Frame size X Pixel aspect ratio
 

When I try to up-convert (render) some 1280X720 files (some shots from my Pentax K-X) to integrate them in my documentary, mostly shot with a Canon HV 20 transcoded to Cineform intermediate codec 1440X1080 24p, how shoud I fill the Custom Settings regarding pixel aspect ratio to make a straight and correct convertion?
When I use the defaut 1,0000 pixel aspect ratio, the image from this transcoding (1280X720 to 1440X1080) appears distorted and with a letterbox.
And the oposite, how should be the custom settings to downconvert from 1440X1080 to 1280X720?
Is there any guide / table with the most used pixel aspect ratio convertions settings?
Thanks

Take everything to square pixel and get rid of this stuff. Otherwise it will drive you NUTS.

Thank you Perrone, but I don`t understand you (my fault).
Can you please orient me step by step how to achieve a correct convertion - ie how to fill the custom setting page to render (for example 1280X720 to 1440X1080)?

1440x1080 is not square pixel. 1920x1080 is. The PAR that you use for HDV stretches the 1440x1080 to 1920x1080. So do that. Once you have real 1920x1080 footage, you can simply resize your 1280x720 to 1920x1080.

You render and output from 1280x720 footage to 1440x1080 right?. In that footage properties, you need to change it default setting 1.000 to 1.3333. This will match up with the HV20 1440x1080 with 1.3333. Give that a try.

Thank you guys.
Bruce, your sugestion worked perfectly.
What would be the the solution for the oposite situation (1440X1080 to 1280X720)?
Thank you again.

well, you would have to down convert your 1440x1080 to 1280x720 and the same thing is to change the default setting to 1.0000 to match the other.