[Heie]

After owning one (and quickly selling) and using another copy during the Sigma 18-34 Art review, I wouldn't buy one for $300, unless it was simply to flip it for profit.

The most overrated lens Pentax makes IMO, and worse off, I'm convinced it's absolutely dangerous for Pentax because I'm afraid they'll continue to rest on their laurels about it.

-Heie

[hjoseph7]

It's not easy shooting at f1.8 with any lens due to the shallow DOF. You really have to nail the focus and gently squeeze the shutter. The 31mm is a painter's lens meaning if you can't paint the scene on canvas, then don't take the picture. Same thing goes for the 77mm in my opinion. It's not just a point and shoot lens. If you really want a lens for travel, I would have chosen the 20-40mm or the cheaper 16-45mm those 2 lenses will give you excellent results in a wide variety of scenes. The same probably goes for the 18-135mm although I don't own that one. It's not that the 31mm is not a great lens for travel, it's just that you have to get use to it and be a little more selective on what you want to shoot.

[knightzerox]

Well after much re-testing and calibration I've come to these observations:

1. The lens if focused properly on the right subject is very sharp, but it's very hard to get the lens to focus consistently from close to far focus.
2. It's slightly softer at 1.8 versus f2 and beyond. By 2.4+ it's very sharp up the range
3. By f5.6 and up, the image sharpness and quality is very much similar and the same to the DAL 35mm 2.4 ( sharpness and even bokeh are close enough, didn't notice any color changes much )

To me, this lens is very strange. It should be very good, and shows that to be the case at certain times, but otherwise it's no different than other basic lenses for certain apertures and above. Again, the lens is absolutely sharper then the DAL 35mm 2.4 until f5.6. But here's the problem, that extra sharpness and clarity only matter if the lens is focused correctly. When viewing farther off subjects in landscape after calibrating the lens for close - mid subjects, the focus is off. After many attempts fixing and re-calbirating, I was still unable to get consistent accuracy. Aiming the lens at a subject 2-3 feet away and then another only 6 inches farther out, the focus was a blur. It was very frustrating and I think that's where I come to terms with this lens. Maybe I have a bad copy, but from what I can see, the lens itself is very good, but has a problem giving consistent and accurate focusing through it's wide open aperture.

My FA43 does not exhibit this problem anywhere near as much, though that lens at 1.9 can also be tricky, but it is much more consistent. And in the end, if I can have a lens that will be accurate and focus correctly consistently to give me a very high quality image, it is more valuable. If I was to shoot this lens manual only or through liveview / CDAF, I think I would have no problem keeping this lens and using it all the time. I thought maybe it was my K3 that was the problem, but then I remembered that I shoot with my other lenses at 1.4 and 1.9 with no problem getting mostly accurate focus 90% of the time. Maybe I am also being more critical, but when I see comparison images which I will upload in my next post, it's hard to justify $1000 vs $140 the DA L goes for these days.

In the end, I'm glad I got to try the lens, and maybe I will re-visit when the FF Pentax comes out, but I will be returning it for something else. I am considering a 35mm limited macro, or I think what I should have kept with, the 20-40 LTD. I can now see how some users are reporting that the image quality from that lens can equal the FA ltd's and DA ltd's as at higher apertures they are very accurate and equally sharp.

Tomorrow I will get to go through this one more time with the FA 77, but I am hoping it will be a keeper. If it is no better than the HD DA 70, back it will go till next time.

[stevebrot]

you have to keep in mind how old the design is...

Please explain how design degrades over time.

Seriously.

Moving on, when I read the OP's post, I immediately felt that focus error is the most likely cause. My experience with fast lenses wide open on dSLR is that they are fiendishly hard to focus precisely wide open due to limited DOF and limitations of the focus systems. The AF system has focus sensitivity of f/2.8 best case using the center column focus points. Manual focus using the stock focus screen has sensitivity of about f/4. Magnified live view or a split image screen are the only methods that have any hope of consistent acceptable focus at f/2 and wider. CDAF may be reasonably good in good light, but my experience has been mixed.

With the K-3, I would also be concerned with camera motion. User experience on this site (myself included) is that the K-3 rewards those who are steady of hand.


Steve

[knightzerox]

Please explain how design degrades over time.

Seriously.

