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09-16-2013, 02:27 PM   #1
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F28 - FA31 Comparison (with photos)

I recently purchased a used F28 2.8 lens and have been contemplating how it compares to my FA31. The easiest way for me is to take photos and look at them side by side. I have posted them below. As we discuss the images please keep in mind my motiviation for purchasing the F28:
1. Size. The FA31 is bigger and heavier than what I want to lug around all day. The F28 is roughly 1/2 the size.
2. Price. I have the FA31 but there are times when I don't want to take a $1k+ lens along with me. In a sense, I don't have to worry so much about the F28.
3. Image Quality. The performance of the F28 is fairly well regarded and has all auto for times when that is necessary. It's not a limited so would I be happy?
4. Perspective. 28mm is great normal perspective for family candids.

The images below were taken this past saturday morning at my son's soccer game using my K5(f11, 1/350, -1EV, iso 200). Light was at a fairly low angle and was challenging at times. Post processing was done in Darktable and limited to adjusting exposure, shadows and highlights, and cropping. Clearly these are just a couple of snaps so artistic value is not high.

In order to avoid introduction of bias, I will wait to label which image is which(of course the exif info is there if you must).

Without further ado:


I am very interested in comments regarding these photos from a lens comparison perspective. Ultimately, I am trying to answer the question "is the F28 good enough for my purposes?"


09-16-2013, 03:13 PM   #2
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I'm pretty sure you dont buy an FA 31 Ltd for f11... but I could be mistaken.

Having owned the F 28/2.8 I can confirm it is a very sharp and capable lens, perfect focal length for everyday use. It's even got some nice bokeh if you want... but pixie dust? I don't think so.

I sold my F28 because I found I was using DA 21/3.2 ltd and FA 35/2 more. I've rationalized that I dont need FA 31 because I have FA 35... were there ever to be a Full Frame in my possession, I'd probably seek out an FA 20 or maybe an FA24..... but you can see from the pile of gear in my sig that I have a problem.. which I currently have under control by telling myself a new camera is coming...

09-16-2013, 03:13 PM   #3
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Well assuming you were shooting both from the same position, the first one is the 31mm due to larger subject size. Given the position of the balls in the background in relation to the kid, I think that supports my guess that the first one is the 31mm.

That being said, the first image is a bit warmer than the second. Looks more "daytime" than the second. The red cap is a bit more saturated in the first image. Shadows are about equal across both. Looking at the wall in the background, there appears to be more clarity in the first picture than the second. This is seen in the lighter rectangular section on the right side. The first image appears more contrasty than the second - I'm looking at the soccer ball.

That's my take on it. Now, looking at the overview - is one image THAT much more amazing in these two shots? I don't think so.
09-16-2013, 04:08 PM   #4
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@Matt: Good point regarding f11. I'll have to compare some at larger aperture.

09-16-2013, 04:17 PM   #5
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B looks just a bit harsher as lighting is concerned so I'm going to say B is the F28 and A is the 31. I've got an A 28 2.8 and like it alot. Much better than the kit lens at that focal length. Sharper too. Wayyyyyy sharper
09-16-2013, 04:23 PM   #6
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Marking the thread so I can follow the discussion.
09-16-2013, 04:27 PM   #7
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Contrast is higher in A, and color is a lot more saturated. The color stripes on the balls really pop. But I don't see anything that can't be done in Lightroom on B to make it look the same. Besides the FL difference of course, which is quite small.
09-16-2013, 06:36 PM   #8
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I believe that the first photo is the 31 as well. I had an FA28 before and it was a good lens. I sold it when I got the 31 and don't regret the decision. The 31 is so good at all apertures and is quite frankly the best lens I have. That said most of the F and FA primes are excellent and I would not hesitate to use them. Personally I would not use the 28 because I have the 31. If I need wider, I use my 21 or 15. In full frame, I would look for a 20 or 24 instead.

Back to other posts, I would compare the two at F2.8 as that would commonly be used in practice with medium to low light conditions and I know which lens I would rather have in those circumstances. As for worrying about the cost of the 31, most photographers (present company not included) haven't a clue about Pentax and the value/quality of the 31.

09-16-2013, 06:49 PM   #9
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For that kind of picture, the F 28 will do you just fine. Although honestly, an 18-55 or even the much maligned 35-80 would do about the same with that type of shot. It isn't quite the right scene to differentiate the two.
09-16-2013, 09:06 PM   #10
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Although very hard to tell from small pictures taken at F11, I believe the 1st one was from 31. Better color.
09-17-2013, 05:29 AM   #11
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I don't understand the reason for not wanting to take out a $1k lens... Unless you're buying it for collection purposes...

If it isn't being used and you're happy with f2.8 just sell the 31!!!
09-17-2013, 03:17 PM   #12
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I guess a better test would be using both lens at f/2.8 in a scene with a background and foreground.
09-17-2013, 04:24 PM - 1 Like   #13
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Part 2.8

Regarding the f11 photos above:
Photo A was taken with the F28
Photo B was taken with the FA31

In retrospect, my cropping may have thrown many of you. My intention was to obtain similar fields but obviously didn't succeed. Sorry about that.
Also of note, I exposed -1EV to preserve highlights and brought exposure back up in PP. The FA31 is +1EV and the F28 is +0.5EV.

Thanks for all the comments!
@chickenavocado: $1k isn't chump change in my book. There are times when I'd rather not risk it, like a trip to the amusement park.

Now, here are two photos taken this evening at f2.8. One with the F28 and one with the FA31. This time I have done nothing in PP except convert to jpeg. I did try to frame them similarly.
1/500(F28) 1/750(FA31) light was changing and in Av mode

Photo A

Photo B

Last edited by al_undy; 09-20-2013 at 03:25 PM. Reason: Clarified which photos I was identifying at beginning of post.
09-17-2013, 04:28 PM   #14
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First beer bottle is the 31 second is the 28.
09-17-2013, 04:47 PM   #15
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QuoteOriginally posted by alamo5000 Quote
First beer bottle is the 31 second is the 28.
I'll agree with alamo.

Man I'm going to have to get me an F or FA 28. Looks very similar to the FA31.

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