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28mm Alternatives

Lenses with 28mm or zooms including 28mm are very common. For years they have been the standard "wide angle" on film. On APS-C sensors like on the Pentax *ist DS, they offer a field of view comparable to a 42mm lens - close to the theoretical standard lens. This means that there is an abundance of lenses available for 28mm. I took the few 28mm lenses I own and took them for a spin. All are M42 and "full-frame" except for the KAF mount APS-C Sigma:

Revuenon 28-70mm 4.0 My favourite M42 zoom
Pentax 28mm 3.5 SMC Takumar Said to be the sharpest 28mm ever produced in M42
Sigma 18-125mm 3.5-5.6 DC APS-C only, lazy zoom
Tokina 28mm 2.0 RMC One of the fastest 28mm there are.
Beroflex 28mm 2.8 Rather large prime - worth the bulk?
Revue 28mm 3.5 Probably the worst build-quality of any lens I have.
+
Sigma 28mm 1.8 Fastest 28mm lens I own.

I shot all photos wide open, plus at f/8.0. I tested the Tokina 28mm 2.0 also at f/3.5, as this is the aperture that the other lenses are roughly wide open. I shot from a tripod, mirror pre-release, took three images with each lens and aperture, manual focus each time from new, picked the best by file size. None of the images have been sharpened or softened or levels adjusted, the crops are the utmost corners. I did not vary the distance, it was 2.8m for all lenses (so roughly 100x focal length). Sorry for the zooms not having precisely 28mm.

I chose this rather bad page design (horizontal&vertical scrolling) because I believe it makes comparing easier.

full frame	Centre	upper left corner	upper right corner	lower right corner	lower left corner
Revuenon 28-70mm 4.0 @ 4.0	Revuenon f/4	Revuenon f/4	Revuenon f/4	Revuenon f/4	Revuenon f/4
Pentax 28mm 3.5 SMC Takumar @ 3.5	Pentax f/3.5	Pentax f/3.5	Pentax f/3.5	Pentax f/3.5	Pentax f/3.5
Sigma 18-125mm 3.5-5.6 DC @ f/4	Sigma f/4	Sigma f/4	Sigma f/4	Sigma f/4	Sigma f/4
Tokina 28mm 2.0 RMC @ 2.0	Tokina f/2	Tokina f/2	Tokina f/2	Tokina f/2	Tokina f/2
Tokina 28mm 2.0 RMC @ 3.5	Tokina f/3.5	Tokina f/3.5	Tokina f/3.5	Tokina f/3.5	Tokina f/3.5
Beroflex 28mm 2.8 @ 2.8	Beroflex f/2.8	Beroflex f/2.8	Beroflex f/2.8	Beroflex f/2.8	Beroflex f/2.8
Revue 28mm 3.5 @ 3.5	Revue f/3.5	Revue f/3.5	Revue f/3.5	Revue f/3.5	Revue f/3.5
Now, all lenses at f/8
Revuenon 28-70mm 4.0 @ f/8	Revuenon f/8	Revuenon f/8	Revuenon f/8	Revuenon f/8	Revuenon f/8
Pentax 28mm 3.5 SMC Takumar @ f/8	Pentax f/8	Pentax f/8	Pentax f/8	Pentax f/8	Pentax f/8
Sigma 18-125mm 3.5-5.6 DC @ f/8	Sigma f/8	Sigma f/8	Sigma f/8	Sigma f/8	Sigma f/8
Tokina 28mm 2.0 RMC @ f/8	Tokina f/8	Tokina f/8	Tokina f/8	Tokina f/8	Tokina f/8
Beroflex 28mm 2.8 @ f/8	Beroflex f/8	Beroflex f/8	Beroflex f/8	Beroflex f/8	Beroflex f/8
Revue 28mm 3.5 @ f/8	Revue f/8	Revue f/8	Revue f/8	Revue f/8	Revue f/8
I now added the Sigma 28mm 1.8 Shot without tripod, not from exactly the same spot.
Sigma 28mm 1.8 (P/K-A) @ 1.8	Sigma 28mm 1.8 @ 1.8	Sigma 28mm 1.8 @ 1.8	Sigma 28mm 1.8 @ 1.8	Sigma 28mm 1.8 @ 1.8	Sigma 28mm 1.8 @ 1.8
Sigma 28mm 1.8 (P/K-A) @ 2.8	Sigma 28mm 1.8 @ 2.8	Sigma 28mm 1.8 @ 2.8	Sigma 28mm 1.8 @ 2.8	Sigma 28mm 1.8 @ 2.8	Sigma 28mm 1.8 @ 2.8
Sigma 28mm 1.8 (P/K-A) @ 8.0	Sigma 28mm 1.8 @ 8.0	Sigma 28mm 1.8 @ 8.0	Sigma 28mm 1.8 @ 8.0	Sigma 28mm 1.8 @ 8.0	Sigma 28mm 1.8 @ 8.0

Conclusion:
Ok, I admit I focused them manually without a viewfinder magnifier. Still, by focusing three or four times and picking the best, I hope some conclusions can be drawn.
The old Revuenon Zoom puts on a fabulous performance with quite some barrel distortion and seems just a tad sharper than the Pentax 28mm 3.5 which has less distortion in exchange. The Sigma shows good performance with its trademark strange distortion which at 28mm looks more like pincushion and the superbright Tokina 28mm/2.0 shows surprisingly little distortion but needs to be stopped down quite a lot for good sharpness. However, due to its extraordinary birghtness, it may well be the only lens (together with a macro) that accompanies my Sigma. The Beroflex does nothing bad but nothing great, the Revue shows almost no contrast which creates bad apparent sharpness - with a contrast-boost, it seems much better suddenly. I would still not recommend it, though.
I am willing to summarize and forecast: If you are looking for an affordable ~28mm wide-normal lens to use on your APS-C dSLR, you may consider old but high-quality lenses for 35mm to perform satisfactorily.

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