Moving on, when I read the OP's post, I immediately felt that focus error is the most likely cause. My experience with fast lenses wide open on dSLR is that they are fiendishly hard to focus precisely wide open due to limited DOF and limitations of the focus systems. The AF system has focus sensitivity of f/2.8 best case using the center column focus points. Manual focus using the stock focus screen has sensitivity of about f/4. Magnified live view or a split image screen are the only methods that have any hope of consistent acceptable focus at f/2 and wider. CDAF may be reasonably good in good light, but my experience has been mixed.

With the K-3, I would also be concerned with camera motion. User experience on this site (myself included) is that the K-3 rewards those who are steady of hand.


Steve

I am also worried that it is jsut teh AF focusing issue ,and from my results, it seems so. I made sure to use only the center point because of the f2.8 sensitivity, I don't use liveview much at all, so for me it is not an option. I do have a different focusing screen designed for f1/4 lenses on my K-30 that I could switch out and the Pentax Magnified eyepiece. But if I have to use AF, and then manually adjust or only use manual focus, for me that wouldn't meet my needs or how I shoot. I tend to stay very still and only shoot in single fire mode after I have composed my shot. At times yes I will P&S things when testing, but I try to compose, focus on my subject, and then fire when steady. I have the lens all packed up but I did not try it on the K-30 with focusing screen, but I'm not sure if I really need to at this point.

[stevebrot]

When viewing farther off subjects in landscape after calibrating the lens for close - mid subjects, the focus is off. After many attempts fixing and re-calbirating, I was still unable to get consistent accuracy.

Calibration yields frustration when precision is lacking. (The point of accurate calibration is hard to find.) Consider too that attempting calibration for distances further than a few meters has the potential to really screw up near and medium distance if not done with absolute accuracy. Do your focus calibration at a relatively close distance (say 20x to 40x the focal length) and the far focus should follow.


Steve

[knightzerox]

Here are two shots of my dog at f2.5 . I would not judge this image on sharpness as they are two different images, and I would give the FA31 the edge here if you look at the eyes.


https://www.dropbox.com/s/p1z9lgvf2wscdwm/DA35mm.jpg?dl=0
https://www.dropbox.com/s/o6wh9ig2esij71k/FA31mm.jpg?dl=0

Here are two at f5.6, where it is very very hard to distinguish between the two. First one is DAL 35mm 2.4

https://www.dropbox.com/s/yvpq51nbrv2rh1u/692.jpg?dl=0
https://www.dropbox.com/s/e3vhq7dgw5t73t3/693.jpg?dl=0

---

Last edited by knightzerox; 06-04-2015 at 07:59 PM.

[yorik]

I also have a love/not-so-much relationship with the 31... My experience with the 43 and 77 was blissful (ok - maybe not so dramatic) from the get go, but with the 31, it was hit-and-miss, and still is to a certain extent. But when it hits, the rendering is indeed wonderful (I care a bit less about extreme sharpness than some). All the same, the only reason I am currently holding onto it is to see how it performs on the FF, and I might sell it in any case. Not because it isn't great, but because there are other lenses (focal lengths) I want more.

[stevebrot]

I have the lens all packed up but I did not try it on the K-30 with focusing screen, but I'm not sure if I really need to at this point.

My opinion is that if you already own the DA 35/2.4 you have little to gain with the FA 31/1.8. The difference in speed is less than one stop and while there are qualitative differences in rendering between the two lenses, the DA 35/2.4 is competitively sharp in the range of shared apertures. It is probably the better choice overall where size and weight are a consideration.

To be honest, one of the reasons why I don't lust after a FA 31/1.8 is that I already own the FA 35/2 (optically similar to the DA 35/2.4). What it lacks in bokeh, it makes up for in size and weight.


Steve

[knightzerox]

Calibration yields frustration when precision is lacking. (The point of accurate calibration is hard to find.) Consider too that attempting calibration for distances further than a few meters has the potential to really screw up near and medium distance if not done with absolute accuracy. Do your focus calibration at a relatively close distance (say 20x to 40x the focal length) and the far focus should follow.


Steve

Yes I've tried some of those distances as well. Once I feel I have it nailed down, it tends to fall apart in real world. Most of my other lenses are calibrated pretty well, but they are also have a smaller aperture as a base. I believe if I didn't have the FA43 or FA 50 1.4 to compare to I would be trying very hard. Since I have an option to return the lens, I think I'll make the safe bet at this time and wait to see what FF lenses Pentax will make for the new model if their is an update.

---------- Post added 06-04-15 at 08:03 PM ----------

My opinion is that if you already own the DA 35/2.4 you have little to gain with the FA 31/1.8. The difference in speed is less than one stop and while there are qualitative differences in rendering between the two lenses, the DA 35/2.4 is competitively sharp in the range of shared apertures. It is probably the better choice overall where size and weight are a consideration.

