Opinions sought. Defective lens?

[MJP]

I need to know what my friends here think of this. Pentax FA 31mm f/1.8 Limited. Costs a ruddy fortune for something that's less than a normal prime on full frame (this is on an APS-C, K-3).

It's sold as being sharp wide open, so I thought I'd test this. Wide open with no post-processing . . .

http://www.flickr.com/photos/56053365@N07/13245177245/sizes/l/in/photostream/

Crop . . .

http://farm8.staticflickr.com/7035/13245202675_6184835774_b.jpg

Now following some heavy post-processing in LR5.3 . . .

http://www.flickr.com/photos/56053365@N07/13246149574/sizes/l/in/photostream/

Crop . . .

http://www.flickr.com/photos/56053365@N07/13245847845/sizes/l/in/photostream/

[HansVilder]

what a waste of money... my galaxy S3 telephone takes a nicer, sharper image than that.

[MJP]

what a waste of money... my galaxy S3 telephone takes a nicer, sharper image than that.

This is my point. I think it's a complete dog.

Sometimes it can pull it off. I just don't understand this lens at all. This is wide open at f/1.8 . . .

[Tywais]

That is some pretty serious chromatic aberration (fringing) and usually always associated with a lens issue though if the sensor uses microlenses they can cause it. But if it doesn't show with other lenses probably not the sensor. Sony, Nikon and some Panasonics have auto correction built into the firmware but probably not the Pentax.

Some information for that lens and fringing. They indicate that CA is well controlled though.

http://www.photozone.de/Reviews/122-pentax-smc-fa-31mm-f18-al-limited-review--test-report?start=1

http://www.ephotozine.com/article/smc-pentax-fa-31mm-f-1-8-al-limited-lens-review-16866

Go about half way down the page on this site and you will see some pretty obvious CA though so maybe normal under certain circumstances - http://www.robertsdonovan.com/?p=1148

[MJP]

That is some pretty serious chromatic aberration (fringing) and usually always associated with a lens issue though if the sensor uses microlenses they can cause it. But if it doesn't show with other lenses probably not the sensor. Sony, Nikon and some Panasonics have auto correction built into the firmware but probably not the Pentax.

Some information for that lens and fringing. They indicate that CA is well controlled though.

http://www.photozone.de/Reviews/122-pentax-smc-fa-31mm-f18-al-limited-review--test-report?start=1

http://www.ephotozine.com/article/smc-pentax-fa-31mm-f-1-8-al-limited-lens-review-16866

Go about half way down the page on this site and you will see some pretty obvious CA though so maybe normal under certain circumstances - http://www.robertsdonovan.com/?p=1148

I think this lens is a load of old pony, perhaps a bad copy. The Made in Japan versions of old (1990's) were great apparently but this didn't seem to translate when they became 'Assembled in Vietnam'. I have an AIV copy and the QC is bad coming off that line reading accounts.

It's fixable in post as you can see and it does have its applications, but for over a grand it's just not a sufficiently versatile lens.

Sell?

Edited March 18, 2014 by MJP

[rhythmworx]

I'm not familiar with Pentax gear but I know your camera is decent and the sensor is not a limiting factor in this case.

For the price that lens goes for (had to google it) V's its quality I would sell personally.

What speed and ISO was the brick shot took with I'm presuming it was handheld?

[MJP]

I'm not familiar with Pentax gear but I know your camera is decent and the sensor is not a limiting factor in this case.

For the price that lens goes for (had to google it) V's its quality I would sell personally.

What speed and ISO was the brick shot took with I'm presuming it was handheld?

All shots shown are handheld at f/1.8. I can't figure out whether this is just characteristic of this lens and shooting stuff wide open at infinity or near infinity is a no-no, as it can perform well under other circumstances once post-processed. But that takes a lot more effort than with other lenses, even the old M42 Soviet's are less demanding.

http://www.flickr.com/photos/56053365@N07/12221278773/sizes/l/in/photostream/

Here's Photozone's verdict . . .

