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07-29-2013, 02:23 PM   #31
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QuoteOriginally posted by tlwyse Quote
What I found was that this new Sigma "blew away" the FA 31mm...yes, it's true.

Just asking to be sure, none of the tested lenses did have a filter attached ?

07-29-2013, 04:32 PM   #32

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QuoteOriginally posted by snake Quote
Additionally, if you're not a fan of AF, then all you have to do is select "MF" and be as picky as you want about the focus point.
In my experience, it doesn't usually work like that,
since the manual focus on AF lenses is generally poor
when compared to dedicated MF lenses.
The throw is too short, and the focus is too loose,
so it's easy to brush the lens off focus accidentally.
07-29-2013, 06:06 PM - 1 Like   #33
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QuoteOriginally posted by tlwyse Quote
Just recieved my new Pentax K-5 IIs (upgrading from K20D) last week and just got the new Sigma 35mm f/1.4 "Art" series lens a couple of days ago. Since I was borrowing a friend's Pentax FA 31mm f/1.8, I thought I'd do an informal test between these two lenses and throw in my Tamron 17-50mm f/2.8 just for grins.

Since the Sigma 35mm was new to me, as is the K-5 IIs....and I've got a shoot planned for Monday....I decided to run through my standard gauntlet of focusing calibration tests using my LensAlign tool. I typically photograph the LensAlign at 25x, 50x and 100x the lens focal length to find the AF adjustment. I was HOPING that the new K-5 IIs would need minimal adjustment compared to my K20D which needs a pretty healthy +8 with all my lenses. Turns out, the K-5 IIs needs about +6 with the couple of lenses I've tested thus far.

What I found in my little lens comparison will probably sound like heresy to the Pentax faithful. As you know, the FA 31mm enjoys some sort of legendary/mystical status and I believed this enough to consider purchasing this lens instead of this new Sigma....but since the Sigma was getting such rave reviews on sites like and others, I thought I'd check this lens out and compare it to teh FA 31mm before committing.

What I found was that this new Sigma "blew away" the FA 31mm...yes, it's true. What was perhaps even more surprising was my lowly Tamron 17-50 did very well and even bettered the FA 31mm at least in terms of sharpness (bokeh, maybe not so much). The one thing I've seen in a few of the Pentax lenses (I've got a DA* 50-135 and a DA Limited 70mm) I own is really bad CA/chromatic aberration. Before I got the Tamron, I thought this was normal....but the Tamron has virtually no perceptible CA which seems pretty amazing to me for a mid-level quality zoom.

Anyway, without further ado, I offer you some 100% and 200% magnified screen shots taken from Photoshop. In all my focusing tests, I ran through a full series from +/-10 in even-numbered increments. From this, I chose the best one visually in Photoshop and also looked at the file size in bytes.......a little trick when doing focusing test series like this is to shoot high-quality JPEGs and then look at the exact file size of all the images.....without fail, the file with the largest file size/least compression is also the one with the best visual focus. On a Mac, you select the file and choose "Get Info" and look at the file size in bytes. On Windoze, you'll right-click and select "Properties" and look at the size in bytes.

In the screen shots, the new Sigma 35mm f/1.4 is on top, the FA 31mm in the middle and the Tamron 17-50mm zoom (set at 35mm) is on the bottom, I didn't move the camera position (tripod) and all were shot with the 2" self-timer to avoid vibration. I also included a 50% zoom showing the LensAlign along with some background.....not the end-all/be-all of bokeh tests but it does reveal some bokeh characteristics.

It appears you have a bad AIV copy of FA31. You should test a MIJ copy. You can tell your AIV copy is bad if there is a big jump in quality from 1.8 to 2.8 (and I suspect there is). FA31 is tack sharp from f1.8, even at wide open, it's one of my sharpest lenses.

Last edited by chesebert; 07-29-2013 at 06:12 PM.
07-29-2013, 07:45 PM   #34
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QuoteOriginally posted by snake Quote
outside of the Pentax SDM realm, AF systems are very reliable and have incredible longevity.
...not my understanding from the whining I have read on the various non-Pentax forums...

As for "beta" chipping.

ROTFL...the Pentax system is passive with the exception of the MTF contact (#7) which identifies the lens...there is essentially no logic to be beta. It is the easiest to support of any mount currently on the market.

(Can't stop...)

07-29-2013, 07:57 PM   #35
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QuoteOriginally posted by snake Quote
shooting at ISO800, trying to get a lock on fast moving subjects in the dark (where 1/100 or above is needed). So AF will win every time
...ISO 800 at 1/100 at f/1.4 ain't that dark*, though it is seriously dim and I can guaranty that AF will not give adequate focus at f/1.4 in that light, if indeed it can lock in a timely manner at all. Manual focus generally is difficult as well due to thin DOF. Higher ISO with smaller aperture is more effective and more likely to give acceptable results. Back-in-the-day, the strategy was to push film to 3200 EI and zone focus using the brighter viewfinder on a rangefinder camera. (The rangefinder patch is virtually unreadable in low light.)


* About EV(100) 4.5. Current Pentax bodies with AF assist lamps can go to EV -1, though my experience when the cameras were demo'ed to me a few month back was that the performance was not that great. But then again, I am not a huge fan of AF. As I said above, I prefer to choose what part of the subject is in focus when the DOF is thin.

Last edited by stevebrot; 07-29-2013 at 08:53 PM.
07-29-2013, 08:49 PM   #36
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That FA31 has definitely some problems.

My $40 M28 F/3.5 is definitely sharper than that wide open. I honestly, don't think that FA31 will earn its feathers with a performance that poor. In fact, some writers have been comparing it to Leica glasses.

That being said, there must be some truth to the talk that among the FA Limiteds, the 31 is the most prone to suspect QA.

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