im looking to put a 2" visual back on my Celestron C6s SCT. I took off the 1.25' one
last night to have a look and i can see in the telescope, the hole through the mirror
to allow light through is quite small. putting on a 2 inch visual back wont make this
hole any biger so im wondering why people always recommend upgrading to a 2" visual back
( along with a 2" diagonal)?
It allows you take advantage of the wide field of view provided by 2" eyepieces. As far as I know, the Celestron 6" SCT (like its larger companions) has sufficient field illumination to use 2" accessories so there is a definite benefit to upgrading. With a 1.25" visual back and diagonal there is no benefit in using eyepieces above 32mm. With 2" however, you can use 40mm or higher. There is no need to buy a 2" visual back and diagonal as 2" diagonals with built-in adapters are available which just screw on to the SCT rear cell. If you want to use a refractor type diagonal (eg if you have a refractor as well and want to use the new diagonal on both scopes) then you will need a 2" visual back also.
  