The genuine M42 to K adapters go for around 30 quid used, I've bought two from these forums and that's about what I paid. However, if all your other lenses are K-mount then it's better to stick with that for ease of switching lenses.

A full frame sensor at a given aperture setting receives twice the light of an APS-C sensor at the same sensor.

Fact.

The same lens used on APS-C will send half the light that comes through it into the mount but onto the area that is not sensor. That's why the field of view is different.

Thanks for that. The K 35/3.5 is one sharp lens. I'm surprised to see such a difference wide open between the FA 35/2 and the older versions.

Another one appeared for sale:

https://www.pentaxuser.com/forum/topic/f-s-pentax-k-35mm-f3-5-52418/p-0#comm

There are plenty of lenses which are very useable on both formats - the humble fast fifty for example. A standard lens on FF and a portrait lens on APS-C. The point is it serves different purposes, making a set of lenses designed for FF unsuitable for use on APS-C because the focal lengths don't serve the same purpose.

I don't see any muddy thinking there, it's entirely true.

The FF upgrade is a myth - almost no Canikon users will upgrade to a FF model, most will never learn to use their APS-C cameras outside of full auto mode.

It makes absolutely zero sense to buy a camera and then buy lenses that are ideal for a different format to use on it, or to buy a camera with one sensor size and spend all your time using it daydreaming about a different one. If you have an APS-C camera now, don't hobble your photography by only buying lenses (which you apparently don't even want) that were designed for a different use. Pentax's attitude to APS-C is ideal - that it's perfectly good, and offers the best available compromise between quality, price, size and weight.

If you want a FF buy, one and lenses to go with it. If you want an APS-C model, buy one and lenses to go with it, not lenses to go with something else.

There's a K 35mm f/3.5 for sale here on the forum:

https://www.pentaxuser.com/forum/topic/pentax-lenses--da-21-ltd--fa-50-1-4--k-35...

I have one, and also the Takumar. They're very nice lenses, although difficult to focus on digital due to being so slow, not so bad on film due to the better viewfinders. Optically they're exceptionally good, of course the K-mount one is easier to use. The K-mounts are much rarer and hence more expensive than the Takumars.

My default 35mm lens for film is the M series 35mm f/2, a very useful lens indeed. I was lucky and paid less for it than a typical K 35/3.5, but normally they be a bit more expensive. I also have an M42 mount Vivitar 35/2.8 which is very good indeed but I'm not sure if it was ever made in a K mount.

DPR have posted a very interesting and remarkably sensible piece on the full-frame myth and the myth of the upgrade path. It's particularly relevant to Pentax as a brand who manufactures primarily APS-C DSLRs with no FF digital option. The vast majority of people who have bought into APS-C thinking they'll move to FF options from the same manufacturer have never done so (and never will).

http://www.dpreview.com/articles/5678273556/opinion-the-myth-of-the-upgrade-path

A DC, WR, collapsible kit lens - nice. I'll be very interested in that one. Good to see SMC isn't dead yet, though maybe they're keeping it around as the "lower quality" option for cheaper lenses, which seems a shame given SMC's proud history. I'm sorry to see it's a DAL though, and that the filter thread is a massive 58mm. That's a funky square hood at the back left - good for keeping the kit size down.

The wifi button suggests the FluCard is dead though, which is probably a good thing for functionality but bad as it will drive up the cost of the camera bodies and some people won't want or use it.

The cashback offer is open for purchases until the 10th, so should still be available. I don't think it's limited to Pro Centres so in theory Argos should qualify.

Lens now sold off the forum. Thanks for looking.