[Nicolas06]

Staff note: This post may contain affiliate links, which means Pentax Forums may earn a small commission if a visitor clicks through and makes a purchase. If you would like to support the forum directly, you may also make a donation here.

---

I love the term thoses reviewers use. "Usefullness"... some other use "decency level" or "barely usable" for a lens that is not at top lp/lw on extreme corner at f/1.4...

So let see the weak look of FA31 at f/1.8 even in web resolution at around 1000px (from flickr):














And let see what photozone say out of it in term of sharpness ...



Ironically, if we compare to 35mm f/1.4 art that is seen as one of the best modern lens out there and we compare the 31mm at f/1.8 and the art f/2 on APSC bodies (the art with 24MP and the 31 with 16MP) we found slightly better center and slightly worse corners for the Art. Couting the added resolution for the Art test and the little less wide apperture (f/2 vs f/1.8) that pretty well show that the 31 doesn't need to fear anything, even for the most modern, most praised lenses.

And the comments from photozone:

"The FA 31mm f/1.8 Limited produced excellent resolution figures in the MTF lab. At f/1.8 the center performance is already very good both in the center as well at the borders. The corners are a bit softer here. The quality increases a bit when stopping down to f/2.8 with a center reaching excellent levels followed by very good borders and corners. The quality remains exceptionally high all the way down to f/11."



I admit I don't own the lens, but I seen many example here on the dedicated threads, looked at many example on the web and such, read many reviews... And I don't feel at all that FA31 is weak sharpness wise at web resolution or is not "fully usefull". I see more that when you are at f/1.8 most of the subject is out of focus anyway, and that's not practical on most occasions except if you are after the effect. There also noticably less contrast and more aberations, but sharpness maintain a very good level. if one get a sample that weak at f/1.8 (like apparently the lenstip reviewer), the best is to get it serviced before the warrenty expire.

---

Last edited by Nicolas06; 11-23-2014 at 09:02 AM.

[ogl]

And the comments from photozone:

"The FA 31mm f/1.8 Limited produced excellent resolution figures in the MTF lab. At f/1.8 the center performance is already very good both in the center as well at the borders. The corners are a bit softer here. The quality increases a bit when stopping down to f/2.8 with a center reaching excellent levels followed by very good borders and corners. The quality remains exceptionally high all the way down to f/11."

Need to understand what Klaus means. Good, very good, excelllent are just LW/PH.

It's K-5's test with very thick AA filter. They say about RESOLUTION!!! Not about sharpness.

My copy of FA31/1.8 has really sharp corners only at f5.6 at K-5IIs and K200D. The corners at f1.8 are no good.
Please, don't mix sharpness and resolution terms.

---------- Post added 11-23-2014 at 10:11 AM ----------

FA ltd are also extremely sharp.

FA31 is simply sharp corner to corner wide open (more than many are at f/8 in corners) and become even better when stopping down.
.

You said
FA31 is simply sharp corner to corner wide open. It's not true. At 16 MP sensor without AA filter - FA31 has not bad f/1.8, but it's hard to say that the corners are sharp. It's really soft. f2 is sharp at the center without any doubts.

You samples are not correct, the pictures are made from very close distance and has small DOF and it has bokeh. We can't appreciate the corners sharpness or resolution.

[IchabodCrane]

In the US, the DA 18-135 is consistently available for $400 or less. Currently, I see it for $349 (maybe w/o hood)

The current pre-order price for the DA 16-85 is currently ~ $750 USD.
....

Maybe you can buy a new DA 18-135 off the back of a truck parked in some dark alley in Brooklyn and pay less than $400. If you order one from a real seller, it's currently $500.

More important, wouldn't it make sense to drop these meaningless apples-to-oranges price comparisons until the DA HD 16-85 is widely available for some period of time? Then we'll know the real price. To date, no one outside of Japan has even put their fingers on one (to my knowledge).

[normhead]

Maybe you can buy a new DA 18-135 off the back of a truck parked in some dark alley in Brooklyn and pay less than $400. If you order one from a real seller, it's currently $500.

More important, wouldn't it make sense to drop these meaningless apples-to-oranges price comparisons until the DA HD 16-85 is widely available for some period of time? Then we'll know the real price. To date, no one outside of Japan has even put their fingers on one (to my knowledge).

http://www.amazon.ca/exec/obidos/ASIN/B0043RTLA6/photoprice1-20
Approx $460...

They usually have them at this place for under $400 (barely) but they are sold out right now. Makes you wonder though.. what's up with the lens? The price seems to be going up, not down. I guess these days you want to buy it as part of a camera kit.
Tamron Lenses, Pentax items in Prodigital2000 store on eBay!

Henry's K-3 + 18-135 = $1299 on sale ($200 off).
K-3 by itself = $949
That's an extra $350 for your 18-135 of you chose to go that route.

---

Last edited by normhead; 11-23-2014 at 10:53 AM.

[robjmitchell]

I do wonder if field curvature is taken into account when measuring border performance in some of these test. The sharpness of my 43ltd is pretty decent is you actually focus there.
Then there is the issue of QA of course.

