You can but it requires an adapter with a glass element so it's not quite as useful as it is on the other marques. I've sold several M42 lenses to Nikon users though so it obviously doesn't bother them that much

Mamiya/Sekor 55/1.4 is worth looking out for if you can find one too. Not as well known so tend to turn up quite cheap.

Yes sort of; the Praktica M42 cameras (LTL, MTL, etc) came as standard with a Meyer Domiplan 50/2.8 - quite possibly the worst lens to grace a camera short of the sort of thing you'll find in an cheap mobile phone these days. For a fee you could upgrade to the Carl Zeiss Jena Tessar 50/.2.8 - still a comparatively slow lens (for a 50) but a massive step up from the Domiplan in terms of IQ (and still about the best lens you can buy for bellows work short of a dedicated macro to this day). For a little more you could get the very competent Pentacon 50/1.8 which was a six element design that would give Japanese offerings a run for their money for far less £££. Finally, if you were particularly flush, you could opt for the Carl Zeiss Jena Pancolar 50/1.8. As discussed above this was as good as (if not better than) similar offerings from the major manufacturers, unfortunately it also pushed the price of a humble Praktica above that of a typical Spotmatic/Takumar (for example) combo hence it wasn't a particularly big seller - most folk going with the more reliable and better engineered Japanese offerings. This is more down to the failings of the camera than the lenses though!

The Pentacon 50/1.8 was the "sweet spot" of price v performance and is by far the most plentiful second hand (the CZJ Tessar was barely less expensive and with an f/2.8 aperture certainly less attractive on paper). Domiplans had a typical life expectancy that just about equalled the time it took to walk home from the shops with your new purchase (I've taken these apart and certain internal components aren't even plastic - they're compressed cardboard like a Trabant body), hence they're not too common either but I tend to think of that as "a good thing".

As for the reviews at the time, don't forget we were engaged in a cold war back then and it was not the done thing to admit (especially in a national publication) that "the enemy" could produce goods as fine as the ones made by our friends. A bit like the way certain magazines (mention no names, just look for the threads) rubbish Pentax products today on the flimsiest of grounds simply because they don't spend as much money advertising with them. The easiest way to dispell these sorts of reports is to either use the lenses yourself or look at results others who do achieve with them - that's certainly a huge benefit the Internet has given us.

The factories at Jena housed some of the finest optical manufacturing facilities ever seen and that didn't change after it fell into Soviet hands. The marketing team (didn't Douglas Adams have some wise words about those sorts?) might have decamped to the West along with most of the money and a team of lawyers prepared to do battle over copyright infringements, but the average factory worker was just as skilled and dilligent after the war as he was when building lenses for Contax rangefinders before it. I've yet to find a "bad" CZJ lens (broken ones yes, but not badly designed).

In the lens' "Auto" mode you select your aperture and the lens remains wide open until a pin on the rear is depressed - unfortunately you need an Auto M42 (like a Pentax Spotmatic) camera body for that. This allows you to focus at open aperture with the lens only shutting down as the shutter is depressed, then opening again straight afterwards.

In the lens' "Manual" mode the aperture opens and closes as you move the ring and stays there. This is the mode that's actually useful to the average DSLR user.

If you set your camera to Av (aperture priority) and your lens to M (manual) then the camera will meter correctly as it just reads the actual amount of light coming through, rather than the amount it's expecting to come through.

Once you get used to the handling you can combine both positions to get a very flexible set up. Set the camera to Av, set the lens to A, set your required aperture on the lens, focus, flick the lens switch to M to shut the lens down, the camera meters and you take the shot. Result!

I'm here and I do own both

Firstly the optical construction is similar (both are 6 elements arranged in 5 groups) but the Zeiss has a cemented pair at the front while the Pentax has its at the rear. How this translates into real-world pictures is that I find the Pentax has a slight edge at portrait lengths and closer (macro on tubes, etc) but the Zeiss is better at infinity where it's possibly the sharpest lens I've ever owned (you really feel you can count the individual leaves on trees on the horizon).

Both have excellent control of contrast and colour (the coatings are obviously similar) but they do render the out-of-focus areas (bokeh) quite differently. The Pentax has a very smooth and creamy bokeh (a bit like a typical modern high quality lens), the Zeiss is more of a "watercolour painting" effect (more like the FA Limiteds). This gives them very different characters and is the reason I keep both for use depending on my mood and subject - I personally prefer the look of the Zeiss more often than not but it's down to your own tastes really.

Construction wise the Pentax wins hands-down. Focus movement is like buttered silk whereas the Zeiss tends to be stiffer and more industrial. Neither are likely to fall apart but it's a bit like comparing the engineering on a Lexus to that on a 1970's British Rail train.

If you're intending using them on a DSLR then the Zeiss wins. M42 lenses are much easier to use on modern bodies than K and M series lenses and you can have proper aperture priority with the Zeiss rather than wide-open only with the Pentax. Of course in full manual mode then the differences are less noticeable.

Is the Zeiss worth more than the Pentax? Probably. If I could only keep one it'd be the Zeiss and the screw thread means it will work (with an appropriate adapter) on your Pentax, Canon, Nikon, Olympus, Sony, Contax, Zenit, Praktica, Edixa, Exacta, Chinon, Ricoh, Samsung, Panasonic, Leica, Rollei... You get the idea.

Would I pay £60 for one? Probably, but I'd only pay about £20-30 for the Pentax. That isn't a reflection on their relative optical qualities, just that the Zeiss will always find a home with another user regardless of which system they take photos with. Good lenses never go out of fashion.

Both my K10D batteries (one genuine, one generic) came with caps so it doesn't look like there's much of a pattern emerging here - rather luck of the draw.

Mmmmmm.... Much cheapness AND a free polarising filter too.... Mmmmmmmm.... Buy it. Buy it. Buy it...

Well the one I sent you probably pre-dates some of your archeological digs so it should feel right at home

Neither of these lenses are duds. He's quite new to photography and didn't know what to buy so he got these and a couple of small primes. He's ended up using the primes mostly as he likes a smaller/lighter set up - hence the money for these is going towards a couple of DA Ltds and the DA*55.

An adjustment layer affects all visible layers below it in the same way - hence the thumbnail appears to be white.

If you want a layer that contains objects to manipulate then you just want a regular layer, not an adjustment one.

Hope that helps