[Shiraz (Ray)]

Maybe take the images with a grain of salt Peter - I doubt that even AP has managed to find a way around atmospheric seeing and sampling theory.

It is only claimed that the images "compare the resolution" - in the little info I have seen, it is not claimed that they are separate images taken under identical conditions, one with and the other without the Barlow. Do you know of any info on how they were taken?

Might be wrong, but my guess is that the image without the Barlow has been synthesised from the one "with" by heavily downsampling and then resampling back up. ie, it is intended only to illustrate in general terms that a Barlow can sometimes produce better results - which is what you want if you are selling them. The presence of strong processing artefacts in the "without" image may possibly be a clue as to what has been done. An alternative possibility is that the camera is a Bayer camera - if it is, the results would possibly be a little more understandable.

If the seeing is really good and a non-Barlow system is undersampling, then a Barlow can certainly help, but that comparo looks more like a guide than a true result.