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11-03-2017, 06:36 PM   #1
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F28 2.8 vs d fa 28-105

Can the old lens offer anything besides a little wider aperture than the new zoom? If you already have the zoom, would it be worth it to pick up a copy of the f28?

11-03-2017, 06:50 PM - 1 Like   #2
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I's about 40% of the weight of the zoom, not much bigger than a pancake lens.
11-03-2017, 07:26 PM - 2 Likes   #3
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I do have both, and for two rather special purposes recently I was glad that I hadn't sold the F28/2.8 as I considered first:

1. The F28 does have an aperture ring. It allows me to mount it reverse in front of other lenses with 49mm filter threads for high-magnification macro work, with very good resolution e.g. for around 4:1 magnification on the D-FA 100mm. The F28 aperture is then controlling the combined lens. It complements the DA15 for that purpose, which reaches even higher magnification and resolution, but needs some makeshift control of the aperture lever.

2. My F28's infinity stop is spot-on. This comes really handy for night (sky) pictures. And every little bit of light helps here with framing and, if needed, focusing, even in live-view on the K-1. It does show quite a bit of coma in the corners wide-open and may need to be stopped down slightly.

I haven't watched out for "sun stars" yet, they might be nice on the pentagonal aperture of the F28. Despite several more lens surfaces, the D-FA 28-105mm, if not even superior, handles bright light sources as well as the F28 when it comes to flare and ghosting. So in general photography, I don't switch to the F28 unless I need a filter which I only have in 49mm or I want a focus scale for calculated DoF control on a 10-stop ND filter.

I suspect that the F28 has lower distortion, but it is rather moderate for the D-FA zoom as well, usually not a problem. The F28 does focus closer (30cm), which at 28mm can already create quite some dramatic perspective distortion to highlight tiny foreground objects.

In general, I like the look and feel of the small F-series primes, more than the FA-series. If only I wouldn't often pick the 50mm/1.7 instead of the 28mm/2.8 or vice versa . They basically have identical looks, size and weight. I decided to keep mine, nice also for a smallish prime set on the K-5.
11-03-2017, 07:50 PM   #4
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Wow! Thanks for the responses! The f28 will screw right onto the d fa 100? Or is there some sort of adapter required? Thanks!

11-03-2017, 08:01 PM - 1 Like   #5
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You need an adaptor, a cheap and lightweight ring with two 49mm threads. Be careful though on the DFA 100 WR, the 28mm is rather heavy for its plastic inner tube. It feels more solid e.g. on manual primes like an M135/3.5, or, for more moderate magnification some 50/1.7.
11-03-2017, 08:46 PM   #6
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JensE, you have now convinced me to hang on to my F28/2.8 despite having three full frame zooms covering that focal length!
11-04-2017, 02:12 AM   #7
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Extending to M2.8/28 comparison

Thanks for this interesting thread - good idea!

I don‘t own the F2.8/28 but the M2.8/28, M1.7/50 and DFAf3.5-5.6/28-105.

Until now I didn‘t think about a comparison of M2.8/28 against the DFA@28. But you convinced me to do so.

Since I appreciated shooting with my M1.7/50 the recent days I imediately captured a serie with ascending aperture from 2.8 respectively 3.5 to 22 @28. Subject was a book shelf one meter in front of the tripod mounted camera. The border area view covering books showing small letters. Natural light falling from behind the camera and right side.

My oberservations for this setup:

The M2.8/28 shows some significant astigmatism at the borders up to f5.6 - that means there‘s a slight double image yielding to an unsharp representation. The DFA shows this too. But it‘s less pronounced. Especially from f8 on I was really surprised how good and sharp the M2.8/28 held up against the DFA@28. But I guess the DFA works better if there‘s more direkt light into the lens.

So in the future for dedicated photo trips I‘ll bear in mind that I have a wide and fast option to go more lightweight using my K-1.
11-04-2017, 02:54 AM - 1 Like   #8
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There are two versions of the Pentax-m 28mm F2.8. They have a different optical design. The newer version looks more like a Pentax-a lens and shares it's optical design with the Pentax-a and Pentax-f 28mm 2.8. The FA 28mm F2.8 AL has a different optical design with just five elements but with an aspherical lens element.

11-04-2017, 04:04 PM - 1 Like   #9
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I don't have the d-fa 28-105, but I've tried a number of 28mm lenses, old and new and would rank the F28/f2.8 at the top in term of performance. I kept using the lens through 4 different pentax bodies and only sold it when i got the 31/f1.8 ltd.
11-08-2017, 07:01 PM   #10
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QuoteOriginally posted by D1N0 Quote
There are two versions of the Pentax-m 28mm F2.8. They have a different optical design. The newer version looks more like a Pentax-a lens and shares it's optical design with the Pentax-a and Pentax-f 28mm 2.8. The FA 28mm F2.8 AL has a different optical design with just five elements but with an aspherical lens element.
I have the FA28mm which is basically my walk around lens

Wide open shots at F2.8


11-09-2017, 03:42 AM   #11
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I love my Pentax smc F28 / 2.8 on K-1, direct from the jpeg camera just reduced,
-Pentax K-1
-Pentax smcF28 / 2.8
-ISO 560
-f 2.8






-I have Tokina ATX PROSV 28-70 / 2.8 and it is incomparable with the F 28 / 2.8 candy of lens

Last edited by mbukal; 11-09-2017 at 04:03 AM.
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