Dear Observer,
 
In August 1996, I decided to block all ISOPHOT observations that were close to 
the detection limits of the instrument as then understood. This suspension was
based on the analysis of a representative sample of faint source observations. 
It indicated that the sensitivity limits which could be achieved in practice 
for detectors P3, C100, and C200 were worse than pre-flight expectations.
 
In the meantime, more experience on the detection of faint sources has been 
collected by the ISOPHOT Instrument Teams, including specific observations 
conducted in engineering time.  Clear recommendations can now be made, both on 
the detection limits that can be achieved and also on the most suitable 
observing modes that should be applied.
 
Dedicated WWW pages are now available which guide the observer in achieving the 
best results for the detection of the faintest sources with ISOPHOT. 
 
Based on this progress, I see no reasons to continue the suspension of faint 
source observations with ISOPHOT. Thus, I urge those observers who still have 
blocked faint source observations to revisit their programme in the light of 
our latest information and to (re-)release the observations.
 
If you want to release your blocked observations or if you want to change
your programme, please notify ISO helpdesk by email.
 
 
Best Regards,
 
M.F. Kessler
ISO Project Scientist