[nicoprod]

Great picture. 20s exposure?

[Digitalis]

That is the light of dawn you see on the beach, but it still wasn't bright enough to reduce the exposure time significantly- Though I only had a few seconds to get that image as the sun was rising fast.

[nicoprod]

That is the light of dawn you see on the beach, but it still wasn't bright enough to reduce the exposure time significantly- Though I only had a few seconds to get that image as the sun was rising fast.

Very nice. I guess the 20s didn't affect the shape of the stars too much...

[ironlionzion]

As I said in the statement you quoted,
We all accept that almost any lens will probably perform at its best two or three stops down. I'm only questioning the infinity part. I'm guessing the lens was designed/intended to be used wide open at infinity to the same extent it was designed to be used wide open at, say, 5ft.

However, you've raised an important point in lens testing. A lot of us use a test target. With a wide-angle or standard lens, maybe we print 5 8.5x11s and put them in the center and corners of the frame, but then you're looking at maybe 7 or 10 ft or so. You can't be far away because the targets just won't be large enough, and at those distances, you have to deal with distance differences between the centers and edges. Plus focus field curvature in some lenses. And with a telephoto, you might not easily have access to a flat surface large enough to get a sufficient distance away without something coming between the camera and target. So, most of us are limited in how we can test lenses at different distances, but I do believe some defects can show up more or less at different focusing distances, not just different apertures.

---------- Post added 03-23-2014 at 12:16 PM ----------

In looking at the 2nd set of example brick wall images, I can see the one side is a little worse than the other, but I can tell you that my Sigma showed more variation and still was "within spec." So you might be fighting an uphill battle there.

I'd suggest printing the 5 test targets and positioning them in the extreme corners and center, and then testing at different apertures. It's just easier to evaluate the relative performance from test targets than from the brick and mortar, although I've used both. On the other hand, test target images didn't help in my case, so what do I know...

People here have sometimes scoffed at my reports of problems with 5 out of 5 55-300s, but I've gotten worse brick and mortar pictures (worse as in more differences from corner to corner, not considering absolute resolution) from every one of them than what I'm seeing in that 2nd set of pictures.

---------- Post added 03-23-2014 at 12:19 PM ----------


I don't think they'll tell you, especially on the phone, whether they're even capable of "calibrating" the lens. Calibrating autofocus, maybe. Centering - I'm not sure they can even test for it (as in measure it with scientific equipment, not by shooting brick walls), much less correct it, unless maybe the lens was just not assembled properly in the first place (has a loose element, for example.) I'd love for somebody who actually knows to tell me I'm wrong.

You are probably correct about "within spec."

Take a look at the sample pics from the 20-40 ltd. HD Pentax-DA 20-40mm f/2.8-4 Limited DC WR Lens Review Their copy seems to display irregular corner sharpness. The extreme right side is always blurrier than the left side. It seems like some level of decentering might be common...which is a little disconcerting given the high prices of these limited lenses.

[Digitalis]

I guess the 20s didn't affect the shape of the stars too much...

At web sizes it isn't visible but there is only slight blurring. 666 /46 would have given me 14.47 seconds to keep the shutter open without the stars blurring using the standard formula. I compromised on a longer exposure because wanted more blur on the clouds and water for visual impact. The stars in the sky and the land appear static - while the water between them is moving.

[Eyewanders]

I've been away on vacation - glad this thread is still providing discussion. I agree about only using an open aperture when needed. In my case, I tested wide open and at 2.8 (still quite wide) and mentioned a while ago about the 2nd copy I'd borrowed to a/b mine against. Here is a quick couple shots from each I took that, again, confirms it for me. My copy is going off to Pentax for estimate on Monday though I am tempted by the Credit card purchase suggestion - could turn into a hassle but if it saves me a couple hundred dollars it may be worth it. At any rate - here are the two shots. They are hand-held, at f/1.8 wide open, ISO 200. These are the last test shots I'll be doing simply because I'm tired of looking at test shots. The results even at this res are quite obvious - VERY obvious when not resized and compressed for posting here.

My "problem" copy


Borrowed "good" copy


---------- Post added 03-29-14 at 10:07 AM ----------

And, this is not a 'same' discussion about expecting miracles while shooting wide open; this is a discussion about legitimate issues with some copies of this particular lens. All I can say is that I spent a fair amount of time shooting with the 'good' copy and it was a joy again and again... I am excited to have a working copy that performs up to my expectations in the near future based on the experience I had that day. Any disappointed I had during the time with the good copy was due to myself as a photographer, not the glass.

---------- Post added 03-29-14 at 10:30 AM ----------

Oooh - I've just agreed to purchase the other good copy. Now I'm set (and set back) - need to get this one repaired in the meantime.

[tibbitts]

Please don't forget to update everyone on the result of attempting to get the "bad" copy repaired.

[Digitalis]

I agree about only using an open aperture when needed

though I will point out if you have an exceptionally good copy of this lens you shouldn't have any reservations about using it at f/1.8 at infinity focus:


Pentax K5IIs - FA31mm f/1.8 ASPH Limited 100% un-sharpened crop @ f/1.8 infinity focus

On a 8"X12" print you would have to be looking very closely indeed to spot that this lens has been used wide open at f/1.8*, by f/2.8 the images from the FA31 will be sharp enough to be printed at any size.

* though to experienced eyes the amount of vignetting is a dead giveaway

[Deimos]

The issue is clear in those last test shots. Im sure this has been a pain but when you finally have a properly performing copy of the lens you should be pretty pleased with it even wide open.

Good luck!

[K McCall]

I'm giving this a friendly bump after taking my FA 77 out this weekend (it seems to have issues very similar to yours). Did you send it into Pentax? Did they give you an estimate yet?