The Pentax SMC-FA 31mm f/1.8 AL Limited is an excellent lens. It is already sharp at f/1.8 and razor sharp at medium apertures. Distortions and CAs are very well controlled. On the downside it vignettes quite a bit at f/1.8 so the ultra-large max. aperture takes its toll here. The bokeh (out-of-focus blur) is very smooth and buttery which is fairly unusual for a lens with aspherical elements. Typical for all Limited lenses the build quality is exceptional and it is a joy to use the lens. It also shares another, rather unfortunate, characteristic with its cousins - a high price tag. Quality comes at a price but 900-1000€/US$ seems a bit over the edge but then it is probably just another example of diminishing returns upon higher investments. Nonetheless it is refreshing to see that Pentax focuses on quality rather than costs - there're enough plastic lenses out there after all.

http://www.photozone.de/Reviews/122-pentax-smc-fa-31mm-f18-al-limited-review--test-report?start=2

[MJP]

This is at f/1.8, ISO 100, 1/6400 sec no post-processing . . .

crop . . .

Edited March 18, 2014 by MJP

[rhythmworx]

I wouldn't expect CA like than on a 1K lens, and at that speed v focal length handshake is not really an issue unless you was in the middle of a sneeze.

I had a quick peek at this thread on another forum (am I allowed to post other forums even if non thai related?) the lens looks decent in most shots but there's only 1 crop shot.

Also I guess a lot of them are post processed.

http://www.pentaxforums.com/forums/130-lens-sample-photo-archive/153328-pentax-fa-31mm-f-1-8-al-limited-samples.html

[Tywais]

Seeing your last shot of the window, that purple fringing is extreme. Doesn't match up with the photozone chart of .4 - .6 pixel CA at all, and those numbers are for the border where it would be worse. The other site shows a bit more on the border but very low on center. Really indicates there is a problem with your particular lens. Any extreme temperature changes?

[MJP]

I wouldn't expect CA like than on a 1K lens, and at that speed v focal length handshake is not really an issue unless you was in the middle of a sneeze.

I had a quick peek at this thread on another forum (am I allowed to post other forums even if non thai related?) the lens looks decent in most shots but there's only 1 crop shot.

Also I guess a lot of them are post processed.

http://www.pentaxforums.com/forums/130-lens-sample-photo-archive/153328-pentax-fa-31mm-f-1-8-al-limited-samples.html

Yes, I've had a big row on PF (which is a strange forum) tonight about this and they even locked the thread. Which is pathetic, but it's a pr!ck fanboy site so what do you expect?

I'd think it's duff, but hazard a guess others are getting the same before post-processing the granny out of RAW shots. Dunno?

[MJP]

Seeing your last shot of the window, that purple fringing is extreme. Doesn't match up with the photozone chart of .4 - .6 pixel CA at all, and those numbers are for the border where it would be worse. The other site shows a bit more on the border but very low on center. Really indicates there is a problem with your particular lens. Any extreme temperature changes?

No temperature issues. I'm thinking it's a duff one. Shouldn't have duff ones coming off the line like this, too many reports of this now.

[Tywais]

Looking at some other forums there have been comments regarding the CA where one mentioned about 1% of his shots have it in high contrast areas. Just saw another poster state the CA is extreme on his K5. So seems very high contrast areas it is a known issue but I wouldn't consider your shots high contrast though.

"The downside is that purple fringing is rather extreme (on a K5). Bare trees against a bright clouded sky makes the entire sky behind the trees glow purple. In postprocessing you can only do so much.

[MJP]

Looking at some other forums there have been comments regarding the CA where one mentioned about 1% of his shots have it in high contrast areas. Just saw another poster state the CA is extreme on his K5. So seems very high contrast areas it is a known issue but I wouldn't consider your shots high contrast though.

"The downside is that purple fringing is rather extreme (on a K5). Bare trees against a bright clouded sky makes the entire sky behind the trees glow purple. In postprocessing you can only do so much.

Think I'll sell it and get a Sigma 35/1.4 Art instead. The irony is I'd come out in pocket on that one, selling used and buying new!

[vaultdweller0013]

Could be a defective lens or could just be how that lens works wide open... Let me put it this way: even my Sony-Zeiss 135mm f1.8 will show some degree of purple fringing if I shoot wide open in direct sunlight. Especially, in the type of scene you are looking at -- a highly reflective area with an sudden, perfectly straight boundary. However, stop down to f4 and it becomes sharp as a tack with no fringing. From what I can tell this is a pretty common issue with large aperture lenses, especially older, pre-digital optical designs (read that as Minolta glass in my case). The other thing to check is that the lens is properly focused. At large apertures, even being slightly out of focus can cause a lot of CA. In a similar scene, I can see the fringe go from green to none to purple in live view when I rack focus from in front to behind the subject.

However, the Sigma 35 Art is supposed to be a incredible lens, so you couldn't go wrong going for it.