[Mistral75]

I do wonder if field curvature is taken into account when measuring border performance in some of these test. The sharpness of my 43ltd is pretty decent is you actually focus there.
Then there is the issue of QA of course.

Photozone's tests do (they refocus for each and every measure), LensTip's I don't know.

[Nicolas06]

I do wonder if field curvature is taken into account when measuring border performance in some of these test. The sharpness of my 43ltd is pretty decent is you actually focus there.
Then there is the issue of QA of course.

Technical reviews typically do it... Actual mere mortal trying to get a shoot have to choose one focus point per shoot still.

[Nicolas06]

You said
FA31 is simply sharp corner to corner wide open. It's not true. At 16 MP sensor without AA filter - FA31 has not bad f/1.8, but it's hard to say that the corners are sharp. It's really soft. f2 is sharp at the center without any doubts.

You samples are not correct, the pictures are made from very close distance and has small DOF and it has bokeh. We can't appreciate the corners sharpness or resolution.

First shoot has corners focussed and sharp... Other shoot show center to border sharpness (not extreme). On some you can zoom and see it quite good and could do an A3 print without any problem.

I agree with you that at f/1.8 you get many time bokeh and so you may not notice the sharpness that much because even for portraiture you'd get 1-2cm of deph of field and most of the subject is out of focus. This doesn't mean the lense can't perform. As for lp/lw we are at same level as the best lenses for same apperture... I don't know what you could ask more from the lense, it is top tier, and performing very well.

Anyway in the end it just mean we don't have same level of expectation when we say sharp. For me FA50 is really soft wide open, FA77 is just OK wide open and is sharp starting f/2.5. At f/4 only a the best lenses can match it. DA 35 plastic wonder is really sharp wide open too.

[thibs]

Yep, and DA50/1.8 is sharper wide open than FA50/1.4@1.8 si in dim light the DA is actually more useful.

[Fototim]

Photozone's tests do (they refocus for each and every measure), LensTip's I don't know.

I have read this many times, but never found a source backing it up. Can you help, please?

[Mistral75]

I have read this many times, but never found a source backing it up. Can you help, please?

"Regarding the MTF tests the procedure DOES NOT rely on the camera's AF system which tends to be very unreliable. The principal idea is the take the AF focus distance as a rough guidance and do several manual focus iterations within a radius of roughly +/-20% around the suggested focus distance. The images with the highest resolution are then analyzed and presented in the final MTF chart. From f/5.6 and up the error margin is pretty much negligible. The margin is higher (because of a more shallow depth-of-field) towards very large apertures which is why the applied focus bracketing gets more detailed here. My best guess is that the normal error margin increases to ~5% here. If there's an excessive amount of CAs or purple fringing the MTF analysis will be affected to an unknown degree. If a lens suffers from field curvature and/or residual aberrations (see below) this is taken into account - in this case the corners are measured independently from the center using different reference images. Depending on the degree of these problems the error margin may increase though."

Source: Photozone Lens Test FAQ

[Fototim]

Thank you :-)

I can't help notice "

If a lens suffers from field curvature ... (my underlining)

What? Give me a break. Field curvature is not something a lens suffers from, it's a feature, and a good one, if you ask me.

I also see that they use the word "If". I read this as they don't take field curvature into consideration by routine. They only do, when they understand that the lens is designed with this feature. I have not seen that they have been explicit about this in a test. So I don't know really.

I think I need to dive deeper into this to know what to think.

[starbase218]

I love the term thoses reviewers use. "Usefullness"... some other use "decency level" or "barely usable" for a lens that is not at top lp/lw on extreme corner at f/1.4...

So let see the weak look of FA31 at f/1.8 even in web resolution at around 1000px (from flickr):

You think 1000px web images are a good benchmark for an EUR 1150 prime lens?

Still, we haven't addressed the elephant in the room: sample variation. I have a 60-250 under repair as it was very soft at f/4 and still not good enough at f/5.6, at least in terms of what you can expect from a lens that price.

Luckily, I have another 60-250 which is fine.

(Don't ask btw, I will lose money when selling it after I get it back. But at least I will be able to sell it with a clear conscience.)

Anyway, I thought this thread was about the 16-85? Beautiful range btw, really useful.

[FantasticMrFox]

Anyway, I thought this thread was about the 16-85?

Which brings me to the question - the lens has been out for about a week now, are there any new non-Japanese reviews or first impressions? Surely someone on this forum must've bought it

[Mistral75]

Thank you :-)

I can't help notice "What? Give me a break. Field curvature is not something a lens suffers from, it's a feature, and a good one, if you ask me.

I also see that they use the word "If". I read this as they don't take field curvature into consideration by routine. They only do, when they understand that the lens is designed with this feature. I have not seen that they have been explicit about this in a test. So I don't know really.

I think I need to dive deeper into this to know what to think.

You're welcome.

Considering their protocol "The principal idea is to take the AF focus distance as a rough guidance and do several manual focus iterations within a radius of roughly +/-20% around the suggested focus distance. The images with the highest resolution are then analyzed and presented in the final MTF chart.", I do not see how they could miss a lens's field curvature.

I must confess I have a hard time understanding what you mean when you write "Field curvature is not something a lens suffers from, it's a feature, and a good one, if you ask me."