IMHO straight back to the seller, unless the description was accurate.

The real solution here is to light the subject properly, use a tripod and then use a small aperture. At the moment the lighting is from the wrong side.

Yes, it would be as sharp at say f5.6, so would the f1.2 lens.

The differences between the 50/55mm lenses are subtle and more to do with other properties that sharpness. We expect all lenses to be sharp.

Older 50mm lenses may peak later, maybe at f11, but may have higher fine resolution. Newer lenses may peak at f5.6 and be more contrasty, at the expense of fine resolution. But it really is something that you get to know after a lens has been used for a while, it's not something that will be obvious immediately, especially in an image for Web.

The short answer is that all Pentax 50mm lenses are essentially excellent lenses. A perfectly assembled f2 will be just as good as the more expensive ones, but they were made in very high quantities so getting a well treated one may be more of a lottery.

Some programs read lines that are not intended to be in the image, thus causing a stripe down the side of an image. It is probably a characteristic of your chosen RAW converter - what are you using?

Pixel mapping is available on the cameras and the "hot pixels" can be mapped out of existence.

Dust is dark specks and these lie on the low pass filter that covers the sensor.

Having set my cameras to continuously record the file numbers, is not knowing the latest file number enough? The only thing that would need to be remembered is how many times the camera has rotated beyond 9999 and as it creates a new folder number at that point even that should not be a problem.

Matt is right about WB - the camera will actually vary the setting around a small margin. So a Daylight setting, for example, will vary slightly depending on the light measured.

This can be switched off though.

I don't think you then need another lens. It is possible to tape a platic bag around a non-WR lens and keep water spray largely at bay.

Personally, the 18-135mm could be ideal, if I were making the trip you are making that would be my lens of choice, plus the 55-300mm protected as best I could.

F2.8 lenses are not essential as increasing ISO can be quite sufficient. The K20D probably should be kept to ISO 400 or lower if at all possible though.

Please only post a question once in one forum - if it turns out it's in the wrong place we can always move it for you.

I've removed the other thread.

Thanks Horst, that seems to indicate that the base plates are the same, which is fine.

What we are talking about here is the ERC, and this is different for each camera type as the body shapes are different. So the MX, ME type and Super A all have a different ERC.

The confusion arose because of the mention of the tripod screw in the ERC, and of course there is no tripod screw fitting in these cases.