Originally posted by liemjerry Thank you all for info and suggestion
I can make conclusion that for build quality (phisically) K 50/1.4 seems best choice but M 50/1.7 is better in chromatic abberation and sharpness but weak in bokeh of course.
I have 3 quotations :
K 50/1.4 is in mint condition (90%), including 3rd front cap, and original rear cap for USD 76,92
M 50/1.4 is in mint condition (95%) including original front cap but without rear cap for USD 65,38
M 50/1.7 is in mint condition (99% almost like new) including original front and rear cap for USD 76,92
for those quotations, which one must I choose for?
Thank you
Like what others mentioned.. I would say your choice of lenses K/M 1.4 are pretty much identical. Actually even 1.4 gives a bit more pleasing bokah, but the nature of 1.4, it makes wide open aperture sharpness way lower than 1.7 even the 1.4 lens is set to be 1.7~1.8ish. Between 1.4 and 1.7, you won't get too much of the boost during the night either.
From your situation, I would say, rather debating on 1.4 vs 1.7, I would.. indeed pick up a even cheaper 50mm 1.8 or 2.0 as alternative options for 1.7, and keep a cheaper 1.4.
My personal opinion is, none of those 3 are my liking really.
for compactness, price, image quality, performance, for large aperture I would go for :
Pentax-A 50/1.2
Pentax-A 50/1.4
Pentax SMC Takumar 50/1.4
Small aperture, but even more compact I would go for :
Pentax-A 50/2.0
Pentax-FA 43/1.9
Pentax SMC Takumar 55/1.8
I currently have Pentax-M 50/2.0, Be honest with you, it's way lower performer than other fifties I have owned. I would personally stay away from M version and early K versions. Early K is just K mount of SMC Takumar version with less of yellow glass element. But it would be bigger, heavier, and more expensive compare to SMC Takumar.
If you want to have nice bokeh, then the choice could be 50/1.2, 50/1.4, or 55/1.8. I found that 55/1.8 has the best bokeh even compare to any version of 50/1.4. As for Pentax-A 50/1.2, it's an unique lens. You simply will never get sharpness till your aperture goes down to F4 or beyond. But it is what it is.. It's a 1.2!! It works best on crazy smooth bokeh and when you absolutely don't need sharpness on the subject. The painting quality of 1.2 is probably strictly to artists (maybe).
Let you have the taste of 55/1.8 (which is a cheap lens BTW.. my had tiny bit trace of fungus and it's still super sharp! I picked up around $30 I believe) Using fairly wide but not widest 50 range, but makes it a 55 (even more telephoto).. It brings up the characteristic similar to medium format. There is a reason why on 645 a 80mm F2.8 although it's F2.8 it gives much better bokeh than a 135 50mm F1.4 but subject is WAY SHARPER!! Because you are in theory at F2.8 compare to F1.4!!! That's why I would say, if you want great bokeh, 50mm F1.4 vs 55mm F1.8.. I would personally pick up 55/1.8 any given day!