 35L and many others L primes and this one as just as good if not better. I just want to figure out my little phonemonom here!



Jan 11, 2013 at 05:17 AM
goosemang
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p.4 #20 · Sigma 35mm f/1.4 DG HSM - AF


heh, i just came in here to make a similar post.

i dialed in my MA a couple of days ago as i posted, but it seems to be a little wonky. sometimes it's spot on, other times it's completely wacked out. i know for a fact that i can get tack sharp images out of this thing - even sharp as hell at 1.4 - but getting them *consistently* is proving to be a challenge.

and i'm not talking about the normal challenges of shooting at 1.4 here..... i'm talking lens is spot on, then i take a photo ten minutes later in the same conditions and it front focuses by five feet.

honestly, i've been thinking about this too much. i need to take a few days off and go take some photographs of things that actually matter.



Jan 11, 2013 at 01:49 PM
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