[Laurentiu Cristofor]

- wide open, it's not sharp as DA40

Naturally, but it should be sharp enough for all applications.

[chesebert]

Your pictures just don't look right to me... it seems like everyone one of them is not correctly focused. I'm wondering if your camera needs an adjustment, as every image looks about the same to me.

This picture here was shot wide open at f/1.9 and even though it's not at a static object, it's pretty obvious that it's correctly focused and is sharp.

You are right. These look like they are at least 200% crop. I must haved messed up the export somewhere.

One thing I didn't mention was that I took the calendar shots from about 15ft away, with calendar measuring only 10x10; and 10ft from the vertical test chart, which is 8.5x11.

Regardless, I have another 31mm on the way to see if I like the new one better.

[chesebert]

Replacement copy update:

So I was a little parinoid with the first copy being "not as good as 40mm wide open." - not sure whether 31mm @ f1.8 == 40mm @ 2.8 in sharpness is the universal truth re the 31mm. The replacement copy arrived a few days ago and I have been testing it since.

Bad news first - the second lens hood wobble to about the same degree as the first lens.

Good news - the second lens is tack sharp at f2.0 in the center and noticably sharper at the edge at the same fstop compared to the first copy. At f1.8, the second copy is just so slightly less sharp than the 40mm at 2.8 in the center (I think 40mm wins on the extreme edge/corner resolution until 31mm gets to f2.8 and beyond). By f2.0, the second copy is slightly sharper than 40mm at 2.8, and after that it was no contest, 31mm is much sharper than 40mm at 4.0, 5.6 and etc. I also notice the second copy appears to be able to focus more accurately than the first. Regarding the manual focus, I noticed that the focus ring on the second copy is slightly more damped, on par with the 77mm.

So where does that leave us -- it appears that wobbleness of the lens hood, while may contribute to softness wide open, may not be the determining factor or at least it would not be sufficient to say wobblenss means softness wide open. My initial impression, at least from reading many threads on this topic, has been that you can't get a tack sharp 31mm unless you get one with no wobbleness in the lens hood. I believe the samples I have in front me provide a counter point to that understanding.

It would be great if others who have compared multiple copies of 31mm side by side can chime in on this issue.

[wlachan]

The issue with wobbly front section is that the optical alignment will shift as the lens orientation has changed due to gravity. What this means is that the lens can be calibrated perfectly for horizontal orientation but the optical alignment will shift in portrait orientation. To complicate things more, different horizontal or portrait orientations will suffer different misalignment. This may or may not be obvious in practice depends on ones experience and expectation.

[Laurentiu Cristofor]

Replacement copy update:

Wow, it sounds quite worrying to encounter such issues in a high end lens like the FA 31! I never did any careful testing of my copy simply because its output has always impressed me since I first used it. I am not even sure how the hood can wobble, given that it's part of the lens and it doesn't extend or contract or do anything that would allow some kind of play. Can you post some images explaining what parts are moving and in what direction?

[chesebert]

Wow, it sounds quite worrying to encounter such issues in a high end lens like the FA 31! I never did any careful testing of my copy simply because its output has always impressed me since I first used it. I am not even sure how the hood can wobble, given that it's part of the lens and it doesn't extend or contract or do anything that would allow some kind of play. Can you post some images explaining what parts are moving and in what direction?

Ok, some clarification. The lens hood is not "moving"; there is simply some play, which results in a very slight wobble that you can feel when you put and take off the lens cap and when you hold the lens hood and wiggle it a bit.

Based on my 2 sample analysis, it appears that all 31mm lens hood wobble (with 50% margin of error I guess) to one degree or another, whether you notice it or not.

[chesebert]

Some photos from the second lens at f1.8 and f4.0. Basic raw conversion + some contrast/color, no sharpening or NR on the crop (full image has some enhanced curve, sharpening and slight NR applied).

f1.8



f4.0


100% crop, f1.8, center



100% crop, f1.8, extreme edge



100% crop, f4.0, center



100% crop, f4.0, extreme edge

---

Last edited by chesebert; 04-13-2012 at 09:41 AM.

[Edgar_in_Indy]

Cool shot, but probably not the best scene for pixel-peeping since atmospheric conditions come into play.

[chesebert]

Second update (it's-getting-warm-outside update)

It was a little over 80 outside today and I took out my 31mm to do some field testing. During the shoot, I noticed that lens hood is pretty solid. I found it was not as easy to move the hood out in the warm temperature as when I was indoors. A potential theory based on my observation today is that the lens hood wobbles less when the ambient temp goes up. Is this possible? How can a mere 20F difference affect the tolerance in a metal lens? Another theory is that the lens hood may just wobble less one day and more the next in a complete random pattern. No difference in picture quality detected, however.

[Edgar_in_Indy]

Another theory is that the lens hood may just wobble less one day and more the next in a complete random pattern.

It may also be effected by how much pixie dust is in the air.

[FireDog]

I have both. Got the 31mm first and was amazed at the IQ. Best lens I have ever used. Then I got the 77mm. If I score the 31mm a 10 the 77mm is a 9.5. That said my 31mm also has the wobble. Only noticed it after I got the 77mm and well past the date of exchanging it. I found it a little disconcerting. After searching these forums I felt a little better. BUT, I still felt at some point it must have an effect on IQ. SO...I got a LensCoat Canon TC weather protector and cut the 2x model down to about 3/4", reversed it so the fabric is on the inside and fitted it to cover the focus ring and part of the petal hood. This applies just enough tension to hold the front of the lens centered and has no effect on auto focus. Looks a little strange. But gets the job done. Wobble gone!

[chesebert]

I am done testing. Finally, some obligatory wide-open FA31 box shots (minimal PP/RAW conversion; no NR or Sharpening)