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Archive 2013 · Sigma 35mm 1.4. Color me impressed, but questions.
  
 
RogerC11
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p.1 #1 · Sigma 35mm 1.4. Color me impressed, but questions.


Just got my Sigma 35mm today. I started shooting around the house and noticed the lens is incredibly sharp wide open, more than than my previous 35L. One thing I have noticed is that the AF is about the same if not better in low light (less hunting). However, I did notice that the lens tends to front focus about an inch or so in low light conditions. In good light, the focus is spot on and sharp as a pin. I was wondering if this was more of an indication in the lack of AF ability of the camera body rather than the lens. I am shooting a rebel t2i with no MF adjust feature. The lens is tack sharp and nails focus in good light but when the the lights get low, it seems to front focus consistently. Is this an indication of a lens miscalibration or weakness in the AF ability of the camera body? I am kinda hesitant to send it back in for an exchange because the lens is so good. Please advise.


Jan 12, 2013 at 08:22 AM
Snopchenko
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p.1 #2 · Sigma 35mm 1.4. Color me impressed, but questions.


I find AF inherently less accurate in low light, especially on wide angle lenses, as contrast level drops and the AF algorithm has less definite detail to grab on to (so my 16-35 looks like it's randomly front focusing even though in reality it's not). In my case it might also be the poor technique though. Note that I'm speaking strictly by feeling and don't know the science involved well.


Jan 12, 2013 at 08:29 AM
RogerC11
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p.1 #3 · Sigma 35mm 1.4. Color me impressed, but questions.


I also find that up close when the subject is larger in the viewfinder, AF seem spot on accurate as well. It is when the AF target is smaller and also in low light is when things tend to get iffy on accuracy. But what you say seems to mirror my experience as well. Just a couple of my better shots, all wide open at 1.4









Jan 12, 2013 at 08:38 AM
 

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RogerC11
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p.1 #4 · Sigma 35mm 1.4. Color me impressed, but questions.


Ok, got to some shooting this morning in better light and it still exhibits the same behavior. Here are some of the examples I'm talking about.


Focus was on the M



Here focus was on the second I

Wondering if I should just wait for the USB dock to come out to fix this or risk exchanging it.





Jan 12, 2013 at 06:34 PM
scalesusa
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p.1 #5 · Sigma 35mm 1.4. Color me impressed, but questions.


Most lenses tend to front focus when you get close to the subject. If your body does AFMA, adjust it to the distance that you normally use. At longer distances, focus errors will often be hiden by the depth of field.


Jan 13, 2013 at 11:58 PM
macrobild
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p.1 #6 · Sigma 35mm 1.4. Color me impressed, but questions.


adjust it to 50 x 35mm = 1,75m to the test target

50mm = 2,5 m

100mm = 5,0 m
etc

Canons own parameters and lens calibration



Jan 14, 2013 at 12:00 PM





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