We have re-analysed all of the SCUBA archive data of the Orion star-forming regions .
We have put together all of the data taken at different times by different groups .
Consequently we have constructed the deepest submillimetre maps of these regions ever made .
There are four regions that have been mapped : Orion A North & South , and Orion B North & South .
We find that two of the regions , Orion A North and Orion B North , have deeper sensitivity and completeness limits , and contain a larger number of sources , so we concentrate on these two .
We compare the data with archive data from the Spitzer Space Telescope to determine whether or not a core detected in the submillimetre is pre-stellar in nature .
We extract all of the pre-stellar cores from the data and make a histogram of the core masses .
This can be compared to the stellar initial mass function ( IMF ) .
We find the high-mass core mass function follows a roughly Salpeter-like slope , just like the IMF , as seen in previous work .
Our deeper maps allow us to see that the core mass function ( CMF ) turns over at \sim 1.3 M _ { \odot } , about a factor of 4 higher than our completeness limit .
This turnover has never previously been observed , and is only visible here due to our much deeper maps .
It mimics the turnover seen in the stellar IMF at \sim 0.1 M _ { \odot } .
The low-mass side of the CMF is a power-law with an exponent of 0.35 \pm 0.2 , which is consistent with the low-mass slope of the young cluster IMF of 0.3 \pm 0.1 .
This shows that the CMF continues to mimic the shape of the IMF all the way down to the lower completeness limit of these data at \sim 0.3M _ { \odot } .