I have an sct/focal reducer giving 1200mm f6 and field a bit smaller than 20 minutes — cant do smaller planetary nebulas and galaxies using my 178MMC due small chip small pixels due to limitation of platesolving. I realise the built in database would rise a lot.
Only option I can see for the present would be buy a bigger chip with small pixels to get field over 0.4 degrees and crop for smaller 178-like field when imaging. (But not ready to buy another yet!)
John Bradshaw