300PDS 100% field of illumination?

[gazza]

Hi,

I have a 300PDS that I am sorting out (difficult as we have had only 1 reasonable night here in the last 6 weeks!). I have found that the secondary mirror is only 70mm on its minor axis. According to https://stellafane.org/tm/newt-web/newt-web.html this only gives a 100% illuminated field of about 8.25mm. Patently undersized if you are using any decent sized chip.

Has anybody fitted a larger secondary? What size did you go for? I'm thinking about either a 3.1" or a 3.5" giving 18.25 or 31mm respectively fully illuminated field. With the larger, I could get away without taking flats for my apsc sized sensor......at the expense of a larger obstruction. My concern is that the larger secondary would be too heavy and therefore may require a new, more robust spider assembly. I'm interested to see if anyone has done a mirror upsize and what your experiences were.

The next choice is who to buy a secondary mirror from - GSO secondaries are cheap, but the chances of getting a good, large one seems a bit risky..., Other brands are expensive, and it seems they will cost nearly half the original OTA price!! Wondering whether it's worth taking a punt on the GSO option....any onfo here much appreciated.

cheers

Gary