[hjb981]

Hey,

Please read the review on Lenstip.com They have an excellent point on the 31mm. There is a huge difference between the Japanese version and the Vietnamiese. Elements are the same, but the quality control is not. You can still get a sharp copy from Vietnam, but chances are that you'll get bad one (so are with the Jap version, but are certainly less).

I have the 31mm from Vietnam, and guess what, it's a b***h to focus. It's razor sharp once you nail it, but it's veeerrrrryyy hard to get it right on. I'm considering to get a split field focusing screen to help me with the issue. I also own a 90mm SL Voigtlander, a pure manual....and I get the focus 99% of the time, meaning that my eyes are still good.

Other options are to use the lens above 5.6, to have some room for error....or JUST RETURN THE LENS, which I didn't do lolol.

Otherwise, the lens is great, but as Lenstip mentions, it's wayyyy to expensive for what you get...I would get the 35mm Samyang instead and use manual all the way through, AF is useless on Pentax anyway if you compare it to Nikon or Canon...

With you on this one... Bokeh, and 3D like effect is great, no complains on that one.

When I try to use for portraits (i have a bad copy!), I end up shooting like 5 or 6 pix to nail the focus. Or I just get tired, get my 90mm, walk a mile away from the subject and take the pic. Lmao

That does not make sense to me... I do not understand how a lens could be made poorly such that it was very hard to focus, but also very sharp and well-performing once focused correctly. That sounds very strange to me, but I may be missing something.

Anyways, the stock focusing screen of the K-5 will show all the un-sharpness of the 90 mm lens when focusing, but not so for the 31 mm. The reason for this is that the screen actually does not show the light below F/2.8 or something like that. The reason for this is that it is optimized to look bright with slow zoom lenses, and a side effect is that you do not see the light hitting it at more gracing angles (the light from a big aperture, like 1.8 for example). Therefore, I think that a split-prism focusing screen will indeed help with the issue, Cachibache, only I suspect that the issue is not the lens, but rather that the stock focusing screen is simply not designed to be used with fast lenses.

I have both a KatzEye split-prism focusing screen and an FA-31 (AIV, bought new). Both are a joy to use, and the lens is really sharp across the frame on my K-5. My KatzEye screen has their OptiBrite treatment, which makes it nicer to use with my slower 18-135 WR zoom (also AIV, as all of them are), but slightly decreases the ease of focusing the fast lens in bright light (according to KatzEye -- I have not tried any of their screens without OptiBrite). I got the FA-31 after the screen, so I have not tried it on a stock focusing screen. I have no complaints on the 18-135 either, although obviously it cannot compete with the 31 when it comes to across-the-frame sharpness at larger apertures (it even cannot achieve very large apertures -- it is F/3.5-5.6).

If you do get a KatzEye or other after-market screen, you will likely have to re-shim it. The thickness of the KatzEye is different from that of the original. Some people will argue that it does not matter because the focusing takes place on the backside of the screen, and hence the distance is the same no matter the thickness of the screen. While it is correct that the distance will be the same, the light-path is not. Any light that hits the screen at a non-perpendicular angle will be refracted, and this happens "sooner" if the screen is thicker, and it therefore will need to be re-shimmed to move it ever so slightly closer to the lens (away from the pentaprism).

A note on the auto focus speed of older lenses: I do not think that it has to do only with the amount of mass that has to be moved, but also on the throw. I think that older lenses tend to have more throw, which means that the angular distance that things have to be moved is longer. This makes precise manual focusing easier, but auto focus slower.

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Last edited by hjb981; 06-26-2012 at 02:44 PM. Reason: spelling, clarification

[lytrytyr]

Anyways, the stock focusing screen of the K-5 will show all the un-sharpness of the 90 mm lens when focusing, but not so for the 31 mm. The reason for this is that the screen actually does not show the light below F/2.8 or something like that. The reason for this is that it is optimized to look bright with slow zoom lenses, and a side effect is that you do not see the light hitting it at more gracing angles (the light from a big aperture, like 1.8 for example). Therefore, I think that a split-prism focusing screen will indeed help with the issue, Cachibache, only I suspect that the issue is not the lens, but rather that the stock focusing screen is simply not designed to be used with fast lenses.

A potential test of this interesting hypothesis
would be for Cachibache to see if the FA 31 focusing is as bad
when performed with contrast-detect or manually in live view.
That sidesteps any issues with the viewfinder screen.

[hjb981]

A potential test of this interesting hypothesis
would be for Cachibache to see if the FA 31 focusing is as bad
when performed with contrast-detect or manually in live view.
That sidesteps any issues with the viewfinder screen.

That is a very good point!

[jpzk]

Hey,

Please read the review on Lenstip.com They have an excellent point on the 31mm. There is a huge difference between the Japanese version and the Vietnamiese. Elements are the same, but the quality control is not. You can still get a sharp copy from Vietnam, but chances are that you'll get bad one (so are with the Jap version, but are certainly less).

I have the 31mm from Vietnam, and guess what, it's a b***h to focus. It's razor sharp once you nail it, but it's veeerrrrryyy hard to get it right on. I'm considering to get a split field focusing screen to help me with the issue. I also own a 90mm SL Voigtlander, a pure manual....and I get the focus 99% of the time, meaning that my eyes are still good.

Other options are to use the lens above 5.6, to have some room for error....or JUST RETURN THE LENS, which I didn't do lolol.

Otherwise, the lens is great, but as Lenstip mentions, it's wayyyy to expensive for what you get...I would get the 35mm Samyang instead and use manual all the way through, AF is useless on Pentax anyway if you compare it to Nikon or Canon...

