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I had an FS152 with 2.7 inch focuser. It would not handle an STL11 (44mm diagonal) let alone a 16803 (52mm diagaonal) without heavy coma with the reducer or without. There was vignetting but able to be flat fielded.
I had a 2.7 inch F6 reducer. It was not useable and gave bad coma to the outer parts of the image.
The TOA flattener gave way too much vignetting and was useless and I returned it.
What worked was getting a 4 inch focuser and 4 inch flattener. Sharp stars to the corner. There also was an FS152 4 inch reducer and that worked but not 100% sharp stars to the corner but not too bad. Since then Tak have released a super reducer. It is quite expensive. I am not sure what sizes it is for - it may be a 4 inch model.
Its not the aperture of the opening, its the corrected image circle where all stars are in focus across the whole field. That's the problem.
It would be worth checking on the Tak Uncensored website in case there have been new flatteners or reducers for the 2.7 inch size.
I suspect that it is a dead end or it certainly was when I had the 2.7 inch focuser on my FS152.
Greg.
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