Stupid question about BD50 to BD25

[timmus]

I'm a newbie. I tried backing up Blade Runner Final Cut using DVDFab Passkey to ISO. The resulting file was only 21.7 GB, so I assumed I had a BD25. I went to ImgBurn and wrote the ISO to a BD25. It does not play on the PS3 (disc not recognized).

I fired up DVD Fab Blu-Ray to Blu-Ray and after it analyzed the disc the target size is "stuck" on BD50. So my questions are:
1. Do movie studios often put 21 GB of content on a BD50 disc?
2. Can writing out BD50 content to a BD25, even if the ISO is less than 25 GB, cause an error? If so, what's the best way to handle those types of discs?

[redwudz]

The main movie may be 21.7GB, and the extras a bit more. With most BDs, the largest .m2ts file is the main movie. Check the 'Stream' folder of the disc.

The PS3 may not recognize the format. You might try multiAVCHD for the main movie or BD Rebuilder if you want menus, extras, etc.

[timmus]

Well, the resulting ISO file (packaging the entire disc) was 21.7 GB, so I don't know how that would inflate beyond 25 GB. Burning that with ImgBurn was a failure, so I assumed maybe there were file structure issues that prevented small BD50s from being written to BD25 without reauthoring.