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02-18-2011, 12:52 PM   #1
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FA 31mm F1.8 AL Lim vs FA 43mm F1.9 Lim

Would love some advice, am looking for a fast prime lens that is sharp. I am selling my FA50mm 1.4, its great and very sharp mid f-stops, but too soft at f/1.4 - f2.5. I would like to replace it with either the 31mm 1.8 or the 43mm 1.9. Is the 31mm 1.8 worth the extra money, is it that much better than the 43mm 1.9.


02-18-2011, 01:11 PM   #2
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FA43 vs FA31

Well it is not really about which one is better than about which one is more useful for you. I had both and kept FA31 just because it provides more angle of view on dSLR. Both are sharp enough, FA43 maybe a little bit sharper than FA31, both have nice bokeh, both are fast. FA31 is heavy and bit bulky, FA43 is light and compact. FA31 is more wide angle than FA43, so the image perspective looks a bit different than FA43. Choose simply by comparing the pictures from both lenses, which perspective do you like more. If you're more inclined to standard lenses - go for FA43 and you'll save a lot of money. And then there's FA35/2 which si something in between.
I personally don't think FA31 is any better than FA43, it is just a different lens.
02-18-2011, 01:59 PM   #3
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Pick the focal length you like, both are very sharp.
02-18-2011, 02:05 PM   #4
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No argument here. Both are excellent and sharp from wide open. But if you like the fast fifty focal length, then the 43 will be most applicable to you.

02-18-2011, 02:31 PM   #5
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I'd suggest that if it is sharpness that you are after, and low DOF, and you didn't mind the FOV of your 50, go with the 43. It's absurdly sharp from f2-2.8, and since the focal length is a little longer, you can get slightly lower DOF shots out of it.

I think they are pretty different, though.

Now I want to go play with my 40 .
02-18-2011, 03:25 PM   #6
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much better view-angle and bokeh
02-18-2011, 04:06 PM   #7
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well, basing from your dilemma regarding sharpness from wide open to f2.5, I would vouch for the FA43. also, I see that you don't seem to have a problem with either focal length and looking for a certain specific rendering regarding sharpness at wide open. so in conclusion, the FA43 would fit perfectly for your need.
02-18-2011, 04:15 PM   #8
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If you want to replace 50 go with 43. It's sharper wide open and gets you closer to the FOV of 50. 31 on the other side is a nice pair with 50/55 mm lens, but definitelly not replacement. Option 3 would be DA*55. Cheaper than Ltds but perfectly sharp even at f1.4

02-18-2011, 06:33 PM   #9
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FA43 is soft wide open. It's quite sharp at f2.8, and really sharp across the frame at f5.6. I haven't used FA31 on DSLR to be certain but its AF is less consistent than FA43. This might have to do with the limitation of Pentax AF though as the AF gets less reliable the wider it does.
02-18-2011, 08:02 PM   #10
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QuoteOriginally posted by wlachan Quote
FA43 is soft wide open. It's quite sharp at f2.8,
I bought a 43ltd recently and have been comparing it w/ my FA50...bokeh seem roughly the same...contrast is a little better w/ the 43, and the 43 isn't massively sharper than the 50 wide open to me...
02-18-2011, 08:59 PM   #11
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Sounds like the 43 would suit you better to replace your 50.
I replaced my 50 with it and im very pleased.

FA43 is sharp wide open and very useable-

Last edited by TOUGEFC; 02-19-2011 at 01:16 AM.
02-18-2011, 09:39 PM   #12
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Definitely useable wide open from my point of view also.
02-19-2011, 12:09 AM   #13
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QuoteOriginally posted by wlachan Quote
FA43 is soft wide open.

Check your camera or give the FA43 to the adjust service.
The FA43 is one of the sharpest Pentax lenses ever:

FA43 at f1.9

02-19-2011, 12:17 AM   #14
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It all depends what you need and what your want to use the lens for.

When I want to travel light with one prime, the FA31 mm is a great focal length that is wide enough. I have done a few overseas trip with the FA31mm mounted on my K-7 (no other lens) and I was very, very happy with the combo. The FA31mm results are always outstanding and the 31 mm focal length is perfect for a one-lens combo.

Food for thoughts...
02-19-2011, 11:20 PM   #15
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I own the 31 Limited, and I can assure you that it is as good as it's reputation suggests. However, the 43 Limited is in the same class, so your decision should be based upon your desired focal length. Which do you think will be more useful given your personal style of photography and given the other lenses at your disposal. Do not concern yourself with differences in quality. Both Limiteds are excellent.


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