To be honest, one of the reasons why I don't lust after a FA 31/1.8 is that I already own the FA 35/2. What it lacks in bokeh, it makes up for in size and weight.


Steve

And from what I have heard, the DAl 35mm 2.4 for is essentially the same lens, but with one of the elements changed I believe. And when calibrated, it's a fantastic lens for that focal length. On my two image samples above, I can't image many being able to distinguish between the two.

[Kozlok]

Since you travel with the 18-135, I seriously would consider the Sigma 30. At 1.4 it's sharper in the center than it needs to be. Yes, the Sigma has lousy corners, always will. But if you want sharp photos of objects, this is my go-to lens. As a bonus, it uses 62mm filters, so you can travel with the Sigma and 18-135 together and carry one CPL and one set of NDs (if you are interested in filters).

Another to consider for slightly wider POV is the Sigma 24mm. Still so-so corners, but seems sharp at max aperture. I know many around here don't like them, but I sure seem to get an awful lot of OOOHHH when I use my Sigmas. As a bonus, you could get BOTH the 30 and 24 and still have $300 for beer.

[RobA_Oz]

If you read widely on this Forum, you'll see that the FA31 Ltd polarises opinions. I have one, though I didn't pay as much as some here have, even though it was new at the time, so I don't have the same impulse to evaluate it as critically as those who paid more. I like it, but it does have some challenges that take getting used to, as others have said.

I also have a DA35/2.8 macro, which I'm a bit surprised hasn't been mentioned in this thread as an alternative, as it's a very well-built and versatile lens, with the ability to function as a normal lens on APS-C (it vignettes slightly on a 35mm sensor), but allowing much closer focussing than the FA31, FA35 or DA35/2.4. It also isn't all that expensive, and it's a lot lighter to carry around than the FA31 (215g versus 345g). The results in both situations (normal and macro) are very good, in my estimation. If you want something that's nicely built, has few operational or IQ vices (focus hunting in some situations is the main vice) and is versatile, you'd do worse than to consider this lens instead of the FA31.

[Sandy Hancock]

If you don't love an expensive lens, send it back. Simple as that.
Nobody expects you to be a martyr.

[clackers]

2. It's slightly softer at 1.8 versus f2 and beyond.

But you knew it doesn't reach its best until F4, right, Knightzerox?


Pentax SMC-FA 31mm f/1.8 AL Limited - Review / Test Report - Analysis


Your point about the difference in money for the DA35 f2.4 (or even FA35 f2) is well-made, but a lot of things in life are expensive to get that final 10 percent in performance over the rest of the pack.

[RAART]

I am also worried that it is jsut teh AF focusing issue ,and from my results, it seems so. I made sure to use only the center point because of the f2.8 sensitivity, I don't use liveview much at all, so for me it is not an option. I do have a different focusing screen designed for f1/4 lenses on my K-30 that I could switch out and the Pentax Magnified eyepiece. But if I have to use AF, and then manually adjust or only use manual focus, for me that wouldn't meet my needs or how I shoot. I tend to stay very still and only shoot in single fire mode after I have composed my shot. At times yes I will P&S things when testing, but I try to compose, focus on my subject, and then fire when steady. I have the lens all packed up but I did not try it on the K-30 with focusing screen, but I'm not sure if I really need to at this point.

TBH I had very similar problem with another lens and did not knew what to do, but when I put the same lens on the another camera, the lens performed absolutely correct in regards of AF perfomance . No more miss-focus and that problem you described before that in the distance the lens just miss-focus but close by all is fine. I did adjustments back and forth and nothing helped however on the other camera was all perfect. I ended up selling the lens locally to someone who had the same model Pentax camera but on his it worked much, much better and was so sharp that I almost regret it selling it. I still do not know why the lens performed excellent on his camera though he had always complained that he had troubles with other lenses and took him a long time until he got one that it works, from me! I told him what I experienced with this lens and why I am selling it but when he tried on his K-3 the lens just worked wonders. He was happy, I was somehow happy as I lost $150 on that lens (purchased brand new and could not returned it anymore, too long time passed by)... Anyway, I hope that this will shed more light...

I only regret that I did not send my camera together with lens to Sigma to adjust or match the lens to the body. Maybe this is something you should try. From now on I always get the camera with me and go to the retailer who has in stock the lens I need and try multiple copies however the salesman is not very happy about, but if he does not do I am walking away. Just my 2c.