A difficult question

Basically my LBA is itching all over the place (which is ridiculous).

What is the cheapest ~f1.4 lens (with minimum decent IQ) available for Pentax?

Using adapter is ok as long as adapter price is included in the "cheapest" argument. M42 is not included unfortunately because (a) good M42 adapters are expensive and (b) the adapter prevents quick lens changing to other K-mount lenses.

Just realised none of my lenses is faster than f2.5 so just wanna look out for a fast one.

Cheers.

look for an old film camera with a 50 1.4 (m,a, or fa).... I've seen old k1000's and mzs and p30's with 50mm lenses going cheap....

You'll struggle to find a cheap 50/1.4. You should be able to find the Pentax-M or A 50/1.7 for sensible money though, especially if you look for cameras with lenses rather than lenses alone.

As for new lenses, the Samyang 85mm f1.4 is a cracker and pretty reasonably priced for a fast prime too.

The sigma 30mm seems to get a lot of love, and I can see why. Nice combination of thin dof and normal-wide focal length.

And better in some respects, but unfortunately relatively rare.

I've had a Chinon 50/1.4 in PK mount which offered respectable IQ and I sold for £30. It is rumoured that the Chinon PK mount lenses were made by Tomioka, who are pretty well respected. The XR Rikenon is believed by some to have been manufactured by Pentax and has a pretty good reputation.

The alternative 'cheap' way of getting a Pentax F/1.4 lens is to buy one with some damage that won't affect IQ, but will affect its value. I got an SMC K 50/1.4 for about half the going rate because it had a dent to the filter ring but with a but of judicious straightening, I can now mount a hood or filter. It's not cosmetically perfect, but has superb IQ.

You could even contemplate one with damage to the front element. There are a number of people over at mflenses.com who have tested lenses with pretty spectacular scratches to the front element that have minimal impact on IQ. I have a Super Takumar 135.2.5 with a single, 10mm scratch on the front and can find no evidence of this in the pictures. The consensus of opinion is that a small number of big scratches is better than abrasion or cleaning marks, which may increase flare.

Scratches on the front element act like a starburst filter It is actually the same thing except the starburst filter has more scratches for marketing reasons. Leica used to suggest painting out front element scratches with matt black paint

Best thing is avoid any lenses with scratched elements front or rear

The Pentax-M 50mm f/1.4 is probably the best/cheapest option for a good lens, although the Pentax-A is probably the best performer.

I too have found the chinons to be quite a pleasant surprise. I have the 50 f1.7, acquired for peanuts ( £3.50) but is a pleasant lens to use. Pretty sharp wide open and IMO very good even just a couple of stops down. Not sure if it is also true for the f1.4, but the ones with 'auto chinon multi-coated' in yellow and green writing are the ones to look for.

for the f1.4 reviewed
link

neville