I am looking at "Lenstip" right now .... and I thought that the FA 31mm Ltd was either MIJ or AIV, not "made in Vietnam".
this is the review I am browsing right now:
Pentax smc FA 31 mm f/1.8 AL review - Summary - Lenstip.com
Is this what you are referring to?

Anyway, mine is AIV (and Made in Japan) and it is one very sharp copy, easy to focus ... one of the best lenses I own.
Whether the AIV lenses (and NOT MIV) have QC issues, I wouldn't know and I suppose I am lucky.

Now, to generalize that AIV 31 mm Ltd lenses have a HUGE (quoted from your text) difference from those MIJ is a bit stretchy.

Another point which I noticed from the said "review" is this: "Our statistics, based on a quite limited sample but still supported by the results of our tests, shows that one Pentax lens, produced nowadays, out of very small number of other specimens, is flawed. "
They acknowledge that their saple size is "limited"; statistically, that just doesn't cut it.

As for ANY other lenses, whether they are from other brands or Pentax, there are always some "bad copies" out there.

Too bad yours is a bad copy.

JP

[hjb981]

Sorry if this is getting off-topic, but for those wanting to learn more about focusing manual lenses on modern cameras: Manual Focusing with AF Camera Systems

[bossa]

Don't forget that that you lose Spot Metering when you install a Split Prism screen.

I had a Canon 'S' in my K-5 but at the end went back to the stock screen and just used Focus Confirmation in the VF. I ended up with better results that way (mainly for my FA*300) but recently sold both K-5.

Since I've been using the D800E I have no problems like this due to the large bright VF.

[hjb981]

Don't forget that that you lose Spot Metering when you install a Split Prism screen.

I had a Canon 'S' in my K-5 but at the end went back to the stock screen and just used Focus Confirmation in the VF. I ended up with better results that way (mainly for my FA*300) but recently sold both K-5.

Since I've been using the D800E I have no problems like this due to the large bright VF.

You are right -- I had forgotten about that. I always use center-weighted metering, and therefore never noticed it, but spot metering could produce over-exposure when small-aperture lenses are used (2.8 or smaller for the KatzEye screen I have in my K-5). A workaround could be to use exposure compensation with small-aperture lenses, but of course this is an extra element of hassle.

[Class A]

There is a huge difference between the Japanese version and the Vietnamiese. Elements are the same, but the quality control is not.

There is probably no point in trying to fight this rumor, but there is absolutely no hard data suggesting that the Assembled in Vietnam copies are of lesser quality than the Made in Japan copies.

Great copies from Vietnam exists just as well as bad copies from Japan.

The real issue is that Pentax does not manage to tightly quality control a lens of this caliber, i.e., built quality and price. For that kind of money one should expect a better standard.

If there are any die hard Japan fans: Sigma still produces their lenses in Japan and many of their EX lenses are superb.

[wlachan]

I have come across maybe 7-9 FA31, both MIJ & AIV. I don't buy the BS that MIJ Pentax lenses received better QC. This is just some people's fantasy. If the brand new lenses that I have purchased the last decade or so are any indication (and I know God hates me because I am a lemon magnet), MIJ Pentax suck on QC, both lenses & bodies. They are great when they work as designed though. My advice? Don't buy FA31 from where refund or exchange will be hxll, new or used. This lens is more prone to optical misalignment due to its structural design. This has to do with how loose they let some critical but imprecisely manufactured parts got into assembling. The good news is that a good one will stay good. So... Good Luck.

[chesebert]

So, I came across this really lovely perfectly made (I mean no wobble whatsoever) silver AIV FA31 the other day and I didn't get it (couldn't really explain that to my wife).

I went home and took another look at my FA31 and took the below photo at f1.8 (sharpness at 0, some contrast/brightness adjustment). I need some some definitive answer to quench my OCD thirst - do I have a reasonably well-made lens (please look at the 100% crop)?

[jpzk]

@chesebert ..... I can't fit that huge picture on my 23" screen !?
Any idea how I can manage to fit it properly?

Thanks.

JP

[chesebert]

@chesebert ..... I can't fit that huge picture on my 23" screen !?
Any idea how I can manage to fit it properly?

Thanks.

JP

oops. forgot to resize. You can always just click through to the Flickr to see the 100% crop.

[wlachan]

That pic is front focused so it is not sharp. But judging from the sharpness evenness on both sides, it doesn't seem to suffer from optical misalignment but you really can't be certain until the test was properly conducted. But if you can't tell, why worry?

[bossa]

So, I came across this really lovely perfectly made (I mean no wobble whatsoever) silver AIV FA31 the other day and I didn't get it (couldn't really explain that to my wife).

I went home and took another look at my FA31 and took the below photo at f1.8 (sharpness at 0, some contrast/brightness adjustment). I need some some definitive answer to quench my OCD thirst - do I have a reasonably well-made lens (please look at the 100% crop)?

The wobble in those lenses is the front optical assembly (focus mechanism actually) and doesn't affect the projection onto the sensor by the rear group. It's kinda like a micro shift lens and really shouldn't affect the image quality at all. Mine is pin sharp and has a slight wobble.

[chesebert]

That pic is front focused so it is not sharp. But judging from the sharpness evenness on both sides, it doesn't seem to suffer from optical misalignment but you really can't be certain until the test was properly conducted. But if you can't tell, why worry?

you have a really good eye. I adjusted by -1 and it's now sharp (unless K5's stupid AF system messes it up, which it does quite often at f1.8)