itmo

The problem is that i do not have a 40mm extension,except the one where the inner diameter is under 2" =) I need a 40mm optical length aluminium tube with M54x1 thread on both ends. I already asked a friend's friend (a metal shop owner..) if he is able to fabricate one for decent price. 

I am focusing for visual observation. Problem is that the standard 2" adapter would provide this extra 40mm but i cannot use it because the inner diameter of the nose of the tube is a bit below 2" , which leads to my barlows and filters hitting it. The skywatcher focuser is designed to be too short, and you need to use a 1.25" adapter or a 2" adapter to reach visual focus. This makes focusing cameras etc. easier since you can just remove the adapters. I just hate those adapters with thumb screws so I have a 2" to 1.25" compression ring adapter with 2" filter threads , and a m54->2" adapter for the focuser. What I now need to get the perfect solution is the 40mm focuser extension M54 to M54 so I can move the M54 -> 2" adapter a bit outwards so it is in the middle of the focuser travel. This way I will have a nice 2" tube with no obstructions which i can drop down to 1.25" with a single adapter. This will also give me the possibility to screw 2" filters into the 2" -> 1.25" adapter so I can use my 1.25" eyepieces and barlows without having to constantly move the filter. 

yes there are multiple adapters with compression rings. for example one which replaces taht one seen in the picture. The problem then becomes focuser travel. Atleast for me. I am in search of a 40mm extension to the focuser tube with M54x1 threads on both ends to bring stuff to focus. 

I would recollimate it since the center of the aperture has moved. 

http://www.skyandtelescope.com/howto/basics/3304176.html?showAll=y

Here is one of the articles analyzing seeing effects on scopes of different size. And there is the most important part too, usually with bad seeing you still have short moments of very good seeing in between. If you stop down the scope you will lose these brief moments of clarity. 

But remember that stopping down also requires recollimation of main mirror AFAIK.

"stopping down" a telescope loses some resolution, but it also makes it easier to focus. IIRC the "large scopes suffer more from atmospheric effects" is [removed word]. The problem is that usually the large scopes are dobs which are fast (difficult to focus and collimate) and miscollimated. Stopping them down makes it easier to focus and makes collimation less critical. Also most 10 or 12 inch scopes have so good resolutions that you would have to be on top of mauna kea to get full use of the resolution all the time. So stopping down a 12incher to 6 or 8 doesnt necessarily lose you too much resolution in already so-so 1.0 to 2.0 arcsecond weather. 

You know how anytime you disassemble and then assemble something, one part is left over and everything still seems to be ok? After a while you have two eyepieces