Which one should I keep?

Yeah, it's the K f/2 which is regarded as a legend. I have yet to see any shots from it I couldn't take myself with a Vivitar f/2, so I wonder if the legend isn't equivalent to the price tag.

Is the glass in the M 28mm F3.5 the same optics as your version? I have the M 28mm F3.5 and advertised it recently for £45 but got no interest whatsoever. I would have thought someone would have wanted it? It is absolutely mint with original case.

Regards
David

PS I've taken it off sale now as I'm not letting it go for next to nothing.

Well done. You caught me out again.



G

From what I have seen the K 35 1:2 is so rare that very few people have any experience of it. The 1:3.5 however, is slightly more common, and those who know it love it.

Scarcity value is a more important factor in the price of these lenses than optical quality.

G

No. The K version is a 8-7 formula and the M version is 6-6. The M28/3.5 is reputedly better than the M28/2.8 and the K28/3.5 is reputedly better than the M28/3.5. I occasionally think about testing my various 28s against each other but usually I end up deciding that going out and taking photographs is more worthwhile!

You're right not to sell the M28/3.5 for peanuts as it is a lovely lens. I already have one which is why I didn't snap it up.

K.

I would sell both & get an M or K f/3.5 instead. The M 28 f/2.8 produces very bland images in my opinion & the slower versions are much, much better. They are not the same optically, but I have both and haven't seen any real difference so far, but I've yet to do much testing. Both are extremely sharp. If you can find an f/2 version then that may be better still, though much more expensive.

I paid £30 for the M version, but only because it was wrongly listed as the f/2.8 version. I'd say £45 is a reasonable price. The K version cost me £75. I should test them & sell one, but that may take me a while...

I think most people want faster lenses, but you have to understand that this is not a lens you buy for speed. You buy it for sharpness, lack of distortion and other fine optical qualities. If you want a fast wide, then you will pay through the nose for it.

I agree with the general sentiment that one should not chase large aperture at the expense of other factors. But it does depend on the lens in question. I recommend the f/2 Close Focus Vivitar lenses not because I use them at f/2, but because they are sharper and more compelling at f/4 than the slower variants.

And I have tested. Put "28mm" into the search engine on my blog and find a bunch of articles. Unfortunately the only Pentax I have had a chance to use was the a f/2.8.