[IgorZ]

Tough choice, too many beautiful lenses. I'd say for me it would be 2/58 takumar... Probably my favorite lens. But it's M42. So I'll go with the 43.

[SSGGeezer]

I can't decide between my FA 77 and my SMC DA 40. Different use cases but both great in their own way. Probably my FA though if I had to choose.

[travelswsage]

My two current favorites are the Sigma 180mm macro or my leitaxed Zeiss 135mm. Great bokeh especially on the 135mm. And you guys will probably laugh but I also really enjoy both Lensbabies -- the 56mm and 85mm. The Zeiss would be my favorite if I could have only one but I use the Sigma 180 more than anything else after my Pentax zooms.

[Paul the Sunman]

If I were limited to one lens, and a prime at that, I wouldn't own a DSLR. It's pointless.

[monochrome]

That's my choice also. Not just in theory; I've been using it a lot this year, both on the K-1 and on my IR-converted K-5.

During the financial crisis I sold all my manual lenses except the K35/3.5 and K50/1.4. It has been fun to rebuild.

[Breakfastographer]

smc Pentax-D FA 100mm F2.8 Macro

Produces pleasing images at all focal distances.

[lytrytyr]

I thought I would post here and ask for your - take everywhere Prime lens that you could be "Mostly Happy" using as your "only" lens.

Taking OP's question seriously, not just asking for a favorite lens,
I would have to say it's the Zeiss ZK 50/2 Makro-Planar.

It does all the usual nifty-fifty jobs, on APS-C and FF,
but then at f/2, where it's still sharp, it's also a low-light demon,
and at 1:2 it does almost everything you'd expect of a macro lens.

It doesn't do wide-angle directly,
but the distortion is low enough to make stitching a reasonable proposition.

None of my other primes is that versatile.

[beachgardener]

out of all the lenses I have at present, I'd choose the DA 35 f2.4 for versatility, a very nice lens for the price.

[garywakeling]

I have been playing with a single lens each month in the Single in Challenge, I have had the easiest time with the F* 300mm 4.5, the DA* 55mm 1.4 and the FA 50mm Macro. As 1 lens to live with I think the FA 50mm Macro would be the one, easy to use as a standard lens and with the bonus of all that macro fun, great question.

[WPRESTO]

Although I don't use it as often as I'd like and should, the 200mm f4 SMCA ED macro has always been my favorite lens. It never disappoints on IQ, only my failures of technique and attention to detail when I trip the shutter.

[bdery]

It's not my absolute favourite, but it'S certainly my most reliable and versatile : FA 43,, Limited.

[TaoMaas]

Hmmm....tough choice. But of the primes I have right now, I'd probably take the F50mm f2.8 macro just because I like close-ups.

[UncleVanya]

DA 15mm!! Always amazed by that little lens and a joy to use.

Love mine also, just can't see the world only through that lens forever...lol.

---------- Post added 06-28-19 at 09:20 AM ----------

If I were limited to one lens, and a prime at that, I wouldn't own a DSLR. It's pointless.

Lol. Play the game
If you are going to post. Pretend you put a prime on right before being stuck on an island for a month as a challenge. You have plenty of batteries and cards as well as shelter and food. What prime would you like to have with you?

---------- Post added 06-28-19 at 09:23 AM ----------

The range of answers is fascinating.

[ffking]

Of the lenses I own, the most used primes - and therefore logically the one's I should keep if I could only keep one, would be the 31mm Ltd on the K-1, because it's a great walk around lens (useful focal length and reasonably small) with a rendition all of its own, and a 100mm f/2.8 macro on the K-3, because I love macro.

[luftfluss]

HD Pentax-DA 35mm F2.8 Limited Macro Reviews - DA Prime Lenses - Pentax Lens Reviews & Lens Database