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07-12-2010, 11:45 AM   #1
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FA 31mm soft?

Good day, i have run some test on my FA31 and it seems to be a little soft. Using the focus test chart, I took several shots at different f stops to see the difference in DOF. Camera is a K20, ISO 100, "natural" setting with no adjustments, AV setting to adjust the f stop. The camera was mounted on a tripod and the shutter delay was used.
This is my shot at f1.8:

It appears quite soft and a considerable amount of purple and green fringing.


At F2.8:

Although it is a tad sharper, there is still some purple and green visible.

At f4:


At f8:


Can anyone suggest a better test? I did expect the lens to perform better wide open but that doesn't mean my expectations are valid. it does not seem to have any back or front focusing issues but a little softer than I expected.
Any suggestion for test or camera adjustments would be appreciated.

Tom

07-12-2010, 12:45 PM   #2
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Hello,

My advise would be to have Pentax confirm the lens is operating correctly through your warranty.

C h u c k C a p r i o l a
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07-12-2010, 01:36 PM   #3
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Sorry Chuck, meant to put this in the lens descussion forum. Would a moderator please move it?

Tom


(EDIT) I will re-post in the correct forum.
Thanks.

Last edited by Waldo Humblebee; 07-12-2010 at 02:31 PM.
07-12-2010, 02:41 PM   #4
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Looks basically correct to me...

07-12-2010, 02:52 PM   #5
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QuoteOriginally posted by Waldo Humblebee Quote
considerable amount of purple and green fringing.
This will happen since the lens is not apochromatic. In fact I'm not sure any Pentax prime is.
07-12-2010, 02:53 PM   #6
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Fringing outside the plane of focus is normal. The lens is corrected for the focus plane.
07-12-2010, 03:00 PM   #7
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Planning a Sale?

So.... Considering that it does not seem to meet your expectattions, may I ask if you are planning a sale and seeking offers? If yes, feel free to PM me when convenient.

Cheers...
07-12-2010, 03:37 PM   #8
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Thanks for the replies. I haven't had much time behind the lens and maybe just needed verification that it is a decent copy.


QuoteOriginally posted by Michaelina2 Quote
So.... Considering that it does not seem to meet your expectations, may I ask if you are planning a sale and seeking offers? If yes, feel free to PM me when convenient.

Cheers...
Michaelina2, I have been told repeatedly that there just is no way of pleasing me. Maybe I should lower my expectations, lol.
Thanks for the offer but I do want this lens.

Tom

07-14-2010, 12:36 AM   #9
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Looks like it behaves much like my FA50 1.4
07-14-2010, 02:18 PM   #10
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The purple and green tint in the OOF areas is perfectly normal.
I believe what you are perceiving as lack of sharpness at f 1.8 is actually lack of contrast as compared to smaller apertures.
Nothing in your f1.8 pic looks abnormal to me.

Moved to lens discussion.
07-14-2010, 03:54 PM   #11
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Thanks for moving and the replies. I had a chance to take it out today an I am very pleased. It's not too soft at all, even at f1.8.




Tom
07-14-2010, 04:06 PM   #12
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For what it is worth, my FA31 performs the same and I felt the same as you when I got mine (new, made in Japan). People set the expectations for this lens so high "Wow, it is razor sharp wide open!" The truth is, although there are many lenses that are more than acceptable wide open, I've yet to use a lens that couldn't benefit from stopping down at least 1-2 stops.
The beauty in this lens is really in the way it renders. Sharpness is just one quality (although the one we pick on the most).
07-14-2010, 05:07 PM   #13
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May I refer you here.
07-14-2010, 05:10 PM   #14
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Merged the two threads since there were replies in both.
(and deleted the duplicate original post)
07-14-2010, 05:25 PM   #15
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QuoteOriginally posted by noahpurdy Quote
May I refer you here.
Yes you may, good read.


QuoteOriginally posted by mel Quote
Merged the two threads since there were replies in both.
(and deleted the duplicate original post)
Thank you Mel for combining the threads. I will try to be more careful in the future. This forum stuff is new to me.

Tom
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