Telescope mod - Getting focus 10-15mm farther outside

[mcbras]

Hello,

I like doing astrophotography and I've put an order for a rotator that has 18mm of back focus.

Right now, in my 8'' reflector along with the image train, the focuser is around 12mm sticking out from the most inner position, on average, for the CCD to reach focus. If I'm thinking things correctly, I know I won't be in focus by 6mm.
So, looking down to my mirror cell, I wonder if I can push the focal point 10-15mm out in the focuser area if I just use some 10-15mm spacers in between the spring and mirror hold bolts. Does this makes sense? I'm not in the mood of cutting down the OTA the same distance.

Anyone tried such thing? I'm pretty much sure that the actual mirror holding aparatus can be separated from the rest of the cell that screws in the sides of the OTA.

Thanks!

[andrew s]

As long as the mirror cell is firmly held it should be ok. The main  issue is that you may lose some light , more vignetting, if the secondary is then too small to illuminate the full field. 

Regards Andrew 

Edited July 10, 2020 by andrew s