The Pentax Converter-A 1.4X-S works well with the 55-300mm on digital

Seems to be a lot of bad language on that Canon site Don?

There's a bit more about PF with the K-5 here

Just search for "purple"

I notice some posts have been removed from this thread? But the total piece of misleading nonsense by eenymac, which unfortunately we see far too much of on the internet has been left in. I tried to correct it with a follow up which has been removed.

How can you ignore all the scientific tests and statistical data provided by the UK's top motoring journalists and take the word of Joe Average who complains on a website that he doesn't like his car because he's sick of the colour

If we applied that to cameras we would all be using Nikon and Canon

What?... they are putting them on display?

Just get the lens and try it This is a really top lens and cement separation sometimes doesn't affect the pictures. In the meantime look out for a good one. Not worth paying for a repair that may not work. You should get a good lens for about £35 or less.

It's already been posted in a thread on here via a link to another site. I can't remember the thread or who posted the original link. It is the K-5 that causes it.

I'm just about to watch Russell Howard so I won't have time to look, but it was on here that I read it, somebody else probably remembers.

The K-5 does have more PF problems than the K-7. Probably better to keep a 2nd body K-7 or K20D for and pics that are likely to have PF problems.

Or use lenses with very low PF.

Good lens bit soft wide open. The original Angenieux on which it was based cost an absolute fortune.

Practice by focusing on the lettering on say a Corn Flakes box.