Problem(s) Encountered:

We were attempting to take a narrow-band Halpha band image of V1974Cyg with the 6567 filter. Upon a 300s exposure, we found significant abberation and halos around each object in the field.

We went to 6691/78 band and took another 300s exposure to find a similar problem.

We were not able to remedy the issue, but noted that a 300s r-band exposure did not seem affected by the problem.

Solutions:

Unfortunately I am fairly sure this problem cannot be fixed with the filter you used. It has occurred because the filter is not flat enough, and thus it is distorting the wavefront. In direct imaging (no OSMOS), this is not usually an issue, as the converging beam is relatively unaffected by mild non-coplanarity in the filter. However, the OSMOS filters are in the collimated beam, and the filters need to be manufactured to a tighter specification. The r-band data are fine as the r-band filter meets this specification.

It is worth noting that this happened with Kitt Peak filters.

If you are interested in new filters, here are the specifications:

http://www.astronomy.ohio-state.edu/MDM/OSMOS/filterspecs.html