[Eyewanders]

I'm giving this a friendly bump after taking my FA 77 out this weekend (it seems to have issues very similar to yours). Did you send it into Pentax? Did they give you an estimate yet?

I did - the total cost from C.R.I.S. excluding my shipping it to them was $143. A further update will be coming soon.

[K McCall]

I did - the total cost from C.R.I.S. excluding my shipping it to them was $143. A further update will be coming soon.

Oooh, thanks for getting back to us! That's really not too bad, especially if they fix it up right. Looking forward to the update!

[Eyewanders]

Well, this saga is not yet complete, and believe me it has turned into a saga. I received it back from CRIS around the time of my last post and thus began another 2 week ordeal trying to speak to the techs there because basically the problem still existed. It is back with them once more, free of charge this time (I should hope so) and is currently listed with a status as "awaiting parts hold". I expected to have it back some time ago... evidently not. The upside however is it will be returned pristine and with warranty. I just am far less than happy about the amount of time and effort all of this is taking. Honestly, I'm very glad I purchase another used copy in the meantime and I just try to forget the other one exists at least for now.
Incidentally it will be for sale once it's been returned and is already listed in that section.
Waiting patiently......

[Wild Mark]

Well, this saga is not yet complete, and believe me it has turned into a saga. I received it back from CRIS around the time of my last post and thus began another 2 week ordeal trying to speak to the techs there because basically the problem still existed. It is back with them once more, free of charge this time (I should hope so) and is currently listed with a status as "awaiting parts hold". I expected to have it back some time ago... evidently not. The upside however is it will be returned pristine and with warranty. I just am far less than happy about the amount of time and effort all of this is taking. Honestly, I'm very glad I purchase another used copy in the meantime and I just try to forget the other one exists at least for now.
Incidentally it will be for sale once it's been returned and is already listed in that section.
Waiting patiently......

It is very unfortunate to hear of your troubles. I hope it resolves for you.

This thread has proved to be a very good one. Reading through it I have seen clear challenges of what is widely regarded as Pentax's best. I wish I had read this thread BEFORE I bought my second hand copy.

After reading this thread I have put my lens to the test. I have levelled the camera with a spirit level and a large piece of graph paper (also levelled) to examine for a decentred - phew I think I am OK although it should be said that there is micro 'relief' in the focusing plane (perhaps I am being a little too exact here).

Auto focus is clearly an issue with this lens. When I auto focus I occasionally/ sometimes get blurry images. Turning to peak focusing and the issue resolves for almost all shots. So my advice on that testing is consider using peak focusing for near shots.

The PFing is nasty almost always. I am surprised at the amount of fringing and displeased. I have other lenses that have been reviewed harshly on PFing that perform much better than the 31mm.

My testing has helped me immensely in determining what this lens should be used for. Compared to my SMC Pentax K 2/28 the 31mm is an abysmal performer wide open for a subject at about 1m. The 28mm has far superior centre sharpness at f2 and maintains its superiority through to f11. The following crops demonstrate this:

28mm centre @ f2 (first) 31mm centre @f2(second)

[Wild Mark]

It is very unfortunate to hear of your troubles. I hope it resolves for you.

This thread has proved to be a very good one. Reading through it I have seen clear challenges of what is widely regarded as Pentax's best. I wish I had read this thread BEFORE I bought my second hand copy.

After reading this thread I have put my lens to the test. I have levelled the camera with a spirit level and a large piece of graph paper (also levelled) to examine for a decentred lens - phew I think I am OK although it should be said that there is micro 'relief' in the focusing plane (perhaps I am being a little too exact here).

Auto focus is clearly an issue with them 31mm. When I auto focus I occasionally/ sometimes get blurry images. Peak focusing and the issue resolves for almost all shots. Based on that testing I would consider using peak focusing for all near shots.

The PF is nasty almost always. I am surprised at the amount of fringing and am displeased. I have other lenses that have been reviewed harshly on PF that perform much better than the 31mm.

Testing has helped me immensely in determining what this lens should be used for. Compared to my SMC Pentax K 2/28 the 31mm is an abysmal performer wide open for a subject at about 1m. The 28mm has far superior centre sharpness at f2 and maintains its superiority through to f11. The following crops demonstrate this:

28mm centre @ f2 (first) 31mm centre @f2(second)

28mm centre @f11 (third) 31mm centre @f11 (fourth)

---------- Post added 06-28-14 at 02:50 PM ----------

28mm centre @f11 (third) 31mm centre @f11 (fourth)

So if I was taking a portrait and had enough time to compose using a manual lens I would opt for the SMC Pentax K 28/2 over the 31mm.

But if corner to corner sharpness was required then I might think twice as the corner performance of the 31mm is better than the 28mm at f2. The 31mm's advantage is well and truly lost @f11 and more than likely lost by f5.6 (not proven though).

So in summary I suspect that my use of the 31mm would be limited and possibly complimentary to the 28mm. In low light I will use the 28mm for portraits and the 31mm for landscape (although not at f1.8 as it is clearly too soft). In better light I would use the 31mm for portraits if AF is required or the 28mm in all other circumstances.

Conclusion: After reading all the reviews of the 31mm I was surprised by the superior performance of the SMC Pentax K 2/28. The 28mm is spot on with no CA/ PF evident while the 31mm is close to horrid (PF). While PF can be corrected it is annoying to know that such an expensive lens has it. The legendary sharpness of the 31mm is not what it seems although I do concede it has very good corner to corner sharpness wide open and the AK gives highly variable results.

More testing will be done, however, I am not convinced that the 31mm will knock the K2/28 lens off its perch.