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06-04-2010, 12:44 AM   #1
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Pentax-F 28/2.8 vs. FA 31/1.8 Limited

Just wondering if anyone has done a direct comparison of image quality with these two lenses? The 31 is of course legendary for image quality, while the 28 has some very favourable reviews and good scores (average 9.38) in the lens reviews database (here) and is a fraction of the size and weight of the 31. The focal lengths of these two are close enough that they could be considered interchangable. It would be too much to expect the little 28 to be as good as the 31, but especially on a cropped sensor, how much better is the 31 in practice?

06-04-2010, 01:54 AM   #2
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I don't think there will be huge diference is sharpness pass f4.
2.8 - 4 I'd expect 31 to beat the hell out of 28 as it's at it's best at those f stops. Part of 31's legend is OOF rendering and "pop" (also called 3D effect). In these two aspects I'd expect 31 to win again.
Also 31 is 1.3 stops faster and it's VERY usable at f stops below 2.8.
31 is using AL element F28 doesn't (but I don't know if that's good or bad as F28 is rated higher than FA28AL).
And of course 31 is beautiful block of metal & glass and F28 is...well not so beautiful piece of plastic and glass (IMO - having said that I used to have F50 and it's built quality was goo)
All of this reflects in prices. Here in UK used 31s go for 700-800 and F28 for 125-150.
If the diferences are worth so much money... you decide.
please bear in mind I NEVER shot F28 and my opinions are based on "knowledge" gathered from the web.
On the other side I have been using 31ltd for over a year now and it's definitely one of the best lenses I have tried (around 15).
06-04-2010, 02:42 AM   #3
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I don't have the FA31, but from what I've seen the lens is indeed at its best around wide open.

Maybe if you don't mind I'll post a few freshly made wide open examples with my F28/2.8?

06-04-2010, 02:57 AM   #4
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Thank you for those good samples. To my eye that is certainly very acceptable bokeh, and at this size the sharpness appears very reasonable.

The 28, being a shorter focal length, will render the out-of-focus areas with slightly less blur for a given aperture and focus distance. The 31 will be able to render the out-of-focus areas more out of focus by virtue of the slightly longer focal length, and the extra stop+ of aperture.

Now, I wonder about corner sharpness and chromatic aberration.

06-04-2010, 04:30 AM   #5
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No thanks. Here are a few more samples with the F28/2.8 for you. These are a bit bigger than the previous ones (1280 x 1024).

I have never seen CA in this lens. I tried to generate it (in the handlebar) but I don't see any.

You can see the sun in the top middle. The F28 is VERY flare-resistant. Also, no ca in the branches.

The obligatory wall shot, at f/2.8

Bottom left corner of the above wall shot at f/2.8.

Bottom left corner of the wall shot at f/4.

Hope this helps!
06-04-2010, 04:36 AM   #6
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I didn't do a direct comparison, but I've owned an F 28/2.8 and now have the 31/1.8, in between I even tried the FA35/2.

They are all very nice lenses, the 31 is definitely much better than the rest in every aspect except the 35 is probably sharper at certain apertures and the 31 at others.

The F 28/2.8 for it's money is a no brainer. Sharp enough. Should fetch at least twice as much as it goes for (I only sold it for $200). An excellent lens. (9.2/10)

The 35 is all the 28 is, and sharper, faster by one stop but obviously not as wide as the 28. A superb lens. (9.5/10)

The 31 is all the 28 and 35 are and have that pop with amazing color, better micro contrast and dreamy bokeh. A legendary lens with performance to match it's cult status. No doubt it's the one with the pixie dust. (10/10)

The Tamron 18-250 I had would be rated at 8/10 on those focal ranges. So, they are all great. The Tamron 28-70 would be rated higher than the 28 at about 9.4/10)

(The ratings are for IQ only. not factoring, size convenience etc. and are obviously subjective, and are put there just to compare these sets of lenses)

Last edited by pcarfan; 06-04-2010 at 04:50 AM.
06-04-2010, 05:15 AM   #7
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just pick a lens already! Even an M42 35mm f/3.5 is a pretty decent lens(surprisingly sharp and compact). Though, the FA31 is indeed in a class of it's own.

though I prefer the FOV from the FA31 :


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