Backfocus RCC1 Newton 200/800 : test result Fast Newtonians · Joel85 · ... · 3 · 165 · 2

Hello,

Here is a post based on  my own experience  (RCC1 - UNC 200/800 FD4), can be helpfull for those who are using the same "setup" (or near)

- standard RCC1 backfocus (BF) is 91,5 mm (connected on M42 corrector/ 94,5 mm -mechanical lenght-  connected on  M48 on corrector)
- "standard" has no sens : real BF depends on F/D ratio and the same corrector will requiered different BF, depending on F/D ratio  ...
- After many (many many ...) tests, the BF RCC1 obtained on UNC 200/800 : 89,53 mm (on M42 -RCC1=optical BF) and 92,53 ( on M48 -RCC1= mecanichal lenght)

On my setup : 

- M48 connection on RCC1 
- mechanical lenght between sensor and RCC1 : 91,7 mm (74,2mm=rings + 17,5 mm asi071)
- filter : IDAS 2,5mm--> 2,5/3=0,83 mm BF (approximatly)
- total : 91,7+0,83=92,53mm

RCC1 lenght "inside" crayford : 20 mm 

Here is a the result (the small default, slightly angular stars,  is because the primary mirror was too tight, and not a BF problem. A pixinsight process was also applied on stars and made them a little  blurry+few other stack problems... hope to publish a better picture next time  )